Al-Sr-La中间合金改性对A356铝合金组织和性能的影响

Effect of Al-Sr-La intermediate alloy modification on microstructure and properties of A356 aluminum alloy

采用Al-Sr-La中间合金对A356铝合金进行改性处理,研究了Sr和La对A356铝合金微观结构和力学性能的协同变质机制。结果表明:添加0.5 mass%的Al-Sr-La中间合金对A356铝合金的改性效果最佳,此时A356铝合金具有优良的显微组织与力学性能,其α-Al相的晶粒细小,二次枝晶臂间距(SDAS)降低至14.2μm,较未改性的A356铝合金降低了36.6%,针状共晶Si转变为蠕虫状共晶Si,平均晶粒尺寸减小至0.86μm。与未改性的A356铝合金相比,添加0.5 mass%的Al-Sr-La中间合金改性后,合金的抗拉强度增加了22.4%,屈服强度增加了11.1%,伸长率增加了89.7%。最后,在实验结果的基础上,结合凝固理论,研究了Sr和La的协同变质机制。Sr吸附于Si相生长界面上,产生孪晶平面,抑制Si相的生长,使得Si以孪晶凹谷机制生长,实现对共晶Si的改性;La则由于Sr对Si的作用,使得La在共晶Si的凹槽处聚集,阻碍了Si的生长,改善共晶Si的形貌。

The Al-Sr-La intermediate alloy was used to modify A356 aluminum alloy,and the synergistic modification mechanism of Sr and La on microstructure and mechanical properties of the A356 aluminum alloy was studied.The results show that the addition of 0.5 mass%Al-Sr-La intermediate alloy has the best modification effect on the A356 aluminum alloy.At this time,the A356 aluminum alloy has excellent microstructure and mechanical properties,the grain size ofα-Al phase is fine,the secondary dendrite arm spacing(SDAS)is reduced to 14.2μm,which is 36.6% lower than that of the unmodified A356 aluminum alloy,and the needle-like eutectic Si phase transforms into worm-like eutectic Si with an average grain size of 0.86μm.Compared with unmodified A356 aluminum alloy,the addition of 0.5 mass%Al-Sr-La intermediate alloy modification increases the tensile strength of the alloy by 22.4%,yield strength by 11.1%,and elongation by 89.7%.Finally,based on the experimental results and combined with solidification theory,the synergistic modification mechanism of Sr and La was studied.Sr adsorbs on the growth interface of Si phase,generating twin planes to suppress the growth of Si phase,causing Si to grow in twin plane reentrant(TPRE)mechanism,achieving modification of eutectic Si.Due to the effect of Sr on Si,La aggregates in the grooves of eutectic Si,hindering the growth of Si and improving the morphology of eutectic Si.