EFFECT OF SOLUTION TREATMENT ON MICROSTRUCTURE, MECHANICAL AND WEAR CHARACTERISTICS OF GRAVITY DIE CAST ALUMINIUM ALLOY

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1 EFFECT OF SOLUTION TREATMENT ON MICROSTRUCTURE, MECHANICAL AND WEAR CHARACTERISTICS OF GRAVITY DIE CAST ALUMINIUM ALLOY Rdh. R, Jfferson J. M nd Drshn G School of Mechnicl nd Building Sciences, Vellore Institute of Technology University Chenni Cmpus, Tmil Ndu, Indi Emil: rdh8vit@gmil.com ABSTRACT Non-ferrous mterils re widely used in industries, especilly becuse of its corrosion resistnce property. Among them Aluminium lloys re widely used becuse of its ese of mchinbility, good therml Conductivity, less weight etc. Presently Aluminum is more used by industries thn steel. Further Aluminium with lloy elements like copper, nickel, mgnesium, tin etc. will enhnce the properties of the mterils nd these lloyed elements hve more industril pplictions. Solution Tretment enhnces the properties of these luminium lloys. This work is focused on synthesis nd chrcteriztion of hexenry luminium Alloy (Al-Cu-Sn-Ni Mg-Fe) by grvity die csting technique. The microstructure nd wer behvior of s cst, solution treted lloys were elucidted by opticl microscopy, pin-on-disc wer test. The mechnicl properties were ssessed by the tensile test, hrdness test nd compressive test. Solution treted luminium lloy showed the remrkble improvement in wer resistnce, hrdness nd tensile strength. The uniformly dispersed thermlly stble θ nd Ω phses in the luminium mtrix re one of the predominnt fctor in improving the hrdness nd tensile properties. The increse in hrdness ws chieved with solution tretment significntly reduced the wer rte. Keywords: hexenry luminium lloy, solution tretment, microstructure, mechnicl properties, wer. 1. INTRODUCTION The demnd for luminium lloy products is incresing primrily becuse of the lrger mounts of cstings being used in utomotive nd erospce pplictions. A wide rnge of cst luminium lloys is vilble for commercil use. The current reserch trend to develop the luminium lloys with higher strength, higher ductility, less weight, nd higher wer resistnce. The het treted luminium lloys re exhibiting higher strength by series of solutionising t higher temperture, wter quenching to room temperture nd followed by geing with some suitble preferred temperture [2]. The CuAl2 (Precipitte) phse ws observed s the min hrdening phse in Al-Cu-Mg lloys. This ttributes the strength of the luminium lloys during geing [2]. The uniformly distributed finer CuAl2 phse is formed in the Al-Cu lloys with the little lloying of Mg nd Ag [3]. Al-Cu-Mg lloy is strengthened with the ddition of Ag which is ttributed by the formtion of homogeneously distributed dominnt strengthening phses such s orthorhombic fce centered cubic Ω phse nd tetrgonl structure θ phse [4]. The tensile strength, wer resistnce nd hrdness of Al-5Cu lloy were refined with the ddition of mster lloy Al5Ti-.75Cu. The grin refinement, uniform dispersion of secondry phses nd higher mount of finer θ precipittes re ttined with the mster lloying reveled the enhncement in the mechnicl properties of Al-5Cu lloy [5]. The lloying of Ce up to.45% improved the tensile properties of Al-Cu-Mg-Ag lloy t room nd elevted tempertures which re ttributed by the formtion of thermlly stble Ω phse [6]. The higher wer resistnce ws chieved in the thixoformed A319 lloy which is due to the finer grins, increse in hrdness nd homogenous dispersion of secondry phses [7]. With the higher contct pressure of 1 MP nd sliding speed 1.5 m/s, the AA775 lloy undergone severe plstic deformtion revels the metllic shiny worn surfce [8]. The wer rte is lwys observed greter with the higher lod irrespective of the lloying elements nd processing conditions [9]. Even though there hs been lots of reserch in the field of developing luminium lloys there re limited works in the re of developing hexenry lloys. The most commonly used processes for developing Al lloys re snd csting, stir csting, cold nd hot chmber pressure die csting. Different lloying elements were tried by vrious reserchers. The most commonly used lloying elements re Copper, Silver, Nickel, mgnesium, Iron, Tin, zinc, silicon, mngnese, clcium, Titnium, chromium, Vndium, Zirconium, rre erth elements. etc., Extensive reserch ws done in binry, ternry nd quternry, luminium lloys. There is very limited works vilble in studying hexenry luminium lloys. The ddition of copper in luminium hs proven to increse the strength, hrdness nd corrosion resistnce. The ddition of nickel will improve the hrdness nd strength t elevted tempertures. Mgnesium cn increse the solution hrdening nd cn improve the bility to strin hrdening. Tin cn increse the ductility nd toughness wheres iron cn improve the strength. Solution tretment is generlly used to improve the properties of s cst luminium lloys by re-dissolving the residul phses in the luminium mtrix [1]. The objective of this work is to develop hexenry luminium Alloy with ddition of 5% Cu 4%Sn, 3% Ni, 2% Mg nd 1% Fe nd evlute its mechnicl properties, tribologicl behvior in detil before solution tretment (BST) nd fter solution tretment (AST). 1371

