quarterly publication rs. 20 april 2020 weld 19 bead 1 journal... · iws day celebrations 2020 the...

Quarterly Publication Rs. 20

APRIL 2020 Weld 19 Bead 1

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AROUND IWS

KNOWLEDGE SHARING

TECHNICAL PAPERS

THE JOURNAL OF

Regn. No. 41817 / 2002

QUARTERLY PUBLICATION

APRIL 2020 Weld: 19 Bead: 1

PRESIDENT

SHRI R PADMANABHAN

Immediate Past President

SHRI S BISWAS

Vice Presidents

SHRI HIMANSHU I GANDHI SHRI S PRABAKARAN

Dr S ARAVINDAN

Hon. Secretary

SHRI N RAJASEKARAN

Hon. Treasurer

Mrs. A SANTHAKUMARI

Members

Dr K Asokkumar Dr A Chandrasekhar

Shri A Maruthamuthu Dr. T Senthil Kumar

Shri G Rajendran Shri V Ganesh Sinkar

Shri M P Jain Dr Shashikantha Karinka

Shi M Kasinathan Shri Gyan Prakash Bajpai

Shri R Easwaran Dr G Padmanabham

Shri S M Agarwal Shri Muneesh Narain

Shri S M Bhat Dr T Prakash

Shri Amit Agarwal Dr S Shanavas

Dr V Balasubramanian Shri Naresh Malli Reddy

Shri T Baskaran Dr Yadaiah Nirsanametla

Dr N Murugan Shri A K Verma

Dr N Raju Dr P Sivaprakash

Editor in Charge Shri S. PRABAKARAN

ASSOCIATE EDITORS Shri Praveen Kumar Lakavat Shri R. Arivalagan

CO-ORDINATORS Dr. N Raju Shri A K Verma

PUBLISHED BY

On Behalf of IWS by

Shri N RAJASEKARAN Hon. Secretary (IWS)

INDIAN WELDING SOCIETY INSTITUTIONS BUILDING, KAILASAPURAM, TIRUCHIRAPPALLI – 620 014

INDIA Websites: www.iws.org.in www.iwsevents.com

E mail: [email protected]

http://www.iws.org.in/http://www.iwsevents.com/mailto:[email protected]

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IWS DAY CELEBRATIONS 2020

The IWS Day 2020 was celebrated at the SK Mazumder Hall,

Institutions Building, BHEL Township, Tiruchirappalli on 14th

March 2020 by HQ and SZ.

Mr. S. Prabakaran, Vice President (IWS) presided over the

function and delivered the IWS day address to the members. In

his address, Mr.

Prabakaran informed

the gathering that in the next couple of days IWS will

inaugurate its Mangaluru Centre. He appreciated the

participants of the weld quiz and skill test conducted by IWS in

association with HRDC, BHEL, for the budding welders. He also

congratulated the winners of the competitions. He distributed

the prizes and certificates. Mr. Prabakaran also cut a cake to

mark the celebrations in the presence of the members.

The skill test was conducted on 12th March 2020 by Mr.

Shanmugam and Mr. Subramanian of HRDC BHEL under the

leadership of Mr. V Sivakumar, SDGM, HRDC. Mr. Prabakaran

thanked with mementos.

Earlier, Mr. S. Singaravelu, Zonal Vice Chairperson, IWS, SZ

welcomed the gathering. Mr. N Rajasekaran, Hon. Secretary,

IWS recalled the history of IWS and the past accomplishments.

Mrs. A. Santhakumari, Hon. Treasurer, IWS proposed the vote

of thanks. Mr. G Rajendran, Imm. Past Treasurer of IWS read

out the President’s Message. Mr. Arunan, Zonal EC member,

SZ announced the results of the quiz and skill test. Mr. N

Parameswaran conducted the proceedings and proposed the vote of thanks.

AROUND

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AT ANNAMALAI NAGAR CENTRE

The Annamalai Nagar Centre celebrated the IWS day with a free workshop on

“Friction Based Joining Technologies” at CEMAJOR, Annamalai University. Prof. Dr

V Balasubramanian, Head, CEMAJOR and NGC member delivered the keynote

address and enlightened the members

about IWS.

Dr K Shanmugam, Dr P Sivaraj and other

senior members participated and

offered their felicitations.

**Reports are awaited from other centres and zones.

AWARDS & RECOGNITIONS

Prof. Dr V Balasubramanian & Dr P Sivaraj were conferred with Panthaki Memorial Award 2019 by IIW.

IWS JOURNAL congratulate the members and other members who received awards.

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LAUNCHING OF MANGALURU CENTRE

IWS added one more feather in cap by launching the Mangaluru Centre of IWS.

Indian Welding Society(IWS) Mangaluru centre has been inaugurated by Honorable Chancellor of Nitte

Deemed to be University and President of Nitte Education trust

Shri N. Vinaya Hegde on 16th March 2020 in the presence of Shri

S Gopinath, Past President, Shri S Prabakaran, Vice President,

Shri N Rajasekaran, Hon. Secretary, Shri G Rajendran, Former

Hon. Treasurer, Shri S Singaravelu, Zonal Vice Chairperson SZ,

office bearers of the local centre, officials of BEML KGF complex

and local industries.

Mr. Vinayak Hegde inaugurated the Mangaluru centre by

lighting the lamp with the dignitaries and unveiling of the

plaque. In his address, Shri Hegde stressed the need for

venturing into newer areas of technology that could provide

employment opportunities. He mentioned that the

mechanical engineering stream has to be restructured with

newer technological inputs to attract the best students.

Indian welding society (IWS) is a registered professional

body devoted to welding in India with its headquarters at

New Delhi and is

promoted by Welding

Professionals from

leading Fabrication

Industries, Academic

& Research Institutes

and progressive minded Welding Consumable & Equipment

Manufacturers. IWS has the national membership of over 3600 and has 65 life members in the

Mangaluru region. Hence it was felt necessary to form

Mangaluru centre to bring all the welding professionals working

in academics and industry together for interactions on a

common platform. The IWS Mangaluru centre is formed with

patronage of Shri N. Vinaya Hegde.

Shri S. Prabakaran Vice President, IWS and General Manager of

BHEL Tiruchy installed the office bearers of the centre and appreciated the initiatives taken by the

Mangaluru centre in attracting good number of life members.

Mr. N. Rajasekaran, Hon. Secretary, IWS offered his felicitation of the newly installed office bearers and

briefed about different activities of the Indian Welding Society. He assured the co-operation and

support from HQ for the centre.

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Shri S. Gopinath, Past President of IWS and former Executive

Director of BHEL Tiruchy gave an overview of the history of

development of Mangaluru Centre.

Earlier, Prof Shashikantha Karinka welcomed the gathering.

Prof. Muralidhara and Dr. Vijeesh Vijayan introduced the office

bearers, Mr. Divijesh performed invocation and Mr. Sudhir J

Shetty ended the programme with vote of thanks. Mr. Melwyn

Castelino compered the programme.

The office bearers of the centre installed in the inauguration

are Dr. Shashikantha Karinka Professor and Head of

Mechanical Engineering of NMAMIT as Chairman of the Centre,

Mr. MJ Shetty Managing Director of Lakshmi Cryogenics as Vice

Chairman of the Centre, Mr. Sudhir J. Shetty CEO of Varun

Engineering Corporation as Hon. Centre Secretary, Mr. Gajanan

S Hegde, Deputy General Manager of Mangalore Chemicals and Fertilizers Limited as Hon. Centre

Treasurer along with Executive Committee Members of the Centre.

