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.
Highlights
High-strength aluminum alloys are very interesting engineering materials due to their high specific strength, forming abilities, good mechanical properties at low temperature and corrosion resistance [1,2,3]
Stir-welding process macrostructure oflocalized asamples) stir zone localized inoffor the center ofa the joint, Themacrostructure joints obtained in the as‐welded statezone
Investigation on Sc-modified AA2519 friction stir-welded joint in the as-welded state and after post-weld heat treatment allowed the following conclusions to be drawn: 1
Summary
High-strength aluminum alloys are very interesting engineering materials due to their high specific strength, forming abilities, good mechanical properties at low temperature and corrosion resistance [1,2,3]. The precipitation hardening of this alloy is realized by a two-step heat treatment—the solution treatment (annealing in 530 ◦ C/2 h and cooling in cold water) and artificial aging (165 ◦ C/10 h) [6,7,8]. After this process AA2519 alloy is strengthened by θ0 precipitates, semi-coherent metastable Al2 Cu phase with body-centered tetragonal crystal structure, which increases its mechanical properties significantly [7]. Despite the advantages of AA2519 alloy, the high concentration of copper causes problems with its welding, Materials 2019, 12, 583; doi:10.3390/ma12040583 www.mdpi.com/journal/materials
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