Available online at ScienceDirect. Procedia Materials Science 11 (2015 ) 55 60

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1 Aville online t ScienceDirect Procedi Mterils Science 11 (2015 ) th Interntionl Biennil Conference on Ultrfine Grined nd Nnostructured Mterils, UFGNSM15 The Effect of L-Intermetllic Compounds on Tensile Properties of Al-15%Mg 2 Si In-Situ Composite A. Akhlghi, M. Noghni,,* M. Emmy Imm Khomeini Interntionl University, Qzvin, Irn School of Metllurgy nd Mterils, College of Engineering, University of Tehrn, , Irn Astrct In this work, n ttempt ws mde to exmine the effect of different L-intermetllic on the microstructure nd tensile properties of Al-15%Mg2Si metl mtrix composite (MMC). The composite ws mde vi in-situ process nd chrcterized y opticl microscope (OM), scnning electron microscope (SEM) equipped with energy dispersive X-ry spectroscopy (EDX) nd X-ry diffrction (XRD) nlysis. Microstructurl chrcteriztion reveled tht L chnges not only the morphology of primry Mg2Si prticles from irregulr to polyhedrl nd cuic shpe. But lso lter the eutectic Mg2Si phse from flkes to rods nd the volume frction of Mg2Si decreses while volume frction of α-al phse increses. L ddition chnge the size of primry Mg2Si from (~17 μm) to (~10 μm) nd the size of eutectic Mg2Si phse is reduced from more thn 4.0 μm to less thn 0.5 μm. This is minly due to the formtion of LSi2 phse during solidifiction, s detected y XRD nlysis. Further results reveled tht s the mount of fine L-intermetllic is incresed, ultimte tensile strength (UTS) nd elongtion vlues of the MMC were lso significntly incresed. The frcture study of the composite showed the L-intermetllic chnges the mode of frcture from rittle to more ductile Pulished The Authors. y Elsevier Pulished Ltd. y This Elsevier is n open Ltd. ccess rticle under the CC BY-NC-ND license Peer-review ( under responsiility of the orgnizing committee of UFGNSM15. Peer-review under responsiility of the orgnizing committee of UFGNSM15 Keywords: Al-15%Mg 2Si in-situ composite; Tensile properties; L-intermetllic compounds. *Corresponding uthor. Tel.: ; fx: E-mil ddress: Mt_noghni@eng.ikiu.c.ir Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the orgnizing committee of UFGNSM15 doi: /j.mspro

2 56 A. Akhlghi et l. / Procedi Mterils Science 11 ( 2015 ) Introduction Tody, the fuel consumption nd pollutnts entering the environment is tken into considertion. Tht's why weight loss is n importnt fctor in reducing fuel consumption in cr nd erospce industry hs provided vriety of reserch fields, Henry et l. (2003), Yng et l. (2011). Aluminum hs low weight nd it is suitle for use s mtrix in metl mtrix composites, Among composite mterils, luminum mtrix composite reinforced with Mg 2Si prticles re incresingly developing due to their fvorle properties such s low density, excellent csting ility, good wer resistnce nd low prices of finl products. Mg 2Si is hrd intermetllic compound with high melting point (1085 C), its low density nd low coefficient of therml expnsion coupled with resonle high elstic modulus mke it good choice s reinforcing gent, Zhng et l. (1999). Zhng showed tht in terms of properties nd solidifiction ehvior, gret similrities exist etween Mg 2Si nd Si, nd etween Al Mg 2Si nd Al Si systems. Fig. 1 shows the equilirium phse digrm of Al Mg 2Si, Zhng et l. (2000). It cn e seen tht during solidifiction of Al-15%Mg 2Si lloy, Mg 2Si phse is formed s the primry phse. Then, -Al nd secondry Mg 2Si co-solidify from the liquid lloy in the nrrow ternry phse re. This pseudo-eutectic rection is completed t ºC, Emmy et l. (2010). L L1 + Mg2SiP Mg2SiP + (Al + Mg2Si) E where E is Eutectic, P is Primry, nd L 1 is Liquid in two phse region. In situ process of fricting metl mtrix composites (MMCs) hs some enefits, such s uniform distriution of reinforcement, well mtrix reinforcement interfce, thermodynmiclly stle system nd much lower costs of production s compred with their counterprts from ex. situ processes, Bhrmi et l. (2012). Unfortuntely, primry Mg 2si phse composites re usully corse, which resulted in the loss of mechnicl properties. It is therefore necessry to e refined y dding lloying elements such s N, Emmy et l. (2011), Ce, Zhou et l. (2005), Sr, Qin et l. (2007), Ti, Li et l. (2008). The im of this reserch is the study of L ddition s modifier to improve the mechnicl properties of Al-15%Mg 2Si composite. 