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 (about 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.