Improving Microstructural and Mechanical Properties of AA2024 Base Metal by Adding Reinforced Strip Width of AA7075 via Vertical Compensation Friction Stir Welding Technique

Abstract

Improving microstructural and mechanical properties of AA2024 base metal reinforced with AA7075 via vertical compensation friction stir welding (VCFSW) have become a very vital research area to reinforce the weak part of nugget zone in welded joints. So this paper presents a novel and simple method to improve microstructural and mechanical properties especially ductility and fracture locations of welded aluminum joints by VCFSW technique. Anyhow, most of the welded parts are subjected to the forming processes so improvement in the property of ductility and fracture behavior of welded joints is required. One solution to increase ductility and improve fracture behavior of welded joints 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 grain boundaries of aluminum which improved ductility and fracture behavior 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 nugget zone in joint without compensation interlayer. By contrast, 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.