Effect of solid solution treatment on microstructure and properties of extruded 7055 aluminum alloy

Abstract

The effect of solid solution parameter and quenching cooling rate on the microstructure and properties of the 7055 aluminum alloy was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and hardness, electrical conductivity, immersion corrosion test methods. The results show that there is obvious coarse phase aggregation in the as-extruded alloy, with an area fraction of 23.8%; after single-stage solid solution at 450 °C/1 h, the coarse phase redissolves obviously, with an area fraction of 7.6%; the coarse phase is further reduced after the double-stage solution at 450 °C/1 h+475 °C/1 h, and the area fraction is reduced to 4.3%. When the second stage solution temperature is increased to 490 °C, the alloy is overburnt. The hardness and electrical conductivity of the alloy decrease after different solid solution treatments, and then increase significantly after aging treatment at 160 °/6 h. The quenching cooling rate has a significant effect on exsolution and corrosion resistance. The alloys with cooling rates of less than 30 °C/min have obvious exsolution of η phase and S phase, which reduce the driving force of subsequent aging precipitation. The quenching sensitive temperature range of the alloy is around 375–200 °C, and the exsolution during cooling can be significantly suppressed by passing through the quenching sensitive temperature range with cooling rates of not less than 60 °/min.

Keywords

7055 alloy / solid solution / exsolution / microstructure / corrosion resistance / cooling rate

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