Numerical Simulation of the Thermo-Mechanical Behavior of 6061 Aluminum Alloy during Friction-Stir Welding

Abstract

In this work, a finite-element model was elaborated to simulate the thermomechanical behavior of 6061 aluminum alloy during friction-stir welding (FSW). It was shown that FSW-induced deformation is a two-stage process. In addition to the stirring action exerted by the rotating tool probe, the material in the near-surface area of the stir zone also experienced a secondary deformation by the shoulder edge after passage of the welding tool. Both deformation steps were found to be comparable in terms of temperature and strain, but the secondary deformation was primarily concentrated in the near-surface layer. The effects of tool rotation and translation rates on FSW temperature and strain were also systematically examined. Depending on particular welding conditions, the peak welding temperature was predicted to vary from 360 to 500 °C, while the cumulative effective strain was from 12 to 45.

Grain Structure Evolution in 6013 Aluminum Alloy during High Heat-Input Friction-Stir Welding

“…Remarkably, the material in the upper section of the stir zone typically exhibited a stronger but more complex textural pattern than that in the weld nugget (Figure 10). This observation was consistent with the formation of the fine-grained layer (Figure 5), thus reflecting the complex character of material flow in this area [16].…”

“…The development of the pronounced fine-grained layer at the upper surface of the stir zone was obviously attributable to the stirring action of the tool shoulder. As shown in some experimental works [17] and numerical simulations [16], the stir zone material should experience a secondary strain induced by the tool shoulder; this effect was due to the backward tilting of the FSW tool. This event is characterized by an extreme combination of large plastic strain, the highest temperature, and (presumably) the highest strain rate, and thus should lead to a drastic microstructural modification at the upper weld surface.…”

“…Those include the geometric effect of strain [3][4][5], continuous recrystallization [6][7][8][9][10][11], or geometric recrystallization [3,[12][13][14][15]. Remarkably, the stir zone material may experience secondary deformation associated with the tool shoulder [16]. This effect is most pronounced at the upper weld surface and may produce a fine-grained microstructural layer in this area [17].…”

“…In this context, of particular interest is an examination of FSW under high heat input conditions. Such FSW is usually realized using a combination of a high spindle rate and a low feed rate, thus being characterized by the highest welding temperature, the largest plastic strain [16], and, perhaps, the highest strain rate. In other words, the high-heat-input FSW comprises the most extreme combination of deformation conditions.…”

Microstructural Evolution and Material Flow during Friction Stir Welding of 6013 Aluminum Alloy Studied by the Stop-Action Technique

“…Another notable issue was also a distinctly different grain-refinement effect near the tool shoulder and the tool probe (locations "c" and "d" in Figure 3), as compared in Figure 4c and d. This result agreed with some numerical simulation works in FSW (e.g., [61]), which predicted a significant difference in thermal and deformation conditions in these areas. The distinct difference in microstructure between the upper weld surface and the nugget zone has also been reported in a number of experimental works [33,34,37,43,[48][49][50][51].…”