Crack elimination and strength enhancement mechanisms of selective laser melted Si-modified Al−Mn−Mg−Er−Zr alloy

In order to increase the processability and process window of the selective laser melting(SLM)-fabricated Al−Mn−Mg−Er−Zr alloy,a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed.The effect of Si alloying on the surface quality,processability,microstructure,and mechanical properties of the SLM-fabricated alloy was studied.The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation,refined the grain size,and reduced the solidification temperature,which eliminated cracks and increased the processability and process window of the alloy.The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%.The yield strength and ultimate tensile strength of the alloy were(371±7)MPa and(518±6)MPa,respectively.These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

Formation and Relative Stabilities of Core-Shelled L12-Phase Nano-structures in Dilute Al–Sc–Er Alloys

First-principles thermodynamic calculations were carried out at the interface level for understanding the precipitation of coherent L12-phase nano-structures in dilute Al–Sc–Er alloys.All energetics,relevant to bulk substitution,interface formation,interfacial coherent strain and segregation,were calculated and used to evaluate the nucleation and relative stabilities of various possible L12 nano-structures.Only matrix-dissolved solute Er(or Sc)can substitute Sc(or Er)in L12-Al3Sc(or Al3Er).The inter-substitution between L12-Al3Sc and Al3Er is not energy feasible.Ternary L12-Al3(Er x Sc 1.x)precipitates tend to form the Al3Er-core and Al3Sc-shell structure with a sharp core/shell interface.Three possible formation mechanisms were proposed and examined.The eff ects of Er/Sc ratio and aging temperature on the relative stabilities of L12-phase nanostructures in Al were also discussed.