Effects of contact body temperature and holding time on the microstructure and mechanical properties of 7075 aluminum alloy in contact solid solution treatment

Abstract

Contact solid solution treatment (CST) of the 7075 aluminum alloy can significantly shorten the solution time, reduce energy consumption and improve production efficiency compared with traditional heating furnace solid solution treatment (FST). CST experiments with different process parameters were carried out with a self-developed experimental device. The effects of contact body temperature and holding time on the microstructure and mechanical properties of the 7075 aluminum alloy in CST were studied by mechanical property tests and microstructure observations. The secondary phase evolution mechanism was explored, and the strengthening mechanisms were also quantitatively evaluated. The results revealed that the solubility of the secondary phase increased as the contact body temperature and holding time were increased, but after a long period at high temperature, the solid solution portion of the secondary phase (mainly Mg2Si) coarsened, resulting in a decrease of the mechanical properties. The secondary phase dissolved most when the sample was pressed at 495 °C for 30 s, and the tensile strength reached 565 MPa after aging, which was better than the T6 strength of 560 MPa. In addition, Orowan precipitation strengthening played a dominant role rather than grain boundary strengthening, and its strength increase was about 442 MPa.