Sr对Mg-9Al-1Si-0.3Zn合金微观组织和力学性能的影响

EFFECTS OF Sr ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Mg-9Al-1Si-0.3Zn ALLOY

研究了Sr元素对Mg-9Al-1Si-0.3Zn(质量分数,%)合金晶粒大小、力学性能和Mg_2Si形貌的影响.利用深腐蚀方法获得了Mg_2Si细化前后的形貌,通过其形貌变化规律研究了Sr元素对Mg_2Si细化的机制.结果表明,Sr通过抑制Mg_2Si生长使汉字状和加料斗形状的Mg_2Si变成规则的正八面体.当Sr的添加量达到0.32%时,Mg_2Si的形貌得到了最好的改善.同时,合金的拉伸强度和塑性随着Sr的添加不断提高.

Mg-Al-Si alloys（AS series alloys） with a high content of silicon performed low ductility and strengths because of large amount of coarse Chinese scripts Mg2Si particles distributed in the matrix.Trace elements,such as Ca,P,Sr and RE were selected to modify the morphology of Mg2Si particles.Among these,Sr showed remarkable modification effect,however,the modification mechanism was not clarified yet.In this work,the effects of Sr on the morphology of Mg_2Si in Mg-9Al-lSi-0.3Zn（mass fraction,%） alloy and the mechanical properties were investigated,and the modification mechanism was explained by comparing Mg_2Si morphologies.The Mg-9Al-lSi-0.3Zn alloy was composed of primary hopper Mg_2Si particles of 40μm in size,coarse Chinese scripts Mg_2Si of 50—80μm,island-like Mg17Al12and the a-Mg matrix.3D hopper crystals and Chinese scripts Mg2Si particles were extracted by the electrochemical method.Both morphologies reveal the ＂corner effect＂ which leads to the preferential growth orientation of edges and corners of the octahedron Mg2Si particle,respectively.When Sr was added into the alloy,the growth rates of both edges and corners of the Mg2Si particles were depressed significantly due to the adsorption of Sr on the surface of Mg2Si particles.When Sr addition went up to 0.32%,Mg2Si phase was fully modified to small polygonal particles of 5—20μm.Moreover,the grain size of the alloy decreased from 210μm to 160μm with Sr increasing,which is in accord with the GRF（growth restriction factor） mechanism.The increasing of mechanical properties is mainly attributed to the refinement of Mg2Si phase.