低压交流脉冲对A357合金凝固宏观组织的影响

针对A357铝合金,利用低压交流脉冲处理,研究了脉冲电流对该合金凝固宏观组织的影响.试验结果表明:低压交流脉冲可实现铸件晶粒整体细化,且细化晶粒的电流密度存在一个阈值和饱和值.在凝固过程的不同阶段施加脉冲电流,发现细化作用只发生在形核阶段.低压交流脉冲电流密度对晶粒密度的影响规律与过冷度的影响相一致,脉冲电流在形核阶段可提供一个附加能量,降低形核势垒,导致晶核增殖,晶粒组织细化.

Effect of Low-Voltage Alternating Current Pulse Treatment on the Macrostructure of A357 Alloy

Based on the A357 aluminum alloy,the effect of low-voltage alternating current pulse(LVACP)on the macrostructure of alloy was investigated by using LVACP treatment.The experimental results indicate that the macrostructure for whole ingot could be refined with LVACP and there was a threshold value and a saturation value for the current density used to refine grain.Although the pulse current was applied to different stages of the solidification,the refinement effect occurs only during the nucleation stage.The effect of current density on grain density was similar to that of undercooling.The nucleation barrier was reduced by providing an additional energy during the nucleation stage,which would lead to a multiplication of the crystal nuclei and refinement of grain.