Study Of 2519 A Aluminium Alloy Friction Stir Welding

2519aluminum alloy is a high-strength and heat-treatable aluminum alloy belonging to the Al-Cu system alloy. Because of its excellent properties of strength, temperature resistance, corrosion resistance and impact resistance property,2519aluminum alloy plays a dominant role in the defense equipment, transportation and aviation aerospace industries. Basing on that, Central South University has developed the2519A aluminum as an important material applied to national defense.7A52aluminum alloy is a super-high strength aluminum alloy and belongs to Al-Zn-Mg system. Owing to its high strength and good corrosion resistance,7A52aluminum alloy is mainly used in national defense, and transportation, which is serving as the second generation armored aluminum alloy. Many researchers have paid much attention to the studies on the welding of2519A and7A52aluminum alloy, and most of their research focuses on traditional fusion welding methods and the welding coefficient is about0.6. There are, however, few effort on the friction stir welding of the2519A aluminum alloy. And the concentration on dissimilar joints of2519A-T87Al alloy to7A52-T6Al alloy produced by friction stir welding is even fewer. Therefore, the purpose of present study is to investigate the friction stir welding of2519A-T87aluminum alloy and dissimilar aluminum alloy(2519A and7A52aluminum alloy).The welding samples in dimensions of260mm×80mm×2.75mm were longitudinally butt-welded using FSW machine designed by the authors. The effect of the welding parameters (rotation and welding speed) on surface morphology, jointed microstructure and mechanical properties were investigated. The tool of type Ⅱ was designed according to the defects produced by the tool of type basing on large amount of experiments. The shoulder of type Ⅱ tool is9mm in diameter and has two grooves, while the shoulder of type Ⅰ tool is7mm in diameter and has just one groove. Using of type Ⅱ tool can substantially reduce the flash and the influence of thermal cycle on the heat-effected-zone, and get sound defect-free joints with water cooling. The2519A aluminum alloy was welded at rotation speed3000rpm and welding speed80mm/min showed the highest tensile strength409.3MPa using the type Ⅱ tool. The 2519A-7A52dissimilar aluminum alloy was welded at rotation speed2100rpm and welding speed40mm/min showed the highest tensile strength369.3MPa using the type Ⅱ tool.The investiment indicated that the welding parameters had significant effect on the form of the joints:when the rotation speed was high or the welding speed was slow, it was easy to form flash which often lead to tunnel defects inside the joints, and to expansion of the scope of heat affected zone with its weakening level deeper. But re-precipitation occurred in the nugget zone can increase the hardness and strength of the area. In the case of slow speed or fast welding speed, the heat input was low, the surface morphology of joints would become loose, the heat affected zone narrowed down with the weakening level lightened. Besides, the over-aging phenomenon in the nugget zone occurred instead of re-precipitation. Thus the hardness and strength of this area remained unchanged. The influence of rotation speed was a more important factor comparing with the welding speed. Water cooling welding was able to significantly reduce the scope of the heat-affected zone to improve the hardness and eliminate the flash to overcome the defects. Precipitates tended to dissolve and grow up in the weld nugget zone when using water cooling. When welding dissimilar2519A and7A52aluminum alloy, the priority is to solve the welding problem of2519A aluminum alloys. The lower-strength7A52aluminum alloy should be placed in the retreating side. The dissimilar aluminum alloys were welded by atomic diffusion, and no metallurgical reaction occurred in the joints.