Effects of Artificial Aging on Material Properties of Die-Cast Al–Si–Cu–Mg–xNa Alloy

The influence of sodium on the microstructural characteristics and mechanical properties of die-cast Al–Si–Cu–Mg (ADC12) alloy has been examined experimentally. Mechanical properties of the die-cast Al–Si–Cu–Mg alloy have increased with the addition of 0.03% Na, because of modification of the shape of the Si eutectic particles from acicular to fine and fibrous appearing. However, the mechanical properties decreased when 0.04% Na or more was added, due to the formation of shrinkage porosity. The fine and fibrous appearing eutectic Si has been created by the interruption of the nucleation and growth of Si eutectic by Na. The mechanical properties of Na containing die-cast ADC12 alloy were further enhanced by a T5 treating which is a low-temperature aging, giving rise to significant precipitation of fine CuAl₂ and Mg₂Si. In contrast, the mechanical properties of die-cast ADC12 T6-treated samples were lower due to the formation of blister defects. Thus, the solid solution process in the T6 treatment may not make severe precipitation hardening of die-cast ADC12 due to overaging. Moreover, severe precipitation hardening occurred by the artificial aging after microstructural refinement by Na.