Wire arc additive manufacturing (WAAM) has received wide attention because of its high deposition efficiency, reduced material waste and low equipment cost. However, WAAM process often generates defects due to its intrinsic characteristics. The integration of additive manufacturing and surface strengthening techniques is an effective solution. To control the non-uniform microstructures, internal defects and residual stresses in the components, achieving three-dimensional strengthening by surface enhancement layer by layer during the additive manufacturing process. This paper reviews the recent research status of hybrid manufacturing processes involving WAAM and surface enhancement techniques, with focus on the potential of laser shock peening, a non-contact surface strengthening process, within these hybrid manufacturing processes. Finally, the paper discusses the challenges and future trends of composite manufacturing processes from the perspective of theoretical development, equipment innovation and online control.

Wire-arc directed energy deposition (WA-DED) process, as an efficient and cost-effective additive manufacturing method, is emerging as a promising technique for fabricating high-performance Mg-Gd-Y-Zr alloys. However, most of the previous studies were limited to exploring the tensile performance at room temperature, which greatly restricted the practical application of such typical lightweight and heat-resistant metallic material at elevated-temperature service environment. Herein, this study investigates the tensile properties and deformation behavior of the as-deposited and heat-treated GW102K Mg alloy at various temperatures (room temperature, 200 ℃, 300 ℃) for the first time. The results indicate that elevated temperatures enhance ductility but reduce strength by promoting slip system activation, as indicated by the tensile properties. Notably, the tensile test temperature and microstructural characteristics determine the severity of the Portevin-Le Chatelier (PLC) effect. Specifically, the tensile test temperature influences the rates of both solute atoms' migration and dislocation annihilation, thus leading to an enhancement and then a decrease in the intensity of the PLC phenomenon. Particularly during elevated-temperature tension, rare-earth (RE) rich regions in the as-deposited samples and dissolved solute atoms in the solution-treated samples promote the PLC effect. Conversely, solute atom depletion and effective dislocation pinning by dense nano-β' precipitates eliminate PLC phenomenon in the solution plus aging-treated samples. Ultimately, the solution plus aging-treated sample achieves a combination of high ultimate tensile strength of 271 MPa along with a decent ductility of 11.1 % at 300 ℃, substantially outperforming conventionally processed Mg-RE alloys. This study therefore offers guidance for regulating PLC effects in WA-DED Mg alloys for elevated-temperature applications.

The preparation of large-sized magnesium rare-earth (Mg-RE) alloy parts using wire-arc directed energy deposition (WA-DED) has clear advantages such as high-efficiency and cost-effective. The impact of Gd content, which is one of the most important RE elements, on the microstructure evolution and mechanical response of the as-deposited and heat-treated Mg-Gd-Y-Zr alloys, deserves to be thoroughly unveiled. Herein, multi-scale microstructure characterization and mechanical evaluation of Mg-xGd-2Y-0.5Zr (wt%, x = 4, 7, and 10) alloys were carried out. Specifically, the increased Gd content facilitates the grain refinement, micro-segregation, and precipitation during the deposition process. As a result, the strength of the as-deposited samples with increased Gd content was improved through refined grain and dispersion strengthening of nano-β", but the ductility was severely deteriorated due to the premature failure caused by excessive β-Mg₂₄(Gd, Y)₅ eutectic phases. Besides, the increased Gd content successfully restrains grain coarsening through higher content of eutectic phase and larger RE-rich region during solution treatment. Following peak-aging treatment, while the increased Gd content does not affect the precipitation types, the content of nano-β' was remarkably enhanced, which leads to excellent strength. Ultimately, a superior yield strength of 239 MPa, an ultra-high ultimate tensile strength of 371 MPa and an elongation of 4 % are achieved in the solution plus aging-treated Mg-10Gd-2Y-0.5Zr alloy. This study thus provides guidelines on the composition modification and post-treatment of WA-DED Mg-Gd-Y-Zr alloys suitable for engineering applications.

