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Investigation of wear and friction properties of Al-Cu-Mg composites

reinforced with SiC/Gr particles.

Monikandan V.V.a

, G. Vijayabhaskarb

, K. Manisekarc

, P. Ravindrand

.

a P.G. Student,

Center for Manufacturing Sciences, National Engineering College, K.R. Nagar-628 503.

[email protected] P.G. Student,


[email protected] Head of department


[email protected] Lecturer

Center for Manufacturing Sciences, National Engineering College, K.R. Nagar-628503.

[email protected]

ABSTRACT

The wear and friction properties of Al-Cu-Mg-based composites reinforced with SiC/Gr particles was examined

under varying applied load (5-20 N) and within a sliding velocity range (1.4-2 ms -1 )and sliding distance range

(500-2000 m) at room conditions. The dry sliding wear behavior was studied using pin-on-disc method against

EN31 counter surface and SIC paper of sizes 600,800 and 1200, giving emphasis on parameters such as friction

coefficient and weight loss as a function of applied pressure, sliding velocity and sliding distance. It was noted that

the wear properties of the composite was deteriorated significantly with rise in applied pressure due to penetration

of counter surface asperities to pin surfaces. It was observed that the weight loss was increased with increase in

sliding distance. While, the friction coefficient followed reverse trend. Both the weight loss and friction coefficient

reduced significantly with rise in sliding velocity.Graphite content formed a tribolayer that reduced friction. In

case of abrasive wear, the alignment of worn SiC precipitates along sliding direction reduces interaction of

counter surfaces and thus reducing the weight loss with rise in applied load.

Keywords: Aluminium based composite, Wear and friction, Effect of sliding speed, sliding distance, and load

1 INTRODUCTION


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from 20 mm to 8 mm by turning operation. Theturned preform was polished using 600 grit siliconcarbide paper.

Figure 1. specimen2.3 Procedures

Dry sliding wear tests were conducted usinga pin on disk tester (model: ED-201, Wear andfriction monitor, Ducom Make, Bangalore). Theschematic of this machine is shown in Figure 2. Pinspecimens of diameter 8 mm and length 15 mm weremachined from powder metallurgy produced billets.Contact surfaces were prepared by grinding againstsilicon carbide paper and cleaning with acetone. Apin-holder loaded the stationary pins vertically on toa rotating EN 31 steel disc of hardness 500 HV. For

abrasive wear tests the disk is replaced by SiC gritpaper. All experiments were conducted under roomconditions. During sliding the load is applied on thespecimen through cantilever mechanism and thespecimens brought in intimate contact with therotating disc or SiC grit paper at track radius of 70mm. Three experimental conditions of load, slidingdistance and sliding velocity are selected for measuring wear and friction.1)Four normal loads (5, 10, 15, 20 N) were appliedusing dead weights, while speed as 500 rpm andsliding distance as 500 m constant.2) Four sliding velocities (1.4, 1.6, 1.8 and 2 m/s)

were attained by varying speed, while load as 15 Nremained constant.3) Four sliding distances (500, 1000, 1500 and 2000m) were attained by varying time, while load as 15 Nand speed as 500 rpm remained constant.

Before and after each test, the pins werecarefully cleaned with acetone and weighed using asensitive electronic balance with a accuracy of 0.1mg to determine the weight loss.

Figure 2. Schematic of the pin-on-disk apparatus

The friction coefficient was computed fromthe recorded frictional force and applied load. (i.e. theratio of frictional force to the applied load). Thisprocedure is repeated for all three experimentalconditions. For abrasive wear tests, the counter facedisk is replaced by SiC grit paper of sizes 600, 800and 1200. The procedure to determine wear andcoefficient of fiction remains the same.

3 RESULTS AND DISCUSSION

3.1 Effect of load on weight lossThe weight loss of the sample as a function

of applied pressure is depicted in Fig. 3. The Fig.shows that the weight loss of the specimen increaseswith increase in load. This is primarily due to thefact with increase in applied pressure, the penetrationof hard asperities of the counter surface to the softer pin surface increases. Again, with increase in appliedpressure surface and subsurface deformation andmicro cracking tendency increases. The effectivewear from the specimen surface is due the combinedeffect of all these factors. It was immediatelyapparent that weight loss was greater at the higher load of 20 N. It should be noted that there is noabrupt rise in weight loss which exhibits the absenceof transitional load up to 20 N.

