Combining solution-, precipitation- and load-transfer strengthening in a cast Al-Ce-Mn-Sc-Zr alloy

A cast Al-9Ce-0.75Mn-0.18Sc-0.12Zr (wt%) alloy is designed to combine three strengthening phases: (i) micronscale Al11Ce3 platelets formed during eutectic solidification, (ii) nano-scale L-12-Al-3(Sc,Zr) precipitates formed during aging, and (iii) Mn in solid solution in the alpha-Al matrix. Microstructural analyses by SEM, TEM, and atomprobe tomography reveal that Mn remains in solid solution in the as-cast alloy, providing solution strengthening with no influence on the eutectic Al-Al11Ce3 microstructure, which provides precipitation- and load-transfer strengthening. During long-term over-aging at 400 degrees C, Mn-rich precipitates grow at the Al-Al11Ce3 interface, with no effect on the microhardness. However, after short aging at 350 C, a high number density of fine L-12- Al-3(Sc,Zr) nanoprecipitates form in the Al matrix (with a coarser size at the Al-Al11Ce3 interface), providing precipitation strengthening. The synergistic combination of the three strengthening mechanisms (solution, precipitation, and load transfer) in our Al-Ce-Mn-Sc-Zr alloy results in higher microhardness after aging at 350 and 400 C, and higher creep resistance at 300 degrees C, as compared to alloys with two strengthening mechanisms: an Al-10Ce-0.93Mn control alloy (without precipitation strengthening from Sc and Zr), Al-Ce-Sc-Zr (without solution strengthening from Mn), and Al-Mn-Zr-Er (without load-transfer strengthening from Ce). Furthermore, these dual-strengthened alloys are more creep resistant than alloys with a single strengthening mechanism (Al-Ce, AlMn, and Al-Sc-Zr), confirming that the three mechanisms can be combined in pairs or all together.