Abstract
Al-7%Si-Mg casting alloys containing 0.2 to 0.8%Mg and 0.04 to 0.8%Fe were preaged at room temperature prior to artificial aging. Hardness, tensile and yield strength decrease by preaging before artificial aging at 140° or 155°C for 5hrs. Ductility or toughness is also improved. Artificial aging at 200°C for 5hrs is unsusceptible to preaging. These facts are discussed on the bases of change in supersaturation caused by cluster formation during preaging and stability of clusters during artificial aging.