It is proposed to have the local office in Nitte Education International at Pumpwell, Mangaluru.

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KNOWLEDGE SHARING ONE DAY SEMINAR ON “RECENT TRENDS IN WELDING TECHNOLOGY” BY IWS

MANGALURU CENTRE

Immediately after the inauguration, the Mangaluru Centre

conducted a one-day Seminar on “Recent Trends in Welding

Technology” by experts

from IWS. The event

attracted about 60

delegates from various industries and students from ITI,

Diploma and Engineering institutions. The resource persons of

the seminar are: Mr. G. Rajendran, Former Hon. Treasurer IWS

& former Addl. GM of BHEL, Mr. N. Rajasekaran, Hon.

Secretary, IWS & Deputy General Manager of BHEL Tiruchy,

Mr. Prashant Hegde, Sr. Manager Inspection department,

OMPL Mangaluru, Mr. S. Singaravelu, Zonal Vice

Chairperson, IWS South Zone & Former Addl. GM, BHEL and

Dr. G. Ravichandran, Former General Manager Welding

Research Institute & Adjunct Professor NMAMIT.

.

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STRUCTURED COURSES

The Southern Zone conducted its flagship course “Welding

Technology for Fresh Engineers Course (EC 056)” during

17.02.2020 – 23.02.2020. 26 students from various

engineering colleges and industries have attended the

course and got benefited by the heavily subsidized course.

Mr. S. Prabakaran, Zonal Chairman, IWS, SZ, inaugurated

the course and distributed the course materials to the

participants.

Mr. N Rajasekaran, Hon. Secretary, IWS offered his felicitations

and shared the genesis of the course. Mrs. A Santhakumari, Hon.

Treasurer, IWS welcomed the gathering. Mr. Pravin Kumar

Lakavath, Course Director & Hon. Treasurer, SZ, proposed the

vote of thanks.

On 23rd February 2020, Mr. N Rajasekaran, Hon. Secretary (IWS) distributed the certificates to the

participants and delivered the valedictory address. Mr. Praveen Kumar Lakavat, Course Director (IWS,

SZ) welcomed the gathering. Mr. G Rajendran former Treasurer offered his felicitations. Mr. N

Parameswaran, Zonal EC member of IWS, SZ proposed the vote of thanks. The participants expressed

that they got benefited from the course and thanked IWS for the noble initiative.

ONE DAY WORKSHOP ON “WELDING AUTOMATION FOR MODERN

MANUFACTURING SECTORS” BY BIT – IWS STUDENT FORUM

Welding automation plays a vital role in many manufacturing industries such as automotive, Aerospace,

Defence, Shipping, etc. To discuss on the latest trends in

welding automation, the BIT – IWS Student Forum under

financial support by IWS, organized the workshop on 14th

February 2020. Furthermore this workshop is exclusively

targeted to improve the knowledge of Young engineering

graduates and faculties and researchers from various

institutions in Southern Zone. 186 delegates attended

the one day event and got benefitted.

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The workshop was inaugurated by the chief Guest Dr. D. Kesavan, Assistant Professor from IIT Palakkad

and Mr. S. Praveen, Regional Manager from M/s. Fronius India limited.

Dr. M. Ravikumar, Professor HOD, Mech, BIT welcomes the gathering

of this workshop and Mr. D. Dinesh introduce the chief guest and

address the participants. Followed by the Four Technical sessions

related to the automation in welding and additive manufacturing in

laser welding, wire + arc additive manufacturing, robotics in TIG + MIG welding and Cold metal transfer

welding by Various experts. Vote of Thanks is proposed by Mr. G. Sundar Raju followed by certificate

distribution in valedictory function.

ONE DAY WORKSHOP ON “EMERGING TRENDS IN JOINING OF THIN SHEETS

AND EVALUATION” BY KSRCT – IWS STUDENT FORUM

The KSRCT – IWS Student Forum organised a One-day workshop on “EMERGING TRENDS IN JOINING OF

THIN SHEETS AND EVALUATION” on 18.02.2020 at the main building seminar hall of the college at

Tiruchengode. Mr. S. ADITHYA NAIR welcomed the gathering. Dr. K. MOHAN introduced the chief guests

Mr. N. RAJASEKARAN, Mr. S. SINGARAVELU and Mrs. A. SANTHAKUMARI. Dr. R. GOPALAKRISHNAN,

Principal presented a memento to Mr. S. SINGARAVELU and the faculty Mr. S. SAKTHIVEL presented a

memento to Mr. N. RAJASEKARAN and the faculty Dr. K. MOHAN

presented a memento to Mrs. A. SANTHAKUMARI.

The chief guest Mr. S. SINGARAVELU delivered the content on the

topic of “THIN SHEETS MATERIALS AND DEVELOPMENT “at 10.00

am. Then the chief guest Mrs. A. SANTHAKUMARI delivered the

content “SOLID STATE WELDING PROCESSES FOR THIN SHEETS” by

11.30 am. Finally, the chief guest Mr. N. RAJASEKARAN delivered

the topic of “ROBOTICS AND AUTOMATED PROCESSES “at 2.00 pm.

Ms. S. MONLISA thanked the guests, professors and pupils.

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TWO DAY NATIONAL WORKSHOP ON “AUTOMATION IN WELDING AND NON

DESTRUCTIVE TESTING” BY Dr NGPIT – IWS STUDENT FORUM

Dr. NGPIT – IWS Student Forum has conducted the

IWS Sponsored Workshop on “Automation in

Welding and Non Destructive Testing” from

13.03.2020 to 14.03.2020. The event has been

inaugurated by the chief guest Dr. N. Murugan,

Professor, PSG Tech, Mr. S. Singaravelu, Former

Additional General Manager BHEL and Mr. N.

Parameswaran, Former Sr. Deputy General

Manager, BHEL. Dr. S. Nandhakumar Professor

HOD, Mech welcomed the gathering of this workshop and Dr. K. Kalaiselvan, Professor of Mechanical

Engineering introduced the chief guest and addressed the participants. Dr. K. Porkumaran Principal

felicitated the gathering. Followed by the eight Technical sessions related to the automation in welding

and non-destructive testing by various experts. Vote of Thanks is proposed by Miss. Kavya Secretary-

Student forum followed by certificate distribution in valedictory function.

ONE DAY WORKSHOP ON “WELDING OF EMERGING POWER PLANT

MATERIALS” BY RIT – IWS STUDENT FORUM

Department of Mechanical Engineering, Ramco Institute of Technology and RIT - Indian Welding Society

Students Forum jointly organized a One day Workshop on Welding Emerging Power Plant Materials on

3rd February 2020 (Monday) to RIT – IWS students Members at Mechanical Seminar Hall, RIT,

Rajapalayam. Dr. S. Rajakarunakaran, HOD/Mech, Mr. S. Maharajan, AP/Mech, Mr. J. Jerold John Britto,

AP (S.G)/Mech coordinated the event. The program started with invocation “Tamil Thai Valthu”. Mr. S.

Maharajan, AP/Mechanical and RIT – IWS coordinator welcomed the gathering. Dr. P. Suresh Kumar,

Associate Professor/Mechanical presided over the function. The chief Guest of the Event Mr. N.

