Effect of Mn element on microstructure and properties of 7000 series ultra high strength rolled aluminum alloy

The effects of Mn on the microstructure and properties of 7000 series rolled aluminum alloy Al-9.94Zn-2.35Mg-2.53Cu-xMn-0.25Zr were studied by means of metallographic analysis, hardness and conductivity test, tensile test and corrosion test. The results show: when Zr content is 0.25%, the addition of 0.41% Mn can significantly inhibit recrystallization and grain growth, and it can also retain dislocations and small-angle grain boundaries better in the subsequent solution aging process. Adding Mn element has a certain extent strengthening effect on the alloy. It can improve the intergranular corrosion resistance of the rolled aluminum alloy, but it slightly reduces the anti-exfoliation corrosion resistance of the rolled aluminum alloy. In addition, the alloy with 0.41% Mn element has higher strength under T6 aging than alloy without Mn element. The tensile strength was increased from 589.5 MPa to 617.6 MPa, and the yield strength was increased from 551.61 MPa to 589.9 MPa, indicating that Mn element can significantly improve the tensile strength and yield strength of 7000 series aluminum alloy. However, the strength of alloys containing Mn elements decreased significantly after the T76 aging. The tensile strength decreased from 617.6 MPa to 566.4 MPa, and the yield strength decreased from 589.9 MPa to 534.2 MPa. It was found that Mn can reduce the time of alloy over-aging, which is not conducive to the strength of the alloy under T76 over-aging.