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《Journal of University of Science and Technology Beijing》 2007-02
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Microstructures and creep properties of high-performance heat-resistant magnesium-alkaline earth alloys

BAI Jing 1),SUN Yangshan 1),XUE Feng 1),YAN Jingli 1),QIANG Jing 1),TAO Weijian 2)1)Department of Materials Science and Engineering,Southeast University,Nanjing 211189,China 2)Welbow Metals Co.Ltd.,Nanjing 211221,China  
The microstructures of Mg-4Al alloys containing alkaline earth Sr and Ca were investigated by optical microscope(OM),scanning electronic microscope(SEM)and transmission electron microscope(TEM),and creep properties were also tested.The as-cast microstructure of the studied alloys consists of dendritic α-Mg and grain boundary second-phases.Divorced eutectic and lamellar eutectic Al_4Sr,and bulky ternary τ phase are observed along grain boundary with 2% of Sr addition to the based alloy.2% of Ca addition results in the formation of lamellar eutectic Mg_2Ca at grain boundary and Al_2Ca particles in grains.In the Mg-4Al-2Sr-1Ca alloy,grain boundary phases are τ phase and lamellar eutectic Mg_2Ca,and Al_2Ca particles are also precipitated in grains.With the increase of Al content in the Mg-4Al-2Sr-1Ca,the coarse irregular-shaped(Mg,Al)_2Ca eutectic forms along grain boundary and its volume fraction gradually increases,meanwhile Mg_2Ca and τ phase gradually decrease.The new fine lamellar Al_4Sr appears when the Al content reaches to 7%.The additions of Sr and Ca improve the creep resistance of Mg-Al alloys significantly,and the Mg-5Al-2Sr-1Ca and Mg-6Al-2Sr-1Ca alloys indicate the best creep properties in all studied alloys.According to the power-law equation,under conditions of 175℃/50~80MPa and 70MPa/150~200℃,the creep behavior of the Mg-4Al-2Sr alloy is diffusion controlled dislocation climb at lower stresses(60MPa)and shows the breakdown of power-law at higher stresses.The creep mechanism of the Mg-4Al-2Sr-1Ca alloy seems to be the combined effect of diffusion controlled dislocation movement and grain boundary sliding.
【Fund】: 国家“863”计划资助项目(No.2001AA331030-01);; 江苏省自然科学基金预研项目(No.BK2004208);; 东南大学优秀博士学位论文基金资助项目
【CateGory Index】: TG113
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