Effect of Ag content and heat treatment on the stress corrosion cracking of Al-4.6Cu-0.3Mg alloy

A201 aluminum alloy, Al-4.6Cu-0.3Mg-0.6Ag, is a high-strength as-cast alloy which is strengthened by Omega-phase and theta-phase. The Omega-phase is a thermal stable strengthening phase, and the theta'-phase is known as the strengthening phase of the binary Al-Cu alloy. The amount of Ag in the alloy and the heat treatment affect the precipitation of the Omega- and theta'-phases as well as the morphology of the phases that precipitate at the grain boundary, affecting the susceptibility of the alloy to stress corrosion cracking. In this study, the susceptibility of various Ag-containing Al-4.6Cu-0.3Mg alloys stress corrosion cracking in a 3.5% NaCl solution was investigated for alloys tempered to T6 and T7 conditions, the retrogression and re-aging heat treatment also applied. The microstructure of the alloys was elucidated by optical microscopy and transmission electron microscopy, and susceptibility to stress corrosion cracking was assessed by performing the slow strain rate test in air and salt solution. The findings indicated that the continuous grain boundary precipitations and the high Ag concentration alloy that exist high density of the Omega- and theta'-phases caused susceptibility to high stress corrosion cracking. The presence of a wide precipitation-free zone and discontinuous large particles in the grain boundary precipitates caused the T7 alloy to have a low susceptibility to stress corrosion cracking. The alloys tempered to the RRA condition cannot reduce susceptibility of the Al-Cu-Mg-Ag alloy to stress corrosion cracking. (c) 2004 Elsevier B.V. All rights reserved.