Laser-based directed energy deposition of novel Sc/Zr-modified Al-Mg alloys:columnar-to-equiaxed transition and aging hardening behavior

The control of grain morphology is important in laser additive manufacturing(LAM),as grain morphology further affects the hot cracking resistance,anisotropy,and strength–ductility synergy of materials.To develop a solidification-control solution and achieve columnar-to-equiaxed transition(CET)in Al-based alloys during LAM,Sc-and-Zr-modified Al-Mg alloys were processed via directed energy deposition(DED).CET was achieved by introducing high potent primary Al_(3)(Sc,Zr)nucleation sites ahead of the solidification interface.Furthermore,the relationship between the solidification control parameters and precipitation behavior of primary Al_(3)(Sc,Zr)nucleation sites was established using the time-dependent nucleation theory.Then,the CET was studied according to the Hunt criterion.The results indicated that coarse columnar grain structure was still obtained at the inner region of the molten pool at low Sc/Zr contents owing to the effective suppression of the precipitation of the primary Al_(3)(Sc,Zr)nucleation sites via rapid solidification during DED.In addition,the relatively low melt temperature at the fusion boundary unavoidably promoted the precipitation of primary Al_(3)(Sc,Zr)nucleation sites,which resulted in a fine equiaxed grains band at the edge of the molten pool.As the Sc/Zr content increased,the solidification cooling rate was not sufficient to suppress the precipitation of the primary Al_(3)(Sc,Zr)nucleation sites,and a fully equiaxed grain structure was obtained.Furthermore,the effect of the layer-by-layer manufacturing process on the subsequent precipitation strengthening of secondary Al_(3)(Sc,Zr)precipitates was discussed.Both the remelting and subsequent aging during thermal cycling should be considered to achieve greater precipitation strengthening.

Interfacial Characteristics and Mechanical Behavior of Hybrid Manufactured AlSi10Mg–Al6061 Bimetal via Selective Laser Melting and Forging

Hybrid manufacturing(HM)uses additive manufacturing(AM)techniques to prepare complex or fine structures on traditional processing parts,which can fully utilize the advantages of AM to form complex parts,and the high efficiency and low cost of conventional processing methods in manufacturing regular components.A bimetal material was produced by selective laser melting(SLM)of AlSi10Mg on the deformed Al6061 alloy substrate in this study.Firstly,the interface characteristics of the two alloys were studied.The results show that a metallurgical interface with a thickness of 100–200μm was formed as the result of the Marangoni convection during SLM preparation.In detail,the circular flow in the melt pool at the interface led to the dilution of alloying elements and the change of microstructure.Moreover,a suitable first-layer thickness can eff ectively suppress the hot cracks at the interfacial region.Based on the optimized results,the hybrid manufactured samples with diff erent SLM processed volume ratios(SLM-part)to the substrate were prepared to study the mechanical properties and the deformation behavior of hybrid parts.The results show that the volume ratio of the SLM-part to the substrate had an influence on the strength and the elasto-plastic behavior by aff ecting the distribution of plastic deformation.