Microstructure of as-extruded 7136 aluminum alloy and its evolution during solution treatment

With the aid of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) analysis and electron backscatter diffraction (EBSD), the microstructure of the alloy in as-extruded state and various solution-treated states was investigated. The results indicate that second phase of the as-extruded 7136 aluminum alloy mainly consists of Mg(Zn, Cu, Al)₂ and Fe-rich phases. The Mg(Zn, Cu, Al)₂ phase directly dissolves into the matrix during solution treatment with various solution temperatures. After solution treated at 475 °C for 1 h, Mg(Zn, Cu, Al)₂ phases are dissolved into the matrix, while Fe-rich phases still exist. Fe-rich phases could not dissolve into the matrix by prolonging solution time. The mechanical property test and EBSD observation show that two-stage solution treatment makes no significant improvement in mechanical properties and recrystallization of the alloy. The optimized solution treatment parameter is chosen as 475 °C/1 h.