Development of design curves for tensile strength and fatigue characteristics of 7075 T73 aluminum FSW butt joints

Aluminum 7075-T73 plates of different thicknesses were welded with varying pseudo heat index (PHI). All welds were made under position control. Earlier studies indicate that there is a relationship between the heat input into the weld process and the weld quality for friction stir welded joints. PHI is a measure of heat input into the weld process and is dependant on processing parameters like rotation speed, travel speed and forge force (or heel plunge). The joints were evaluated for their strength and for fatigue life to investigate the response of weld quality in relation to PHI. Ultimate tensile strengths were plotted against PHI with statistically based lower tolerance bounds (T90 and T99) with 95% confidence intervals using the methods mentioned in Military Handbook (MIL-HDBK-5). The study revealed that the ultimate tensile strengths of butt joints, and the corresponding fatigue life decreased with the increase of PHI.