Skin solidification during high pressure die casting of Al–11Si–2Cu–1Fe alloy

Surface regions of Al–11Si–2Cu–1Fe alloy castings produced by high pressure die casting (HPDC) were examined and three microstructural features were observed. In locations of direct melt impingement, there was not an α-Al rich layer. In most surface locations, a porosity-free α-Al rich layer was observed. However, in surface locations of low impact of melt, a porosity-free layer being a mixture of α-Al dendrites and fine eutectic formed before the α-Al rich layer. Solidification conditions of the surface regions were then considered. This was done by examining the possible effects of the processing features (high filling velocity, high applied pressure, and thin gate) of HPDC on heat transfer during filling and subsequent solidification. This analysis suggested that the α-Al rich layer was the result of solidification during the brief moment of the applied pressure immediately after die filling.