原位自生Mg_2Si/A1-Si复合材料的稀土与锶盐变质研究

研究了稀土与锶盐复合变质及热处理对原位自生Mg2Si/Al-Si复合材料微观组织的影响。结果表明:随冷却速度的加大,SrCl2与RE复合变质剂对Mg2Si/Al-Si凝固组织中初生α-A1与共晶Si相的变质作用均加强,初生α-A1晶粒生成量增多同时形貌发生趋向球状的转变,共晶Si相形貌则发生板片状向短棒状的转变;在冷却速度较低的砂型铸造条件下,Mg2Si/Al-Si材料凝固组织中,三元共晶Si相受变质剂作用不明显,依然呈板片状生长,此时其可作为三元共晶Mg2Si相的异质形核基底,共晶Mg2Si便依附其上生长;热处理可使Mg2Si/Al-Si铸态组织中共晶硅相转变成细小的颗粒状,断网状的共晶Mg2Si转变成细小的棒状甚至颗粒状,优化了材料组织。

Study on Multiple Modification of Rare Earths and Strontium Salt on in-situ Mg2Si/A1-Si Composites

The influences of multiple modifications of rare earths and strontium salt to heat treatments on microstructures of in-situ Mg2Si/Al-Si composites were studied in this article.Experimental results indicate that the modification capacity of rare earths and strontium salt on the composites will become more strong,with cooling rate increased.which results in the amount of α-A1 produced rising with its shape changing to sphere-like,and results in the morphology of trinary eutectic silicon changing from short sticks to coarse flakes;On the lower cooling rate condition,trinary eutectic silicon is almost unmodified and then can serve as heterogeneous nucleation site for trinary eutectic Mg2Si phase;eutectic silicon in composite is fined to particles in a heat treatment process,and Chinese characters-like eutectic Mg2Si is broken into fine stripes or even particles under melting treatment condition.