Effect of high pressure die casting on the castability, defects and mechanical properties of aluminium alloys in extra-large thin-wall castings

The manufacturing of extra-large thin-wall castings using high pressure die casting is one of the most significant challenges for structural applications requiring excellent ductility. The present study aims to understand the effect of process parameters on the castability, defect formation and mechanical properties of aluminium alloys in extra-large thin-wall castings with a maximum flow length of 1230 mm in the 2.8 mm thick channel. Numerical simulation and experimental verification were carried out to tailor the process parameters in high pressure die casting. It is found that the process parameters can significantly affect the castability and mechanical properties of as-cast components. For a complete casting, the yield strength is slightly increased but the elongation is significantly decreased at the locations further away from runners. A new concept of effective flow length (EFL) is proposed and used to assess the castability in extra-large thin-wall high pressure die castings. Under the optimum casting condition, the EFL can reach 525 mm, at which the ratio of EFL to wall thickness is 187 and the yield strength and elongation are greater than 120 MPa and 10%, respectively. Although the extra-large thin-wall castings can be geometrically filled under several conditions, the heterogeneity of mechanical properties is the most significant concern, in which the variation of elongation is overwhelmingly important for the structural applications requiring excellent ductility under as-cast conditions. Therefore, the criteria of casting quality should consider both geometrical soundness and the homogeneity of mechanical properties in the casting body.