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Abstract This paper systematically evaluated the effect of oxide, wire source and heat treatment on the mechanical properties of wire + arc additively manufactured (WAAM) INCONEL 718. Comparison of the as deposited grain structure was made with laser-powder based AM and wrought INCONEL 718. Results showed that oxides formed during deposition had no effect on the mechanical properties since a 0.5μm thick passivation layer consisting of Cr 2 O 3 and Al 2 O 3 formed upon deposition and prevented further oxides from forming inside the bulk. Wires from different suppliers resulted in around 50 MPa difference in UTS possibly due to the slight compositional variation and uncertainties in TiN inclusion. Standard heat treatment improved the strength from 824 MPa to 1110 MPa in the horizontal direction, but the average strength was 105 MPa lower than the wrought alloy. The as deposited WAAM INCONEL718 featured large columnar grains and numerous Laves phase, as compared to the fine grains of laser powder bed fusion and wrought INCONEL 718. This starting microstructure led to less favourable and less numerous precipitates forming during heat treatment, which is the main reason for the strength mismatch. A different heat treatment would not help due to the starting microstructure. [ABSTRACT FROM AUTHOR]

Wire + Arc Additive Manufacture (WAAM) has been shown to be suitable for manufacturing large-scale metallic parts. However porosity in the deposited aluminum material restricts the application of WAAM for aluminum alloys. In this study inter-layer rolling process was employed during the deposition of aluminum alloys and its influence on porosity was investigated. Samples of straight walls were prepared with both the 2319 aluminum alloy wire and the 5087 aluminum alloy wire. Inter-layer rolling was employed between each and every deposited layer. Different rolling loads of 15 kN, 30 kN and 45 kN were applied, greatly reducing the quantity of the pores for both alloys. With a rolling load of 45 kN the pores larger than 5 μm in diameter were eliminated. In additional, the influence of post-deposition heat treatment on porosity was investigated on the as-deposited samples as well as on the samples built with inter-layer rolling of 45 kN load. A different behavior of pores’ formation and growth was found between 2319 alloy and 5087 alloy, both for as-deposited status and heat-treated status. Post-deposition heat treatment increased the area of the pores for both alloys. After the post-rolling heat treatment, no pores larger than 5 μm in diameter was found re-initiated for both alloys. [ABSTRACT FROM AUTHOR]

Wire + Arc Additive Manufacture (WAAM) attracts great interest from the aerospace industry for producing components with aluminum alloys, particularly Al–Cu alloy of the 2000 series such as 2219 alloy. However the application is restricted by the low strength properties of the as-deposited WAAM metal. In this study two strengthening methods were investigated – inter-layer cold working and post-deposition heat treatment. Straight wall samples were prepared with 2319 aluminum alloy wire. Inter-layer rolling with loads of 15 kN, 30 kN and 45 kN were employed during deposition. The ultimate tensile strength (UTS) and yield strength (YS) of the inter-layer rolled alloy with 45 kN load can achieve 314 MPa and 244 MPa respectively. The influence of post-deposition T6 heat treatment was investigated on the WAAM alloy with or without rolling. Compared with inter-layer rolling, post-deposition heat treatment can provide much greater enhancement of the strength. After T6 treatment, the UTS and YS of both of the as-deposited and 45 kN rolled alloys exceeded 450 MPa and 305 MPa respectively, which are higher than the properties of the wrought 2219−T6 alloy. The strengthening mechanisms of this additively manufactured Al–6.3Cu alloy were investigated through microstructure analysis. [ABSTRACT FROM AUTHOR]

Wire + Arc Additive Manufacture is an Additive Manufacturing process that requires a substrate to initiate the deposition process. In order to reduce material waste, build and lead time, and improve process efficiency, it is desirable to include this substrate in the final part design. This approach is a valid option only if the interface between the substrate and the deposited metal properties conform to the design specifications. The effect of substrate type on the interface microstructure in an aluminium part was investigated. Microstructure and micro-hardness measurements show the effect of substrate alloy and temper on the interface between the substrate and deposited material. Microcracks in the as-deposited condition were only found in one substrate. The deposited material hardness is always lower than the substrate hardness. However, this difference can be minimised by heat treatment and even eliminated when the substrate and wire are made of the same alloy. Dataset License: CC0 [ABSTRACT FROM AUTHOR]

Abstract Wire + arc additive manufacture is developed for producing large-scale metallic components. In this paper, maraging steel parts were produced, and the microstructure and mechanical properties were investigated. The microhardness and tensile strength of the as deposited alloy reduced from the bottom to the top due to the transient thermal cycling, which resulted in partial aging and non-uniform formation of intermetallic compounds along the building direction. Solutionizing, followed by 3 h aging, significantly reduced the microstructural heterogeneity and increased the mechanical properties by 24.7% through the formation of large amounts of finely distributed precipitates. The as deposited alloy possessed superior strength to the wrought alloy in solutionized condition but inferior to the later in aged condition, which was attributed to the less pronounced aging response of the low-angle columnar grains characterized microstructure and the presence of retained and reverted austenite. Graphical abstract Image 1 Highlights • Wire + arc additive manufacture (WAAM) was applied to produce maraging steel structures. • Microstructure evolution of WAAM alloy was characterized and correlated with the layer-by-layer building manner. • Mechanical properties of WAAM alloy were tested and correlated with the aging response of WAAM microstructure. • Retained austenite content was measured and correlated with the tensile strength loss. [ABSTRACT FROM AUTHOR]

