Effect of solution treatment on the strength and fracture toughness of aluminum alloy 7050

The effect of the solution treatment on the tensile property and fracture toughness of aluminum alloy 7050 were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile test and the plane-strain fracture toughness test. The results show that with increasing single-stage solution temperature, the volume fraction of the residual phase decreases, but the volume fraction of the recrystallized grains and the size of the sub-grains increase. Thus, the strength and fracture toughness of the single-stage solution treated samples increase first and then decrease. The enhanced solution treated samples result in an improved dissolution of the residual phase, a lower recrystallized grains fraction and smaller sub-grains, which leads to a higher strength and fracture toughness than that of the single-stage solution treated samples. The grain structure of the high temperature pre-precipitation treated samples is similar to that of the enhanced solution treated samples. However, the high temperature pre-precipitation treated samples exhibit a lower strength and fracture toughness, due to a mass of AlZnMgCu phase precipitating from the matrix.

Research highlights▶ Solution treatment is a primary and key step for 7xxx series aluminum alloy which requires a good compromise between strength and fracture toughness. The specimen treated with an enhanced solution exhibit a significant increase in yield strength and fracture toughness because the residual phase can be re-dissolved into the matrix beyond the overburning temperature of the single-stage solution treatment. The high temperature pre-precipitation treatment increases the resistance to intergranular corrosion and exfoliation corrosion, but decreases the mechanical properties. However, the effect of the high temperature pre-precipitation treatment on the fracture toughness has been seldom reported. ▶ In this paper, the effects of the single-stage solution treatment (ST), the enhanced solution treatment (EST) and the high temperature pre-precipitation treatment (HTPT) on the tensile property and fracture toughness of the 7050 aluminum alloy were studied. These results can give indispensable information for optimizing the solution processing parameters.