Soldagem por ponto por fricção das ligas de alumínio 5A06-O/2219-T87: caracterização mecânica e microestrutural

Abstract

Refill Friction Stir Spot Welding (RFSSW) is a solid-state joining technique for welding dissimilar and similar materials applied to light alloys and thermoplastics. Thus, the purpose of this work was to evaluate the feasibility of joining the aluminum alloys 5A06-O and 2219-T87 by the refill friction stir spot welding process for aerospace applications, as well as to determine an optimized process condition to maximize the shear strength of the welded joint. By applying Box-Behnken, a design of experiments model, it was possible to determine the model fit and the influence of the process parameters on shear strength, with penetration depth being the most influential parameter, with a contribution of 49.76%. Through a material flow analysis, it was possible to have an understanding of the microstructural formation during the process. The microstructure presented the heat affected zone (HAZ), thermomechanical affected zone (TMAZ) and stir zone (SZ), the latter being divided into the probe influenced zone (SZ-P) and the shoulder influenced zone (SZ-S). In addition, typical geometric features such as the hook and bonding ligament, and a transition region between the HAZ and TMAZ, called onion structure, resulting from mixing between the materials due to tool movement, were also observed. Thermal cycle was measured for the optimized condition, and the temperatures in the zones influenced by the clamping ring, shoulder and probe were 407 ºC, 488 ºC and 498 ºC, respectively. Fractographic analyses, after the shear tests, were performed for the optimized condition tested at room temperature and negative temperature (-55 ºC). For both conditions the fracture occurred by through the weld mode, where the crack initiates and propagates through the bonding ligament. From this study, it was possible to conclude that the RFSSW process presented itself as a suitable alternative for producing welds between 5A06-O/2219-T87 alloys.