Enhancement ductility of friction stir welded aluminum blanks AA2024 via adding interlayer strip width of AA7075

Abstract

This paper presents a novel and simple method to improve and enhance the ductility of welded aluminum blanks by friction stir welding technique. Anyhow; most of welded parts are subjected to the forming processes; so the ductility of friction stir tailor-welded aluminum blanks is an important key property. One solution to increase ductility is the use of interlayer compensation strip width as a reinforcement which has superior mechanical properties between two blanks of base metal during friction stir welding process. The effect of changing interlayer compensation width was investigated on the microstructural characterization (by an optical microscope, scanning electron microscope and transmission electron microscope) and mechanical properties (using microhardness, tensile and bending tests). Microstructure observations revealed that the tailor-welded joint without compensation interlayer contains micro-voids in the stir zone; while in tailor-welded joints with compensation interlayer the voids completely disappear on the microscale. x-ray diffraction detected that the use of compensation interlayer of AA7075 between two AA2024 blanks led to the appearance of two precipitates of intermetallic phases, Al2Cu and Mg2Zn, on the grain boundaries of aluminum which improved ductility of welded joints. Ductility enhanced till 54.4 % at compensation interlayer width 2 mm when compared to the joint without compensation interlayer. Lower hardness values were detected at the nugget zone in joint without compensation interlayer. On the other side; highest hardness values in the softened regions were obtained in compensation interlayer joints. Finally; the highest bending angle occurred without any cracks in case of compensation interlayer of 2 mm at ultimate bending load.