The Influence of Post-Weld Heat Treatment on the Microstructure and Fatigue Properties of Sc-Modified AA2519 Friction Stir-Welded Joint

Abstract

The aim of this research was to investigate the influence of post-weld heat treatment (PWHT, precipitation hardening) on the microstructure and fatigue properties of an AA2519 joint obtained in a friction stir-welding process. The welding process was performed with three sets of parameters. One part of the obtained joints was investigated in the as-welded state and the second part of joints was subjected to the post-weld heat treatment (precipitation hardening) and then investigated. In order to establish the influence of the heat treatment on the microstructure of obtained joints both light and scanning electron microscopy observations were performed. Additionally, microhardness analysis for each sample was carried out. Fatigue properties of the samples in the as-welded state and the samples after post-weld heat treatment were established in a low-cycle fatigue test with constant true strain amplitude equal to ε = 0.25% and cycle asymmetry coefficient R = 0.1. Hysteresis loops together with changes of stress and plastic strain versus number of cycles are presented in this paper. The fatigue fracture in tested samples was analyzed with the use of scanning electron microscope. Our results show that post-weld heat treatment of AA2519 friction stir-welded joints significantly decreases their fatigue life.

Research on the Friction Stir Welding of Sc-Modified AA2519 Extrusion

“…Al 3 Sc precipitates improve properties of aluminum alloy in many ways including an increase of mechanical properties and recrystallization temperature as well as grain refinement [27][28][29][30]. Previous research performed by authors of this paper reveals that Al 3 (Sc,Zr) precipitates do not dissolve due to the FSW process and form dispersion of fine precipitate in the stir zone [10]. Additionally, the increase of recrystallization temperature allows to limit the grain growth in the heat-affected zone during welding process.…”

“…Using FSW it is possible to obtain high-quality joints of aluminum alloys, what makes this technology very attractive for the automotive, aerospace, and shipbuilding industry [2,4,5]. Recent research indicates that this technology also provides wide possibilities in the manufacturing of light-alloy based metal-ceramic composites, welding of dissimilar alloys, and modification of surface [6][7][8][9][10]. The main idea of the FSW process is affecting a workpiece with a rotating tool consisting of pin and shoulder [1][2][3]11].…”

“…In the case of friction stir welding, this problem does not occur because the temperature of the process is lower than Al/Al 2 Cu eutectic temperature [2,[17][18][19]. For this reason, FSW has a great potential in terms of joining high-strength aluminum alloys having high copper concentration, such as AA2219 and AA2519 [10,18,[20][21][22]. AA2519 is an alloy with great interests, particularly in military applications due to its high specific strength and good ballistic performance [10,23,24].…”

“…For this reason, FSW has a great potential in terms of joining high-strength aluminum alloys having high copper concentration, such as AA2219 and AA2519 [10,18,[20][21][22]. AA2519 is an alloy with great interests, particularly in military applications due to its high specific strength and good ballistic performance [10,23,24]. This alloy also is a component of some of light-alloy laminated composite plates with excellent ballistic resistance [25,26].…”

“…AA2519 used in this investigation is non-heat-treated condition, so it consists of soft aluminum matrix and hard Al 2 Cu precipitates. Such system subjected to the friction stir welding results in the dissolution of Al 2 Cu precipitates in the stir zone forming the supersaturated solution [10]. In contrast to an alloy subjected to the precipitation hardening process, the microhardness of non-heat-treated alloy increases in the stir zone due to grain refinement and in the microstructure, there is no strengthening phase (e.g., θ') to dissolve, coarse or overage [31][32][33].…”