Influência da geometria do pino da ferramenta de soldagem nas propriedades mecânicas em juntas dissimilares AA7075-T651 E AZ31B soldadas pelo processo FSW.

Abstract

The use of light alloys in the transport sector is essential to increase the efficiency and autonomy of vehicles. In this sense, alloys with good mechanical resistance and low specific weight, such as aluminum alloys AA7075 and magnesium alloys AZ31B, stand out. However, these alloys are difficult to weld using conventional welding processes, and unconventional processes such as friction stir welding (FSW) appear as a good alternative to the weldability of these alloys. The present work dealt with the evaluation of the influence of the tool pin geometry on the microstructure and mechanical properties in joints of dissimilar alloys AA7075 and AZ31B welded by the FSW process, the pin geometries studied were: smooth cylindrical, threaded cylindrical, smooth conical and hexagonal faceted. The welds were carried out using an automatic universal milling machine, with rotation of 565 RPM, advance of 75 mm/min, offset of 0.5 mm for the magnesium side, inclination angle of 3° and advance on aluminum. Tensile, root bending and microhardness tests were carried out, and microstructure analysis was also carried out. fracture surface and chemical analysis by EDS. In the tensile test, all joints failed in the elastic region, well below the yield limit of the AZ31B alloy, all joints had similar tensile strength limits. In the bending test, the highest load supported (717 N) was on the joint welded with the smooth cylindrical tool. In the microhardness test, in the mixing zone, the welded joints had an intermediate result between the two base metals. In the microstructure analysis, the joint that showed the most defects was the one welded with the smooth conical geometry pin and the one that showed the least was the joint welded with the threaded cylindrical geometry pin. In the analysis of the fracture surface, it was found that it was a brittle fracture, followed by catastrophic failure for all joints. In the chemical analysis, the presence of intermetallic compounds was found in the joint welded with the smooth cylindrical tool. It was evident that among the tool pins used, the threaded cylindrical and smooth cylindrical pins were those that provided the best results, in terms of the macro and microstructure and the mechanical properties of the AA7075 and AZ31B alloy joints welded by the FSW process.