Temperature Dependence of the Tensile Behavior of Cast and Extruded Al-7Si-0.3Mg Alloys in 213-673 K

The temperature dependence of tensile properties of an A356 cast alloy is studied. The solution-treated, natural aged and peak aged specimens of the A356 cast alloy have been tensile tested in the temperature range of 213–673 K at the strain rate of 5.7 × 10⁻⁴ s⁻¹. The data are also compared with that of extruded A356 specimens, in which more uniform silicon particles distribution is achieved. Independent of the particle distribution, both the cast alloy and the extruded alloy show a similar temperature dependence of tensile properties, implying that the tensile properties of the cast alloy are mainly determined by the precipitation of Mg₂Si. At temperatures below about 573 K, the yield stress of the solution-treated cast specimens increases, while that of the peak aged specimens decreases gradually with increasing temperature. The yield stress of the natural aged specimens is nearly temperature independent. Corresponding to the high yield stress regime, the elongation of the solution-treated and natural aged specimens decreases drastically. At higher temperature at which dissolution of Mg₂Si occurs, softening and recovery of the ductility are observed in all the specimens. On the temperature regime of about 223–373 K, the solution-treated specimens exhibit the Portevin-LeChatelier effect which is dependent on the concentration of vacancies and solute atoms. Since both vacancies and solute atoms are depleted during aging, the flow instability is absent in all aged specimens.