细化变质处理对铸造A356铝合金组织性能及共晶硅生长机制的影响

Effect of Refinement and Modification on Microstructure, Properties and Eutectic Silicon Growth Mechanism of Cast A356 Aluminum Alloy

摘要:

研究了采用新型Al-5Ti-1B-1RE中间合金和Al-10Sr中间合金对A356铝合金进行单一或复合细化变质处理后的组织、力学性能和共晶硅生长机制的影响。结果表明：单一细化变质处理中Al-5Ti-1B-1RE中间合金对A356铝合金中α-Al相有明显的细化作用,合金的强度和维氏硬度显著提高；Al-10Sr 中间合金对共晶硅有强的变质作用,合金的伸长率明显提高；而经复合细化变质处理后α-Al相形状和尺寸变得更均匀细小,晶界更清晰,共晶硅相几乎都转变成更弥散、更细小的纤维状,片层状共晶硅也几乎完全消失,共晶硅长度由铸态40-60 μm降低到1-2 μm之间,达到完全变质效果,其力学性能显著高于铸态、单一细化变质剂处理的A356铝合金。未细化变质的A356铝合金中的共晶Si的生长方式为典型的小平面台阶生长,复合细化变质处理的共晶硅以孪晶凹槽机制生长为主,小平面生长特征逐渐减弱直至消失。

Abstract:

The microstructures, mechanical properties and eutectic silicon growth mechanism of A356 aluminum alloy treated by novel Al-5Ti-1B-1RE and Al-10Sr master alloy with individual or composite refinement and modification were studied. The results showed that under individual addition condition, the Al-5Ti-1B-1RE master alloy had a significant refinement effect on α-Al phase in A356 aluminum alloy and the tensile strength σb, yield strength σs and Vickers hardness of the alloy were significantly improved. Al-10Sr master alloy had a strong modification effect on eutectic silicon, and the elongation δ of the alloy was obviously improved. Under composite addition condition, the shape and size of α-Al phase in A356 aluminum alloy became more uniform and finer, and the grain boundaries were clearer. The eutectic silicon phases were almost converted into dispersed, fine fibrous shape, and the lamellar eutectic silicon almost completely disappeared. The length of the eutectic silicon was reduced from the as-cast state of 40-60 μm to 1-2 μm, achieving a complete modification effect. Its mechanical properties were much higher than those of the as-cast, any single refiner and modifier treated A356 aluminum alloy. The growth mode of eutectic Si in the unrefined and unmodified A356 aluminum alloy was typical small-plane step growth. The eutectic silicon with composite refinement and modification was mainly grown by the twin plane re-entrant edge mechanism, and the growth characteristics of the facet were gradually weakened until disappeared.