Abstract: A 7050 aluminum alloy hot forging for automobile was selected, and the specimens were rapidly heated to 746 K with a rate of 20 K/min and held for 1 h. Then the specimens were rapidly transferred to the PAG polymer solution with concentrations of 0% (water), 5%, 10%, 20%, 30% and air to quench respectively, and finally the aging treatment was carried out using the T74 process (393 K for 6 h and 436 K for 12 h). The effects of different PAG quenchant concentrations on the residual stress, second-phase particles, tensile strength and yield strength of the 7050 aluminum alloy specimens were analyzed. The results show that with the increase of PAG quenchant concentration, the residual stress of the aluminum alloy specimens gradually weakens, the volume fraction of the second phase gradually increases, and the tensile strength and yield strength gradually decrease. Considering comprehensively, the PAG quenchant concentration of 10%-20% can meet the technical requirements, with which the quenched specimens of the 7050 aluminum alloy have relatively low residual stress, the tensile strength is 512-519 MPa and the yield strength is 472-478 MPa, and meeting the mechanical properties requirements of tensile strength greater than 510 MPa and yield strength greater than 455 MPa.

Key words: PAG quenching medium, 7050 aluminum alloy, microstructure, mechanical properties