2 2. EXPERIMENTAL PROCEDURES 2.1 Alloy synthesis The melting of pure luminium ingot long with the micro lloying elements (Cu - 5%, Sn - 4%, Ni - 3%, Mg - 2%, Fe - 1%., Al - Blnce) re crried out in the induction furnce. The melt ws stirred well for 1 mins t temperture of 68 C nd degsser tblets were used for degssing the melt. The molten metl ws super-heted nd held t the temperture of 7C for 5 mins nd then the melt ws trnsferred to steel mould of grvity die csting. The specifiction nd photogrph of the furnce is given in Tble 1 nd Figure 1. The cst lloy is shown in Figure 2. The cst hexenry lloy ws then mchined s per ASTM stndrds for mechnicl chrcteriztion. 2.2 Solution tretment Solution tretment is crried out by heting hexenry luminium lloy t 43 C (Figure-3) below solidus temperture (A) with holding time of 3 mins (B). The lloy ws wter quenched to room temperture to chieve mximum supersturted lloying elements for subsequent geing (C) nd llowed to sty in room temperture for 3 mins (D). Then the lloy ws ge hrdened t the temperture of 19 C for 3 hours to chieve mximum strength nd llowed to cool to room temperture by nturl convection (E-G). 3. MECHANICAL CHARACTERIZATION Brinell hrdness test (BHN), tensile test nd compression tests were crried out s per ASTM stndrds ASTM E 1-8, ASTM E 8M -4 nd ASTM E 9-9 respectively. The Brinell hrdness test ws performed using steel bll indenter of 1.5 mm dimeter for 6 sec. Vickers hrdness test is performed on the specimen of dimeter 2mm using dimond cone indenter with lod of 25gf for 6 sec. The specimen of 12.5 mm dimeter nd 75 mm guge length used for tensile test before nd fter frcture is shown in Figures 4 & 5. The specimen of dimeter 2mm (l/d ~1) used for the compression test is shown in Figure WEAR MEASUREMENTS The wer studies were crried out using pin on disc teeter s per ASTM G99 stndrd. The Pin-On-Disc mchine is verstile unit designed to evlute the wer nd friction chrcteristics on vriety of mterils exposed to sliding contcts in dry or lubricted environments. The sliding friction test occurs between sttionry pin stylus nd rotting disk. Norml lod, rottionl speed, nd wer trck dimeter cn be vried. Electronic sensors monitor wer nd the tngentil force of friction s function of lod, speed, lubriction, or environmentl condition. These prmeters s well s the coustic emissions t the contct re mesured nd displyed grphiclly utilizing the Tribo DATA softwre pckge. The dimeter nd length of the specimen re 8 mm, 55mm respectively. The sliding speed ws set to 21 rpm nd wer is mesuring time (1-1 min) nd lod (1N, 2N, 3N). The wer rte nd coefficient of friction of luminium lloy ws estimted by weight loss in the specimen fter ech test shown in eqution (1 nd 2) Wer rte = wer 1 5 d 2 mm3 Nm lod slid.dist. (1) frictionlforce( F ) lod ( P) (2) Co-efficient of friction = 5. MICROSTRUCTURAL CHARACTERIZATIONS The specimen ws prepred by polishing using wter proof emery sheets rnging from 6-1 grits nd then polished with Al2O3 brsives, nd finlly etched using Krolls regent (92 ml distilled wter + 6ml nitric cid + 2ml hydrofluoric cid). Figure-1. Induction furnce. Figure-2. Cst hexenry luminium lloy. Figure-3. Solution tretment cycle. 1372

