Microstructure evolution and stress corrosion cracking sensitivity of friction stir welded high strength AA7085 joint

Abstract

Influence of welding process parameters on stress corrosion cracking (SCC) sensitivity through thickness of 12 mm thick AA7085-T7452 joints by single-sided and double-sided friction stir welding (FSW) was investigated via the slow strain rate tensile (SSRT). The corrosion morphology of joint indicates that the coarse precipitates distributed on the grain boundary acts as corrosion cathode, causing the dissolution of the surrounding matrix which acts as anode and forming a corrosion crack initiation site under tensile stress. Different weld zones exhibit diversity in corrosion resistance and the heat affected zone (HAZ) has the largest SCC sensitivity compared with other microstructural zones. The reduction of Cu content in FSW joints increases the SCC sensitivity. The decrease spacing of grain boundary precipitates (GBPs) for the SS-60 joint and in HAZ from the top to bottom with the higher thermal cycle enhance the SCC sensitivity of FSW joints. Combined actions of the above three factors lead to the characteristic of SCC sensitivity for FSW high strength AA7085 joint.