Fracture toughness of base and weld metal of aluminum alloy EN AW 7049A T652 FSW joint

Abstract

The paper analyzes the impact of the tool geometry on the friction stir welding (FSW) method on fracture toughness values of the base metal (BM) and weld metal (WM) of butt-welded joints of a high-strength aluminum alloy. Values of fracture toughness KJIc were obtained using single-edge notched bend (SENB) specimens with fatigue pre-cracks sampled from the BM and TMAZ (thermo-mechanically affected zone). The single specimen method was used according to ASTM E 1820, and parameters of elastic-plastic fracture mechanics were determined (CTOD crack tip opening displacement and the J integral). Although the welding tools had different values of cone angle (α = 2.5–10°) and the variable length of the pin (h = 5.1–5.4 mm) at a constant ratio of the number of tool revolutions and the speed of welding, the largest value of fracture toughness has the retreating side of the weld, then the advancing side of the WM, while the BM has the lowest value. This is the effect of the recrystallization process in the retreating side of the WM due to the combined rotating and straightforward motion of the tool, during which the softened material is repeatedly transformed from one side to the other side around the center of the tool.