SILVA, J. G.; http://lattes.cnpq.br/9388867963868232; SILVA, José Galdino da.
Résumé:
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.