Low-cycle fatigue of friction stir welded Al–Mg alloys

Abstract

The following alloys EN-AW 5058 H321 and EN-AW 5059 H321 (Alustar) were welded by FSW (friction stir welding) method. The FSW welds showed better properties in comparison to the joints welded by the MIG method. The test of microstructure proved the proper structure of the weld which consisted of following: welded nugget, thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and unaffected material. The surface microanalysis (EDS) showed particles containing Fe and Mn and particles containing Si and Mg in the weld nugget of 5083 alloy. These are likely to be the phases: (Mn,Fe)Al 7 and Mg 2Si. Particles containing Fe and Mn were visible in the weld nugget of the Alustar alloy. The low-cycle fatigue life test was carried out in the symmetric cycle: in air and in 3.5% NaCl. Fatigue life of 5083 alloy welded by FSW method, exposed in 3.5% NaCl solution was lower than that of the specimens tested in air. The Alustar alloy welded by the new FSW method demonstrated higher fatigue life in comparison to the same alloy welded by the traditional MIG method. The fatigue zone showed cleavage fracture, changing into a ductile cracking on the fracture faces of the tested specimens. The fatigue cracks crossed the weld nugget.