Rajasekaran, Hon. Secretary (IWS) & DGM (Unit II), Bharat Heavy Electricals Limited, Tiruchirappalli has

delivered the inaugural address. He narrated about RIT IWS and its unique function in organizing

technical talk and lectures in the past and assured that RIT IWS will organize technical talks, workshops

and seminars to students in future by assisting and providing eminent resource persons from BHEL and

WRI for conducting events. He mentioned the importance of welding in specific applications like

defence, boiler industries, constructions, railways, aircraft industry, under water welding. He also

explained the following privileges from IWS to RIT – IWS students’ forum.

• Student Forum Certificate from IWS to the institution

• IWS Membership ID Cards to all Student Members

• Financial Assistance of Rs. 10,000/- for one day Programme and Rs. 15,000/- for two days

programme on First Come First Served basis.

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• IWS Journal with technical articles as E-Journal for all

Members

• 5 free delegate s for the International events of IWS

from your student forum.

• Faculty Support for Seminars / Conferences /

Workshops / all lecture programmes from the panel

of Experts of IWS

• Support for Projects Works of the student

• Participation in lecture programme of Zones/Centres, free of cost/Highly subsidised rate by the

student members

• One copy of the Proceedings of IWS Events as complimentary copy to the library of the Institute.

The following topics were deliberated during the workshop.

S. No Name of the Expert and their Designation Topics to be delivered

1. Mr. S. Singaravelu, Consultant and Former AGM,

WTC, BHEL. Zonal Vice Chairman, IWS (South Zone) Advanced Materials for Power Plant Industries

2. Mr. N. Parameswaran, Former DGM, BHEL. Zonal

Executive Committee Member, IWS ( South Zone) Testing and Weldability of Stainless Steel

3. Mr. N. Rajasekaran, DGM, BHEL, Hon. Secretary,

IWS.

Processing of 9Cr-1Mo Steel and Welding

Defects

ONE DAY WORKSHOP ON “ADVANCES IN WELDING TECHNOLOGY & CAREER

OPPORTUNITIES’ FOR POLYTECHNIC STUDENTS

On the request from the alumni of the SSPTC, Sirkali, a One Day Free Workshop

on “Advances in Welding Technology & Career Opportunities” was conducted

at the college premises, for the final and 2nd year mechanical students. Mr. N

Rajasekaran, Hon. Secretary conducted the workshop. More than 140

students participated and got benefitted from the programme.

FREE LECTURE PROGRAMMES

SPIN ARC WELDING

Indian Welding Society joined hands with the Institution of Engineers, the Indian Institute of Welding,

Tiruchirappalli Branch & The Indian Institute of Metals in organising a lecture programme on “SPIN ARC

WELDING” by Mr. S V Prasad, Managing Director of Swastik Associates, and Tiruchy at the IEI building

on 21st January 2020.

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In his lecture Mr. Prasad said, “Spin arc welding utilises a unique weld torch in which the welding

electrode rotates in a circular motion at a high rate of speed.

Centrifugal force propels molten droplets across the arc creating a

consistent and sound weld bead. This enables high deposition rate

welding for significant increase in productivity”

He further said, “The process’s origins go back to the early 1980s

when Dick Roen, an engineer who worked with Martin Marietta,

had trouble welding certain aluminium alloys that were part of the solid rocket boosters for the space

programme. He invented the technology to weld hardened aluminium alloys literally in his basement.

Roen patented it in 1982, but that patent has since expired. The technology sat dormant for years until

several colleagues who knew Roen came together and formed Weld Revolution in 2012.

The technology, which works with any constant-voltage GMAW power source, is in the welding gun and

can be attached to any wire feeder. It’s designed for mechanized and robotic setups, and a kit is

available to adapt the system for hand welding. The gun itself has a motor that rotates the contact tip.

The controlled rotation occurs very quickly; typical settings are between 2,000 and 4,000 RPM. The

operator can set the spin diameter and speed.

As the spin diameter increases, the bead width increases. This process can be used for weld overlay or

surfacing also by varying the spin diameter. The system can rotate the wire clockwise or counter

clockwise, and which to choose usually depends on the weld direction to ensure the arc energy focuses

on the leading edge of the weld pool. If you’re welding left to right, you typically rotate the wire

clockwise; if you’re welding right to left, you rotate the wire counter clockwise.

One of the key benefits of the process is to be able to control the depth of penetration through the

rotation and the technology allows welding to occur out of position in more situations”.

Earlier Mr. S Singaravelu, zonal Vice Chairperson, SZ welcomed the gathering and introduced the

speaker Er. N. Rajasekaran, Hon. Secretary, IWS and Er. R Selvaraj, Hon. Secretary, IIW India, Tiruchy

branch felicitated the speaker.

DIGITAL IMAGE PROCESSING

On 4th February 2020, Mr. V Deepesh, Sr. Manager (NDT), BHEL

delivered a lecture on “Digital Image Processing – An Industrial

Radiographic Perspective” in the lecture programme jointly organised

by Indian Welding Society, Institution of Engineers, the Indian

Institute of Welding & The Indian Institute of Metals.

In his lecture he said, “With increased emphasis on product reliability

and with a generally renewed emphasis on cost control, it is natural that the NDT also should turn to

image processing as a potential method of improving the radiographic techniques. The questions being

asked usually concern the applicability of image processing for more certain detection of defects,

sometimes in the context of increasing the sampled population of an entire fabrication process at little

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increase in cost, sometimes in the context of making it possible for less experienced personnel to make

satisfactory examinations, sometimes simply in the context of obtaining better radiographic resolution.

In those applications where the principal desire is for higher throughput, the problem often becomes

one of automatic feature extraction and mensuration. Classically these problems can be approached by

means of either an optical image processor or an analysis in the digital computer. Optical methods have

the advantage of low cost and very high speed, but are often inflexible and are sometimes very difficult

to implement due to practical problems. Computerized methods can be very flexible, they can use very

powerful mathematical techniques, but usually are difficult to implement for very high throughput.

Recent technological developments in microprocessors and in electronic analog image analysers may

furnish the key to resolving the shortcomings of the two classical methods of image analysis”.

He further said, “Examples of applications of image processing to non-destructive testing include weld

inspection, dimensional verification of reactor fuel assemblies, inspection of fuel pellets for laser fusion

research, and, somewhat peripherally, medical radiography.

Digital image processing can contribute to an enhanced visualization. From endoscopic image

sequences, so called panoramic images can be computed, which show an overall view of a cavity and

allow for the check of an inspection result at a glance. By means of filtering and masking of the recorded

images, poorly exposed image portions, e.g. under exposed or over exposed, can be discarded. Thus

overall views with nearly homogeneous illumination level can be presented to the user”.

Earlier Er. S. Samidas, past chairman, IWS, SZ welcomed the gathering and introduced the speaker Er.

N. Rajasekaran, Hon. Secretary graced the occasion.

SKILL DEVELOPMENT IN WELDING

Mr. Venkatnarayanan, Chief Executive, Centroid Engineers India Pvt. Ltd.,

Coimbatore and Chairman of IWS, Coimbatore Centre delivered a lecture on

“Skill Development in Welding”, the contemporary topic on 18th February

2020. The well attended programme was organised by Indian Welding

Society, the Indian Institute of Welding, the Institution of Engineers, & The

Indian Institute of Metals. Following are the highlights of his lecture.

• Schooling does not assure employment but skill does.

• Skill development refers to the identification of skill gap and filling the gap to achieve the goal.

• Skill development is important in the overall development of a professional or a student.

He also explained in detail about various skill development initiatives of

Government of India. He also highlighted the role and services of AWS, WRI,

IIW, IIW (India), IWS, etc. in skill development for welding through various

programmes. Mr. R Selvaraj, Hon. Secretary of IIW India, Tiruchy felicitated the

speaker and presented the memento. Mr. N Rajasekaran, Hon. Secretary, IWS

graced the occasion.

