Microstructure characteristic and elevated-temperature mechanical properties of Al-Ce-Cu (-Mn-Zr) alloys

In this study, several Al-7Ce-xCu (x=14, 16, 18, 20 wt.%) alloys were prepared to investigate the microstructure characteristic and mechanical properties. In the as-cast condition, all these alloys consist of polygonal primary Al₈CeCu₄, micro-scale Al₈CeCu₄ eutectic grains, eutectic Al₂Cu and the Al matrix. When T6 treatment was applied, the dimensions of the eutectic Al₈CeCu₄ increase and flake-to-spheroidal transformation was detected, together with the occurrence of $\theta \prime$ nanoprecipitates in the matrix. It was found that with the Cu content increasing, the microhardness of the alloys at 300 ^oC increase rapidly and then tend to level off. When the Cu content is high to 20 wt.%, the soft Al matrix has been surrounded by eutectics, which is supposed beneficial for elevated-temperature strength. Then, on the basis of the Al-7Ce-20Cu alloy, a combination of 0.5Mn and 0.3Zr was introduced to achieve alloying performance, followed with similar T6 treatment. Phase evolution from Al₈CeCu₄ to Al₂₄Ce₃Cu₈(Mn, Zr) was detected, while most of the precipitates were identified to be $\theta \prime \prime$. The tensile strength of the alloy at both room temperature and 300 ^oC is increased with the 0.5Mn and 0.3Zr alloying. The strengthening mechanism was discussed, together with theoretical calculations. This study may be referred for designing Al-Ce-based alloys for elevated-temperature applications.