An Experimental Insight on the Selection of the Tool Tilt Angle for Friction Stir Welding of 7075 T651 Aluminum Alloys

Abstract

Objectives: To determine the optimum tool tilt angle for friction stir welding (FSW) Al 7075-T651 alloy plates by investigating the mechanical and metallurgical properties of the joints. Methods/Statistical Analysis: Al 7075-T651 plates of 6.5mm thickness are welded varying the tool tilt angle from 0 to 6 degrees. The mechanical properties like tensile strength and microhardness are evaluated. The testing of tensile specimens is done as per ASTM E8 M-04 standards. The Vickers hardness has been investigated at the weld center in the transverse direction. The microstructural changes occurring are studied with the help of metallographic inspection. Scanning electron microscopy (SEM) has been adopted to evaluate the fracture mode of the tensile specimens. Findings: An important welding parameter in FSW that influences the welding quality is the tool tilt angle. In this paper the results of Al 7075-T651 joints welded by FSW with varying tilt angle are investigated for their mechanical strength and metallurgical properties. Evaluation of the tensile strength is carried out and put in relation with the microstructure investigations. From the experimental analysis it is observed that the weld joints made with two degree tool tilt angle are defects free resulting into the best mechanical and metallurgical properties compared to other joints. The fracture surface examination with the scanning electron microscope shows that the fracture surface of the joints are largely governed by the change in the tilt angles. The observations of fracture surface under SEM shows that the joint made with two degree tilt angle failed in a ductile mode whereas all the other joints failed in brittle mode. Application/Improvements: 7000 series aluminum alloys are a family of alloys that are practically unweldable by fusion welding processes. FSW procedure can be economically utilized to weld such alloys. This study will benefit to direct the selection of tool tilt angle during FSW of Al 7075 T651 plates.