LAUSR

Abstract The influence of slow-shot speed on primary silicon particles (PSPs) and porosity of AlSi17Cu2.5 alloy in high pressure die casting (HPDC) was investigated. Both PSPs and porosity were identified in the microstructure. It was found that variation of the slow-shot speed could generate significant influence on both volume fraction and distribution of the PSPs and porosity. The area fraction of PSPs reached a maximum of ˜0.19% when the slow-shot speed was 0.05 m/s. An increase of the slow-shot speed could reduce the PSPs content and increase the microstructure heterogeneity, e.g., multiple PSPs-rich and PSPs-free ring-shape regions formed. Detailed feature of the PSPs in casting was highly dependent on the PSPs formed in the shot sleeve. Affected by solidification shrinkage, the volume fraction of the porosity increased exponentially from the surface to the center of the sample. However, the precipitation of PSPs released large amount of latent heat and promoted local feeding of the melt. The porosity decreased abruptly at the PSPs-free region and reached a local minimum at a particular distance from the surface.