Effect Of Electric Current Pulse On The Structure Of Directionally Solidified Al-Si Alloy

Electric current pulse (ECP) can markedly change the solidification structure and improve the mechanical properties of metal. Many researchers have studied the effect of ECP on the crystal growth of non-faceting single phase alloy, such as Al-4.5wt.%Cu alloy. However, the influence of ECP on directional solidification structure of non-faceting/faceting alloy is not available. As a typical non-faceting/faceting alloy, Al-Si alloy was widely used due to its excellent mechanical properties. So, the aim of this article is to investigate the influence of ECP on the directional solidification structure of Al-Si alloy.Experimental results show that the ECP has a significant effect on the directional structure of Al-Si alloy. As for the complex regular structure (CRS) in the eutectic and hypereutectic alloy, the number and area percentage of the CRS is found to increase when the ECP is applied. In Al-15.5wt.%Si hypereutectic alloy without ECP, there is a peak value in the area percentage of the CRS with the decrease of pulling rate. Furthermore, the growth process of CRS with and without ECP is investigated. There is not observed difference in the samples with and without ECP. The new lamellae continually still appear at the front of the CRS, and old lamellae disappear at the rear of the CRS during its growth.The application of ECP improves the stability of the solid-liquid interface of Al-3wt.%Si hypoeutectic and decreases the primary dendrite arm spacing during directional solidification. In addition, it is found the ECP can change the distribution of Si element in Al-20.5wt.%Si hypereutectic samples. When the ECP is applied, the primary Si is significant enriched at the initial growth stage of samples, and then sharply decreases as the growth length increases.According to the typical solidification theory and the effect of ECP, these results are mainly attributed to the heat effect and force effect of ECP which can change the growth process of Al-Si alloy during the directional solidification. Due to the rise of temperature gradient which can go up when the ECP is applied, the stability of the solid-liquid interface of Al-Si hypoeutectic (Al-3wt.%Si) are enhanced. In addition, the crowding effect of ECP and increase of temperature gradient are reasons to decrease the primary dendrite arm spacing. It is considered that the forced convection which induced the force effect of ECP plays a pivotal role in the change of CRS and Si element distribution.