Influence of pre-stretching on quench sensitive effect of high-strength Al-Zn-Mg-Cu-Zr alloy sheet

The influence of pre-stretching on quench sensitive effect of high strength Al-Zn-Mg-Cu-Zr alloy AA 7085 sheet was investigated by tensile testing at room temperature, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The water-cooled and aged alloy exhibits higher strength than the air-cooled and aged alloy; 2.5% pre-stretching of tensile deformation exerts little effect on strength of water-cooled and aged alloy but increases that of air-cooled and aged one, and therefore the yield strength reduction rate due to slow quenching decreases from about 3.8 % to about 1.0 %, reducing quench sensitive effect. For the air-cooled alloy, pre-stretching increases the sizes of eta ' strengthening precipitates but also increases their quantity and the ratio of diameter to thickness, resulting in enhanced strengthening and higher strength after aging. The reason has been discussed based on microstructure examination by TEM and DSC.