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FEEDBACK From: MP Jain

Date: Mon, 6 Apr, 2020, 06:30

Subject: Re: IWS Journal Jan 2020 issue

To: Indian Welding Society

Cc: nrajas

Dear all at the editorial team of IWS Journal,

My compliments for bringing out an excellent edition of the journal. Its rich in content, visually appealing and well laid out. Keep the excellent

work going. MP Jain, New Delhi 9818279411.

From: yerriswamy wooluru

Date: Fri, 20 Mar, 2020, 10:05

Subject: Re: IWS Journals July 19 and Oct 19 Issues

To: Indian Welding Society

Dear Sir,

Thanks for sending the July 19 and Oct 19 issues of IWS journals…………….

………..I am very happy to note that Shri N Rajashekaran sir is Hon.Secretary, I would like to publish papers in the journal of IWS in association with

WRI engineers and researchers and use my expertise in Quality engineering as i did my PhD in Quality Engineering. (Robust Design and DOE) to

optimize welding process parameters of various welding Technologies over there.

Looking forward to associate with WRI experts and sharing my knowledge in preparation of journal articles.

Thanking you sir,

Dr. Yerriswamy Wooluru, Associate Professor, Industrial Engineering and Management Department, JSS Academy of Technical Education,

Bangalore, Karnataka state 560060, Mobile:9945065521

From: Honavar Electrodes Pvt. Ltd.

Date: Tue, Mar 17, 2020 at 2:29 PM

Subject: RE: IWS DAY 2020 - Message from President

To: ,

Mr. N. Rajasekaran,

Hon. Secretary (IWS).

Dear Mr. Rajasekaran,

Many thanks for your mail of the 13th instant with Greetings on the IWS Day 14th March 2020. I felt very happy after going through the inspiring

and informative message from our worthy President. It is so very heartening to read it.

a) Our Society has been chosen as the WINNER of PROFESSIONAL ASSOCIATION OF THE YEAR AWARD 2019 BY THE APAC association of Event Bank,

Singapore.

b) Starting an Add ON Course in welding technology for the mechanical engineering students.

c) Starting an Industry Based Elective in Welding with a Polytechnic in the south.

d) It is a novel idea to tap CSR funds under section 135 of Companies Act in the area of education, training and skill development through IWS.

Overall, all these efforts will enhance the status of IWS, and also win due recognition for Joining Technology on a very much wider plane from the

Government, Industry and Society. ……………………………………

……………I wish the President a highly successful term in leading the Society to greater heights.

Thanks & regards,

D. S. HONAVAR

DIRECTOR

HONAVAR ELECTRODES PVT. LTD.

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JOINING OF ALUMINIUM ALLOY TUBES WITH CARBON STEEL

TUBES BY MAGNETIC PULSE WELDING TECHNIQUE

1S. Muthukumaran, 2S. Malarvizhi, 3V. Balasubramanian & 4Bhavani Sankar Cherukuri 1, 2, 3 Centre for Materials Joining & Research (CEMAJOR)

Department of Manufacturing Engineering, Annamalai University 4Magpulse Technologies Private Limited, Peenya Industrial Estate, Bengaluru

[email protected]

Abstract

Joining of aluminium alloys with carbon mild steel using the fusion welding technique

is highly difficult because of the formation of solidification defects like, porosity, alloy

segregation, hot cracking, etc. To overcome these problems solid state welding

techniques such as explosive welding and magnetic pulse welding, can be used.

Magnetic pulse welding (MPW) is a solid-state welding process, in which joints are

made at overlap configuration at higher speed and cost effective. In this

investigation, dissimilar aluminium alloy AA 6063 T6 tube and Mild steel IS 1239 tube

were joined using MPW technique. A central composite design model was developed

for establishing the relationship between important MPW process parameters such

as stand-off distance (SoD), working length and voltage with the bonding strength

of the joints. Empirical relationships were established correlating the tensile shear

fracture load and interface hardness of the joints and MPW process parameters.

Response surface methodology was used for optimization of the MPW process

parameters. From the results, it is understood that the working length had significant

effect on the quality of magnetic pulse welded dissimilar joints.

Keywords: Magnetic Pulse Welding, Dissimilar Joint, Response Surface Methodology,

Tensile Shear Fracture Load.

1.0 INTRODUCTION

Lightweight construction and energy efficiency are having a strong impact on the new product

development (NPD). The recent engineering system should concentrate on developing the

ground-breaking lightweight design and, at the same time, the global environmental and

economic advantages of the entire product lifecycle (PLC). particularly for the automotive

industry the subject of lightweight design represents one of the most major innovation drivers

and technology trends [1]. The use of the steel and aluminium dual metallic welding structure

has become the preferred alternative to light weighting in industrial manufacturers, which surely

involves the connection between steel and aluminium. Researchers are from different countries

have perform exhaustive research on the connection between the structures of steel and

aluminium [2]. Much attention has been paid to joining different metals. In particular, steel and

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aluminium joining are key for fabricating multi component structures used in cars and ships [3].

In order to form a metallurgical bond, heating is required, but in the case of dissimilar-metal joints

(Al/Steel), a high heat input often leads to formation of brittle and continuous intermetallic

phases that might weaken the mechanical properties of the bond [4].

Magnetic Pulse Welding (MPW), which is considered as a ‘‘solid state welding process", Similar

to explosive welding [5], has increase the attention of the welding community since it enables to

join similar as well as dissimilar materials in microseconds, without the need for contact work

piece and welding consumables. MPW is closely analogous to explosive welding and relies on the

dynamic effects when the joining components collide at high impact speeds. When using the

cylindrical configuration, the parts to be joined are inserted concentrically into a coil shown in

Figure 1, leaving an acceleration gap. MPW uses an electromagnetic pulse of very short duration

(

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have greater influence on the tensile shear fracture load of the magnetic pulse welded joints were

identified.

2.2 Working limits of parameters

The experiment trial runs were carried out using 1 mm thick pipe of AA 6063 T6 and 1 mm pipe

of IS 1239 low carbon steel to find out feasible working limits of magnetic pulse welding

parameters. Different combination of parameters was used to carry out the trial runs. The welded

surface and weld quality were inspected to identify the working limits of the welding parameters

leading to the following observation. If the voltage was extended 12 kV there were the joint is

separated for, for voltage is greater than 16 kV, the flyer gets high deformation were observed

on the weld joints. If the voltage was less than 12 kV there were the joint is separated, for voltage

is greater than 16 kV aluminium tube is undergo higher deformation were observed on the

welded joints. If the stand-off distance was less than 0.5 mm the joint is separated (not welded)

for standoff distance greater than 2.5 mm the flyer aluminium gets (Impact placed) deformed. If

the working length was lower than 6.5 mm the joint is separated for working length greater than

8.5 mm the weld is separated were observed.

2.3 Development of design matrix

Based on the above condition the feasible limits of the parameters were chosen in a way that the

AA 6063t6 alloy and is 1239 should be welded without any weld defects. Among a wide range of

factors, three factors and fire levels central composite design matrix were selected to optimize

the experimental conditions Table -3 presents the range of factors consider and Table -4 shows

20 sets of coded conditions used to form design matrix. The method of designing such matrix is

introduced else were for the convenience of recording and processing experimental data, upper

and lower levels of the factors were coded as +1.682 and -1.682 respectively.

