Laser directed energy deposition additive manufacturing using friction stir channelling extruded wire

Abstract

This paper investigates a new ‘forged’ wire additive manufacturing processing, in which the metal wire is produced as a by-product from stationary shoulder friction stir channelling (SS-FSC) under the severe plastic deformation mechanism (known as CoreFlow®), and then used as the feedstock in directed energy deposition with a laser beam and wire feedstock (DED-LB/w) additive manufacturing. For the first time, the ‘by-products’ produced in the SS-FSC process, which are ‘forged’ 6082 aluminium alloy wire, were tested with built-tracks using DED-LB/w. Process mapping was built to demarcate the melting states, including the stable, dripping, and incomplete melting regimes, over a wide range of laser energy densities (92 to 303 $\mathrm{kJ}·s·g^{-1}·{\mathrm{cm}}^{-2}$). Metallurgy tests were also conducted to reveal the evolution of the microstructure and defect formation of the deposited tracks. It was found that: (i) Stable deposition with a grain size of $9-20\mathrm{\mu m}$ can be achieved with optimised processing parameters, i.e., energy density $243\mathrm{kJ}·s·g^{-1}·{\mathrm{cm}}^{-2}$ with a laser power $3.8\mathrm{kW}$, a scanning speed $0.8\mathrm{cm}·s^{-1}$ and a wire feed rate $2.0\mathrm{cm}·s^{-1}$; (ii) The substructure morphology is gradually transitioned from columnar at the track bottom to cellular ($8.9\pm 1.8\mathrm{\mu m}$) at the top, driven by an increased cooling rate; and (iii) The built track porosity is mainly composed of gas pores that are small (equivalent diameter of $20-50\mathrm{\mu m}$) and spherical, primarily resulting from the ambient gas, the SS-FSC extruded wire oxides and contaminations. The study supports resource-efficient, low-carbon manufacturing via reuse of by-products, in alignment with the Net Zero Strategy.