Ca和La对Mg-5Sn-2Si合金组织和蠕变性能的影响

Effects of Ca and La on Microstructures and Creep Properties of Mg-5Sn-2Si Alloy

利用Mg-20%Ca(质量分数,下同)和Mg-20%La中间合金分别对Mg-5Sn-2Si合金进行变质处理,研究Ca和La对Mg2Si相的变质效果,并进行了高温蠕变实验。结果表明:Ca和La对Mg2Si相起到了良好的变质效果,初晶Mg2Si颗粒消失,粗大树枝晶得到有效细化,且有CaMgSi(花瓣状)和La5Si4(棒状)新相生成。经过Ca和La变质后合金的蠕变速率大幅度降低,在250℃和60MPa应力下,Mg-5Sn-2Si-2Ca和Mg-5Sn-2Si-2La的稳态蠕变速率分别减少到未变质时的1/48和1/28。蠕变抗力提高的原因可能与Mg2Si相细化、新相生成后位错的滑移和晶界的滑动受到阻碍有关。

The Mg-5Sn-2Si alloy was modified by the Mg-20%Ca（mass fraction, the same below）and Mg-20-La master alloys separately. The modifying effects of Ca and La on the Mg2Si phase were in- vestigated, and high temperature creep testing was conducted as well. The results showed that Ca and La had a good modifying effects on Mg2 Si phase, granuliform primary Mg2 Si phase disappeared and the morphology and distribution of the coarse dendritic Mg2 Si were obviously affected and new flower- like CaMgSi and rod-like LasSi4 compounds were found in the alloys. The creep rate of the alloy with the modifying of Ca and La decreased significantly, under 250~C ,60MPa stress conditions. The steady creep rate of Mg-SSn-2Si-2Ca and Mg-SSn-2Si-2La alloys decreased to 1/48 and 1/28 respectively, compared with the unmodified alloy. The reason for the increase of the creep resistance may have to do with that the Mg2Si phase was refined as well as dislocation slipping and grain boundary sliding were much more blocked after the new compounds generated.