• Rolling process is integrated into the WAAM to refine the grains. • A new heat treatment is applied for Inconel 718 to further enhance the strengths. • The columnar dendrites change to equiaxed grains with interlayer rolling process. • Finer grains and isotropic mechanical properties are obtained in warm rolling. • The strengthening mechanism of the hybrid WAAM and rolling process is revealed. Wire - arc additive manufacture (WAAM) is suitable for Inconel 718 components due to its high deposition efficiency. However, large columnar dendrites decrease the mechanical properties and can cause severe mechanical anisotropy. Cold rolling and warm rolling through flame heating have been investigated to analyze their effects on microstructure and tensile properties compared to as-deposited WAAM material. Standard solution and double aging (SA), as well as homogenization followed by solution and aging (HSA) heat treatments were compared. The results show that the large columnar dendrites change to finer equiaxed grains 16.4 μm and 26.2 μm in size for warm and cold rolled alloy, respectively. This increases to 22.5 μm and 30.1 μm after HSA treatment. The microhardness and strength of rolled material increase significantly and the warm rolled material after HSA treatment exceeds that of the wrought alloy. While the as-deposited and cold rolled samples both show significant anisotropy, isotropic tensile properties are obtained for warm rolled plus HSA heat treated samples. Finer equiaxed grains with more dispersive distributions of γ' and γ" strengthening precipitation contribute to the superior mechanical properties for warm rolled material. For both the cold and warm rolled material, there was an elongation decrease due to precipitated particles, which also led to a trans-granular ductile fracture mode. The strengthening mechanism of the hybrid rolling process was analyzed and found to be related to work hardening, grain boundary strengthening, precipitated strengthening phases and the δ phase. [ABSTRACT FROM AUTHOR]

The wire with a composition of Al Cu4.3% Mg1.5% was customized and used to deposit the WAAM alloy with the power source of cold metal transfer. The microstructure, defect, and mechanical properties of the as-deposited and heat-treated WAAM alloys were studied. Key findings demonstrated that the microstructure of the as-deposited alloy was characterized by a hierarchical distribution of dendrites, equiaxed grains, and a slight number of columnar grains. The volume fraction of the network-like scattered coarse particles of second phases θ + S reduced by 95% after the T6 heat treatment. With an average microhardness of 161.4 HV, the mean yield strength and ultimate tensile strength of the WAAM alloy increased by 116% and 66% achieving 399 MPa and 485 MPa in the horizontal direction after heat treatment. The precipitation of a high density of needle-shaped metastable S′ precipitates was responsible for the significantly enhanced mechanical properties. However, this WAAM alloy has exhibited an anisotropic tensile property. A considerable number of sharp-angled defects like linear and chain-like micropores, which generally depress the mechanical properties, were formed in the WAAM alloys. Unlabelled Image • The Al Cu4.3-Mg1.5 alloy was fabricated by wire + arc additive manufacturing. • The average microhardness reached 161.4 HV for the heat-treated alloy. • The mean YS and UTS of the heat-treated alloy achieved 399 MPa and 485 MPa. • Mechanical properties were improved by precipitation strengthening. [ABSTRACT FROM AUTHOR]

The application of wire + arc additively manufactured (WAAM) aluminum alloys has been restricted by the porosity defect, which is generally detrimental to the mechanical properties. Suppressing of micropores in the WAAM components has attracted considerable attention in recent years. Inter-layer rolling was introduced to eliminate micropores during the WAAM deposition of the Al–Cu6.3 and Al–Mg4.5 alloys. The distribution characteristics and individual morphology of micropores were revealed by the X-ray diffraction tomography. Key findings demonstrated that the number, volume, size, and roundness of micropores in rolled alloys decreased similarly with increasing loads, eventually achieving a density of over 99.9%. After the heat treatment, the homogeneous distribution of fine (around 5.3 μm) and spherical (0.70–0.74) micropores was realized in the 45 kN rolled alloys. All the evaluated indicators of micropores in the 45 kN rolled + heat treated alloys were superior to the post-deposition heat treated state. The evolution mechanisms include the reprecipitation of hydrogen pores, formation of vacant voids, and re-opening of unclosed pores. The hybrid technique of WAAM + rolling + heat treatment has great potential in promoting mechanical properties of WAAM alloys. The results will provide a theoretical guidance for the design of high-performance WAAM aluminum alloy components. Image 1 • Rolling was introduced to additive manufacture to eliminate micropores. • Micropores number, volume, size, and roundness decreased with increasing loads. • Fine and spherical micropores homogeneously distributed by hybrid technique. • Evolution mechanisms include H precipitation, microvoid formation, pore reopening. [ABSTRACT FROM AUTHOR]