高性能碱土耐热镁合金的显微组织和蠕变性能  

Microstructures and creep properties of high-performance heat-resistant magnesium-alkaline earth alloys

作　　者：白晶[1] 孙扬善[1] 薛烽[1] 晏井利[1] 强婧[1] 陶卫建 

机构地区：[1]东南大学材料科学与工程学院,南京211189 [2]云海特种金属有限公司,南京211221

出　　处：《北京科技大学学报》2007年第2期198-204,共7页Journal of University of Science and Technology Beijing

基　　金：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

摘　　要：利用光学显微镜(OM),扫描电镜(SEM)及透射电镜(TEM)系统研究了碱土元素Sr和Ca加入Mg-4Al基合金后的显微组织,并测试了其抗蠕变性能.实验合金的铸态组织均由α-Mg和沿枝晶界分布的第二相组成.2%Sr加入基体合金中能观察到沿晶界的离异共晶和层片共晶Al4Sr相及块状三元τ相.2%Ca的加入则形成了晶界层片Mg2Ca共晶和晶内的Al2Ca颗粒.而在Mg-4Al-2Sr-1Ca中,晶界相为块状τ相和层片状Mg2Ca共晶,晶内也析出Al2Ca颗粒.在Mg-4Al-2Sr-1Ca基础上提高Al含量,粗大不规则共晶(Mg,Al)2Ca相在晶界处形成并不断增多,Mg2Ca及τ相逐渐减少,当Al含量到7%时,出现了新的细小层片状Al4Sr相.Sr、Ca元素加入Mg-Al合金,改善了合金的抗蠕变性能,其中Mg-5Al-2Sr-1Ca和Mg-6Al-2Sr-1Ca合金显示所有实验合金中最好的蠕变抗力.根据Power-law公式,在175℃/50～80MPa和70MPa/150～200℃蠕变下,Mg-4Al-2Sr合金在较低应力(<60MPa)下蠕变表现为扩散控制的位错攀移机制,而在高应力下出现Power-law公式的失效;Mg-4Al-2Sr-1Ca合金蠕变则受到了扩散控制的位错机制和晶界滑移机制的共同作用.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 a-Mg and grain boundary second-phases. Divorced eutectic and lamellar eutectic Al4Sr, and bulky ternary r 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 Mg2Ca at grain boundary and Al2Ca particles in grains. In the Mg-4Al-2Sr-ICa alloy, grain boundary phases are r phase and lamellar eutectic Mg2Ca, and Al2Ca particles are also precipitated in grains. With the increase of Al content in the Mg-4Al-2Sr-ICa, the coarse irregular-shaped （Mg, Al）2Ca eutectic forms along grain boundary and its volume fraction gradually increases, meanwhile Mg2Ca and r phase gradually decrease. The new fine lamellar Al4Sr 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-ICa 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--80 MPa and 70 MPa/150 -- 200 ℃, the creep behavior of the Mg-4Al-2Sr alloy is diffusion controlled dislocation climb at lower stresses （ 〈 60 MPa） and shows the breakdown of power-law at higher stresses. The creep mechanism of the Mg-4Al-2Sr-ICa alloy seems controlled dislocation movement and grain boundary sliding.

关 键 词：镁合金 锶 钙 显微组织 抗蠕变性能 

分 类 号：TG146.22[一般工业技术—材料科学与工程]