Enhancing mechanical properties of 7055 Al alloy by adding 1 wt.% Mg and tailoring the precipitations

Abstract

The 7055-Mg alloy with the chemical composition 1 wt.% Mg higher than that of 7055 aluminum alloy was prepared by the powder metallurgy route. The mechanical strength of the 7055-Mg alloy was significantly improved by comparison with the 7055 alloy doping with other elements and particles. The microstructural and mechanical property evolutions of the alloy were systematically studied. The results reveal that the sample fabricated in this work has fine grains and a uniform microstructure. The addition of 1 wt.% Mg promoted the precipitation of η’ phase, which greatly shortened the PA time of 7055 alloy and improved the preparation efficiency of the alloy. The peak-aging (PA) state was obtained by ageing at 120 ℃ for only 16 h after solution treatment. It was also found that the volume fractions and sizes of η’ phases could be tailored by post heat treatment, thus optimizing the mechanical properties of samples. The 120 ℃/16 h sample has an excellent combination of the high ultimate tensile strength (UTS) of 701 MPa and good elongation of 6.7%. After 64 h aging, the alloy showed a slight tendency of over aging. However, the UTS of 120 °C/64 h sample is still up to 684 MPa, indicating that the alloy has excellent over-aging resistance. The main strengthening mode of the alloy is Orowan dislocation bypass mechanism. This study provides an effective approach for improving the mechanical properties of 7055 alloy and expects to inspire the composition design of aluminum alloy.