2.4 Experiments

The experiments solution heat treated AA 6063 T6 aluminium alloy of 1mm wall thickness the

length of 60mm, diameter- 30mm fixed and seam welded carbon steel of 1mm wall thickness the

length of 60mm as shown in Figure 1, lab joint consignation was prepared to fabricate MPW joints

and also SD is playing a manger change on steel tube diameter 27,26,25,24,23mm respectively.

The initial joint consignation was obtained by securing the tubes in position using High Density

Polyethylene (HDPE). The direction weld was normal to the aluminium positioned direction.

Single pulse was used to fabricate the joints.

The fabricated joints were sliced from the MPW joint by Electron Discharge Marching (EDM) to

attain required shape size, as shown in Figure 1(a). Each specimen three strips (samples)

prepared. Two tensile shear specimens were set to evaluate the tensile shear fracture load.

Photos of fabricated joints and samples are shown in Figure 2(b). Tensile shear fracture test was

carried out in an electromechanical controlled universal testing machine and the average values

of two results are presented in Table 4. One Sample were surface-ground using 120 grit size belt

with the help of a belt grinder, polished using grade 1000, grade 2000 and grade 2500 sandpaper.

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The specimens were further polished by using aluminium oxide. Macroscopic and microscopic

inspections are done by optical microscopy. The MPW joint profile (Macrographs and

Micrographs) as shown in Figure 3 and Figure 5.

2.5 Development of empirical relationship

Response surface methodology (RSM) is a collection of mathematical and statistical techniques

that is useful for analysing problems, in which a response of interest is influenced by several

variables and the objective is to optimize this response. The response function of the joint, tensile

shear fracture load (TSFL), is a function of Voltage (V), Stand-off distance (D), and Working length

(L) and it can be expressed as:

TSFL = f (V, D, L) (1)

The second order polynomial (regression) equation used to represent the response surface ‘Y’ is

given as:

Y = b0+∑bixi+∑biixi2+∑bijxixj+er (2)

and for three factors, the selected polynomial could be expressed as:

TSFL = { b0+ b1(V)+ b2(D)+ b3(L)+b11(V2) +b22(D

2) +b33(L2) +b12(VD) +b13(VL)+ b23(DL) } kN (3)

where b0 is the average of responses; bi and bij are the coefficients that depend on the respective

main and interaction effects of the parameters. In order to estimate the regression coefficients,

a number of experimental design techniques are available.

In this work, central composite design which precisely fits the second order response surface was

used. All the coefficients were obtained by applying central composite design using the Design

Expert statistical software package. After determining significant coefficients, the final

relationship was developed using only these coefficients. The empirical relationship to predict

tensile shear fracture load of magnetic pulse welded aluminium tube with carbon steel tubular

joints is given as:

TSFL = { -65.14 + 0.035 V + 8.88 D +1 6.85 L + 0.09 VD + 5×10-3VL - 0.85 DL - 9.96×10-3 (V)2

–1.14 (D)2 - 1.08636 (L)2 } kN

2.6 Checking adequacy of developed relationship

The capability of the developed relationship was tested using the analysis of variance technique

(ANOVA). In this technique, if the calculated Fratio value of the developed model is less than the

standard Fratio (from F-table) value at a desired level of confidence (95%), the model is adequate

within the confidence limit. The ANOVA test results are presented in Table 5. It is understood

that the developed relationship is passable at 95% confidence level.

The model F-value of 244.3 implies that the relationship is significant. There is only a 0.01%

chance that this large “model F-value” could occur due to noise. Values of “prob>F” less than

0.0500 indicate the relationship terms are significant. In this case, V, D, L, VD, VL, DL, V2, D2, and

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L2 are significant model terms. Values greater than 0.1000 indicate the relationship terms are not

significant. The “lack of fit F-value” of 1.39 implies that the lack of fit is not significant compared

to the pure error. Coefficient of determination “r2” is used to find how close the predicted and

experimental values lie. The value of “r2” for the above-developed relationship is also presented

in Table 5, which indicates high correlation existing between the experimental values and

predicted values. The “Pred. R-squared” of 0.99 is in reasonable agreement with the ‘adj R-

squared’ of 0.98. “Adeq precision” measures the signal to noise ratio.

3.0 OPTIMIZATION OF MPW PARAMETERS

The response surface methodology (RSM) was used as an optimization tool to search the

optimum values of the process variables. The empirical relationship developed in the previous

section was framed using the coded values. The optimization was done on coded values and then

converted to actual values. Design Expert statistical software package was used to optimize the

process variables. Under the optimum conditions, a maximum tensile shear fracture load of 2.359

kN was obtained.

Response surfaces were developed for the empirical relationship, taking two parameters in the

‘X’ and ‘Y’ axes and response in ‘Z’ axis. The response surfaces clearly indicate the optimal

response point. The optimum tensile shear strength of MP welded AA 6063 T6 to IS 1239 was

exhibited by the apex of the response surface, as shown in Figure 6(a, b & c).

Contour plots show distinctive circular mound shape which is indicative of possible independence

of factors with response to display the region of optimal factor settings. By generating contour

plots using software for response surface analysis, the optimum is located with reasonable

accuracy by characterizing the shape of the surface. If a contour patterning of circular shaped

contour occurs, it tends to suggest the independence of factor effects while elliptical contours

may indicate factor interactions. The optimum response for MP welded AA 6063 T6 tube to IS

1239 tube is shown in Figure 6 (d, e & f).

4.0 ANALYSIS OF RESPONSE GRAPHS AND CONTOUR PLOTS

RSM optimization technique developed 3D response surface graphs and contour plots are,

formed based on the developed model by considering one parameter in the middle level and the

other two parameters are variables.

Figure 4(a and d) shows the 3D response surface graph and contour plot, with increasing stand-

off distance at a given voltage, the TSFL fist increases to a maximum value and afterwards shown

a decrease. Standoff distance 0.5 mm to 1 mm and increase in voltage 12 kV to 15 kV, at the time

of collision, kinetic energy of the outer tube (AA 6063 T6) is lower due to lower standoff distance

due to that impact velocity is reduced and tensile shear fracture load is decreases. At standoff

distance 1 mm to 2 mm at a given voltage the maximum TSFL (2.35 kN) is achieved. In the case

the kinetic energy of the outer tube (AA 6063 T6) is increases at critical voltage converted to heat

by massive plastic deformation of the metals. This deformation affects the interface and vicinity,

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resulting in a significant temperature increase [11] and strain hardening effect also increases [12].

The temperature rise of the interface softens the metals [13], and in some cases, melts local

pockets or a thin continuous layer along the interface. In some cases, wavy interface morphology

appears with short-term periodicity. Standoff distance 2 mm to 2.5 mm at a given voltage, the

TSFL is decreases. In the case of increasing stand-off distance, it is directly proportional to the

angle of collision and kinetic energy of the flyer (aluminium). The plastically deformed metal with

increasing kinetic energy increasing the shearing effect and decreasing the stability of the flyer.

Its lead to decreases the TSFL. Figure 4 (b and e) shows 3D response surface graph and contour

plot, with increasing working length at a given voltage, the TSFL fist increases to a maximum value

and afterwards shown a decrease with working length is increases. Working length 6.5 mm to 7.5

mm and increase the TSFL, because of the flyer is at the open end and is located in the middle of

the field shaper or coil (where the magnetic flux density is maximum), this area is subjected to

the maximum magnetic pressure, concentrated on the centre of the coil and also the collision

velocity is higher. Its converted to heat by massive plastic deformation of the flyer metals.

