Dissimilar Friction Stir Welding of Immiscible Titanium and Magnesium

Abstract

The dissimilar friction stir welding of the immiscible combination (i. e., titanium and magnesium) was performed. The thin foil aluminum was inserted between pure titanium and pure magnesium in order to react the two immiscible materials. The welding parameters (i.e., aluminum foil thickness, probe offset and welding speed) were optimized to acquire a sound joint. Also, the influence of the welding conditions on the formation of reaction layer at the interface, aluminum distributions in the magnesium matrix and tensile strength of the joints was systematically examined. With the increasing thickness of the aluminum filler material, the size and amount of the welding defects generated inside the magnesium stir zone (SZ) increased due to the poor material flow. The dissimilar joint between titanium and magnesium fabricated with a thin aluminum filler material and with the optimized probe offset and welding speed shows a high tensile strength because of the properly thin intermetallic compound layer formed at the weld interface and inhibition of the brittle intermetallic compounds formation inside the SZ on the magnesium side during the FSW. The tensile property results indicated that the highest tensile strength of approximately 150 MPa, which is ~88% of the joint strength of pure magnesium can be obtained in the optimized dissimilar titanium and magnesium joint, and it fractured at the heat affected zone (HAZ) in the magnesium.