2. Experimentl Industrilly pure Al (>99.8% purity), Mg nd Si metls were used to prepre Al 5.5 wt. %Si 9.7 wt. Mg lloy. Al 15%Mg 2Si composite s primry ingots were prepred in n electricl resistnce furnce using 10 kg SiC crucile. The prent lloy ws remelted within smll SiC crucile (with 1 kg cpcity) in resistnce furnce in order to prepre lloys with 0, 0.05, 0.1, 0.3, 0.5, 1, 2, nd 3 wt % L. When the temperture reched 760 C, Al- 15%L contining mster lloy ws dded to the molten composite. After clening off the slg, lloys with different compositions were poured into preheted cst iron mold (up to 200 º C) to produce tensile test specimens (Fig. 2). Fig.1. Equilirium phse digrm of Al Mg 2Si pseudo-inry section, Zhng et l (2000). Fig.2: () Cst iron mold; () tensile test dimensions. The mold ws prepred ccording to ASTM B108/ B108M-12e1 (Fig. 2). The min dvntge of this mold is the ppliction of n pproprite uphill filling system nd feeding design, providing low turulence mnner of fluid flow which consequently results in reduced gs entrpment nd porosity in cst specimens. The size of tensile test specimens considered for the mentioned mold ws consistent to ASTM B557M-10 stndrd, s shown in Fig. 2. Microstructurl studies were mde on polished smple surfces which were selected from the guge length portion of the test rs (6 mm dimeter) (Fig. 2). The cut sections were polished nd then etched y HF (5%) for out 10s t

3 A. Akhlghi et l. / Procedi Mterils Science 11 ( 2015 ) room temperture to revel the structure. Quntittive dt on the microstructures were determined using n opticl microscope nd were nlysed with imge nlysis softwre (Digimizer). The microstructurl chrcteristics of the specimens were exmined y scnning electron microscopy performed in Veg Tescn SEM equipped with the energy dispersive X-ry nlysis (EDX) ccessory. Tensile test ws crried out on computerized testing mchine (Sntm STM-20) t room temperture to otin UTS nd elongtion vlues t strin rte of 1 mm/min. The frcture surfces of tensile test specimens were lso exmined with SEM. 3. Results nd discussion 3.1. Microstructurl chrcteriztion In the microstructure of Al 15% Mg 2Si composite, ccording to the pseudo-inry phse digrm (Fig. 1), Zhng et l. (2000), consists of drk fceted prticles of primry Mg 2Si nd right α-al grins in mtrix of Al Mg 2Si eutectic cells. Consequently, primry Mg 2Si prticles will ct nturlly s heterogeneous sites for the nucletion of α- Al in order to decrese the interfcil energy, Zhng et l. (1999). This explins why ll Mg 2Si prticles re surrounded y lyer of α-al, s seen in Fig.3. Fig. 3 f relted to the ddition of L vlues (0% to 3%). As is cler from the Fig. 3, with the ddition of the different mounts of L, the microstructurl chnges were found to e ssocited with the formtion of new intermetllic phse. To recognize this intermetllic, XRD nlysis of the smples contining 5% L ws redirected. c d e f Fig. 3. Microstructure of Al-!5% Mg 2Si composite s function of L ddition.() 0%; () 0.1%; (c) 0.3%; (d) 0.5%; (e) 1%; (f) 3%. Figure 4 clerly shows the XRD ptterns of the composite fter dding 5 % L. These oservtions cn clerly shows the effect of LSi 2 phse on the microstructure of the composite. The presence of LSi 2 phse hs een lso reported y Yng et l. (2000).

