Effects of Trace Ag and Heat Treatment on the Mechanical Properties and Corrosion Resistance of Al-Zn-Mg-Cu Alloys

The effects of trace Ag and heat treatment on the mechanical properties and corrosion resistance of Al-9.6Zn-2 Mg-1.6Cu (AA7056) alloys were investigated. The results revealed that Ag atoms could refine the size of precipitates, increase the number of precipitates, and shorten the width of the precipitate-free zone. The evolution of precipitates led to the effective improvement of strength and corrosion resistance of the Al-9.6Zn-2 Mg-1.6Cu alloy. In addition, after over-aging treatment, grain-boundary precipitates were precipitated discontinuously, which in turn retarded anodic dissolution in a corrosive environment and subsequently improved corrosion resistance. However, the strength of the alloy decreased after the over-aging treatment due to the coarsening of the precipitates in the matrix. By the application of retrogression and re-aging, the alloys still exhibited fine intragranular precipitates as well as discontinuous grain boundary precipitates. The addition of trace Ag with retrogression and re-aging treatment prevented the deterioration of the mechanical properties and improved the corrosion resistance of the Al-9.6Zn-2 Mg-1.6Cu alloy.