Figure 4(c and f) shows the 3D response surface graph and contour plot, with increasing standoff

distance at a given working length, the TSFL fist increases to a maximum value and afterwards

shown a decrease.

The elements diffusion during MPW process by the high energy impact is expected. It is mainly

due to the sudden transformation from one metal to another one cross the interface that is the

primary term for the element diffusion. In addition, the permanent severe plastic deformation

for high velocity impact causes the transient process with high temperature and high pressure,

which makes for the mutual diffusion of basic elements across the interface. Therefore, more

than one factor simultaneously results in the basic elements diffusion during MPW process. One

small region was chosen to conduct the small region scanning energy spectrum analysis, as shown

in Figure 6 (b). The mass percent of Fe and Al elements are 21.18% and 78%, respectively. And

also, the multi-direction micro-cracks and the micro-apertures present in the transition zone, as

shown in the Figure 6 (a). The severe shear deformation by the high velocity collision causes high

density dislocations and its crossing and irreversible climbing, which produces dense voids and

vacancies. A little air in the initial gap is trapped and cannot escape in time during the MPW

process, which generates the voids. The transient melt and solidification process because of the

severe plastic deformation results in the micro-voids and high impact energy damages the welded

interface, as shown in the Figure 6(a).

5.0 CONCLUSIONS

1) An empirical relationship was developed to predict tensile shear fracture load (TSFL) of

magnetic pulse welded AA 6063 Al alloy tube with IS 1239 carbon steel tube using response

surface methodology. The developed relationship can be effectively used to predict the

TSFL of magnetic pulse welded joints at 95% confidence level.

2) A maximum TSFL of 2.398 kN was obtained under the welding condition of 13.14 kV, 1.62

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SoD, 7.32 L, which is the optimum MP welding condition for AA 6063 T6 with IS 1239 and

confirmed by RSM.

3) Working length has the greatest influence on TSFL, followed by applied voltage, and stand-

off distance.

4) The metallurgical joint consists of two interfaces, one transition zone and two basic metals.

The mutual diffusion of Fe and Al elements occurs across the interface and in the transition

zone. The multi-direction micro-cracks and the micro-apertures present in the transition

zone.

ACKNOWLEDGEMENTS

The first author wishes to record sincere thanks to M/s. Magpulse Technologies Pvt Ltd, Peenya Industrial Estate,

Bengaluru for the financial support provided through Magpulse Research Fellowship and also providing welding

facility to carry out this investigation.

References

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Development & Lifecycle Process". Procedia Manufacturing 8 ( 2017 ) 409 – 416.

[2] Xu Zhidan, Cui Junjia, Yu Haiping, Li Chunfeng, " Research on the impact velocity of magnetic impulse welding of

pipe fitting". Materials and Design 49 (2013) 736–745

[3] Yusuke Aizawa, Junto Nishiwaki, Yohei Harada, Shinji Muraishi, Shinji Kumai. "Experimental and numerical analysis

of the formation behavior of intermediate layers at explosive welded Al/Fe joint interfaces". Journal of Manufacturing

Processes 24 (2016) 100–106

[4] Yu, H., Fan, Z., Li, C., "Magnetic pulse cladding of aluminum alloy on mild steel tube", Journal of Materials Processing

Technology (2013), http://dx.doi.org/10.1016/j.jmatprotec.2013.08.013.

[5] A. Stern, V. Shribman, A. Ben-Artzy, and M. Aizenshtein, " Interface Phenomena and Bonding Mechanism in

Magnetic Pulse Welding". JMEPEG (2014) 23:3449–3458 @ ASM International.

[6] R.N. Raoelison, N. Buiron, M. Rachik, D. Haye, G. Franz, " Efficient welding conditions in magnetic pulse welding

process". journal of Manufacturing Processes 14 (2012) 372–377.

[7] K.J. Lee, K. Shinji, A. Takashi, and T. Aizawa, Interfacial Microstruc- ture and Strength of Steel/Aluminum Alloy Lap

Joint Fabricated by Magnetic Pressure Seam Welding, Mater. Sci. Eng. A, 2007, 471(1-2), p 95–101.

[8]Lanza, M.; Lauro, A.; Scanavino, S.Fabrication and weldability in structures. AL Alumin. Alloys. 2001, 13,80–86.

[9] Haferkamp, H.; Niemeyer, M.; Dilthey, U.; Trager, G. Laser and electron beam welding of magnesium materials.

Weld. Cutt. 2000, 52, 178–180. Materials 2014, 7 3753

[10] Chudakov VA, Khrenov KK, Sergeeva YA, Gordan GN. The effect of temperature to which the material is heated on

the process of formation of intermetallic compound in magnetic pulse welding. Weld Prod 1980;27(9):23–5.

[11] Hampel H, Richter U. Formation of interface waves in dependence of the explosive welding parameters. In:

International conference on high energy rate fabrication, Leeds; 1981. p. 89–99.

[12] Szecket A. The triggering controlling of stable interface condition in explosive welding. Mater Sci Eng 1983;57:149–

54.

[13] Jaramillo D, Inal OT, Szecket A. On the transition from waveless to a wavy interface in explosive welding. J Mater

Sci 1987;22:3143–7.

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Table 1 Chemical composition wt% of the base metals

Material Si Mn Fe C Al

AA 6063 T6 0.25 0.5 0.3 98.6

IS 1239 1.4 98.34 0.2

Table 2. Mechanical properties of base metals

Materials 0.2% Yield strength Tensile strength (MPa) Hardness (HV 0.025 kgf)

Elongation in 50mm gauge length (%)

AA 6063 T6 214 240 83 12

IS 1239 320 442 125 20

Table 3: Important MPW parameters and their working range

No Parameter Notation Unit Levels

-1.682 -1.00 0 +1.00 +1.682

1 Voltage V kV 12 13 14 15 16

2 Stand-off-distance D mm 0.50 1.00 1.50 2.00 2.50

3 Working Length L mm 6.50 7.00 7.50 8.00 8.50

Table 4 Design matrix and experimental results

Expt. No Coded Values Actual Values TSFL (kN)

V D L V D L 1 -1 -1 -1 13 1 7 1.73

2 +1 -1 -1 15 1 7 1.5

3 -1 +1 -1 13 2 7 2.35

4 +1 +1 -1 15 2 7 2.32

5 -1 -1 +1 13 1 8 1.5

6 +1 -1 +1 15 1 8 1.3

7 -1 +1 +1 13 2 8 1.29

8 +1 +1 +1 15 2 8 1.25

9 -1.50 0 0 12 1.5 7.5 2.34

10 +1.50 0 0 16 1.5 7.5 2.07

11 0 -1.50 0 14 0.5 7.5 1.1

12 0 +1.50 0 14 2.5 7.5 1.76

13 0 0 -1.50 14 1.5 6.5 2.04

14 0 0 +1.50 14 1.5 8.5 0.90

15 0 0 0 14 1.5 7.5 2.1

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Table 5 ANOVA test results

Source Sum of squares df Mean square

F value P Value (Prob>F)

Model 4.36 9 0.48 244.3 < 0.0001 V-V 0.069 1 0.069 34.81 0.0002 D-D 0.38 1 0.38 193.64 < 0.0001 L-L 1.47 1 1.47 740.22 < 0.0001 V-D 0.016 1 0.016 8.17 0.0170 V-L 5E-5 1 5E-5 0.025 0.8770 D-L 0.36 1 0.36 182.18 < 0.0001 V2 1.43E-3 1 1.43E-3 0.72 0.4157 D2 1.18 1 1.18 593.35 < 0.0001 L2 1.06 1 1.06 536.07 < 0.0001

