Influence of Cu/Li Ratio on the Welding Forces and Mechanical Properties of Two Bobbin Tool Friction Stir Welded Al-Cu-Li Alloys

Abstract

Increasing space activities produce a high number of space objects and lead to increasing collision risks which urges leading industries to look for future removal strategies. Material substitution in order to raise demisability during atmospheric reentry is a possible solution. Modern aluminum lithium alloys are under consideration to replace high-temperature melting materials like titanium. Further, friction stir welding was proposed as suitable joining technology in order to avoid high heat inputs during manufacturing. In this work, two modern Al-Li-Cu alloys, AA 2060 and AA 2196, in peak-aged temper were welded using the stationary shoulder variant of bobbin tool friction stir welding. Identical process parameters led to defect-free welds in both alloys. The macrostructural and microstructural features are shown and analyzed. The welds were mechanically tested to an efficiency of 78 and 70% of the base metal ultimate tensile strength for AA 2060 T8 and AA 2196 T8, respectively. The process forces as well as the thermal cycle experienced by the workpiece material were used to explain the mechanical performance. The difference in composition regarding the Cu/Li ratio of the alloys was taken into account when the mechanical properties were correlated with the thermally affected microstructure of the weldments.