Effect of additives and heat treatment on the tensile properties of 354 alloy at 25 °C and 250 °C

Abstract

The present study was performed on 354 alloy containing Al-9% Si-1.8% Cu-0.5% Mg. Six alloys were prepared using 0.2wt% Ti grain-refined 354 alloy, comprising alloy R (354 + 0.25% Zr) considered as the base or reference alloy, and five others, viz., alloys S (354 + 0.25% Zr + 2% Ni), T (354 + 0.25% Zr + 4% Ni), U (354 + 0.25% Zr + 0.75% Mn), V (354 + 0.25% Zr + 0.75% Mn + 2% Ni), and Z (354 + 0.25% Zr + 0.15% Sc). The tensile data showed that the UTS and percent elongation values of R, S, T, U, V and Z alloys increased in the one-step solution heat-treated (SHT 1) condition compared to the as-cast case. The multi-step solution heat treatment (SHT 2) displayed higher tensile properties than those achieved with SHT 1 treatment. The use of the T62 treatment, incorporating the SHT 2, allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in both UTS and YS. Without stabilization, T6 and T62 treatments provide the best improvements in both UTS and YS values of all alloys. The best tensile properties of alloys tested at room temperature after stabilization at 250°C for 200h are obtained with the T6 heat treatment. After T62 treatment, Alloy U showed the maximum increase in UTS and YS values. Addition of Zr, Ni, Mn and Sc to 354 alloys improves the high temperature tensile properties. Alloys S and U perform better when tested under high temperature conditions, after one hour stabilization at 250°C. After 200h stabilization at 250°C, however, the strength of the T6-treated alloys is reduced considerably, while the ductility is increased, with alloy R showing the highest percent elongation, ~ 19%, which is attributed to the precipitation of a high density of coarse Al2Cu phase particles during the prolonged stabilization treatment at 250°C.