Influence of laser pre-precipitation on the corrosion resistance of Al-Zn-Mg-Cu alloy with deep cryogenic treatment

Abstract

A recently developed AA7075 was subjected to solid solution, high temperature laser surface treatment, deep cryogenic treatment, and artificial aging. The microstructure evolution and precipitation behavior were examined, and their effects on corrosion behaviour were analyzed. The results showed that coarse η phases disappeared and a large number of smaller η phases were formed after high temperature laser surface treatment. Most of the phases dissolved into Al matrix during solution and fine η phases precipitated in laser treatment. η′ phases appeared in the high temperature laser surface treatment samples. Mg element precipitated in deep cryogenic treatment. It was concluded that the precipitation of AA7075 during heat treatment followed the sequence of solid solution → GPI (Guinier Preston) zones → metastable η′ → stable η. Reasonable laser scanning power owned the best corrosion resistance. The reasonable sample which the laser power was 1000 W showed much better corrosion resistance due to the coarsening and separation of grain boundary precipitations.