Microstructure-driven formation of a chemically graded corrosion layer in PBF-LB/M fabricated dual-phase Mg–8Li–0.5Ca wt.% ultralight alloy

Abstract

In this study, a dual-phase Mg-8Li-0.5Ca wt.% ultralight alloy was successfully fabricated using powder bed fusion - laser beam/metals (PBF-LB/M). The as-built microstructure consisted of α(Mg) enriched with microscale Mg-Ca precipitates and β(Li) containing nanosized needle-like precipitates. Compared with cast counterparts, PBF-LB/M enabled substantial grain refinement to below 2 µm. The corrosion performance of PBF-LB/M and cast alloys as reference materials was systematically evaluated in NaCl and PBS solutions. In both conditions, degradation was governed by microgalvanic interactions between α(Mg) and β(Li), however, PBF-LB/M alloy exhibited more controlled degradation kinetics due to its refined and homogeneous microstructure. In NaCl, the improved corrosion resistance was associated with the formation of Li 2 CO 3 -enriched layer combined with Mg(OH) 2 , limiting chloride-induced film breakdown. In PBS, a distinct behaviour was observed: while the cast alloy formed a mixed Mg/Li phosphate layer, the PBF-LB/M sample developed a Li-rich outer surface composed predominantly of LiOH and Li 2 CO 3 . A chemically graded corrosion layer formed, characterized by Mg-rich inner products and Li-enriched outer compounds. The formation of Li 2 CO 3 , with a favourable Pilling–Bedworth ratio and low solubility, contributed to enhanced surface stability. Additionally, PBF-LB/M extracts meet cytotoxicity requirements according to ISO 10993-5. These findings demonstrate that PBF-LB/M processing significantly modifies corrosion mechanisms in dual-phase Mg–Li alloys and highlight the potential of ultralight Mg–Li–Ca systems for biodegradable biomedical applications.