Residual 0.020 10 1.983E-3 Lack of fit 0.012 5 2.309E-3 1.39 0.3622 Pure error 8.283E-3 5 1.657E-3 Cor total 4.38 19

Standard Deviation 0.045 R-Squared 0.99

Mean 1.84 Adj R-Squared

0.99

C.V % 2.42 Pred R-Squared

0.98

Press 0.100 Adeq Precision

47.284

Fig 1 Dimensions of joint configuration (Unit: mm) Fig 2 Dimensions of TSFL specimen: (a) Schematic diagram of extraction of tensile specimens; (b) MPW extracted TSFL specimen

(a) (a)

(b) (b)

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Experiment No: 1 [ 13 kV, 1 SoD, 7 L]

Experiment No: 3 [ 13 kV, 2 SoD, 7 L]

Expt No: 4 [ 15 kV, 2 SoD, 7L]

Expt No: 9 [ 12kV, 1.5 SoD, 7.5 L]

Fig 3 Macrograph of some of the MPW joints

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TSFL

(a

)

(e) (b)

(f) (c)

(d) TS

FL

TSFL

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Fig 4 Contour plots and Response graphs for MPW AA 6063 T6 with IS 1239

Expt No Parameters Micrographs

200 X 500 X

2

V = 15 kV, D = 1 SoD, L = 7 L

3

V = 13 kV, D = 2 SoD, L = 7 L

4

V = 15 kV, D = 2 SoD, L = 7 L

9

V = 12 kV, D = 1.5 SoD, L = 7.5 L

Fig 5 Micrographs of some of the MPW joints

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Fig 6 MPW Interface Scanning Energy Spectrum Analysis Result

(a) (b)

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BEHAVIOUR OF LASER KEYHOLE WELDING INDUCED POROSITIES IN

THE CORROSIVE ENVIRONMENT

M. Umar & P. Sathiya*

Department of Production Engineering, National Institute of Technology, Tiruchirappalli, Tamilnadu, India-

620015.

*Corresponding Author: [email protected]; Tel.: +914312503510; Fax: +914312500133

ABSTRACT

In this work, the keyhole induced porosities were produced on a marine grade 5083

aluminium alloy using Yb: YAG laser beam welding process. In order to understand

the behaviour of those porosities with the corrosive medium, the surface containing

porosities were immersed in the chloride solution and its corrosion parameters were

observed using potentio dynamic polarization method. After corrosion, the corroded

surface was studied under scanning electron microscope and observed a curious

result that, on the corroded surface two porosities were affected by the chloride

solution and one remained undamaged. It was identified that the outer surface of

that intact porosity comprised of a higher concentration of Fe and Mn particles which

are cathodic. Hence, the intact porosity acted itself as a localized cathode and

induced selective dissolution of aluminium around it and prevented self-pitting. The

results indicated that, unlike the hydrogen gas porosities, the keyhole induced

porosity contains a higher amount of cathodic particles can remain undamaged even

in the corrosive environment.

Keywords: Aluminium; Laser Welding; Porosity; Corrosion; Atomic Force Microscopy.

1.0 INTRODUCTION

The AA5083 Aluminium alloys are the most widely used material in shipbuilding due to their

excellent corrosion resistance and the oxide layer (Al2O3) forming over the alloy surface protects

it from structural degradation [1, 2]. However, the heat added during welding of aluminium alloys

dramatically reduces its corrosion resistance by altering its metallurgical characteristics like

precipitation of anodic second phase particles such as Mg2Si and Al3Mg2 in the fusion zone (FZ)

and heat affected zone (HAZ). Application of laser beam welding (LBW) is one of the possible

alternates to minimize the common problems associated with other joining processes and still,

porosity remains a severe issue in LBW of AA5083 aluminium alloys. The keyhole induced porosity

is one of the two primary mechanisms associated with aluminium welding and the other

mechanism is driven by the low boiling-point elements such as magnesium and hydrogen. The

shape of these porosities are perfectly spherical and often seen in aluminium weldments if the

amount of hydrogen is not controlled [3-6]. Fuyong et al. [7] investigated the effect of casting

porosity on the corrosion and found that specimens have porosity experienced a higher corrosion

rate due to the partial breakdown of passive film and acceleration of micro-galvanic coupling.

mailto:[email protected]

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Zhang et al. [8] revealed the significance of porosity in long-term corrosion behaviour of coated

mild steel. It was observed that the porosity defects increased the rate of corrosion by decreasing

the stability of passive film and increasing the passive current density. Yafei et al. [9] have

reported the role of inclusions in pit initiation and propagation in pipeline steel. The inclusions

with distinctive compositions of Al-Mg-S-O-Ca were found to be responsible for the formation of

circular pits and the corrosion pits were similar to the pitting morphology of nanostructured Al-

Mg alloys in alkaline solution as reported by Mala and Constance [10].

Though the role of porosity in corrosion and its formation mechanisms were presented in the

previous studies, the behaviour of laser keyhole induced porosities in severe conditions have not

been reported elsewhere. Hence, in this work, the keyhole induced porosities were produced on

a 5083 aluminium alloy using LBW process and its interaction behaviour with the corrosive

medium was investigated. The surface consists of porosities were exposed in the 3.5% NaCl

solution and the data were obtained through the potentiodynamic polarization method.

Furthermore, the corrosion surface morphology was characterized using various advanced

microscopy techniques and the activities of porosity in the chloride solution were discussed.

2.0 MATERIALS AND METHODS

In order to produce the keyhole induced porosities, a butt joint was made on a 3 mm thick

AA5083-H111 alloy sheet using a 6-axis KUKA robot Yb: YAG laser beam welding machine with

the welding process conditions such as laser power of 2 kW, welding speed of 200 mm/min and

a spot diameter of 0.369 mm. Pure argon was used as a shielding gas with the flow rate of 20 lpm.

The weight % of major alloying elements existing in the base alloy are as follows: Cu (0.02), Si

(0.12), Fe (0.4), Mg (4.57), Mn (0.94), Cr (0.06), Ni (0.01), Ti (0.027), Zn (0.02) and balanced with

Aluminium. After welding, the samples were cut, ground, polished and etched with Poulton's

solution for microstructural evaluation. To obtain the corrosion parameters, the

potentiodynamic polarization test was performed in an IVIUM electrochemical workstation

equipped with a three-electrode system (reference, counter and working electrode). All the

electrodes were immersed in the 3.5% NaCl solution and the potential voltage was varied

between -1 V/SCE and +1 V/SCE with the scan rate of 1 mV/s. From the polarization curve, the

data were acquired in terms of corrosion potential (Ecorr) and pitting potential (Epit) and,

thereby, the width of the passive region (∆Epit) was calculated using the below-mentioned

equation:

∆Epit = Epit - Ecorr (mV) (Eq 1)

The microstructural and elemental features of the weld and porosity were observed before and

after corrosion using a scanning electron microscope (SEM) coupled with an energy dispersive

spectrometry (EDS). Atomic force microscopy (AFM) technique was used to examine the pitting

morphology of corroded surface as well as the porosity.

