Wear Behavior of Commercial Aluminium Engine Block and Piston under Dry Sliding Condition

Transcription

1 Wer Behvior of Commercil Aluminium Engine nd under Dry Sliding Condition M. S. Kiser, Swgt Dutt Astrct In the present work, the effect of lod nd sliding distnce on the performnce triology of commercilly used luminium-silicon engine lock nd piston ws evluted t mient conditions with humidity of 80% under dry sliding conditions using pin-on-disc with two different lods of 5N nd 20N yielding pplied pressure of 0.30MP nd 1.4MP, respectively, t sliding velocity of 0.29ms -1 nd with vrying sliding distnce rnging from 260m- 4200m. Fctors nd conditions tht hd significnt effect were identified. The results showed tht the lod nd the sliding distnce ffect the wer rte of the lloys nd the wer rte incresed with incresing lod for oth the lloys. Wer rte lso increses lmost linerly t low lods nd increse to mximum then ttin plteu with incresing sliding distnce. For oth pplied lods the piston lloy showed the etter performnce due to higher Ni nd Mg content. The worn surfce nd wer deris ws chrcterized y opticl microscope, SEM nd EDX nlyzer. The worn surfce ws chrcterized y surfce with shllow grooves t lods while the groove width nd depth incresed s the lods increses. Oxidtive wer ws found to e the predominnt mechnisms in the dry sliding of Al-Si lloys t low lods. Keywords Wer, friction, grvimetric nlysis, luminiumsilicon lloys, SEM, EDX. A I. INTRODUCTION LUMINIUM-SILICON lloys hve een used in trio components involving sliding movements with contcting counter-ody [1]-[3]. The response of these components gretly depends on their mteril-relted prmeters, e.g., the nture shpe, size, content, nd mode of distriution of given micro-constituents. Also, service/test conditions influencing the wer chrcteristics of mterils include lod, speed, temperture, environment, counter-ody roughness, nd configurtion of the sliding pir, reltive to constnt design spect [4]. It hs een oserved tht even minor ltertion in ny of the prmeters cn chnge the sliding wer ehvior significntly. Thus, it is essentil to chrcterize the mteril for their mechnicl properties nd sliding wer ehvior in s mny situtions s possile. This would enle us to develop etter understnding out the response. Aluminium-silicon sed lloys re well-known csting lloys with high wer resistnce, low therml expnsion coefficient, good corrosion resistnce nd improved M. S. Kiser is working s Deputy Director in the Directorte of Advisory, Extension nd Reserch Services, Bngldesh University of Engineering nd Technology, Dhk-1000, Bngldesh, phone: ; fx: ; (e-mil: mskiser@it.uet.c.d). Swgt. Dutt is with the Institute of Approprite Technology, Bngldesh University of Engineering nd Technology, Dhk-1000, Bngldesh (e-mil: swgt_dutt@it.uet.c.d). mechnicl properties in wide rnge of temperture. These properties led to the ppliction of Al-Si lloys in utomotive industry, especilly for cylinder locks, cylinder heds, pistons nd vlve lifter [5]-[7]. Wer is nother mjor filure of engine lock mteril. This process is ttriuted to couple of fctors. Firstly, the presence of hrd prticles nd chemicls in cooling nd luriction fluid results in rsive nd corrosive wer. Secondly, erosive wer is lso significnt from the impct of hot ir nd gses. Third, friction etween the lock wll nd piston ring cn produce dhesion even in oil luriction. Finlly, ftigue lso contriutes to the wer of engine lock. Vrious types of luminum lloys re continully eing developed to improve their wer resistnce. Among these lloys, luminum-silicon (Al-Si) lloys hve een found to e eneficil in mny industril pplictions nd considered to e pproprite sustitutes for cst iron components. The ddition of silicon in luminum lloys improves their wer, csting, mchining nd corrosion chrcteristics [8], [9]. The im of the present investigtion is to oserve the structure nd dry sliding wer ehviour of the commercilly used luminium silicon lock nd piston so tht specific recommendtion cn e put forwrd towrds the triologicl use of this lloy for locl utomoile spre prts mnufcturers. II. MATERIAL AND METHODS The mterils used in the current study were