Study of process/structure/property relationships in friction stir welded thin sheet Al-Cu-Li alloy

Microstructure evolution in friction stir welds produced in artificially aged Al-4Cu-1Li-0.36Mg-0.14Zr-0.28Ag alloy over a range of process parameters was studied using transmission electron microscopy. Process parameters did not have a major effect on the weld microstructure and mechanical properties. The stir zone exhibited an appreciable decrease in hardness relative to the unaffected base metal due to dissolution of T-1 and theta' precipitates. The heat affected zone exhibited almost complete dissolution of theta' precipitates and partial dissolution of T-1 precipitates. The effect of process conditions on T-1 precipitate density in the heat affected zone was studied and it was found that dissolution was experienced at lower tool rotation speed to traverse rate ratios, while welds produced at higher tool rotation speed to traverse rate ratios experienced both dissolution and growth of T-1 precipitates. The results obtained on this thin sheet aluminium alloy were compared to those of friction stir welds produced in thicker sections of the same alloy.