Effect of Non-isothermal Retrogression and Re-aging on Microstructure and Properties of an Al-Zn-Mg-Cu Alloy

The effects on microstructure and comprehensive properties of an Al-Zn-Mg-Cu alloy with different non-isothermal RRA treatments are investigated by tensile test, intergranular corrosion test, electrochemical corrosion test, and transmission electron microscopy. The results showed that after 24 h of pre-aging treatment at 120 degrees C, heating at a rate of 4 degrees C/min to 200 degrees C (i.e., 20 min of heating), quenching with water, and then non-isothermal retrogression re-aging treatment at 120 degrees C for 24 h, the comprehensive properties of the alloy were the best. The tensile strength, yield strength, elongation, intergranular corrosion depth, corrosion rate, and conductivity of the alloy are 619 MPa, 566 MPa, 9.8%, 14.4 mu m, 0.422 mm/a, and 23.6 MS/m, respectively. After pre-aging treatment, the matrix precipitates in the alloy partially dissolved during non-isothermal retrogression treatment, and the average size of the matrix precipitates decreased. After re-aging treatment, the grain boundary precipitates in the alloy exhibit an increased size, while the matrix precipitates become more diffused. Additionally, the absence of precipitation free zone becomes more noticeable.