热处理对不同冷速Al合金共晶相形貌及含量的影响

选取成分为Al-5.17Cu-2.63Si(合金A)、Al-4.29Cu-1.09Mg(合金B)和Al-2.09Si-1.66Mg(合金C)三元铝合金,分别进行不同冷速下的凝固实验。对比研究不同凝固速率下得到的共晶相形貌与含量在接近各合金体系三元共晶温度下热处理前后的变化行为。结果表明:同一合金冷速越慢,得到的原始组织二次枝晶间距越大,合金A的石墨型、砂型、保温型冷却组织的二次枝晶间距分别为24.17、63.32和99.88μm,合金B的二次枝晶间距分别为24.35、82.78和139.42μm。均匀化热处理的热扩散过程可以明显地溶解非平衡共晶相,由于原始组织的尺度不同,共晶相所处的溶解阶段与溶解程度不同。合金A的石墨型、砂型、保温型组织热处理后与热处理前的共晶相含量比值分别为0.44、0.49和0.68,合金B的共晶相含量比值分别为0.084、0.30和0.38。

Influence of heat treatment on morphology and quantity of eutectic phases of Al alloys with different cooling rates

The solidification experiment with different solidification rates was carried out on three ternary alloys of Al-5.17Cu-2.63Si(alloy A),Al-4.29Cu-1.09Mg(alloy B) and Al-2.09Si-1.66Mg(alloy C).The influence of heat treatment on morphology and quantity of the non-equilibrium eutectic phases at the temperature close to the ternary eutectic point was investigated.The results show that the second dendrite space increases with decreasing the solidification rate.The secondary dendrite spacing of alloy A is 24.17 μm for the graphite mould,63.32 μm for the sand mould,and 99.88 μm for the insulated mould,respectively,and the corresponding values of alloy B are 24.35,82.78 and 139.42 μm.The nonequilibrium eutectic phases can be dissolved in the diffusion process during the heat treatment process.And the quantity of the dissolved eutectic phases depends on the initial microstructure.For alloy A the ratio of eutectic phase volume fraction after heat treatment to that before heat treatment are 0.44,0.49 and 0.68,for the initial microstructure of graphite mould,sand mould and insulated mould,respectively,and the corresponding values of alloy B are 0.084,0.30 and 0.38.