Porosity in wire-arc directed energy deposition of aluminum alloys: Formation mechanisms, influencing factors and inhibition strategies

Wire-arc directed energy deposition (DED) offers advantages such as high forming efficiency and the ability to create parts without potential constraints on size. It possesses unique advantages in the high-efficiency production of large or ultra-large alloy metal components, for example aluminum. However, the issue of porosity in wire-arc DED aluminum alloys has been a subject of widespread discussion. Porosity defects can induce stress concentration and site for crack formation and propagation. This deterioration results in diminished tensile strength and fatigue resistance, limiting the potential applications of wire-arc DED in aluminum alloy builds. To this end, for the first time, this review offers a thorough examination of prevalent porosity imperfections in wire-arc DED aluminum alloys, including gas pores, shrinkage cavities and porosity arising from the volatilization of elements. Particular emphasis is placed on elucidating the formation mechanisms and spatial distribution of hydrogen pores, which constitute the primary pore defects in wire-arc DED aluminum alloys. Moreover, the research scrutinizes the influence of various wire-arc DED techniques, arc modes, process parameters, and shielding gas environments on porosity formation. The inhibition strategies of porosity defects in wire-arc DED aluminum alloys, including laser-arc hybrid additive manufacturing, ultrasonic vibration assistance, external magnetic field, inter-layer rolling, inter-layer friction stir processing, ultrasonic peening treatment, laser shock peening, and hot isostatic pressing, are further summarized. Ultimately, this work anticipates the future trajectory of wire-arc DED aluminum alloys, offering valuable guidance for the fabrication of high-quality wire-arc DED aluminum alloy intricate components.