STUDY OF THE EFFECT OF AGING CONDITION ON STRENGTH AND

HARDNESS OF 6063-T5 ALLOY

Supervised by : Dr. G.I.P. De Silva

Presented by : E.M.A.N. Ekanayaka S.A.D.T. Dharmarathna

INTRODUCTION

Aluminium - The most abundant metal in the earth crust

• 8% by weight of the earth’s solid surface

Properties - Durability, light weight, good extrudabilityand surface finish

Pure metal and the alloy used as alternatives for other metals (ferrous and non-ferrous), ceramics and wood

Sri Lankan demand

• Structural applications: Window and Door Frames, Partitioning, L bars, U bars

2

ALUMEX (PVT) LTD.

Project was industrially focused on “Alumex”

Product: Extruded Aluminium articles

Raw material: 6063-T5 Aluminium alloy

3

ISSUES

Production cannot meet the present increased demand

Relatively high cost of products

4

PRODUCTION PROCESS

5

Casting

Homogenizing

Extrusion

Age Hardening

Surface Treatments

REMEDY

Reduction of time in the Age Hardening process

6

OBJECTIVES

To reduce the Age Hardening Time

To reduce the Energy Consumption

To upgrade the Mechanical Properties

7

LITERATURE REVIEW

8

6063-T5 Aluminium alloy

6063 Age Hardenable Aluminium alloy

• Main alloying elements: Mg (0.2 ~ 0.6 wt%)

Si (0.45 ~ 0.9 wt%)

T5 - Cooled from an elevated temperature andartificially aged

9

6063-T5 Aluminium alloy

Second Phase: Mg2Si

Solid solubility of Mg2Si decreases from 1.85 wt. %

at the eutectic temperature of 595 C

Al-Mg2Si quasi binary system forms10

Age hardening

Maximum hardness is achieved if the precipitates canresist cutting by dislocations, and are too close topermit by-passing of dislocations.

Strengthening a metal by introducing small particles of another phase which barriers dislocations motion

Cutting through:When the precipitates are too small

Bowing and By pass:When precipitates are too strong to be cut and inter-particle space become large

11

The Age Hardening Process

12

SSSS

Solution treatment

Age hardening treatment

Al-Mg2Si quasi binary system

GP zones – First form of precipitates (unstable) Needle Shaped with the long axis along [100] of the matrix

Sequence of precipitates in Al-Mg2Si

13

Al-Mg2Si quasi binary system

Sequence of precipitates in Al-Mg2Si

β΄ phase – Developed rod shape with Hexagonal crystal structure

Maximum hardness14

Al-Mg2Si quasi binary system

Sequence of precipitates in Al-Mg2Si

β phase - Equilibrium phase with FCC crystal structure

Alloy is over aged – Hardness decreases

15

Al-Mg2Si quasi binary system

16

Closely spaced fine precipitates

• Resist dislocation Bowing and By pass

Strong large precipitates

• Resist cutting by dislocations

This is called a Bimodal Precipitate Structure

17

Closely Spaced Fine Precipitates

Strong Large Precipitates

Increased Hardness+ =

CONCEPT

Two Step Aging Process

18

19

Homogeneous Nucleation of a Solute Cluster

r = radius of solute cluster

ΔG = free energy needed to form a spherical

cluster of radius r

GV = change in free energy per unit volume

σ = surface free energy per unit area

rc = critical radius of the cluster

Gibbs-Thompson equation

S = Amount of super saturation at a particular temperature

K = Temperature dependent constant ( K 1/ T )

rc= Critical radius of a cluster at the relevant temperature

When T increases, rc increases

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At temp. T1 clusters nucleate and

grow - Size distribution: rmin – rmax

When temp. is raised from T1 to T2,

critical radius is raised from rc1 to rc2

If cluster radius r > rc2, the cluster will

survive and continue to grow

If cluster radius r < rc2, the cluster will

be unstable and will dissolve. Butre-nucleation may occur.

This results a Bimodal PrecipitateStructure with both closely spacedfine precipitates + strong largeprecipitates, which results betterMechanical Properties.

