Microstructure and Mechanical Properties of a Highly Alloyed Al-Zn-Mg-Cu-Zr Alloy Under T6I4 and T6R6I4 Agings

The microstructure and mechanical properties of a highly alloyed aluminum alloy Al-11.3Zn-3.1 Mg-1.6Cu-0.2Zr under four kinds of aging were investigated. The matrix precipitates were featured by eta + eta' for T6 and RRA, GP zone for T6I4, and GP zone + eta' for T6R6I4 (T6 + Retrogression + T6I4), respectively. The grain boundary precipitates were featured by continuous GBPs for T6, and discontinuous GBPs for RRA, T6I4, and T6R6I4. The precipitate-free zone width exhibited a decreasing trend from RRA to T6, to T6R6I4, and finally to T6I4. The alloys subjected to T6I4 and T6R6I4 exhibited higher tensile strength and ductility. The precipitate strengthening of the four aged alloys was quantitatively analyzed and discussed in detail. T6I4 and T6R6I4 alloys exhibited a yield strength of 787 MPa and 751 MPa, ultimate tensile strengths of 792 MPa and 778 MPa, and elongation values of 7.8% and 8.3%, respectively.