3.2 Effect of load on friction coefficient

The coefficient of friction is the ratio of friction force to applied load. As seen from Fig. 4which shows that there was a decrease in coefficient


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of friction with increase in load. There were noentrapped SiC particles between counter surfacesleading to less coefficient of friction. Similar toweight loss characteristics, here too absence of abruptrise of friction coefficient indicates that there is notransitional load up to 20 N.

Figure 3. Weight loss as a function of load

Figure 4. Friction coefficient as a function of load

3.3 Effect of sliding distance on weight loss

Fig. 5 shows the weight loss as a function of sliding distance at applied load of 15 N to 70 mm of track radius and sliding velocity of 1.4 m/s. Initiallythe temperature of the contact surface is less and theasperities are sharper, stronger and rigid, thus atinitial stage the wear is mainly due to fragmentationof asperities and removal of material due to cuttingand flowing actions of penetrated hard asperities intothe softer surface. Also, as the time progresses, thefrictional heating increases and higher temperatureleads to softening of the surface materials and theasperity contacts are readily deformed.

Because of combined actions of load,(Normal and shear stress acting on the higher stress

points of asperities make them deform) and slidingdistance subsurface microcracks are generated whichfinally leads to removal of wear debris. As a result, itis expected that weight loss will increase withincrease in sliding distance.

Figure 5. Weight loss as a function of slidingdistance3.4 Effect of sliding distance on coefficient of friction

Fig. 6 shows coefficient of friction as afunction of sliding distance at applied load of 15 N,70 mm of track radius and sliding velocity of 1.4 m/s.The plot shows that coefficient of friction decreaseswith increase in sliding distance. During sliding, thecontact surfaces were heated by frictional heating andsurface, subsurface deformations. While the counter surfaces are in relative motion, the frictional heatingis continuous because of insufficient time for heatdissipation. In addition, because of relatively lesstemperature, the temperature gradient of thespecimen surfaces with respect to the bulk of thespecimen and the surrounding environment is less.This also leads to slower rate of heat dissipation, after certain period, temperature rises significantly andthen temperature gradient increase; this results inhigher rated of heat dissipation. Again because of greater flowability of the material on the specimensurface, sliding action is more; this reduces frictionalheating and consequently coefficient of friction.

3.5 Effect of sliding velocity on weight loss

Weight loss versus pressure and slidingspeed curves for the Al-based composite were shownin Figure 7. The curve shows that the weight loss of the material decreased with increase in slidingvelocity. Smearing can be produced by bothmovement of wear material from one place to another on the wear surface and its back transferring from thedisc surface to sample surface, while scratches are


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caused by ploughing action of hard particles. It maybe observed in this work that as the sliding speedincreased, the area of smeared material increased andscratches become deeper. Since more smearing leadsto lower wear loss, Al-based composite is expected toexhibit higher wear resistance which was vindicated

by the plots shown in the Fig. 7.

Figure 6. Friction coefficient as a function of sliding distance

Figure 7. Weight loss as a function of slidingvelocity

3.6 Effect of sliding velocity on friction coefficient

Coefficient of friction decreased with rise insliding velocity as shown in the curve of the Fig. 8.Graphite addition influences friction coefficient.There was reduction in friction coefficient whichcould be attributed to the presence of smearedgraphite layer at the sliding surface of the wear

sample which acts a solid lubricant. This lubricantfilm prevents direct contact of the two surfaces. Thedecreased coefficient of friction due to increasedaddition of graphite particles has also been observedby many workers.

Figure 8. Friction coefficient as a function of sliding velocity

3.7 Effect of load on weight loss for abrasive wear

The weight loss as a function of load isshown in Figure 9. As the plot shows the weight lossgradually decreases with increase in applied load for all the grit sizes of 600, 800, and 1200. Thesubsurface deformation rise leads to alignment of stronger precipitates along the sliding direction. Inaddition temperature also leads to greater flowabilityof surface materials and thus increase greatly thepossibility of compaction of wear debris on thespecimen surface. Thus effectiveness of the abrasiveaction of the counter surface asperities reduces whichleads to reduction in weight loss; the same was meantfor all grits.

