铸型冷却强度对脉冲电流细化纯铝凝固组织的影响

通过改变脉冲电流参数和铸锭的冷却速度,研究了脉冲电流细化纯铝的规律.试验结果表明:在较快的冷却速度下脉冲电流峰值对组织细化程度的影响明显强于脉冲频率的作用.当频率超过200Hz后电流的热效应导致细化效果反而变差,同时电流的作用存在一个极限值,当电流峰值达到125A之后细化效果明显增强,但是继续提高参数,细化效果并没有随之提高.在较慢的冷却速率下,由于增加了脉冲电流的有效作用时间以及晶核迁移的时间,易于获得等轴晶组织.

Effect of Mold Cooling Intensity on Solidification Structure of Pure Al Refinement Under Electric Current Pulse

By adjusting the pulse current parameters and the cooling rate of molten aluminum, the influence of electric current pulse (ECP) on as-cast pure aluminum was studied. The results show that under the fast cooling rate, the peak pulse current has stronger impact than the pulse frequency on solidification structure of pure Al. After pulse frequency reaches to 200 Hz, the effect of ECP becomes bad with increasing of pulse frequency due to the Joule heat effect of current. The pulse current has obvious influence on the solidification structure when the peak value of current achieves to 125 A, on the other hand the effect of refinement does not become better with increasing of the peak value. Under the slow cooling rate, it is easy to achieve fine equiaxed grain due to the increase of effective time of pulse current and immigration of crystal nucleus.