Dissimilar friction stir welding of 2219-T8 and 2195-T8 aluminum alloys: part I—microstructure evolution and mechanical properties

The need for 2219 aluminum alloy and 2195 Al–Li alloy dissimilar friction stir welding (FSW) arises as the conventional 2219Al alloy was gradually replaced by the novel 2195Al alloy in fabrication of fuel tanks. However, the systematic investigation about the effect of welding parameters and material positioning on the microstructure evolution and mechanical properties of dissimilar FSW 2219Al/2195Al joints is lacking. In the present study, 2219Al-T8/2195Al-T8 plates were subjected to FSW under rotation rates of 800–1200 rpm and welding speeds of 200–800 mm min −1 with placing 2219Al-T8 alloys on the advancing side (AS) and retreating side (RS), respectively. The results showed that sound FSW joints were obtained under all the welding conditions. Welding parameters and material positioning affected the joint strength and fracture failure behavior. The FSW thermal cycle resulted in low hardness zones (LHZs) on both the 2219Al-T8 and 2195Al-T8 sides. The LHZ on the 2219Al-T8 side, characterized by partial coarsening of θ ′ (Al 2 Cu) precipitates and dissolution of the residual precipitates, showed the minimum hardness in the entire FSW joints. When 2219Al-T8 alloy was placed on the AS, the LHZ on the 2219Al-T8 side experienced higher peak temperature, and therefore more dissolution of θ ′ than that on the RS, thereby obtaining higher tensile strength. The tensile strength of the FSW joints at room temperature and − 196 °C largely increased as the welding speed increased from 200 to 400 mm min −1 . The FSW joints presented much higher tensile strength at − 196 °C than that at room temperature under the identical welding parameters and material position. The FSW joints fractured along the LHZ on the 2219Al-T8 side during tension. For the bending testing, the up and down bending failure angles were about 91–117° and 88–109°, respectively, with the weak zone appearing in “S” line or HAZ on the 2195Al-T8 side.