Effects of quench aging treatment on microstructure and tensile properties of thixoformed ZA27 alloy

Abstract

The effects of quench aging heat treatment on microstructure and tensile properties of thixoformed ZA27 alloy were investigated. The results indicated that the microstructure of the alloy became into polygonal b phase particles after solid solution treatment at 350uC for 48 h. The b particles then decomposed into a and g phases which would coarsen during the subsequent aging at 150uC. It was observed that the Zn concentration in the b phase near the polygonal boundaries was higher than that within the b particles. As a consequence, both the decomposition speed of the former b phase and the subsequent coarsening speed were faster than those of the latter b phase. Thus, a and g phases near the boundaries were always coarser than those within the particles during aging. Owing to the coarsening, the ultimate tensile strength continuously decreased with increasing aging time. The percentage elongation increased up to 10 h, but decreased with aging time owing to bad deformation accommodation and low bonding strength between particles. Cracks initiated from some defects (e.g. inclusions and porosities) during tensile test, and the path for the cracks to propagation changed with the aging time.

Effect of aging on fracture toughness and stress corrosion cracking resistance of forged 7475 aluminum alloy

“…It is well known that the stress corrosion cracking resistance of aluminum alloy is proportional to conductivity [1] . And the magnitude of conductivity refl ects stress corrosion cracking resistance.…”

“…7475 alloy is a precipitation-hardenabale alloy with a high strength and hardness,good fracture toughness and stress corrosion cracking resistance (SCC), developed by Aloca on the foundation of 7075 alloy [1] . The heat treatments have a strong effect on the strength,SCC and fracture toughness of the alloy.The minimum variation of the microstructure will result in a significant variation of the performance.…”