Microstructure, mechanical and corrosion behaviour of friction stir welding of AA6061 Al alloy and AZ31B Mg alloy

Abstract

The present investigation emphasizes studying the impact of the rotational tool speed and traverse speed on microstructure, mechanical properties, and corrosion behaviour of Al alloy AA6061 to Mg alloy AZ31B friction-stir welds. Results indicated that the use of the 1000 rpm rotation speed of the tool and 40 mm/min traverse speed led to increased weld strength and corrosion resistance. Owing to more heat generation, the surface of every friction stirs welded joint became rougher, and a keyhole can be observed. A maximum temperature of 311°C was observed for 1000 rpm of rotation speed and 40 mm/min of traverse speed, and a minimum temperature of 191°C was observed for 600 rpm of rotation speed and 80 mm/min of traverse speed. A minor tunnel defect can be partially observed at traverse speeds of 60 mm/min; the size of the tunnel defect becomes more prominent as the traverse speed rises to 80 mm/min. The joint with little or no defects was extracted at any rotational tool speed and a low traverse speed of 40 mm/min. The maximum value of UTS of 121 MPa was observed due to the better mechanical interlocking phenomena. It is approximately 41% of UTS of Al alloy AA6061 and 50% of UTS of Mg alloy AZ31B. Frictional heat, heavy plastic distortion, and grain refinement in the nugget zone are the reasons for the higher hardness value found mostly in weld nuggets. The FSW specimens indicate a primarily brittle type of failure, and a fracture of the cleavage type was seen with an excessive volume of intermetallic layer. Compared to both alloy side weld regions, the Mg alloy area weld zone was more corroded and had more cracks and gaps than the Al alloy side.