Effect of slow shot speed on externally solidified crystal, porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal (ESC), porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM) and laboratory computed tomography (CT). Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy. The AlSi9MnMoV alloy, which was designed with trace multicomponent additions, displays a notable grain refining effect in comparison to the AlSi10MnMg alloy. Refining elements Ti, Zr, V, Nb, B promote heterogeneous nucleation and reduce the grain size of primary α-Al. At a lower slow shot speed, the large ESCs are easier to form and gather, developing into the dendrite net and net-shrinkage. With an increase in slow shot speed, the size and number of ESCs and porosities significantly reduce. In addition, the distribution of ESCs is more dispersed and the net-shrinkage disappears. The tensile property is greatly improved by adopting a higher slow shot speed. The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa (increased by 11.52%), and the elongation is enhanced from 3.72% to 6.34% (increased by 70.52%).