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 indi- cate 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℃ 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 ℃/1 h.