3 6. RESULTS AND DISCUSSIONS Figure-4. Tensile test specimen. Figure-5. Tensile test specimen fter frcture. 6.1 Mechnicl properties The tensile strength improved from 114 MP to 117 MP fter solution tretment nd elongtion incresed from 4.75% to 5.47%. This my be due to the evolution of new interdentritic networks of CuAl2 nd the homogeneous dispersion of residul phses of dditive elements Cu, Mg, Sn, Ni, Fe in the α-aluminium mtrix during solution tretment [1]. The tensile test grphs re shown in Figures 7 & 8. At solution tretment of 43 C, the ultimte tensile strength nd hrdness ws improved. The solution time ws mintined t 3 min which will not llow excess dissolving of residul phses in α-al mtrix so tht the strength won t be compromised becuse if the solution time is greter thn 6 mins there will be grin growth which significntly ffects the tensile strength. The increse in tensile strength is due to the lloying composition nd structure of the script morphology phses. The ddition of tin fvors for the trnsformtion of pltelet phse like structure to script morphology phse ttributed for enhncing the strength of the lloy. BHN test ws conducted t three different untreted specimens nd there vlues re 76.5, 74.2, nd 78.1 which resulted in n verge vlue of BHN test ws conducted t three different solution treted specimens nd there vlues re 93.6, 94.4, nd 96.8 which resulted in n verge vlue of The vickers hrdness of hexenry lloy ws 82 Hv BST nd 118 Hv AST. During quenching, the time for dissolution of lloying elements in the solid solution ws insufficient t the higher temperture [2]. The super sturted lloy mtrix exhibits the internl stresses due to the very low dissolution t the room temperture. The increse in hrdness ws observed in the wter quenched lloys due to its rpid cooling rte phenomenon. The compressive strength of solution treted luminium lloy decresed from 499 MP to 464 MP. This slight reduction in compression strength my be due to loss in interconnectivity of the intermetllic phses while the temperture in solution tretment used ws round its solidus temperture. The compression test grphs re shown in Figures 9 & 1. Figure-6. Compression test specimen fter deformtion. 1373

4 Hrdness HV s cst Al-5Cu-.2(Al-5Ti-.75C) Al-5Cu-.2(Al-5Ti-1B) Al-5Cu-.2(Al-5Ti-.3C) wter quenched Al-5Cu Al-6.2Cu-.6Mg-.1Sn Al-6.2Cu-.6Mg-.6Sn Al-6.2Cu-.6Mg Homogenised Al-6.2Cu-.6Mg-.1Sn Al-6.2Cu-.6Mg-.8Sn A-6.2Cu-.6Mg-.6Sn Al-6.2Cu-.6Mg-.4Sn Al Mg-.2Sn Soluti on s cst treted Al-6.2Cu-.6Mg Hexenry Alloy Hexenry Alloy

5 Figure-7. Tensile test stress strin grph for BST. Figure-1. Compression test lod vs elongtion grph for AST. 6.2 Microstructure As cst condition (BST) The opticl microstructure (Figure 11) shows the primry solid solution (brighter res) re uniformly dispersed long the region of grin boundries nd the non-equilibrium eutectic solid solution between the grins (drk res) showing script type morphology [2]. It revels the presence of α-aluminium mtrix, secondry phses such s (Al-Cu-Mg, Al-Cu-Sn, Al-Cu-Ni, Fe, nd Al-MgSn) nd its intermetllic compounds. The dendritic structures re reveled in the s cst condition. Figure-8. Tensile test stress strin grph for AST Solution treted condition (AST) The dendritic structures s seen in the cst condition get erdicted by this solution tretment. The opticl microstructure (Figure-12) shows the presence of two secondry phses in the region of grin boundries: bright pltelet like structure ws identified s CuAl2 which remined unchnged fter the solution tretment nd drk discontinuous pltelet like structure revels script morphology with the ddition of higher tin content [2]. The presence of irregulr shped pores is seen due to the fstest cooling rte. The corsening of grins ws observed due to the precipittion of phses within the grins nd grin boundries, when the solution temperture is grdully incresed re shown in Figure-12. Figure-9. Compression test lod vs elongtion grph for BST. 1375

6 6.3 Wer behvior nd morphology The Wer behvior of hexenry luminium lloy ws nlyzed with the vrition of the wer loss dt with respect to lod nd time in (Figure-13). The opticl microscopes of worn surfces of luminium lloy BST nd AST re shown in (Figures 14 & 15). The worn surfce shown deep well seprted grooves nd it is found tht the grooves re long the sliding direction, but not mny crcks re seen. However, crck propgtion is observed long the sme sliding direction. It ws shown those wer depths nd wer rte of s cst hexenry luminum lloy is incresed with increse of sliding time nd lod pplied BST. The increse in wer rte of s cst lloy re due to the increse in brsive scoring mrks due to the higher depth of penetrtion cused by the ppliction of higher contct pressure [9]. The dhesive wer ws noticed with the solid phse of welding of prticles from one surfce to nother, when s cst lloy is subjected to the sliding lod of 1N s shown in Figure-14 () [1]. Figure-11. Microstructure BST. Figure-12. Microstructure AST. Wer (microns) 2 N BST & AST Wer (microns) 1 N BST & AST Wer (Microns) 12 Wer (Microns) Before BST Before BST After AST Time (min) After AST Time (min)

