Effects of Welding and Weld Heat-Affected Zone Simulation on the Microstructure and Mechanical Behavior of a 2195 Aluminum-Lithium Alloy

摘要

The microstructures, tensile properties, and fatigue properties of a 2195-T8 Al-Li alloy subjected to a weld heat-affected zone (HAZ) simulation and gas-tungsten-arc (GTA) welding using a 4043 filler metal, with and without a postweld heat treatment, were studied. The principal strengthening precipitate in the T8 base alloy was the T_1 (Al_2CuLi) phase. The HAZ simulation resulted in the dissolution of T_1 precipitates and the formation of T_B (Al_7Cu_4Li) phase, Guinier-Preston (G-P) zones, and #delta#' (Al_3Li) articles. When the HAZ simulation was conducted at the highest temperature of 600 deg C, microcracks and voids also formed along the grain boundaries (GBs). In the specimens welded with the 4043 alloy, T (AlLiSi) phase was found to form in the fusion zone (FZ). An elongated T_b phase and microcracks were observed 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 secondary T particles in the FZ, the dissolution of T_B phase, and the reprecipitation of the T_1 phase in the HAZ. Both the HAZ simulation and welding gave 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. Although the postweld heat treatment improved both the hardness and tensile properties due to the reprecipitation of T_1 phase in the HAZ and a smaller interparticle spacing in the FZ, no increase in the fatigue strength was observed because of the presence of microcracks in the HAZ.