Inspection of Friction Stir Weld Joint on Metal Matrix Composite

Abstract

The study examines the quality of friction stir welded joints made with butt joints on a metal matrix composite. In the composite, AA6061 is the matrix and silicon carbide is the reinforcement. Joints were made with three different pin profiles: circular, triangular and square. Macroscopic and microscopic images were used to qualitatively assess the joints. With the circular pin-profiled tool, the joints had distinctive onion ring patterns on their surface. Plasticized metal flows uniformly from the advancing side to the retreating side. While using triangular and square pin tools, weld spatters were formed along the retreating side of the joint. During the joining process, the plasticized material intermittently flowed. Inspection of the weld cross-section showed a major tunnel defect. The circular pin could not transfer materials that were not sufficiently plasticized. Plasticized material below the triangular pin tool was splashed by the tool pin edges. The bottom of the joint got enough weldment due to this. As a result, there were bind defects along the advancing and retreating sides of the joint. A square pin tool did not cause any defects in the weld joint. Because the tool pin had more edges, the weldment was deposited uniformly throughout the joint. Various zones of the joint showed grain restructuring. Using the circular pin profile tool, a noticeable plane separated thermo-mechanically and heat-affected zones. When using triangular and square pin tools, the three zones transitioned gradually. When using the square pin tool, the grain size was smaller along the stir zone and the thermo-mechanically affected zone. A square pin profile permitted greater frictional heat, which led to plasticization of the weldment and the pin. Based on comparisons with the other two counterparts, the friction stir welded joint made using the square pin tool had superior quality.