commercil luminum-silicon engine lock nd piston. The lloys were nlyzed oth y wet chemicl nd spectrochemicl methods. The chemicl compositions of the lloys re given in Tle I. The smple of 12 mm length nd 5 mm dimeter were mchined from the cst r for wer study y following ASTM Stndrd G The end surfce (5 mm di) of the pin smples were polished using emery ppers 1, 0, 2/0. Afterwrds, the smples were polished in fine grde wheel polisher. Lter, the end surfce ws clened in running wter. Finlly, the smples were dried in cetone. Cst iron discs were used s the counter-ody mteril. The hrdness of the cst iron discs ws round RC 50. One of the surfces of the disc ws grinded y surfce grinding mchine nd clened with cotton. The frictionl nd wer ehviors of the luminium lloys were investigted in pin-on disc type wer pprtus y following ASTM Stndrd G During the wer tests, the end surfce of the pin smples were pressed ginst horizontl rotting cst iron disc. Two different lods of 5 N nd 20 N were used throughout the test, which yielded nominl contct pressures of 0.30 MP nd 1.4 MP. The tests 860

2 were conducted t the sliding speed of 0.29 ms -1 with vrying sliding distnces rnging from 260 m 4200m. All the tests were crried out in mient ir (humidity 80%) under dry sliding condition (without luriction). The wer deris produced during the wer tests were collected for stereomicroscopic investigtion. After completion of wer tests, smples were clened with cetone. At lest four tests were done for ech type of mteril. Wer rtes were clculted from verge vlues of weight-loss mesurements. Wer rte ws estimted y mesuring the mss loss ( W) fter ech test. Cres hve een given fter ech test to void entrpment of wer deris. It is clculted tht W to sliding distnce (S.D) using: W.R = W/S.D (1) Microstructurl oservtion of the worn specimens were done crefully y using OPTIKA Microscope with CCD cmer (Model: OPTIKA) ttched to PC t different mgnifictions nd some selected photomicrogrphs were tken. The SEM investigtion nd EDX nlysis were conducted y using JEOL scnning electron microscope with n energy dispersive X-ry nlyzer (Model: Link AN ) ttched. TABLE I CHEMICAL COMPOSITION OF AL-SI ENGINE BLOCK AND PISTON (WT %) Alloy Si Mg Cu Ni Fe Zn Mn Al Bl Bl III. RESULTS AND DISCUSSION A. Wer Test Figs. 1 nd 2 elucidte the vrition of weight loss with the vrition of sliding speed for oth engine lock nd piston lloy t pplied pressure of 0.30MP (Norml Lod 5N) nd 1.4MP (Norml Lod 20N) respectively. Moreover, Figs. 3 nd 4 depict the vrition of wer rte with the vrition of sliding speed for oth engine lock nd piston lloy t pplied pressure of 0.30MP (Norml Lod 5N) nd 1.4MP (Norml Lod 20N) respectively. Other prmeters, such s sliding velocity (0.29 ms -1 ), surfce roughness (2 µm), nd humidity (80%) re identicl for these four figures. It cn e seen from Fig. 1 tht, t lower pplied pressure (0.30MP) the weight loss t ll sliding distnces vry insignificntly for oth lock nd piston. As the sliding distnce increse the weight loss increses for oth the lloys. At reltively higher pplied pressure (1.4MP) oth the lloys show higher weight loss s compred to weight loss t low lod nd t ll sliding distnces (Fig. 2). However, for higher pplied pressure, differences in weight loss vlues for lock nd piston re evident. The lock showed higher weight loss t reltively low nd high ends of sliding distnce. Weight loss, gm Distnce, m Fig. 1 Vrition of weight loss (gm) with the vrition of sliding distnce (m) t pplied pressure of 0.30MP (Lod 5N) nd sliding Weight loss, gm Distnce, m Fig. 2 Vrition of weight loss (gm) with the vrition of sliding distnce (m) t pplied pressure of 1.4 MP (Lod 20N) nd sliding Figs. 3 nd 4 present the wer rte vs. sliding distnce plot for oth lock nd piston. At lower pplied pressure, it cn e oserved tht wer rte incresed t steep rte initilly for oth lock nd piston nd fter certin point onwrds ttined constnt vlue (Fig. 3). In the cse of higher pplied pressure, the nture of the curves re quite similr to tht of the lower pplied lod, only difference is in the vlue of wer rte incresed quite significntly for oth the lloys (Fig. 4) with lock showing higher vlues