Influence of the Pin Shape on the Flow Characteristics of the Plasticity Metal in the Friction Stir Welded Al-alloy

Friction stir butt joints of 2024 aluminum alloy plates with a thickness of 20mm and 10mm were welded by several types of pin profiles, that is, different conicity of the pin, different screw number on the pin surface, different tip shape of the pin and different clearance between the tip of the pin and the back plate. The morphology feature of the weld macrostructure was analyzed to deduce the material flow behavior in the friction stir weld. Some results were obtained as follow, the size of the weld nugget is increased with the decrease of the pin’s conicity. That is, the smaller conicity of the pin promote the weld materials flow along the pin, the flow amount of weld plastic materials along the pin’s surface can be promoted adequately if reducing the pin conicity from 25°to 15°. The nugget area enhances significantly when the screw number on the pin’s surface increases. By using pin with multiple screws on its surface, the channel for plastic metal flow along the pin’s surface increases, the flow of the weld plastic materials is enhanced significantly. If the tip of the pin is plane and the distance from the pin tip to the bottom of weld is small, it is easily to form an alclad penetration defect at the weld bottom. Reducing the length of the pin or changing the shape to spherical tip, the aluminum clad on the bottom surface of the plate maybe remain at the surface, no alclad penetration defect forms. But if the length of the pin is too short, another type of defect, lack of penetration, will form at the bottom of the weld.