INFLUENCES ON MECHANICAL PROPERTIES OF FRICTION STIR WELDED JOINTS BY Al CLAD ACCUMULATION

Abstract

Friction stir welding (FSW) is increasingly used in joining the high strength aluminum alloys. Compared to traditional fusion welding methods, one of advantages of FSW is to obtain defect– free joints more easily. Besides the forms of FSW tools and welding parameters, certain characteristics of the base material can also affect the quality of welded joints. There is usually a protective layer on aluminum alloy surface to prevent corrosion, called Al clad. Generally the mechanical properties of Al clad are significantly lower than those of the base metal. In this paper, tensile and three–point bending tests were applied to investigate the influence of accumulated Al clad on mechanical properties of joints. The mechanism of reducing the mechanical properties of joints, caused by the accumulated Al clad was analyzed by OM, SEM and EDS. The results show that the mechanical properties of the welded joints are lower than those of the joint with which the bottom Al clad on the base material is removed before or after welding. The Al clad tiled on bottom of the base material is squeezed to both sides of the onion ring in the role of the FSW tool and gathered in the bottom after welding. Due to the poorer mechanical properties of Al clad than the base metal, the Al clad aggregation positions become the weak areas in the joints, leading to the formation of the micro cracks in the joints under tensile stress where the micro cracks continue extending to generate macro cracks under the continuous * Q Ik^6~6F? 6 50875146 $xU7rP : 2010–06–10, $x+27rP : 2010–08–17 T 4 : X 0, 9, 1985 A , 5 DOI: 10.3724/SP.J.1037.2010.00276