thn piston t lower nd higher relm of the investigted sliding distnce rnge. The competition of frictionl het softening nd strin hrdening determined the down -nd-up trend. Figs. 3 nd 4 clerly indicte tht the wer rtes of oth the lloy incresed with incresing the lod from 5N to 20N. The wer rte for engine lock incresed from 6x6-10 gm/m (5N) to 1.6x10-5 (20N) t sliding distnce of 1000 m. For ll sliding distnces, the wer rte for oth the lloys incresed one order of mgnitude with incresing lod from 5N to 20N. For oth pplied pressures the piston lloy showed lower wer rte s compred to tht of lock lloy. The result is due to the presence of higher percent of Ni nd Mg in piston lloy s seen from the chemicl nlysis (Tle I). Ni forms n intermetllic Al 3 Ni which 861

3 increses s Ni content increses. This intermettlic increses the strength of the piston lloy leding to lower wer rte. More over Mg ddition is eneficil to enhnce the rsion resistnce of the lloy due to uniformly distriution of hrd prticles nd reduction of friction coefficient [10]. The sliding movement occurs in very smll res t the peks nd over time. The ruptures or reks t the peks increse the contct re nd results in rise in temperture. The increse in the lod cuses rise in friction. Wer rte, gm/m 1.8x x x x x x x x x Distnce, m Fig. 3 Vrition of wer rte (gm/m) with the vrition of sliding distnce (m) t pplied pressure of 0.30 MP (Lod 5N) nd sliding Wer rte, gm/m 1.8x x x x x x x x x Distnce, m Fig. 4 Vrition of wer rte (gm/m) with the vrition of sliding distnce (m) t pplied pressure of 1.4 MP (Lod 20N) nd sliding Aluminium silicon csting lloy redily oxidizes in ir in the initil durtion of ruing. An increse in the lod leds to incresed wer nd loss of the metl. The initil ruing durtion reks the surfce lyers, which clens nd smoothes the surfces nd increses the strength of the connections nd contct etween the surfces. The friction force due to the tillge effect etween the surfces increses the temperture etween them. This effect results in dhesion nd increses the deformtion t the surfce lyers, leding to further loss of the metl. B. Opticl Microscopic Oservtion In this study of dry sliding wer of two Al-Si lloys ginst cst iron counter-ody, the wer ws descried s mixed mode of elstic-plstic contct where Archrd s lw ws oeyed. The pplied pressure rnge investigted ws 0.30 MP nd 1.4 MP. This rnge of pplied pressure ws previously found to exhiit mild wer (MW) in these lloys [11]. In Fig. 5 re presented the worn surfces for oth lock nd piston lloys t different lods nd sliding distnces. Firstly, it cn e oserved tht for given lloy nd for given lod, s the sliding distnce increse the wer mrks ecomes more visile nd deep. In some portions of the investigted worn surfce there re evidence of crter formtion. It cn lso e seen tht for given lloy nd t given sliding distnce, s the lod is incresed the wer mrks lso ecomes more deep nd prominent. Incresing the lod from 5N to 20N lso increses the frction of flky wer deris. At low lods nd t ll sliding distnces, the wer mrks in the worn surfces of lock nd piston lloy re similr in nture wheres t higher pplied lods the wer mrks in the worn surfces of lock re more deep nd intense thn tht of the piston lloy leding to their higher mteril loss nd corresponding high wer rte. The wer mechnisms in the dry sliding of Al-Si lloys cn e clssified s oxidtive wer. Oxidtive wer occurred t low pplied lods. In this wer process n luminium oxide lyer (l0-80 pm) formed on oth the wering Al-Si surfce nd the counter-fce [11]. Wer occurred firstly y oxidtion of the sperities nd then secondly y frcture nd compction of the oxidized wer deris into this film. The wer rte ws low, due to the mount of metl removed eing confined to the thickness of this oxide formtion. Some loclized deformtion of the sustrte nd frcture of the Si prticles ws oserved. Oxidtive wer ws considered to e generlly independent of the Si content or Si prticle size. Under conditions of mild wer triolyer ws formed on the surfce of Al-Si lloys. This lyer ws found to consist of n ultrfine mixture of luminium, silicon nd α- iron. The formtion of this surfce resulted from the trnsfer of mteril from oth the Al-Si lloy pin mteril nd the steel counter-fce. It ws lso found tht the oserved iron-rich lyer, formed on the Al-Si surfce due to mutul mteril trnsfer etween the sliding surfces, ws composed of n ultrfine mixture of Al, Si nd α-fe (<1 µm). Furthermore, it ws rgued tht s wer continued, the deposition reched stge where these trnsferred lyers could not dhere nd ecme detched [11]. 862

