Microstructure and Low Cycle Fatigue Properties of AA5083 H111 Friction Stir Welded Joint

Abstract

The present paper aims to analyze the microstructure, microhardness, tensile properties, and low cycle fatigue (LCF) behavior of friction stir welded (FSW) butt joints. The material used in this study was the 5 mm thick 5083 H111 aluminum alloy sheet. Butt joints of AA 5083 H111 were manufactured at different operating parameters of the FSW process. The effect of the welding parameters on microstructure, microhardness, and tensile properties was investigated. Based on microstructure analysis and strength tests, the most favorable parameters of the FSW process were settled on the point of view of weld quality. Then, LCF tests of base material and friction stir welded specimens made of 5083 H111 were carried out for the examined welded samples under selected friction stir welding parameters. The process of low-cycle fatigue of 5083 H111 aluminum alloy was characterized by cyclic hardening for both: base material and FSW joint. It was revealed by a decrease in the width of the hysteresis loop with the simultaneous significant increase in the values of the range of stress. It was determined that fatigue cracks are initiated by cyclic slip deformation due to local stress concentration from the surface in the corner of the samples for the base material and the heat-affected zone for FSW joints. For all tested strain amplitudes, the fatigue crack propagation region is characterized by the presence of fatigue striation with secondary cracks.

Research on the Properties and Low Cycle Fatigue of Sc-Modified AA2519-T62 FSW Joint

“…The obtained value of the cyclic strength coefficient (504.37 MPa) is almost three times lower than for the base material (1518.1 MPa) [ 52 ]. Although, the decrease of cyclic strength coefficient is expected for welded joints, in this case, the reported drop is significant and the obtained value is similar to the values reported by research [ 31 , 36 , 55 , 56 , 57 ]. In the next step, the parameters of the stabilized loops were used for establishing the plots of elastic and plastic strain amplitudes vs. number of reversals, presented in Figure 15 .…”

“…Based on our own research, we can state that post-weld heat treatment decreases the fatigue strength of AA2519 FSW joints significantly [ 33 ] and the optimal welding parameters for welding of AA2519-T62 lie within the range of 600–800 rpm tool rotation speed and 100 mm/min welding velocity, giving relatively high joint efficiency (around 80%) and good fatigue properties [ 34 ]. Considering the issue of high complexity, which is evident in the behavior of FSW joints during cyclic loading in the low cycle fatigue regime, a number of factors have to be taken under examination, susceptible to the high plastic strain amplitude (e.g., heat-affected zone, low-hardness zone, stir zone/thermo-mechanically affected zone interface) [ 34 , 35 , 36 , 37 ]. LCF is important from the point of view of estimating the durability of structural elements at the design stage of the structure, during its operation, as well as in the analysis of the assessment of the structure life (and the possibility of its extension).…”

The influence of welding parameters on macrostructure and mechanical properties of Sc-modified AA2519-T62 FSW joints

“…Comparing to the advancing side, the retreating side is characterized by the highest heat input, what significantly reduces the strength of this area (especially in precipitate-hardened aluminum alloys) [26]. The heat causes a series of microstructural changes in HAZ including a coarsening of the strengthening phase and grain growth, which decrease the fatigue resistance and make crack propagation easier [27][28][29]. Especially the lowest hardness zone (LHZ), often became the failure location due to its both low hardness and high value of hardness gradient [12,27].…”

Effect of Cavitation Peening on Fatigue Properties in Friction Stir Welded Aluminum Alloy AA5754

“…FSW is an ecological and green technology, as it can reduce material waste and avoid harmful gas emissions due to conventional welding [11,12]. However, the fatigue life and strength of conventional FSWed metal is considerably lower than those of base metal [13][14][15][16][17][18][19]. Thus, it is worthwhile to develop a method to improve fatigue properties of FSWed metals.…”