Research On Friction Stir Welding Of 2A70 Al Alloy Thick Plate

As the development of the large range, high Mach number, high mobility, large-scale, light and fast in weapon systems, the new materials and advanced manufacturing technology are required continuously to meet the growing market demand. Friction Stir Welding (FSW) is a new solid-phase welding technology with the advantages of small welding distortion, solid welding, energy saving, no defects (cracks or porosities), which been widely used in aerospace, shipbuilding, transportation, etc. In this paper, for 2A70 aluminum alloy plate in 20mm thickness, FSW welding process and defect analysis have been researched in the mixing head design, welding parameters optimization, etc.Three kinds of friction stir tools with thread, three thread chute and three-pyramid thread were designed and the surface appearance of FSW welded seam and the mechanical properties of the joint and other related experiments were carried out. The results show that the friction stir tool with three-thread chute is the best choice with the good welded seam surface and the high joint mechanical properties.The result of taguchi experiments show that welding speed, stir tool rotation speed and tool tile angle have significant effects on FSW weld mechanical properties. Among them, the welding speed is the most significant parameter. The surface appearance, the joint internal quality and the mechanical properties in different welding parameters were studied. In the rotation speed 300rpm, welding speed 110mm/min, the inclination of the tool 3°and the indentation depth 0.5mm, the joint has the best mechanical properties. The tensile strength of the joint can reach more than 80% value of the base material.Combination of friction stir welding characteristics, the formation mechanism of the defects, such as the surface divided layer of the welded seam, surface grooves, incomplete penetration, cracks, holes tunnel, miscellaneous folder, clad layer and weak integration was analyzed and the measurements were proposed to reduce the welding defects and improve the joint qualities.