4 c 200µm d the form of drk, rown powder. The microgrph (Fig. 6) shows the deris produced t lod of 20 N ws minly composed of very fine, equixed prticles ut lso contined plte-like nd rion-shped iron prticles in smller mounts. The fine nd lrge deris prticles were mixture of Al, Si, Fe, nd oxygen. The rion-shped prticles hd n ppernce similr to mchined chips, nd were minly composed of Fe indicting tht they were cut from the steel counter-fce. e g i Fig. 5 Opticl microgrph of worn surfces efore wer () lock, () piston, fter wer t pplied pressure of 0.30MP for 15 min (c) lock, (d) piston, for 4 hours (e) lock, (f) piston, t pplied pressure of 1.40MP for 15 min (g) lock, (h) piston nd for 4 hours (i) lock (j) piston Fig. 6 shows the typicl wer deris collected from the wer test. At low lods the wer deris ws equixed, lminr nd consisted of smll iron content. An increse in the pplied norml lod formed wer deris of vrious shpes nd sizes. The deris size rnged from few microns, to few millimeters. Visully, the deris produced t 20 N ppered in f h j 200µm Fig. 6 Wer deris collected from wer test t 1.4 MP (20N) pplied pressure nd sliding distnce of 4200m for (), () C. SEM nd EDX Oservtion The SEM microgrphs of s-received Al-Si lock nd piston re shown in Figs. 7 () nd () respectively. Fig. 7 SEM microgrphs of s-received Al-Si () lock nd () piston The microstructure consisted of minly primry Al dendrite, eutectic Si, Al 15 (Fe, Mn) 3 Si 2, Mg 2 Si nd few numer of Ferich intermetllic phses on α-al mtrix in the inter-dendritic region. It cn e seen tht the eutectic Si phse is flke-like 863

5 nd ciculr morphologies. Two type of NiAl 3 phse re the plte-like nd needlelike morphologies [7]. The SEM microgrphs of the worn surfces of Al-Si lock nd piston re shown in Figs. 8 nd 9. The corresponding EDX profile nlysis of the lock lloy for the selected re of the SEM is shown in Figs. 8 () nd (c). The weight percentge of elements found y EDX nlysis in these res were 37.67% O, 51.03% Al, 5.60% Si, 0.75% Mn, 3.74% Fe nd 0.76% Cu, 0.44% Zn nd, 22.23% O,.04% Mg, 58.01% Al, 15.49% Si, 2.27% Fe, 0.72% Ni, 0.80% Cu, 0.42% Zn respectively. 0.86% Cu, 0.13% Zn respectively. The EDX dt clerly revels the high oxide content in the selected res which suggest the oxidtive wer ws the dominnt process. In cse of lock lloy the EDX nlysis of the investigted res revels tht the oxide content is unevenly distriuted. Wheres for piston lloy the oxide content is roughly uniform which cn e responsile for lower wer rte for the piston lloy. This cn e due to the vrition of chemicl composition of the lloys. c Fig. 8 SEM imges of worn surfces of luminium engine lock fter wer t 1.4 MP pplied pressure nd sliding distnce of 4200m The corresponding EDX profile nlysis of piston lloy for the selected re of the SEM is shown in Figs. 9 () nd (c). The weight percentge of elements found in these res were 33.82% O, 0.12% Mg, 48.00% Al, 5.69% Si, 0.17% Mn, 10.61% Fe,0.42 Ni, 1.01% Cu, 0.1% Zn nd 33.93% O,.15% Mg, 48.45% Al, 5.99% Si, 0.45% Mn, 9.70% Fe, 0.34% Ni, c Fig. 9 SEM imges of worn surfces of luminium engine piston fter wer t 1.4 MP pplied pressure nd sliding distnce of 4200m Generlly, trnsferred lyer either in continuous or discontinuous form ws oserved for the smples. The widths of the surfce grooves were etween 4 µm nd 20 µm. In this wer process n luminium oxide lyer (l0-80 µm) formed on oth the wering Al-Si surfce nd the counter fce. Wer occurred firstly y oxidtion of the sperities nd then secondly y frcture nd compction of the oxidized wer deris into this film. The wer rte ws low, due to the mount of metl removed eing confined to the thickness of this oxide 864

