Influence of process parameters on microstructural evolution and mechanical properties in friction stirred Al-2024 (T3) alloy

Commercial Al-2024 (T3) alloy was friction stir welded at various heat index (HI) values using bead on plate approach. Quantitative analysis using electron microscopy and differential scanning calorimetry (DSC) revealed a complex variation in the precipitation evolution of Guinier-Preston-Bagaryatskii (GPB) zone and Al2CuMg (S phase) precipitates in nugget and heat affected zone (HAZ). Differential scanning calorimetry data also suggested formation energy of GPB zone equal to -236 J g(-1). Tensile properties attained a maximum for HI values close to 3.94 in the nugget region, which was attributed to corresponding minimisation of the volume fraction of coarse S phase to the profit of GPB zone. The precipitation of fine S phase precipitates resulted in higher tensile properties in HAZ as compared to those in nugget for all HI values. Experimental data were used to determine major strengthening mechanisms by using constitutive relationships.