Microstructure and mechanical properties of 7A56 aluminum alloy after solution treatment

The effect of solution treatment on the microstructure and mechanical properties of a novel 7A56 aluminum alloy plate was investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), conductivity, hardness and tensile tests. The results indicate that the coarse second phases in the hot-rolled plate mainly consist of AlZnMgCu quaternary phase and Al₇Cu₂Fe phase, and no Al₂CuMg phase is found. The amount of the second phases gradually reduces with the increase in temperature (450–480 °C) and time (1–8 h) during the solution treatment, and the soluble particles are completely dissolved into the matrix after solution treatment at 470 °C for 4 h, while the residual phases are mainly Fe-rich phase along the grain boundaries. The recrystallization fraction of the alloy gradually increases with the degree of solution treatment deepened. When the temperature exceeds 480 °C, over-burning takes place. The mechanical properties of samples treated at 470 °C for various times were tested. After the solution treated at 470 °C for 4 h, the quenching conductivity and peak-aged hardness of the alloy are 30.8%IACS and HV 204, respectively. The ultimate tensile strength and yield strength of the samples aged at 120 °C for 24 h are 661 and 588 MPa, respectively.