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Abstract:In order to build a better understanding of the relationship between depositing mode and porosity, microstructure, and properties in wire + arc additive manufacturing (WAAM) 2319-Al components, several Al-6.3%Cu deposits were produced by WAAM technique with cold metal transfer (CMT) variants, pulsed CMT (CMT-P) and advanced CMT (CMT-ADV). Thin walls and blocks were selected as the depositing paths to make WAAM samples. Porosity, microstructure and micro hardness of these WAAM samples were investigated. Compared with CMT-P and thin wall mode, CMT-ADV and block process can effectively reduce the pores in WAAM aluminum alloy. The microstructure varied with different depositing paths and CMT variants. The micro hardness value of thin wall samples was around 75 HV from the bottom to the middle, and gradually decreased toward the top. Meanwhile, the micro hardness value ranged around 72-77 HV, and varied periodically in block samples. The variation in micro hardness is consistent with standard microstructure characteristics.

As the properties of wire + arc additively manufactured Al-6.3Cu alloy cannot meet the applying requirements, a double-wire + arc additive manufacturing system was built to add magnesium into Al-Cu deposits for higher mechanical properties. Two commercial binary wires aluminum-copper ER2319 and aluminum-magnesium ER5087 were chosen as the filler metal to build Al-Cu-Mg components with different compositions by adjusting the wire feed speed. The microstructure and morphology of thin wall samples were characterized by optical micrographs (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Vickers hardness and tensile properties were investigated. The microstructure of Al-Cu-Mg deposits was mainly composed of coarse columnar grains and fine equiaxed grains with non-uniformly distributing characteristics. With higher Cu but lower Mg content, the strengthen phase turned to Al2Cu + Al2CuMg from Al2CuMg, and the micro hardness presented an increasing trend. The isotropic characteristics of ultimate tensile strength (UTS), yield strength (YS) and elongation were revealed in these samples. The UTS was about 280±5 MPa both in horizontal and vertical directions for all samples. The YS showed an increasing trend from 156MPa to 187MPa with the same content trend, while elongation decreased from 8.2% to 6%. The fractographs exhibited typical brittle fracture characteristics.

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Restricted by the type of commercial aluminum wire, 2024 aluminum alloy cannot be built through conventional single wire + arc additive manufacturing technology. By simultaneously feeding two wires (ER2319 and ER5087) and adjusting the wire feed speed, 2024 aluminum alloy deposits can be achieved with double-wire + arc additive manufacturing process. Heat treatment procedures (solution + natural/artificial aging) were conducted for further improving the properties. The microstructure and mechanical properties of as-deposited and heat-treated 2024 aluminum alloy deposits were tested and analyzed. The microstructure differed in different conditions. Obvious dendrite morphology in as-deposited condition disappeared after heat treatment, and the phases turned to be α-Al + Al2Cu from α-Al + Al2Cu + Al2CuMg. After heat treatment, layer distributing characteristics of the phases became obvious. Post-deposition heat treatment can improve the micro hardness, strength and horizontal elongation of WAAM 2024 aluminum alloy deposits. The elongation along vertical direction decreased.

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2024 aluminum alloy deposits were produced with wire + arc additive manufacturing procedure. Solution treatment + natural aging processes with different solution treatment temperature were conducted to improve the properties. The microstructure and mechanical properties were investigated. After heat treatment the distributing characteristic of the second phase changed to be dispersive from continuous in as-deposited condition. Solution treatment + natural aging process can significantly improve the properties of WAAM 2024 aluminum alloy. With higher solution treatment temperature, the micro hardness, tensile properties and elongation presented an increasing trend. After 503°C solution treatment + natural aging process, the micro hardness, ultimate tensile strength, yield strength and elongation were 143HV, 497MPa, 330MPa and 16%, respectively, which can nearly meet the applying requirement.

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