Microstructure and performance of high-speed laser-welded joints in novel heat-resistant Al–12Ce–0.4Sc alloy

Effects of heat treatment on the microstructure and performance of laser-welded joint for the novel heat-resistant aluminum alloy Al–12Ce–0.4Sc were studied. The results show that heat treatment has little effect on the tensile properties of welded joints at room temperature but exhibits a significant effect on the creep properties at high temperature of 300 ℃. The microhardness distribution in the fusion zone is uniform, with a value significantly higher than that of the aluminum base in the base material, but lower than that of the large blocky Al₁₁Ce₃ phase. Fractures occurred in the base material during the tensile tests at both room temperature and 300 ℃ high temperature for all joints. The elongation during the tensile test at 300 °C high temperature of the joint welded by cast base material (CA-LW) was approximately twice as high as that of the joint with post-heat treatment welded by cast base material (CA–LW–HT). The CA–LW–HT joint exhibited the best creep resistance with a steady-state creep rate of 3.2 × 10–8 s⁻¹ at 300 ℃ and 55 MPa, which was two orders of magnitude lower than that of the CA–LW joint. A significant reduction in grain size and change in the form of the precipitated phases in the fusion zone were identified as the primary reasons for higher microhardness and strength in the fusion zone than in the base material. The grain size in the fusion zone was less than 1/10 of that in the base material, and large blocky primary Al₁₁Ce₃ in the base material almost completely disappeared after the welding process, as the microstructure transformed into eutectics of primary α-Al and nanoscale Al₁₁Ce₃/Al. Mild Sc enrichment observed at the Al₁₁Ce₃/Al matrix interface in the fusion zone significantly contributed to the maintenance of outstanding high-temperature performance in the fusion zone.