Caracterização, avaliação e otimização das propriedades mecânicas de juntas de liga de magnésio AZ31 soldadas pelo processo FSW

Abstract

In the midst of the modern world in which we currently live, the search for materials that combine a satisfactory resistance/weight ratio has been a stage of worldwide interest in the industrial sector, especially the transport sector. In this context, magnesium alloys gain prominence when used in automobile components to improve their efficiency. However, one of the challenges in applying these materials is obtaining welded joints, as this type of material has presented limitations when subjected to conventional processes by electric arc fusion. In this sense, the solid-state friction stir welding process appears as a good alternative for joining these alloys. Therefore, this work aims to evaluate the influence that welding parameters have on the microstructure and mechanical properties of welded joints made of AZ31 magnesium alloy. The joints were produced based on different conditions defined through experimental planning using a three-axis universal milling machine. Microstructural and mechanical characterization of the welded joints were carried out, according to optical microscopy and uniaxial tensile and Vickers microhardness tests, respectively, as well as fractographic analysis of the fracture surfaces via scanning electron microscope. The results demonstrated a good visual appearance of the joints, showing the absence of cracks and lack of filling. Different levels of mechanical resistance were obtained, reaching 197 MPa. The average grain sizes of the mixing zone were smaller than those of the base material, showing reductions of up to 74%. Resulting in obtaining higher levels of microhardness in cases of smaller grain size. The fractographic images showed a considerable presence of dimples, characterizing ductile fracture of the welded joints. Therefore, the varied temperature levels resulting from the different welding parameter conditions imposed were decisive for the microstructural behavior, which consequently influenced the mechanical behavior.