Research on the preparation of over-sized lightweight magnesium rare-earth (Mg-RE) components using the wire-arc directed energy deposition (WA-DED) is progressively gaining attention in the advanced manufacturing fields. Herein, to satisfy the demand of ultrahigh load-bearing, the Zn-modified Mg-10Gd-2Y-1Zn-0.5Zr (GWZ1021K) alloy was designed for exploring the influence pattern of Zn element on the microstructure and properties of Mg-10Gd-2Y-0.5Zr (GW102K) with high RE content. Specifically, the Zn element enables finer and more homogeneous grains in the as-built GWZ1021K (18.2 μm) than that in the as-built GW102K (23.9 μm), owing to more nucleation sites and precipitation of nano-γ" and nano-γ' to impede grain growth during the intrinsic heat treatment. After solution treatment, the eutectic phases and RE-rich regions completely disappear in both GW102K and GWZ1021K, yielding elongations of up to 14.6% and 13.2%, respectively. Notably, the high-temperature solution process allows the growth of nano-γ" and nano-γ', as well as the segregation of RE/Zn clusters and subsequent atomic rearrangements to form the 14H long period stacking ordered (LPSO) structures. Following peak-aging treatment, although dense nano-β’ is precipitated in both GW102K and GWZ1021K, the Zn element facilitates the precipitation of nano-β₁ to relieve the stress concentration induced by the two adjacent nano-β′ and basal 14H-LPSO structures work together to hinder the movement of both basal and non-basal dislocations. As a result, the GWZ1021K alloy achieves an ultra-high strength with an ultimate tensile strength of 403 MPa and a yield strength of 278 MPa, which far exceeds the reported average level of the WA-DED Mg-RE alloys. This study thus sheds new light on the fabrication of ultrahigh-strength Mg-RE alloy components by WA-DED process through appropriate composition modification.

The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality, which has promising application potential in a large number of industrial areas. In this study, two components composed of ERCuAl-A2 aluminum bronze (CuAl9) and Inconel 718 nickel-based superalloy were fabricated with different deposition orders by wire-arc directed energy deposition. Subject to changes in heat input and thermophysical properties of the substrate, the transition region of the deposited Cu–Ni component with the bottom half of CuAl9 and the top half of Inconel 718 is narrow and serrated. This region features a laminated intermetallic compound layer due to the convection and rapid cooling in the molten pool. In contrast, the Ni–Cu component deposited in the opposite order exhibits a 2 mm gradient transition zone. Within this region, a large number of diverse precipitates were found as well as regional variations in grain size due to the multi-layer partial remelting. Both two components show strong bonds and their tensile specimens tested along the vertical direction always fracture at the softer CuAl9 side. Excellent tensile properties along the horizontal direction were obtained for Cu–Ni (Ultimate tensile strength: 573 MPa, yield stress: 302 MPa, elongation: 22%), while those of Ni–Cu are much lower due to the existence of the solidification cracks in the transition zone. The results from this study provide a reference for the additive manufacturing of Cu/Ni dissimilar alloy components, as well as their microstructure and mechanical properties control.

Mg-Gd-Y-Zr alloy, as a typical magnesium rare-earth (Mg-RE) alloy, is gaining popularity in the advanced equipment manufacturing fields owing to its noticeable age-hardening properties and high specific strength. However, it is extremely challenging to prepare wrought components with large dimensions and complex shapes because of the poor room-temperature processability of Mg-Gd-Y-Zr alloy. Herein, we report a wire-arc directed energy deposited (DED) Mg-10.45Gd-2.27Y-0.52Zr (wt.%, GW102K) alloy with high RE content presenting a prominent combination of strength and ductility, realized by tailored nanoprecipitates through an optimized heat treatment procedure. Specifically, the solution-treated sample exhibits excellent ductility with an elongation (EL) of (14.6 ± 0.1)%, while the aging-treated sample at 200 °C for 58 h achieves an ultra-high ultimate tensile strength (UTS) of (371 ± 1.5) MPa. Besides, the aging-treated sample at 250 °C for 16 h attains a good strength-ductility synergy with a UTS of (316 ± 2.1) MPa and a EL of (8.5 ± 0.1)%. Particularly, the evolution mechanisms of precipitation response induced by various aging parameters and deformation behavior caused by nanoprecipitates type were also systematically revealed. The excellent ductility resulted from coordinating localized strains facilitated by active slip activity. And the ultra-high strength should be ascribed to the dense nano-β′ hampering dislocation motion. Additionally, the shearable nano-β₁ contributed to the good strength-ductility synergy. This work thus offers insightful understanding into the nanoprecipitates manipulation and performance tailoring for the wire-arc DED preparation of large-sized Mg-Gd-Y-Zr components with complex geometries.

In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting (SLM) was employed to achieve nearly full dense and crack-free AZ91D components with fine equiaxed grain structure. The formation mechanism of typical pore defects (gas pore, lack-of-fusion pore and keyhole pore) and melting modes (keyhole mode and conduction mode) were systematically studied by varying the laser power and scanning speed. The morphology and volume fraction of the pores under different processing conditions were characterized. A criterion based on the depth-to-width ratio of the melt pool was established to identify different melting modes. The strength and ductility (tensile strength up to 340 MPa and uniform elongation of 8.9%) of the as deposited AZ91D are far superior to those of the casting components and are comparable to those of its wrought counterparts. The superior balance of strength and ductility of SLMed AZ91D, as well as the negligible anisotropic properties are mainly ascribed to the extremely fine equiaxed grain structure (with average grain size of ~1.2 μm), as well as the discontinuous distribution of β-Al₁₂Mg₁₇ phases. It thus provides an alternative way to fabricate high-strength magnesium alloys with complex geometry.