4 58 A. Akhlghi et l. / Procedi Mterils Science 11 ( 2015 ) Fig. 4. () XRD ptterns of Al 15%Mg 2Si composite with 5% L dditions; () SEM microgrph of the Al 15%Mg 2Si 5%L composite. As expected, the size nd shpe of these phses will hve direct impct on microstructure nd tensile properties. From Fig.3, it is cler tht the morphology of primry prticles Mg 2Si in Al-15%Mg 2Si composite is lmost dendritic or irregulr shpe ut with dded L, it chnges to polyhedrl nd cuic shpe (Fig. 3(c-f)). Also, it seems tht with incresing L, the α-al phse volume frction is incresed. Another importnt chnge occurs in eutectic re Mg 2Si. With incresing L content (wt %), the morphology of Mg 2Si eutectic lters from flke like to fier or dot like. Further microstructurl studies depicted tht the size of Mg 2Si eutectic is chnged from 4 μm t 0.3 % L ddition to less thn 0.5 μm t 1 % L (Fig. 5). Investigtion on the size nd volume frction percent of primry Mg 2Si prticles is shown in Fig. 6. The results showed tht the size of of primry Mg 2Si prticles when 0.5% dded L to composite is 17 μm ut 3 wt % L dditions dditions reduces the size of primry Mg 2Si prticles to 10 μm. Also, with the ddition of vrious mounts of L the volume frction percent of primry nd eutectic Mg 2Si is stedily declining. It is cler tht L t lower content modifies the Mg 2Si phses ut t higher contents, it tends to rect with Si to form L contining intermetllics. Fig.5. SEM microgrph of Al-15%Mg 2Si composite with different mount L for explins different size of Mg 2Si eutectic () 0.3%; () 1 % Tensile properties The UTS nd elongtion vlues of the specimens s function of dded L re shown in fig. 6. As is cler from fig. 7 tht oth UTS nd elongtion vlue re decresed for MMCs with less thn 0.3 wt % L ut when the mount of L is greter thn 0.3% n increse in tensile properties is oserved. This result in the form intermetllic compounds contining L nd their effects linked. In MMC with 0.3% L, the intermetllic compounds hve needle shpe nd increse in stress concentrtion is expected which leds to the loss of strength. But L t higher vlues (0.3%), the shpe of such intermetllic chnges from needle to flke/fier shpe. On the other hnd, the size of Mg 2Si primry prticles is smller nd the morphology of eutectic Mg 2Si is chnged from flke like to fier nd dot-like shpe tht

5 A. Akhlghi et l. / Procedi Mterils Science 11 ( 2015 ) these results re the min reson for incresed UTS vlue. Aout chnge in the percent elongtion, it cn e rgued tht up 0.3 % of L dded, the formtion of intermetllic phse s needles shpe dmging effect on the elongtion vlue ut in mounts greter thn 0.3% L, to form LSi 2 phse, incresingly more silicon used so the phse mtrix α-al is incresed tht oviously, these results will increse the percentge of elongtion. Fig. 6. () The size nd volume frction of primry Mg 2Si prticles s function of L dditions; () Tensile properties of Al 15%Mg 2Si MMC s function of L content Frctogrphy Frcture surfces of the unmodified nd L. modified Al 15% Mg 2Si composite re shown in fig7 (-). Fig. 7. Frctured surfces of () L-free Al 15%Mg2Si MMC; () Al 15%Mg2Si 2%L MMC. As fig. 7 depicts, frcture surfces of the unmodified Al 15% Mg 2Si composite hve very decohered primry Mg 2Si nd density of fine dimples on their frctured fces re low which indictes rittle frcture. The frcture plnes for lmost ll corse Mg 2Si prticles exhiit cler clevge chrcteristic creting rpid frcture deriving from their intrinsic rittleness. As known, dimples with honeycom ppernce re chrcteristics of ductile mode of frcture. Frcture surfce in fig. 7 depicts tht modified composite with 2wt% L contins severl crcked prticles nd fine dimples ccompnied y few decohered primry Mg 2Si prticles. As previously mentioned, with incresing the mounts of L, silicon is expected to e used t the sme time nd thus the volume frction Mg 2Si primry nd eutectic Mg 2Si structure is decreses. So the volume frction of α-al mtrix is incresed. As result, percent elongtion increses nd the frcture mode convert from rittle to ductile.

