Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy
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摘要
The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.
The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.
The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.
引文
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[12]Buha J.Mechanical properties of naturally aged Mg-Zn-Cu-Mn alloy.Materials Science and Engineering A,2008,489(1-2):127-137.
[13]Golmakaniyoon S,Mahmudi R.Effect of aging treatment on the microstructure,creep resistance and high-temperature mechanical properties of Mg-6Zn-3Cu alloy with La-and Cerich rare earth additions.Materials Science and Engineering A,2015,620:301-308.
[14]Sun X G,Dong Y,Lin X P,et al.Effects of Cr precipitation strengthening process of Mg-Zn-Al-Cu alloy.Special Casting and Nonferrous Alloys,2010,30(3):279-282.(In Chinese)
[15]Zhang Y,Huang X F,Ma Y,et al.Effects of Sm addition on microstructural evolution of Mg-6Zn-0.4Zr alloy during semisolid isothermal heat treatment.China Foundry,2017,14(2):85-92.
[16]Buha J.The effect of micro-alloying addition of Cr on age hardening of an Mg-Zn alloy.Materials Science and Engineering A,2008,492(1-2):293-299.
[17]Zhu H M,Luo C P,Liu J W,et al.Effects of trace Cu addition on the microstructure and tensile properties of ZK60 alloy.Materials Science Forum,2010,654:655-658.
[18]Zhang L,Chen J C,Yu J.Analysis of valence electron structure of GP zone in Cu-Cr alloy.Rare Metals and Cemented Carbides,2006,34(4):28-31.(In Chinese)
[19]Liu Y,Yuan G Y,Lu C,et al.Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase.Transactions of Nonferrous Metals Society of China,2007,17(s1):353-357.
[20]Buha J and Ohkubo T.Natural aging in Mg-Zn(-Cu)Alloys.Metallurgical and Materials Transactions A,2008,39(9):2259-2273.
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[22]Sun H,Zhou M Y,Qu X N,et al.Microstructure evolution of AZ80-0.2Y magnesium alloy processed by semi-solid isothermal and induction heat-treatment.The Chinese Journal of Nonferrous Metals,2017,27(10):1988-1995.(In Chinese)
[23]Zhang L,Cao Z Y,Liu Y B.Microstructure evolution of semisolid Mg-14Al-0.5Mn alloys during isothermal heat treatment.Transactions of Nonferrous Metals Society of China,2010,20(7):1244-1248.
[24]Hu G X,Cai X,Rong Y H.Fundamentals of materials science.Shanghai:Shanghai Jiao Tong University Press,2010:150-151.(In Chinese)
[25]Wu G H,Zhang Y,Liu W C,et al.Microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment.Journal of Magnesium and Alloys,2013,1(1):39-46.
[26]Li Y D,Chen T J,Ma Y,et al.Effect of rare earth 0.5%addition on semi-solid microstructural evolution of AZ91D alloy.The Chinese Journal of Nonferrous Metals,2007,17(2):320-325.(In Chinese)
[27]Zhu G L,Xu J,Zhang Z F,et al.Effect of high shear rate on solidification microstructure of semisolid AZ91D alloy.Transactions of Nonferrous Metals Society of China,2010,20(s3):868-872.
[28]Zhu M F,Su H Q.A study on producing ZA12 alloy with globular structure using semi-solid isothermal treatment.Foundry,1996(4):1-5.(In Chinese)
[29]Cao F R,Guan R G,Chen L Q,et al.Microstructure evolution of semisolid AZ31 magnesium alloy during reheating process.The Chinese Journal of Nonferrous Metals,2012,22(1):7-14.(In Chinese)
[30]Du X H,Zhang E L.Microstructure and mechanical behavior of semi-solid die-casting AZ91D magnesium alloy.Materials Letters,2007,61(11-12):2333-2337.
[2]Chen J,Zhang Q,Li Q A.Effect of Y and Ca addition on the creep behaviors of AZ61 magnesium alloys.Journal of Alloys and Compounds,2016,686:375-383.
[3]Buha J.Natural ageing in magnesium alloys and alloying with Ti.Journal of Materials Science,2008,43(4):1220-1227.
[4]Ravi K R.Thermodynamic designing of heat treatable Mg-Zn-X(X=Sn,Y)alloy suitable for semi-solid processing.Transactions of the Indian Institute of Metals,2016(6):32-39.
[5]Yan H,Rao Y,Chen G.Rheological behavior of semi-solid AZ91D magnesium alloy at steady state.Journal of Wuhan University of Technology(Materials Science Edition),2015,30(1):162-165.
[6]Yang M B,Shen J,Pan F S.Effect of Sb on microstructure of semi-solid isothermal heat-treated AZ61-0.7Si magnesium alloy.The Chinese Journal of Nonferrous Metals,2009,19(1):32-39.
[7]Kim J M,Kim K T,Jung W J.Effects of isothermal heating procedure and strontium addition on semisolid forming of AZ91magnesium alloys.Metal Science Journal,2013,18(6):698-701.
