Effects of welding and weld heat-affected zone simulation on the microstructure and mechanical behavior of a 2195 aluminum-lithium alloy

The microstructures, tensile properties, and fatigue properties of a 2195-T 8 Al-Li alloy subjected to a weld heat-affected zone (HAZ) simulation and g as-tungsten-arc (GTA) welding using a 4043 filler metal, with and without a postweld heat treatment, were studied. The principal strengthening precipi tate in the T8 base alloy was the T-1 (Al2CuLi) phase. The HAZ simulation r esulted in the dissolution of T-1 precipitates and the formation of T-B (Al 7Cu4Li) phase, Guinier-Preston (G-P) zones, and delta' (Al3Li) particles. W hen the HAZ simulation was conducted at the highest temperature of 600 degr eesC, microcracks and voids also formed along the grain boundaries (GBs). I n the specimens welded with the 4043 alloy, T (AlLiSi) phase was found to f orm in the fusion zone (FZ). An elongated TB phase and microcracks were obs erved to occur along the GBs in the HAZ close to the FZ interface. The T-1 phase was not observed in the HAZ. The postweld heat treatment resulted in the spheroidization of primary T phase and the precipitation of small secon dary T particles in the FZ, the dissolution of T-B phase, and the reprecipi tation of the T-1 phase in the HAZ. Both the HAZ simulation and welding gav e rise to a considerable decrease in the hardness, tensile properties, and fatigue strength. The hardness in the FZ was lower than that in the HAZ Alt hough the postweld heat treatment improved both the hardness and tensile pr operties due to the reprecipitation of T-1 phase in the HAZ and a smaller i nterparticle spacing in the FZ, no increase in the fatigue strength was obs erved because of the presence of microcracks in the HAZ.