Fundamental Study on the Development of Pure Magnesium Parts by Additive Manufacturing: An Experimental and Computational Analysis

초록

The low density and high biocompatibility of Mg-based materials make them suitable for lightweight structural and biomedical applications. In this study, we explored the use of selective laser melting (SLM)-an additive manufacturing process wherein metal powders are consolidated in a layer-by-layer manner, allowing the fabrication of complex components. SLM typically involves complex physicochemical phenomena and results in laser-processing defects, which makes it difficult to predict the densification mechanisms of the melt pool. Therefore, a full-scale model was developed to investigate the thermal behavior of the melt pool (e.g., temperature gradient distribution, melt pool dimensions, and cooling rate) and the resultant densification activity under various laser energy density (eta) values. In parallel, experimental investigations of the densification behavior and microstructural evolution were undertaken with the same SLM processing parameters. The challenges associated with the SLM processability of Mg were comprehensively addressed. Both the peak temperature gradients within the molten pool and molten pool dimensions increased with increasing eta, and an opposite trend was observed for the cooling rate. A low eta (i.e., high scanning speed) results in a low operating temperature and short liquid lifetime, which in turn lead to poor wettability and many pore-chain and balling defects. However, high eta values generated melt pool instability, which resulted in extensive evaporation, cracks, and porosity. The SLM-processed samples had fine twin-like microstructures as a result of rapid solidification. The experimental and simulation results agreed well, validating the thermal behavior of the molten pool and underlying physical mechanism.

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