Investigation of Microstructure and Fracture Mechanism of Al-5.0Mg Alloys Fabricated by Wire Arc Additive Manufacturing

The complicated heat cycling of multilayer deposition during the process of WAAM-CMT leads to an anisotropic microstructure and mechanical properties in different directions. To study the anisotropy of the microstructure and mechanical properties of Al-5.0Mg alloys in different orientations, the as-cast Al-5.0Mg alloys are used. Optical microstructural observation, analysis by SEM, EDS, and x-ray diffraction, microhardness testing, and tensile tests were carried out. The microstructural analysis demonstrated that the microstructure in the horizontal direction is relatively homogeneous and the as-cast Al-5.0Mg alloy has uniform intermetallic compounds and a more even microstructure. The main phases in WAAM-CMT-fabricated Al-5.0Mg and as-cast Al-5.0Mg alloys include the α-phase (Al) and the β-phase (Al3Mg2). Mechanical tests (tensile test and microhardness test) highlight that the sample made by WAAM-CMT possesses better properties in the horizontal direction, but these are weaker than the as-cast alloy. The fractures of the vertical sample, horizontal sample, and the as-cast alloy all belong to ductile fracture. The different sizes of fracture pits in the as-cast alloy and the WAAM-CMT-manufactured Al-5.0Mg are related to the grain size and second phase distribution.