The influence of thermal treatment on microstructure and mechanical properties of the Si-rich Al–Mg–Si–Sc–Zr alloy

The paper studies the Al–Mg–Si alloy that does not contain scandium and zirconium, as well as the silicon-rich Al–Mg–Si–Sc–Zr alloy. Multistage thermal treatment was carried out for the Al0.3Mg1Si0.3Sc0.15Zr alloy, which included annealing at a temperature of 440 °C for 8 h, high-temperature annealing at 500 °C for 0.5 h, and artificial aging at a temperature of 180 °C with soaking for 5 h. The Al0.3Mg1Si alloy was annealed at 550 °C for 8 h, and then artificial aging was carried out similarly to the alloy with Sc and Zr additives. To study the fine structure, transmission electron microscopy was used. In the as-cast condition and after each stage of thermal treatment, the mechanical properties of the alloys were determined. It has been found that in an alloy doped with Sc and Zr, the formation of Al3Sc particles occurs already at the stage of formation of the cast structure. During subsequent artificial aging, the supersaturated solid solution decomposes with the formation of β" (Mg5Si6) particles improving mechanical properties. It has been found that in the scandium-containing alloy, fewer β" (Mg5Si6) particles are formed, as a result of which its strength properties are slightly worse than those of the base alloy are. Moreover, these particles are larger than in an alloy that does not contain scandium. This is explained by the fact that complete quenching is impossible for an alloy with scandium additives.