Investigation of Heat-Assisted Dissimilar Friction Stir Welding of AA7075-T6 Aluminum and AZ31B Magnesium Alloys

This study investigates the successful joining methods of dissimilar metals of AZ31B Mg and AA7075-T6 Al alloys. The specimens were joined by using open-flame heating system and investigated the effect of the friction stir welding (FSW) process parameters on the welding quality, transverse rupture strength (TRS), tensile strength, microhardness, and microstructure of the resulting specimens. The welding experiments were conducted based on the Taguchi mixed-orthogonal-array for tests, L-16 (4(2) x 2(2)), at a constant spindle speed of 500 rpm using a K10 grade carbide mixing tool with two different tilt angles (0 degrees and 3 degrees), and two tool tip geometries (square and triangle). The specimens were successfully welded, and the test results revealed that the welding temperatures and forces had the strongest effect on the welding quality. The achieved maximum tensile strength and TRS were approximately 122.1 MPa and 712.1 MPa, respectively, at a tool travel speed of 20 mm/min, tool offset value of 0.75 mm, tool tilt angle of 3 degrees, and using a triangle tool tip. The microstructural analysis indicated that a dynamically recrystallized and grain refinement structure formed in the welded zone depending on the temperature and on the excessive deformation. The increase in the microhardness values depends on the intermetallic compounds ratio and fine-grained structure in the welded zone.