Wide-spread utilization of wire-arc additive manufacturing (WAAM) technologies require the development of high-performance aluminum alloys with a robust processing window. Suitable alloys have to be modified to reduce their susceptibility for hot cracking - a common means is grain refinement via inoculation. Here, an advanced Al–Mg–Si alloy with a TiB 2 containing structural refiner is processed using WAAM. As a result, no macroscopic cracks are observed in the deposit. The microstructure consists of fine (<30 μm) and equiaxed grains that do not show any crystallographic texture. Both characteristics are considered to result from preferential heterogeneous nucleation yielding a reduced tendency for epitaxial nucleation. No coarsening of the heterogeneous nucleants is observed when comparing wire and WAAM deposit microstructures. After a two-step heat treatment, where negligible grain coarsening is observed during the solution heat treatment, the yield strength reaches ∼ 265 MPa irrespectively of the tensile direction. Gained results provide the basis for the application of an advanced Al–Mg–Si alloy using the WAAM technology. • Theoretic concepts of grain refinement revisited. • WAAM processing of a structurally refined Al–Mg–Si alloy yields crack-free specimens. • Microstructure consists of fine (<30 μm), equiaxed grains. • No crystallographic texture present resulting in isotropic yield strength. • Yield strength of ∼ 265 MPa achieved via a two-step heat treatment. 

Microstructure and mechanical properties of a structurally refined Al–Mg–Si alloy for wire-arc additive manufacturing

Wide-spread utilization of wire-arc additive manufacturing (WAAM) technologies require the development of high-performance aluminum alloys with a robust processing window. Suitable alloys have to be modified to reduce their susceptibility for hot cracking - a common means is grain refinement via inoculation. Here, an advanced Al–Mg–Si alloy with a TiB2 containing structural refiner is processed using WAAM. As a result, no macroscopic cracks are observed in the deposit. The microstructure consists of fine (

Cellular materials are recognized for their high specific mechanical properties, making them desirable in ultra-lightweight applications. Periodic lattices have tunable properties and may be manufactured by metallic additive manufacturing (AM) techniques. However, AM can lead to issues with un-melted powder, macro/micro porosity, dimensional control and heterogeneous microstructures. This study overcomes these problems through a novel technique, combining additive manufacturing and investment casting to produce detailed investment cast lattice structures. Fused filament fabrication is used to fabricate a pattern used as the mold for the investment casting of aluminium A356 alloy into high-conformity thin-ribbed (~ 0.6 mm thickness) scaffolds. X-ray micro-computed tomography (CT) is used to characterize macro- and meso-scale defects. Optical and scanning electron (SEM) microscopies are used to characterize the microstructure of the cast structures. Slight dimensional (macroscale) variations originate from the 3D printing of the pattern. At the mesoscale, the casting process introduces very fine (~ 3 µm) porosity, along with small numbers of (~ 25 µm) gas entrapment defects in the horizontal struts. At a microstructural level, both the (~ 70 μm) globular/dendritic grains and secondary phases show no significant variations across the lattices. This method is a promising alternative means for producing highly detailed non-stochastic metallic cellular lattices and offers scope for further improvement through refinement of filament fabrication.

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Macro-, meso- and microstructural characterization of metallic lattice structures manufactured by additive manufacturing assisted investment casting.

Efficient grain refinement of Al alloys induced by in-situ nanoparticles

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Shuncheng Wang

Papers

Grain size prediction and investigation of 7055 aluminum alloy inoculated by Al–5Ti–1B master alloy