3.0 RESULTS AND DISCUSSION

It can be seen from Fig. 1 that the cold working process produced elongated grains in the base

metal (BM) microstructure with a nonuniform dispersion of second phase particles such as

Al3Mg2, Mg2Si, Al6Mn or Al6 (Fe,Mn) and α-Al(Mn,Fe)Si [4, 11-15]. The interface between FZ

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and BM experienced grain growth whereas the transformation of columnar dendrites to equiaxed

dendrites ensued from the fusion boundary to the weld pool centre was attributed by the

different heating/cooling rates. The temperature gradient (G) is maximum at the fusion boundary

and minimum at the weld centre. On the contrary, the grain growth rate (R) is minimum at the

fusion boundary and maximum at the weld centre [4-6]. As a result, the degree of undercooling

(G/R) gradually increases from the weld centre to the fusion boundary.

Fig. 1 SEM micrograph showing the existence of porosity in the CDZ of FZ.

This leads to the formation of equiaxed dendrites in the middle of the FZ and columnar dendrites

facing perpendicular to the fusion boundary [5]. The encircled portion in Fig.1 shows a keyhole

induced porosity entrapped at the columnar dendrite zone (CDZ) or bottom of the FZ during rapid

solidification. It is evident that a bubble (keyhole induced porosity) was formed during LBW due

to the instability of keyhole and moved to the rear side of the molten pool and stayed in at the

bottom of the FZ without getting collapsed with the reformed keyhole. This is due to the

recirculation flow of the molten pool at the front wall and insufficient temperature to float the

bubbles to the top surface of the molten pool [16]. Also, it is believed that the high thermal

gradient induced Marangoni flow is responsible for the recirculation at the melting front and

other researchers in [5,6,15,16] were reported similar mechanisms. These process induced

porosities are sized at the micron level and are often seen at the bottom as well as the toe of the

weld [5,6]. The approximate diameter of the porosity observed in this study was 62.102 μm and

it is comparable with previously reported results [6,12,15].

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Fig. 2 Potentiodynamic polarization curve.

Afterward, the FZ had porosities was exposed to the chloride solution and the electrochemical

measurements were taken. The corrosion parameters (Ecorr = -1050 mV, Epit = -728 mV, ∆Epit =

322 mV) were determined from the Tafel curve shown in Fig. 2. It is indicating that the stable

passive film and cathodic particles present on the weld surface reasonably delayed the pit

initiation though porosities were present. Since the cathodic elements have higher corrosion

potential than the alloy matrix, the cathodic particles present in the alloy surface usually resist

or delays pit initiation during corrosion [7,10].

Fig. 3 Corrosion mechanism and surface feature of porosities: (a) SEM image of the corroded

surface showing dissolved and intact porosity. (b) The 3-D image observed through AFM showing

unaffected surface of 3rd porosity. (c) Profile extraction curve is showing pit measurements.

The presence of Fe and Mn-rich particles or intermetallics (Al6(Fe,Mn)) on the 5083-alloy surface

induces localized cathodic reaction which increases the width of passive region and results in

noble corrosion resistance [17].

In addition, the corroded surface was studied under SEM and the resultant image is shown in Fig.

3a. It is evident that the alloy matrix had undergone localized alkaline corrosion and got corroded

severely than the porosities due to its anodic nature. The pits were formed at various sites and

propagated along the grain boundaries caused an intensive pitting attack through which the

substrate got corroded thoroughly. The shape and distribution of pits are related to the

electrochemical nature of the elements present in the alloy surface [17]. In Fig. 3a, the points 1

and 2 indicate the traces of porosities that are dissolved in the chloride solution and left a cup-

shaped depression whereas point 3 signifies a spherical porosity which remains undamaged.

According to the investigations [7-12], a porosity or an inclusion present on the alloy surface

induces severe localized corrosion and maximizes the rate of corrosion. The porosity formed

between the passive film and the substrate could act as a direct path for the chloride solution to

penetrate and interact with the subsurface and results in severe corrosion [8]. The former

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mechanism was evident in the case of porosities 1 and 2 in which the chloride solution used them

as a channel to reach the substrate and finally corroded the substrate as well as the porosities.

In order to verify the existence and surface features of unaffected porosity, the corroded surface

was analysed through AFM and the results are shown in Fig. 3(b-c). It is evident from the profile

extraction curve that (see Fig. 3c), there was no sign of pitting on the porosity surface and the

curve was somehow replicating the top surface of it. However, a very few micron level ups and

downs are there on the curve and the tribological features of porosity were responsible for that.

The surface of keyhole-induced porosities could be irregular due to the traces of fluid flow

present on the outer wall whereas the hydrogen-induced porosities have smooth surfaces [16].

Some deeper pits are evident in the nearby region (see Fig. 3b) and anodic dissolution of major

alloying elements such as Al and Mg could be caused it. The pits formed nearby porosities might

be attributed to the localized rise in pH around cathodic particles generating hydroxyl ions which

dissolve anodic inclusions [16].

Fig. 4 EDS analysis on the intact porosity. (a-f) Mapping results. (g and h) Point analysis result.

Still, the fact behind the existence of porosity 3 even after corrosion remained concealed until

the EDS analysis was performed on it. The Figs. 4(a-f) are showing the results of EDS mapping

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analysis and it is evident that the porosity surface comprised of a higher concentration of cathodic

particles like Fe and Mn whereas a minimal amount of Mg was detected on it. The vaporization

of Mg during keyhole welding could be the reason for it. The dispersion of Fe and Mn were

identical on the porosity surface (see Fig. 4e and 4f) while a random distribution of other

elements can be seen in Fig. 4(b-d). The former results were verified with the EDS point analysis

and it confirms that a higher amount of Fe (16.60 %) and Mn (10.45 %) particles were existing on

the porosity surface which is quite significant. The reason behind this accumulation of Fe and Mn

particles on the porosity surface were not clear at the moment. In general, the Fe and Mn

particles are cathodic in nature and resists the pit propagation intensely [10-12, 15]. Since the

outer surface of porosity contains a higher concentration of cathodic Mn and Fe particles, it acted

itself as a localized cathode and induced galvanic coupling between the porosity and aluminium

matrix which led to the selective dissolution of Al around it. This detrimental effect caused a

severe corrosion attack at the interface region and produced deeper pits [7,10]. Also, the

accumulation of oxide particles occurred at the interface region (see Fig. 4d) due to the oxygen

reduction on the porosity surface during cathodic reaction with the sequential growth of

hydroxide anion [7,10,12]:

O2 + 2H2O + 4e 4OH (Eq 2)

The migration of chloride ions from the solution towards the anodic sites was reported as a

significant factor in this occurrence [9]. Hence, based on the results observed, it is identified that

the keyhole induced porosity composed of cathodic particles can resist corrosion and remains

undamaged.

4.0 CONCLUSION

The keyhole induced porosities were produced on a marine grade 5083 aluminium alloy and the

interaction behaviour of those porosities with chloride the solution was analysed using various

microscopy techniques.

• The corrosion resistance of laser keyhole-induced porosities is different from hydrogen gas

porosity.

• The corrosion potential of porosities depending on its surface composition.

• The porosity comprised of a higher concentration of Fe and Mn particles can act as a

localized cathode and induce selective dissolution of aluminum around it and prevent self-

pitting.

• This study suggests that unlike the hydrogen gas porosity, the keyhole induced porosity

contains a higher amount of cathodic particles can remain undamaged in the alloy surface

even after corrosion.

ACKNOWLEDGMENT

The authors would like to express their most profound appreciation and sincere thanks to the

Department of Science and Technology - Science and Engineering Research Board (DST-SERB),

New Delhi, India, for financially supporting this entire research work, under the sponsored

research project sanctioned No.SB/EMEQ-168/2014, dated 29-01-2016.

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