Effect of Ti content on microstructure and properties of Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi aluminum alloy

Abstract

The effects of different Ti contents of 0, 0.34 wt% and 0.81 wt% on the microstructure and properties of hot extruded Al-9.9Zn-2.6Mg-0.91Cu-0.2Zr-xTi alloy were studied by means of metallographic analysis, XRD analysis, hardness and conductivity test, tensile property test and corrosion test. The results show that the addition of Ti in the alloy can inhibit recrystallization and grain growth, and can refine the grain obviously when the solid solution treatment is 450 °C × 2 h + 460 °C × 2 h +470 °C × 2 h and aging treatment is 120 °C × twenty four h. When the content of Ti varies in the range of 0–0.81 wt%, with the increase of Ti content, the number of undissolved phases increases and dislocation strengthening increases. However, the electrical conductivity of the alloy decreases gradually, and the hardness and room temperature tensile strength first basically remain unchanged and then decrease (the strength of the alloy decreased from 740.05 MPa to 738.5 MPa and then to 700.09 MPa). The elongation of the alloy decreases slightly after fracture, and the intergranular corrosion resistance increases first and then decreases. With the increase of Ti content, the peak stress of hot compression of the alloy increases first and then decreases at 250 °C. Therefore, considering the properties, the optimum composition of the experiment is Al-10.2Zn-2.59Mg-0.92Cu-0.184Zr-0.34Ti. Its room temperature tensile strength is 738.5 MPa, and the elongation after fracture is 7.5%, and the peak thermal compression stress at 250 °C is 357.4 MPa(Increase by 48% compared with Ti-free alloys).