Friction Stir Lap Welding of Mg/Ti Dissimilar Alloys Using a Slight Penetration Depth

Friction stir lap welding was applied to join AZ31B Mg alloy and Ti-6Al-4V alloy using a slight penetration depth. The microstructure and tensile properties of the joints formed using different rotating speeds were investigated. The results showed that a dispersion layer comprising Ti fragments with size of less than 15 μm formed in the stir zone near the lap interface. A wave-like pattern formed on the surface of the bottom Ti alloy, leading to micromechanical interlocking. A 2.1-μm-thick Al enrichment layer formed at the lap interface when using the rotating speed of 1400 rpm, resulting in metallurgical bonding. The joints fractured at the lap interface, and the local region of the fracture surface on the Ti alloy side was covered with Mg alloy. The tensile shear strength of the joints increased with increase of the rotating speed, and the maximum tensile shear load reached 9765 N for the joint prepared at 1400 rpm.