Microstructure evolution and microhardness of the novel Al–Cu–Li-xSc alloys fabricated by laser rapid melting

Al–Li alloys containing scandium serve as excellent lightweight materials. However, the number of Al₃Sc phases is extremely less due to the minor addition of Sc, resulting in deficient microhardness. Laser rapid melting has the advantage of enhancing solid solubility of alloying elements during rapid solidification, which becomes a critical technique to explore new components of alloys. This study aims to investigate the effects of major Sc content (0, 1, 3 and 5 wt%) on microstructure and microhardness of Al–Cu–Li-xSc alloys fabricated by laser rapid melting. The primary Al₃Sc particles could greatly refine grains in Al–Cu–Li-1Sc alloy. With the increase of Sc content, more clustered Al₃Sc particles nucleated during the latter stage of solidification but the grain refinement effect was not obvious. The growth restriction factor (Q) was calculated to determine the degree of constitutional supercooling (ΔT_CS) that served as segregation of Sc during solidification. The spiculate T₁ (Al₂CuLi) precipitates heterogeneously nucleated on the Al₃Sc dispersoids. The maximum value of microhardness is 167 HV obtained in aged Al–Cu–Li-5Sc alloys. The novel Al–Cu–Li-xSc alloys can be designed as gradient hard Al–Li alloy materials.