6 formtion. Some loclized deformtion of the sustrte nd frcture of the Si prticles ws oserved. Sliding mrks re oserved on ll the worn surfces which re of typicl ploughing ction in comprtively soft metl. It is lso seen tht the depth nd width of the sliding mrks increses with increse of pplied lod nd sliding distnce. The worn surfce is reltively rough nd exhiits rther corse nd deep sliding mrks. In contrst, the corseness nd deepness of the sliding mrks increses with incresing lod on the tested lloys. At reltively low speeds nd lods, the het generted y the sperity contct leds to oxide formtion on the luminum surfce. The lyer is thin nd cn deform elsticlly contriuting to very low wer rtes which cn e considered s mild wer. Incresing the lod cuses dhesion to occur etween the two mterils in contct nd removl of the surfce oxide in the form of lminr prticles. At low lods the wer deris ws chrcterized y drk-rown coloured powder mixed with Fe, Al, nd Si nd O, very fine equixed prticles, smll mounts of rion shped prticles (Fe chips), nd Plte-like prticles (Fe-Al-Si-O). At reltively high lods Plte-like prticles composed of Fe, Al, nd Si nd O nd metllic Al flkes (Al-Si) ws oserved [11]. The worn surfce ws chrcterized y surfce with shllow grooves t lods while the groove width nd depth incresed s the lods increses. IV. CONCLUSIONS The lod nd the sliding distnce ffect the wer rte of the luminium engine lock nd piston lloys. The wer rte incresed with incresing lod for oth the lloys. Wer rte lso increses lmost linerly t low lods nd increse to mximum then ttin plteu with incresing sliding distnce. For oth pplied lods the piston lloy showed the etter performnce due to higher Ni nd Mg content. The worn surfce ws chrcterized y surfce with shllow grooves t lods while the groove width nd depth incresed s the lods increses. Oxidtive wer ws found to e the predominnt mechnisms in the dry sliding of Al-Si lloys t low lods. The significnce of luminium oxide formtion regrding the formtion of wer deris nd the overll wer process still remins controversil. ACKNOWLEDGMENT This work is supported y CASR of Bngldesh University of Engineering nd technology nd is prt of project Studies of recrystlliztion, wer nd corrosion ehvior of luminium piston nd piston lock. Thnks to Deprtment of Glss nd Cermics Engineering for providing the lortory fcilities. [3] A. D. Srkr nd J. Clrke, Friction nd wer of luminium-silicon lloys, Journl of Wer, 1980, 61(1-2), [4] M. M. Mru nd D. K. Tnk, Influence of loding, contmintion nd dditive on the wer of metllic pir under rotting nd reciprocting luricted sliding, J. Brz. Soc. Mech. Sci. & Eng., 2006, 28(3), [5] H. Lio, Y. Sun nd G. Sun, Correltion etween mechnicl properties nd mount of dendritic α-al phse in s-cst ner-eutectical-11.6%si lloys modified with strontium, Mterils Sciencend Engineering A, 2002, 335(1-2): [6] R. Kils, V. Rdmil, Structure determintion nd structurerefinement of Al 2CuMg precipittes y quntittive high-resolutionelectron microscopy, Journl of Ultrmicroscopy, 2001, 88(1), [7] L. Ls, J. M. Rodrigues-Ide, Wer ehviour of eutectic ndhypereutectic Al-Si-Cu-Mg csting lloys tested ginst composite rke pd, Mterils Science nd Engineering A, 2003, 363(1-2), [8] Z. Muzffer, K. Erdem nd G. Serp, Influence of Cu ddition on microstructure nd hrdness of ner-eutectic Al-Si- xcu-lloys, Trns. Nonferrous Met. Soc. Chin, 2011, 21, [9] J. Clrke nd A. D. Srkr, Wer chrcteristics of s-cst inry luminium-silicon lloys, Journl of Wer, 1979, 54(1), [10] R. L. Deuis, C. Surmonin nd J. M. Yellup, Dry sliding wer of luminium composites- review, Journl of composites science nd technology, 1996, 57, [11] R. L. Deuis, C. Surmonin nd J. M. Yellup, Reviews on the Influences of Alloying elements on the Microstructure nd Mechnicl Properties of Aluminum Alloys nd Aluminum Alloy Composites, Interntionl Journl of Scientific nd Reserch Pulictions, 2012, 2(6), 1-7. REFERENCES [1] A. Mzhery nd M. O. Shnih, Microstructurl nd rsive wer properties of SiC reinforced luminum-sed composite produced y compocsting, Trns. Nonferrous Met. Soc. Chin, 2013, 23, [2] M.M. Hque nd A. Shrif, Study on wer properties of luminium silicon piston lloy, Journl of Mterils Processing Technology, 2001, 118,