Correlation between microstructure and tensile properties of Al–Si alloy produced by high-pressure diecasting

We investigated the correlation between microstructure and tensile properties of a complex-shaped high-pressure diecasting (HPDC) Al–Si alloys at different local solidification conditions. The increase in cooling rates during solidification (from 5.8 to 39.2 °C/s) and after solidification (from 0.6 to 114.5 °C/s) result in the refinement of α-Al dendritic arm spacing (DAS), eutectic Al/Si, and Fe-rich intermetallic compounds (IMCs). High cooling rate regions contain small spherical gas pores with maximum sizes below 500 μm, whereas low cooling rate regions contain large, irregular-shaped shrinkage pores with maximum sizes of ∼900 μm. The yield strength of HPDC Al–Si alloys is mainly influenced by the strengthening effects of grain boundary and eutectic Si particles, which are determined by local solidification conditions. Porosity is an important factor in determining the ultimate tensile strength and tensile elongation of HPDC alloys. Fine spherical pores have a minimal effect on cracking. However, large, irregular shrinkage pores act as primary crack initiation sites, causing premature fracture and consequently deteriorating both ultimate tensile strength and ductility. This demonstrates that controlling both the constituting phase and porosity by optimizing local solidification conditions is important for controlling the tensile properties of HPDC Al–Si alloys.