Influence of melt flow on the formation of defect band in high pressure die casting of AZ91D magnesium alloy

The characteristics of defect band under different melt flow patterns in high pressure die casting of AZ91D magnesium alloy were investigated. Results showed that the distribution of defect band followed the contour of melt flow. On the side close to the skin layer, the porosity in defect band was uniformly distributed and followed the contour of melt flow, while on the other side close to the casting center, the porosity in defect band was nonuniformly distributed and had a poor consistency with the contour of melt flow. During filling process, the flow speed and solid fraction inside and outside the contour of melt flow were much different. Thus, the crystals in the contour of the melt flow would rotate and fragment under the flush of melt flow, resulting in a larger gap between crystals and the formation of an aggregated porosity in the defect band.