Oscillating Laser-Arc Hybrid Additive Manufacturing of AZ31 Magnesium Alloy

Abstract

To overcome the instability of the traditional magnesium alloy additive process, the research on oscillating laser-arc hybrid additive manufacturing (O-LHAM) for AZ31 Mg alloy was developed first, and it focused on the effect of beam oscillation on process characteristics, such as macroscopic morphology, porosity defects, microstructure, and mechanical properties of thin-walled components. The increasing oscillation frequency was effective in suppressing the defects, including lack of fusion, wavy hump, internal porosity, etc. Compared with the case without oscillation, the average grain size of O-LHAM samples was refined from 22–32 μm to 18–20 μm at 300 Hz, while the percentage of Al8Mn5 and Mg17Al12 precipitation increased from 1.42–1.61% to 2.55–3.32%. For this reason, a stirring laminar flow was induced using the oscillating laser in the melt pool, with the ability to disrupt the grain structure and provide more nucleation sites, which is beneficial in reducing the average grain size and promoting the precipitation of the precipitated phase. Meanwhile, for the component without pores, the ultimate tensile strength is 205 MPa, slightly less than the base, but the elongation is 20.7%, twice that of the base. The tensile fracture is characterized by a large number of dimples and some ductile tearing ridges, demonstrating good ductility, which is associated with the grain refinement and precipitation strengthening induced using the oscillating laser. The results indicated that O-LHAM would be an effective method for manufacturing Mg alloy fast and well.