Study on the Effects of the Composite Addition of Al-5Ti-0.8C and La on the Microstructure and High-Temperature Mechanical Properties of ZL205A Alloy

The effects of Al-5Ti-0.8C and the rare-earth element La on the microstructure and high-temperature mechanical properties of ZL205A alloy were investigated. We found that the grains of 0.1%La + 0.3%Al-5Ti-0.8C alloy were fine, the morphology of the as-cast Al₂Cu phase was fragmented, and the precipitated phase was fine after T5 treatment. In particular, the high-temperature mechanical properties of 0.1%La + 0.3%Al-5Ti-0.8C alloy were significantly improved above 250 °C. The reason for the increase in high-temperature plasticity was attributed to the Al-La phase and the TiC particles, which refined the grains and reduced the tendency for intergranular fracture at high temperatures. More importantly, the high-temperature strengthening mechanism of the Al-5Ti-0.8C master alloy compounded with La was a result of the TiC introduced by the Al-5Ti-0.8C alloy, and the Al₁₁La₃ formed by the addition of La refined the grains in the matrix, promoted the precipitation of the needle-like θ'(Al₂Cu) phase, reduced the size of the θ'(Al₂Cu) phase, decreased the PFZ (Precipitation Free Zone), and increased the θ'(Al₂Cu) phase number, hindering dislocation and grain boundary motion.