Comparing evolution of precipitates and strength upon aging of cast and laser-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%)

The microstructural evolutions, upon solidification and subsequent aging, and associated hardening effects for both cast and laser-surface-remelted Al-8Ce-0.2Sc-0.1Zr (wt.%) hypo-eutectic alloy are investigated with focus on precipitation and coarsening behavior of their Al₁₁Ce₃ and L1₂-Al₃(Sc,Zr) precipitates. Laser surface remelting, which produces solidification conditions typical of additive manufacturing (AM) processes, suppresses formation of undesirable primary Al₁₁Ce₃ and Al₃(Sc,Zr) precipitates on solidification. It also greatly refines the interlamellar spacing of the eutectic Al₁₁Ce₃ phase, thus enhancing the Orowan strengthening effect as compared to the cast alloy, beyond the load-transfer effect from the Al₁₁Ce₃ phase. Subsequent aging at 325 °C leads to further hardening of both alloys due to secondary Al₃(Sc,Zr) nanoprecipitation, with much more pronounced hardness increases in the laser-remelted alloy, owing to a higher number density of finer Al₃(Sc,Zr) nano-precipitates, as compared to the cast alloy. This improvement is rationalized by an enhancement of Al₃(Sc,Zr) nucleation rate upon aging of laser-remelted alloy, as compared to the cast alloy, considering differences in elemental supersaturation within the α-Al regions of these alloys. Prolonged aging, up to 1000 h, at 325 °C causes the hardness of both alloys to decline relatively slowly, implying that this alloy is suitable for AM processes and subsequent applications where high strength and good heat resistance are needed.