21

Industrially Practiced Age Hardening Process

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Solution treatment

Age hardening treatment

Process was re-performed within the laboratory

Results were used as reference values

•Measured Hardness(HV) – 47.05

•Total Time (Age Hardening) – 270 min

Parameters Varied During the Process

1st step temperature - T1

Time to reach the 1st step temperature - t1

Soaking time in the 1st temperature - t2

2nd step temperature - T2

Time to reach the 2nd step temperature - t3

Soaking time in the 2nd temperature – t423

T2

T1

t5t4t3t2t1

Temperature (oC)

Time (min)

LIMITATIONS

Furnace Limitation• The industrially acceptable range: 150oC to 250oC

Energy Consumption

Total Time Consumption• Below 270 min

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CONSTANTSTime to reach the 1st step temperature: t1

• 60 minutes

2nd step temperature: T2

• 225oC

Time to reach the 2nd step temperature: t3

• 30 minutes

25

T2

T1

t5t4t3t2t1

Temperature (oC)

Time (min)

STAGE 1 - VARIABLES1st step temperature: T1

• Altered within150oC-200oC

Soaking time in the 1st temperature: t2• Varied from 45 min- 90 min for each set of temperatures

Soaking time in the 2nd temperature: t4• Varied Combinations-15 min and 30 min

26

T2

T1

t5t4t3t2t1

Temperature (oC)

Time (min)

All Specimens were Solution Treated

• At 540oC for 3 hours

• To remove age hardening imposed

• Dissolve all precipitates

27

Muffle Furnace

A set of combinations among the above variables were developed

Heat treatments were performed using the Super C furnace for 2 samples per combination.

28

Super C Furnace

Hardness was tested using Vickers Hardness tester

• 3 per sample 6 per combination

• Average was recorded

Optimum suitable parameters determined using hardness obtained

29Vickers Hardness Tester

Aging Time and Temperature Combinations

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1st step 2nd step Hardness

(HV)Temperature Time Temperature Time

150oC 60 min 225oC 15 min 37.85

150oC 90 min 225oC 15 min 38.25

175oC 45 min 225oC 15 min 39.10

175oC 60 min 225oC 15 min 41.68

175oC 75 min 225oC 15 min 47.58

175oC 90 min 225oC 15 min 45.93

200oC 60 min 225oC 15 min 35.05

200oC 90 min 225oC 15 min 37.87

t4 – maintained as 15 minT1 – varied from 150oC to 200oC

T2

T1

t5t4t3t2t1

Tem

per

atu

re (o

C)

Time (min)

Hardness – Not Satisfactory

31

32

t4 – maintained as 30 min

T1 – varied from 150oC to 200oC

T2

T1

t5t4t3t2t1

Tem

per

atu

re (o

C)

Time (min)

1st step 2nd stepHardness

(HV)Temperature Time Temperature Time

150oC 60 min 225oC 30 min 41.47

150oC 90 min 225oC 30 min 41.25

175oC 45 min 225oC 30 min 40.92

175oC 60 min 225oC 30 min 51.68

175oC 75 min 225oC 30 min 52.05

175oC 90 min 225oC 30 min 43.78

200oC 60 min 225oC 30 min 36.42

200oC 90 min 225oC 30 min 40.62

Reference Hardness (HV) – 47.05

DERIVATION

1st Step Temperature (T1) : 175oC

1st Step Soaking Time (t2) : 60 min

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Rejections

• 150oC – Low hardness in acceptable time duration

• 200oC – Higher energy consumption

Current Status 1st step temperature : 175oC

Time to reach the 1st step temperature : 60 min

Soaking time in the 1st temperature : 60 min

2nd step temperature : 225oC

Time to reach the 2nd step temperature : 30 min

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225

175

30t4306060

Tem

per

atu

re (

oC

)

Time (min)

35

2nd step soaking time “t4” was altered

• 0 ~ 60 min – 10 min intervals

Different sets of combinations were developed

Samples prepared as standard tensile test specimens

Tensile Test Sample

1.72mm(Gauge Length)

150 mm

14mm

66 mm

STAGE 2

Heat Treatment - Super C• 2 specimens per combination

Hardness - Vickers Hardness Tester• 3 per sample 6 per combination

• Average was recorded

Tensile Strength – Tensile Testing Machine

36Tensometer

Combinations and Results for varied “t4”

