Effect of Pre-Annealing Treatment on Microstructure and Stress Relaxation Stability of a Solution-Aging Treated Al-Cu-Mg-Ag Alloy

Abstract

Stress relaxation stability is a key index to evaluate the high-temperature service capacity of heat-resistance aluminum alloys. Since stress relaxation stability is highly sensitive to the characteristics of grains and precipitates of alloys, a heat treatment method involving pre-annealing and solution-aging (T6) was proposed to simultaneously regulate the microstructure and precipitates of an Al-Cu-Mg-Ag alloy in this work, so as to improve its stress relaxation stability. The effect of the pre-annealing temperature on the grain size, precipitates, stress relaxation stability, and tensile mechanical properties was systematically investigated. With increase in the pre-annealing temperature, the grain size and the number density of precipitates of the alloy exhibited an increasing tendency at first and then decreased, while the precipitate size exhibited a decreasing tendency at first and then increased. This interesting phenomenon was found to be associated with an interaction of precipitation and recrystallization, where their occurrence order changed with increasing the pre-annealing temperature. As a result, the Al-Cu-Mg-Ag alloy with 325℃ pre-annealing+T6 treatment exhibited the best stress relaxation stability, which is attributed to its large-grained microstructure as well as high-density and fine-sized Ω precipitates.

Keywords: Al-Cu-Mg-Ag alloy, Pre-annealing, microstructure, Stress relaxation stability