Microstructural analysis of the A356 Al alloy produced by the evaporative pattern casting process

摘要

This study investigated the influence of several processing parameters, including the gating system design, the coating thickness, the application of a vacuum and the pouring temperature, on the microstructures of the EPC A356 Al alloy. Due to the endothermic nature of the degradation reactions of the EPS patterns and the sequential flow characteristic in the Al EPC molds, the melt front experiences a constant chilling effect during the pattern I cavity filling process. As a result, the microstructures of the EPC Al castings differ slightly from those produced in the conventional empty cavity molds. It has been found that, in the EPC process, the Al-Si eutectic content increases slightly toward the, downstream of the castings, and that an accumulated eutectic zone in the tip of 'the castings (melt front) can be observed as well. Nevertheless, in the CO{sub}2 process, the eutectic content remains more or less constant along the flow direction of the castings, and also no accumulation of eutectic phase has been detected at the melt front. The present results indicate that the SDAS is reduced by changing the gating system from S-T-V to T-S-H, but is increased with increasing the coating thickness and the pouring temperature, and also by the application of a vacuum. Regarding the casting porosity, the results show that the porosity content decreases progressively from the gate entrance toward the melt front. In addition, the porosity content is only slightly affected by different gating systems' employed and by varying the coating thickness, but is significantly increased by raising the pouring temperature and by the application of a vacuum.