37

Sample noHeat Treatment

t4 (min)Hardness

(HV)

Tensile Strength

(N/mm2)1st Step 2nd Step

1 Reference _ 47.05 228.41

2 175oC - 60 min 225 oC - 0 min 0 45.08 170.27

3 175oC - 60 min 225 oC - 10 min 10 45.38 182.72

4 175oC - 60 min 225 oC - 20 min 20 46.83 199.34

5 175oC - 60 min 225 oC - 30 min 30 49.13 228.41

6 175oC - 60 min 225 oC - 40 min 40 51.10 240.86

7 175oC - 60 min 225 oC - 50 min 50 47.88 240.86

8 175oC - 60 min 225 oC - 60 min 60 45.33 232.56

Graph of Hardness Vs “t4” value

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45.08 45.38

46.83

49.13

51.10

47.88

45.33

32.00

37.00

42.00

47.00

52.00

57.00

0 10 20 30 40 50 60

Har

dn

ess

(H

V)

t4 value (min)

47.05

Graph of Strength Vs “t4” value

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170.27

182.72

199.34

228.41

240.86 240.86

232.56

100.00

120.00

140.00

160.00

180.00

200.00

220.00

240.00

260.00

0 10 20 30 40 50 60

Ten

sile

Str

en

gth

(N

/mm

2)

t4 value (min)

228.41

Theoretically

• Absorbed heat energy (E) = mcE= Heat energy

m = Mass of samples

c = Specific Heat Capacity

= Temperature Difference

• Since m and c are constant

• Energy Ratios = Ratio of areas under the graphs

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Temperature (oC)

Time (min)

Energy Comparison

EFFECTIVENESS – Varied “t4”

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Sample noHeat Treatment

t4 (min)Total Time

(min)

% Time

Saving

% Energy

Saving1st Step 2nd Step

1 Reference_

270 0 0

2 175oC - 60 min 225oC- 0 min 0 180 33.33 45.59

3 175oC - 60 min 225oC- 10 min 10 190 29.63 39.96

4 175oC - 60 min 225oC- 20 min 20 200 25.93 34.33

5 175oC - 60 min 225oC- 30 min 30 210 22.22 28.71

6 175oC - 60 min 225oC- 40 min 40 220 18.52 23.08

7 175oC - 60 min 225oC- 50 min 50 230 14.81 17.45

8 175oC - 60 min 225oC- 60 min 60 240 11.11 11.82

Optimum was selected considering above results

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225

175

3040306060

Tem

per

atu

re (o

C)

Time (min)

205

90

Tem

per

atu

re (o

C)

Time (min)30150

Developed Process Process at Alumex

Hardness (HV) = 51.10

Tensile Strength (N/mm2) = 240.86

Total Time (min) = 220

Hardness (HV) = 47.05

Tensile Strength (N/mm2) = 228.41

Total Time (min) = 270

Microstructure Observations

Microstructure • Selected sample and reference

• Viewed using Metallurgical microscope (X200)

• Idea about grain size

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Metallurgical Microscope

44

After optimized Two Step Aging Treatment

Polishing Agent: Polycrystalline Diamond Powder

Etchant: 5% HNO3 + 2% HF Solution

Microstructure Observation

After “Alumex” Practiced Aging Treatment

Polishing Agent: Polycrystalline Diamond Powder

Etchant: 5% HNO3 + 2% HF Solution

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225

175

3040306060

Tem

per

atu

re (

oC

)

Time (min)

PROGRESS

Property / parameter Practiced Process Developed Process

Hardness (HV) 47.05 51.10

Tensile Strength (N/mm2) 228.41 240.86

Total Time (min) 270 220

Time Saving (min) _ 50

% Time Saving _ 18.52

% Energy Saving _ 23.08

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CONCLUSION

Considering Production Rate, Production Cost andEnhanced Mechanical Properties the following AgeHardening Treatment is recommended.

225

175

3040306060

Tem

per

atu

re (

oC

)

Time (min)

THANK YOU

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