7 Wer (microns) 3 N before BST & AST 3 Wer (Microns) BST Before AST After Time (min) Figure-13. Wer under different loding conditions. It ws observed tht the depth of wer nd wer rte ws decresed fter solution tretment. The reduction in wer loss ws due to the improvement in hrdness of luminum lloy chieved with solution tretment [2]. The worn surfce shown deep well seprted crters. Crcks re lso observed which re spred perpendiculr to the sliding direction. It is found tht the crters re long the sliding direction, but not mny crcks re seen. However, crck propgtion is seen long the sme direction s sliding. Figure-15 (c) depicted the mechnism of oxidtive nd brsive wer in the solution treted lloy subjected to the sliding lod of 3 N. Lod t 1N () () Lod t 2 N 1377

8 (b) (b) Lod t 3 N (c) Figure-14. wer morphology of hexenry lloy BST () 1N (b) 2N nd (c) 3 N. (c) Figure-15. wer morphology of hexenry lloy AST () 1N (b) 2N nd (c) 3 N. 1378

9 Wer rte 1-5 mm3/nm [8] 1 N 3 N 2 N 1 N 3 N 2 N 1 N 3 N 2 N thixoformed 1 N s cst 1 N 1 N Solution treted [8] 2 N s cst [8] Al-12SiAl-12Si-4Mg Al-12Si-4Mg-2CeAl-12Si-4Mg-3Ce 4Mg-5Ce [9] A319 [9] A319 [9] Hexenry Alloy [9] 3 N 1 N 1N 3 N 2 N 1 N 3 N 2 N 1 N

10 7. CONCLUSION AND FUTURE WORK The following conclusions re drwn from the study of s cst nd solution treted hexenry luminium lloy: ) It is evident tht the wer resistnce of solution treted lloy improved by 13%, Hrdness incresed by 24% nd tensile strength incresed by bout 3%. Wheres compressive strength decresed by 7 %. b) A solution tretment t 43 of 3 min cuses corsening of grins nd eutectic phses dissolved in luminium mtrix re most importnt to the improvement in tensile strength nd hrdness. c) The presence of lloying elements Cu,Sn,Mg,Ni in the solid solution of luminium significntly promotes the grin refinement. d) It ws observed s the strengthening effect ws beneficil with the limittion in the ddition of lloying elements. e) f) It ws found tht improvement in tensile strength is ttributed by the uniform dispersion of dominnt strengthening Al2Cu phses in luminium mtrix through solution tretment. The solution temperture nd ging temperture cn be vried nd we cn exmine the chnge in properties with respect to both the tempertures. g) The wer rte ws reduced significntly with the formtion of oxide lyer nd hrdness is one of the significnt fctors in wer resistnce. corrosion crcking of Al-4.6 Cu-.3 Mg lloy. Mter. Chem. Phys. 91(2): [4] Min S, Chen KH, Hung LP. 26. Effects of Ag ddition on mechnicl properties nd microstructures of Al-8Cu-.5 Mg lloy. Trns. Nonferrous Met. Soc. Chin. 16(4): [5] Wng T, Go T, Zhng P, Nie J, Liu X Influence of new kind of Al-Ti-C mster lloy on the microstructure nd mechnicl properties of Al5Cu lloy. J. Alloys Compd. 589: [6] Xio DH, Wng JN, Ding DY, Yng HL. 23. Effect of rre erth Ce ddition on the microstructure nd mechnicl properties of n Al-Cu-Mg-Ag lloy. J. Alloys Compd. 352(1): [7] Alhwri KS, Omr MZ, Ghzli MJ, Slleh MS, Mohmmed MN Evlution of the microstructure nd dry sliding wer behviour of thixoformed A319 luminium lloy. Mter. Des. 76:169-8 [8] Ruiz-Andrés M, Conde A, De Dmborene J, Grcí I Wer Behvior of Aluminum Alloys t Slow Sliding Speeds. Tribol. T. 58(5): [9] Ansyid AS, Dud AR, Ghzli MJ. 21. Dry sliding wer behviour of Al 12Si 4Mg lloy with cerium ddition. Mter. Des. 31(1): [1] Kori SA, Chndrshekhrih TM. 27. Studies on the dry sliding wer behviour of hypoeutectic nd eutectic Al Si lloys. Wer. 263(1): h) The precipittion studies to be crried out which re essentil for nlyzing the formtion of precipittes when the luminium lloy is subjected to the solution tretment nd geing conditions. REFERENCES [1] Li B, Pn Q, Chen C, Wu H, Yin Z Effects of solution tretment on microstructurl nd mechnicl properties of Al-Zn-Mg lloy by microlloying with Sc nd Zr. J. Alloys Compd. 664: [2] Bnerjee S., Robi P. S., Srinivsn A. & Lkvth P. K. 21. Effect of trce dditions of Sn on microstructure nd mechnicl properties of Al-CuMg lloys. Mter. Des. 31(8): [3] Chng CH, Lee SL, Lin JC, Yeh MS, Jeng RR. 25. Effect of Ag content nd het tretment on the stress 138