Effect of repetitious retrogression and re-aging treatment on the microstructure, strength and corrosion behavior of powder hot-extruded 7055 Al alloy

The precipitation evolution, mechanical properties and corrosion behavior of powder hot-extruded 7055 Al alloy treated by repetitious retrogression and re-aging (RRA) were investigated. The results suggest that the dominant intragranular precipitates after different numbers of RRA treatment change from GP zones +η' phase (RRA1) to η' phase (RRA2, RRA3) and then to η' phase + η phase (RRA4), and both strength and corrosion resistance deteriorate with the increase of RRA repetition times. Transmission electron microscope (TEM) observation indicates that the coarsening and transformation of intragranular precipitates during repetitious RRA treatment induce the decrease of strength, while the increases in the area fraction of grain boundary precipitates (GBPs) and the width of precipitate free zones (PFZs) are detrimental for the corrosion resistance of the alloy. Therefore, the RRA1 treatment can achieve the best comprehensive performance of the powder hot-extruded 7055 Al alloy with excellent strength and good corrosion resistance.