热处理对Mg-5Sn-1Si合金组织及硬度的影响

Effect of heat treatment on microstructure and hardness of Mg-5Sn-1Si alloy

采用Ar气保护制备了Mg-5Sn-1Si(质量分数,%)合金,并研究了合金的铸态组织和在480℃固溶处理及180℃和280℃不同时效热处理对合金组织中析出相演变的影响及组织与硬度的关系。结果表明,合金铸态组织由α-Mg、共晶Mg2Si、共晶Mg2Sn三相组成;经480℃固溶处理后Mg2Sn相完全固溶,粗大的Mg2Si相得到少量球化;时效处理过程中Mg2Si相得到球化。在180℃时效时,Mg2Sn无沉淀析出,硬度较低,时效保温24 h仅为24.1 HV。在280℃时效时,细小的Mg2Sn相弥散析出并使合金的硬度明显升高,时效保温18 h达到峰值硬度47.6 HV,并随时间的延长出现过时效现象。280℃时效初期,组织中形成较宽的无析出带(PFZ),随着时效时间的延长无析出带PFZ消失。

Mg-5Sn-1Si （mass fraction,% ） magnesium alloy was prepared by casting under argon atmosphere protection in electricresistance furnace. The as-cast microstructure, the precipitated phases evolution and the relation between microstructure and hardness of the Mg-5Sn-lSi alloy heat-treated were investigated, the heat treatment processes were soild solution at 480 ℃ , and then aging at 180 ℃ and 280 ℃, respectively. The results show that the as-cast Mg-5Sn-lSi alloy mainly consists of dendrites α-Mg, eutectic Mg2Sn phase and eutectic Mg2Si phase. The Mg2Sn phase is completely redissolved and the large block Mg2Si phases get slightly globularity during the solid solution treatment at 480 ℃ for 14 h. However, the Mg2Si phases get globularity in the process of aging treatment. No Mg2Sn phase precipitation is observed in the alloy aged at 180 ℃ , the Mg-5Sn-lSi alloy exhibits the obvious aging hardening behavior, but showing lower hardness, it is only 24. 1 HV when aging at 180 ℃ for 24 h. On the contrary, the hardness increases obviously with Mg2Sn phase dispersive precipitation when aging at 280 ℃ , and the hardness peak value is 47.6 HV for the alloy aged at 280 ℃ for 18 h, and there is over-aging with extension of aging treatment time. Precipitation free zones （PFZ） form at early stage of aging at 280 %, and the PFZ disappears with extension of aging time.