6 60 A. Akhlghi et l. / Procedi Mterils Science 11 ( 2015 ) Conclusions The morphology of primry Mg 2Si chnged from irregulr to polyhedrl nd cuic shpe nd its verge prticle size decresed from 17 μm to 10 μm fter dding L to Al-15% Mg 2Si composite. With the ddition of L to Al-15% Mg 2Si composite nd formtion LSi 2, the volume frction of Mg 2Si prticles nd eutectic is decresed ut lph phse is incresed. Size of eutectic Mg 2Si phse is reduced from out more thn 4 μm to less thn 0.5 μm fter dding 1%L to Al- 15% Mg2Si composite With the ddition of 0.3% L, UTS is decresed from 217 to 199 MP nd elongtion vlues decresed from 5.5 to 4.2 %, ut fter dding 3%L, UTS is incresed to 223 MP nd elongtion vlues incresed to 6 %. The frcture surfce exmintions of the Al-15% Mg 2Si composite reveled rittle mode of filure in cst composite, however modifiction y L incresed fine dimples nd reduced the numer of decohered prticles. References Bhrmi, A., Rzghin, A., Emmy. M., Khorshidi, R., The effect of Zr on the microstructure nd tensile properties of hot-extruded Al- Mg2Si composite. Mterils nd Design, 36, Emmy, M., Nemti, N., Heidrzdeh, A., 2010.The influence of Cu rich intermetllic phses on the microstructure, hrdness nd tensile properties of Al-15% Mg2Si composite. J Mter Sci Eng A, 527: Emmy, M., Khorshidi, R., Honrkhsh Rouf, A., The influence of pure N on the microstructure nd tensile properties of Al-Mg2Si metl mtrix composite. Mter Sci Eng A, 528: Henry, H., Alfred, Y., Niyi, L., John, E.A., Potentil mgnesium lloys for high temperture die cst utomotive pplictions: review. Mter Mnuf Processes. 18: Li, C., Liu, X., Zhng, G., Heterogeneous nucleting role of TiB2 or AlP/TiB2 coupled compounds on primry Mg2Si in Al-Mg-Si lloys. J Mter Sci Eng A, 497: Qin, Q.D., Zho, Y.G., Liu, C., Cong, P.J., Zhou, W., 2007.Strontium modifiction nd formtion of cuic primry Mg2Si crystls in Mg2Si/Al composite. J Alloys Compd, 454: Yng, M., Ling, X., Yi, Z., Pn, F., Effects of zirconium ddition on s-cst microstructure nd mechnicl properties of Mg 3Sn 2C mgnesium lloy. Mter Des, 32: Zhng, J., Fn, Z., Wng, Y.Q., Zhou, B., Microstrucrl refinement in Al-Mg2Si in situ composites. Journl of Mterils Science Letters, 8(10): Zhng, J., Fn, Z., Wng, Y.Q., Zhou, B.L., Microstructurl development of Al-15 wt.% Mg2Si in situ composite with mischmetl ddition. J Mter Sci Eng A, 281: Zhou, Y.G., Qin, Q.D., Zhou, W., Ling, Y.H., Microstructure of the Ce-modified in situ Mg2Si/Al-Si-Cu composite. J Alloys Compd, 389:L1-4.