[8]Yang M B,Liang X F,Zhu Y,et al.Effects of zirconium addition on as-cast microstructure and mechanical properties of Mg-3Sn-2Ca magnesium alloy.Materials and Design,2011,32(4):1967-1973.
[9]Hu Y B,Zhao C,Wu F Z,et al.Research status and development of Mg-Zn-Cu seriesalloy.Hot Working Technology,2012,41(2):16-19.(In Chinese)
[10]Zhu H M.A study of aging behavior,microstructures and mechanical properties of cast Mg-6Zn-xCu-0.6Zr(x=0-2.0)alloys.Ph.D.Thesis.Guangzhou:South China University of Technology,2011:15-17.(In Chinese)
[11]Zhu H M,Sha G,Liu J W,et al.Microstructure and mechanical properties of Mg-6Zn-xCu-0.6Zr(wt.%)alloys.Journal of Alloys and Compounds,2011,509(8):3526-3531.
[12]Buha J.Mechanical properties of naturally aged Mg-Zn-Cu-Mn alloy.Materials Science and Engineering A,2008,489(1-2):127-137.
[13]Golmakaniyoon S,Mahmudi R.Effect of aging treatment on the microstructure,creep resistance and high-temperature mechanical properties of Mg-6Zn-3Cu alloy with La-and Cerich rare earth additions.Materials Science and Engineering A,2015,620:301-308.
[14]Sun X G,Dong Y,Lin X P,et al.Effects of Cr precipitation strengthening process of Mg-Zn-Al-Cu alloy.Special Casting and Nonferrous Alloys,2010,30(3):279-282.(In Chinese)
[15]Zhang Y,Huang X F,Ma Y,et al.Effects of Sm addition on microstructural evolution of Mg-6Zn-0.4Zr alloy during semisolid isothermal heat treatment.China Foundry,2017,14(2):85-92.
[16]Buha J.The effect of micro-alloying addition of Cr on age hardening of an Mg-Zn alloy.Materials Science and Engineering A,2008,492(1-2):293-299.
[17]Zhu H M,Luo C P,Liu J W,et al.Effects of trace Cu addition on the microstructure and tensile properties of ZK60 alloy.Materials Science Forum,2010,654:655-658.
[18]Zhang L,Chen J C,Yu J.Analysis of valence electron structure of GP zone in Cu-Cr alloy.Rare Metals and Cemented Carbides,2006,34(4):28-31.(In Chinese)
[19]Liu Y,Yuan G Y,Lu C,et al.Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase.Transactions of Nonferrous Metals Society of China,2007,17(s1):353-357.
[20]Buha J and Ohkubo T.Natural aging in Mg-Zn(-Cu)Alloys.Metallurgical and Materials Transactions A,2008,39(9):2259-2273.
[21]Nayeb-Hashemi A A,Clark J B(Eds).Phase diagrams of binary magnesium alloys.ASM International,1988:92.
[22]Sun H,Zhou M Y,Qu X N,et al.Microstructure evolution of AZ80-0.2Y magnesium alloy processed by semi-solid isothermal and induction heat-treatment.The Chinese Journal of Nonferrous Metals,2017,27(10):1988-1995.(In Chinese)
[23]Zhang L,Cao Z Y,Liu Y B.Microstructure evolution of semisolid Mg-14Al-0.5Mn alloys during isothermal heat treatment.Transactions of Nonferrous Metals Society of China,2010,20(7):1244-1248.
[24]Hu G X,Cai X,Rong Y H.Fundamentals of materials science.Shanghai:Shanghai Jiao Tong University Press,2010:150-151.(In Chinese)
[25]Wu G H,Zhang Y,Liu W C,et al.Microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment.Journal of Magnesium and Alloys,2013,1(1):39-46.
[26]Li Y D,Chen T J,Ma Y,et al.Effect of rare earth 0.5%addition on semi-solid microstructural evolution of AZ91D alloy.The Chinese Journal of Nonferrous Metals,2007,17(2):320-325.(In Chinese)
[27]Zhu G L,Xu J,Zhang Z F,et al.Effect of high shear rate on solidification microstructure of semisolid AZ91D alloy.Transactions of Nonferrous Metals Society of China,2010,20(s3):868-872.
[28]Zhu M F,Su H Q.A study on producing ZA12 alloy with globular structure using semi-solid isothermal treatment.Foundry,1996(4):1-5.(In Chinese)
[29]Cao F R,Guan R G,Chen L Q,et al.Microstructure evolution of semisolid AZ31 magnesium alloy during reheating process.The Chinese Journal of Nonferrous Metals,2012,22(1):7-14.(In Chinese)
[30]Du X H,Zhang E L.Microstructure and mechanical behavior of semi-solid die-casting AZ91D magnesium alloy.Materials Letters,2007,61(11-12):2333-2337.
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