Influence Of Tool Profile On The Weld Formation In Bobbin Friction Stir Welding Aluminum Alloy

As a new type of friction stir welding technology, bobbin friction stir welding was undertaken in order to solve successfully some problems, such as self-supporting and incomplete penetration. In this paper,5A06 aluminum alloy plates were fabricated by bobbin friction stir welding, and the design of the bobbin friction stir welding tools was optimized. The effect of tool profile on the weld formation and plastic flow of the weld was analyzed, and the rule of metal flow was summarized.When a split type tool is used to bobbin friction stir welding 5A06 aluminum alloy plates of 10mm thickness, there are some problems about bobbin friction stir welding tools used in the preliminary experiment, especially pin and positioning pin are usually broken during the welding. To solve the problems, the tool structure is designed effectively.The tool pin and shoulder shapes have an important influence on the weld formation. Compared with the convex shoulder, the weld formation is very poor for concave shoulder due to smaller contact area between the shoulder and plastic material resulting in less frictional heat. With increasing groove number in the shoulder, the plastic material is converged easily, and the weld formation is better. For welding 5A06 aluminum alloy plates of 6mm thickness, the convex angle of 1°n the shoulder is best. When a pin with left thread is used, plastic metal flows along the thickness direction, and material overflows along the edge of the shoulder. The weld formation is the best when a pin with three grooves is used. Due to bad plastic flow, the weld produced by a left thread pin with three grooves is the worst, and the welding cracks appear in the weld.Compared with conventional friction stir welding, the flow rule in the weld for bobbin friction stir welding 5A06 aluminum alloy plates of 6mm and 10mm thickness is similar. Because of lower shoulder, the thermal models for bobbin-tool friction stir welding change. The soft constraint of cold metal around the pin is not enough, and which leads to worse plastic flow. Compared to the weld of 10mm thickness, the temperature gradient in 6mm weld is smaller, and which is not easy to appear the defects such as holes. The microhardness distribution of the joints for bobbin-tool friction stir welding is W shape. The hardness in 6mm and 10mm weld is about 104.1HV and 101.4HV, respectively, and which is not different obviously.