The effect of Ni and V trace elements on the mechanical properties of A356 aluminium foundry alloy in as-cast and T6 heat treated conditions

In this study, the tensile properties of unmodified A356 alloys with trace additions of Ni or V were investigated. The nominal concentrations of these elements were set at 600 and 1000 ppm, respectively. Specimens obtained from sand and permanent mould casting in as-cast and T6 heat treated conditions were examined. It was found that the precipitation of Ni-rich intermetallics strongly influences the tensile properties of the sand cast A356 alloy in as-cast condition, leading to a reduction of both the yield strength (Rp0.2) and ultimate tensile strength (UTS) by 87% and 37%, respectively. Conversely, the V addition increased Rp0.2 and UTS by 42% and 25% due to a solid solution strengthening effect. After T6 heat treatment, the sand cast A356 alloys containing V exhibited slightly higher mechanical properties as compared to the A356 reference alloy (≈18%), whereas the detrimental effect of Ni was eliminated. The cooling rate became the main parameter influencing the mechanical properties of permanent mould cast alloys: no significant differences in mechanical properties were observed between the reference alloy and Ni- or V-containing alloys in both as-cast and T6 conditions.