Figure 9. Weight loss as a function of load

3.8 Effect of load on friction coefficient forabrasive wear

The friction coefficient as a function of loadis shown in Figure 10 for all grit sizes of 600, 800,and 1200. There was gradual reduction in frictioncoefficient with increase in load. The graphite forms


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a tribo layer which prevented metal to metal contactand lowered the coefficient of friction.

Figure 10. Friction coefficient as a function of load

4 CONCLUSIONS Tribological behavior of Al-based composite hasbeen experimentally analyzed, leading to followingconclusions.1, Increase in weight loss due to increase in loadindicates the penetration of hard counter surfaceasperities to a softer pin material. There is no abruptrise in weight loss and friction coefficient whichshows that there was no transitional load up to 20 N.

3, The weight loss of the composite had increasedwith increase in sliding distance, owing to combinedaction of load, sliding distance and sliding speedwhich removes wear debris from asperity contacts.The friction coefficient decreases with increase insliding distance due to continuous relative motion of counter surfaces.

4, It was observed that weight loss decreases withincrease in sliding velocity. When sliding velocityincreases the area of smeared material becomes morewhich leads to lower weight loss. , The coefficient of friction decreases with increase in sliding velocity.

The graphite forms a Tribolayer which preventsmetal to metal contact and consequently decreasingfriction coefficient.

5, For abrasive wear, the weight loss graduallydecrease with increase in load because of alignmentof precipitates along sliding direction which reducesmetal to metal contact. This lead to the reduction of weight loss with increase in applied load. The friction

coefficient also decreases with increase in appliedload.

5 REFERENCES

[1] Adel Mahamood Hassan, Abdalla Alrashdan,Mohammed T. Hayajneh, Ahmad Turki Mayyas(2009) Wear hehavior of Al-Mg-Cu-basedcomposites containing SiC particles Tribologyinternational, Vol.42, 1230-1238

[2] Das S. Das K. (2007) Abrasive wear of zirconsand and alumina reinforced Al-4.5 wt% Cu alloymatrix composites-a comparative study, Compositesscience and technology, Vol.67, 745-751

[3] R.N. Rao, S. Das, D.P. Mondal, G. Dixit (2009)Dry sliding wear behavior of cast high strengthaluminium alloy (Al-Zn-Mg) and hard particlecomposites Wear, Vol.267, 1688-1695

[4] C.Y.H. Lim, S.C. Lim, M. Gupta (2003) Wear Behaviour of SiC P-reinforced magnesium matrixcomposites Wear, Vol.255, 629-637

[5] Temel Savaskan, Yasin Alemdag (2008) Effectof pressure and sliding speed on the friction and wear properties of Al-40Zn-3Cu-2Si alloy; A comparativestudy with SAE 65 bronze Materials Science andEngineering VOL.A 496, 517-523

[6] F. Akhlaghi, A. Zare-Bidaki (2009) Influence of graphite content on the dry sliding and oilimpregnated sliding wear behavior of Al 2024-graphite composites produced by in sity powder metallurgy method Wear, Vol.266, pp.37-45

[7] Sang-Chul Kim, Moon-Tae Kim, Sungkyu Lee,Hyungsik Chung, Jae-Hwan Ahn (2005), Effects of copper addition on the sintering behavior andmechanical properties of powder processed Al/SiC pcomposites Journal of materials science, Vol.40,441-447

[8] Veeresh Kumar G.B., C.S.P Rao, Bhagyashekar

M.S. and Selvaraj N. (2009) Mechanical andTribological behavior of Al7075-Al 2O3 CompositesJournal of manufacturing engg., Vol.4,. 105-110.

[9] R.A. Saravanan, M.K. Surappa, (2000)Fabrication and characterization of pure magnesium-30% vol.% SiC p particle composite, Material scienceengineering Vol.A276, 108-116

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