SIMILAR AND DISSIMILAR FRICTION STIR WELDING OF AA7075

Friction stir welding (FSW) is a solid–state, hot–shear joining process, in which a rotating tool with a shoulder and terminating in a threaded pin, moves along the butting surfaces of two rigidly clamped plates placed on a backing plate. The shoulder makes firm contact with the top surface of the workpiece. Heat generated by friction at the shoulder and to a lesser extent at the pin surface, softens the material being welded.
 Severe plastic deformation and flow of this plasticized metal occurs as the tool is translated along the welding direction. Material is transported from the front of the tool to the trailing edge where it is forged into a joint. Different joint types can be friction stir welded such as butt, lap and fillet joints. This process (FSW) was invented by the TWI in 1991. From that time research and development in FSW and associated technologies has taken great places in many companies, research institutes and universities and international conference series dedicated to its study.
The 7xxx aluminum alloys are age hardenable, with good combination of strength, fracture toughness, and corrosion resistance in both thick and thin wrought sections. The addition of zinc with other elements, notably copper, magnesium, and chromium, produces very high strength, including the highest strength available in any wrought aluminum alloy. Aluminum alloy 7075 is a high strength 7xxx alloy. Its composition limits is: 1.20 to 2.0 Cu, 2.1 to 2.9 Mg, 0.30 Mn max, 0.40 Si max, 0.50 Fe max, 0.18 to 0.28 Cr, 5.1 to 6.1 Zn, 0.20 Ti max, 0.05 max other (each), 0.15 max others (total), bal.