Effect of Transition Metals Addition on Tensile Properties of Al–Si–Cu-Based Alloys at 25 °C and 250 °C: Role of Heat Treatment

Abstract

The tensile data showed that strength and percent elongation of the Zr-containing 354 (Al–9%Si–1.8%Cu–0.5%Mg) alloys increased in the one-step solution heat-treated condition compared to the as-cast case. The multi-step solution heat treatment displayed higher tensile properties than those achieved with single-step solution heat treatment. The use of the T6 treatment, incorporating the multiple solution heat treatment, allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in the alloy strength. The best tensile properties of alloys tested at room temperature after stabilization at 250 °C for 200 h are obtained with the T6 heat treatment. The addition of Zr, Ni, and Mn to Al–Si alloys improves the high-temperature tensile properties of the 354 alloy. Alloys containing 2%Ni or 0.75%Mn perform better in case of high-temperature conditions, with 1-h stabilization at 250 °C. After 200-h stabilization at 250 °C, the strength of the T6-treated alloys—regardless of the type of solution heat treatment process, is reduced considerably, while the ductility is increased, with base alloy showing the highest percent elongation, ~ 19%. The reduction in strength may be attributed to the alloy softening which occurs after such long stabilization time at the high testing temperature (250 °C).