Experimental Investigation of Welding Defects in Butt Joining of Aluminum Alloy by Friction Stir Welding: Effects of Tool Pin Profile and Process Parameters

In this paper, the microstructural and mechanical properties as well as the defects in the joining of aluminum sheets using the friction welding method are investigated. First, the microstructural properties of the friction stir welding zone are investigated, and then the effect of process parameters on the microstructural properties is discussed. The grain size in the stir zone was greatly improved compared to the base metal, which resulted in the improvement of the mechanical properties in this zone. Then, the effect of process parameters on the grain size was investigated. Welding defects, which is one of the most important reasons for joint failure, were investigated and the effect of tool pin profile and process parameters on the formation of defects in the welding area were discussed. For instance, by using the rotational speed of 500 rpm, a defect-free joint can be produced by the threaded pin even in the traverse speed of 500 mm/min, while the amount for the square and triangular pin profiles were 400 and 315 mm/min, respectively. Finally, the hardness of the welded area was studied in different samples. The hardness of the weld metal was lower than that of the base material due to the annealing of hardness which was generated as a result of primary rolling process. The hardness decreased by increasing the ratio of rotational speed to tool traverse speed.