Magnesium alloys, with appropriate mechanical strength, excellent biodegradability, and good biocompatibility, have emerged as highly promising bone repair materials. However, their excessively high corrosion rate and poor wear resistance severely restrict their application in medical implants. This study aims to modify the surface of self-made Mg-1Mn-2Zn alloys using laser surface remelting (LSR) technology to optimize its microstructure and properties, thereby providing a theoretical basis for the promotion of medical magnesium alloys. With self-made Mg-1Mn-2Zn alloys as the research objects, the matrix properties were first optimized through T6 aging heat treatment (heating from 360 ℃ to 420 ℃, holding for 10 hours, then holding for another 2 hours followed by natural cooling). Subsequently, LSR treatment was conducted at four laser powers: 600 W, 800 W, 1 000 W, and 1 200 W (with a scanning speed of 10 mm/s, spot diameter of 4mm, overlap rate of 30%, and argon protection). The changes in the microstructure and properties of the alloys before and after treatment were systematically investigated through metallographic microstructure observation, X-ray diffraction (XRD) analysis, microhardness testing (with a load of 50 gf and a loading time of 15 s), sliding friction and wear tests (with GCr15 as the friction pair, at a load of 20 N, frequency of 2 Hz, and duration of 30 min), electrochemical corrosion tests (in simulated body fluid SBF at 37 ℃ at a scanning speed of 1 mV/s), and biocompatibility tests (CCK-8 method, live/dead cell staining, cell adhesion experiments using MC3T3-E1 osteoblasts). After LSR treatment, a uniform molten layer was formed on the alloy surface. The interface between the melted zone and the matrix showed a crescent shape, with the surface slightly concave. The width and depth of the molten pool increased with the increase of laser power (the molten pool size was the smallest at 600 W and the largest at 1 200 W, and the growth rate slowed down when the power exceeded 1 000 W). In terms of microstructure, the grains in the molten layer were significantly refined (all dendritic crystals), with the smallest dendrite arm spacing at 600 W, and the grains gradually coarsened as the power increased. XRD analysis revealed that the phases remained α-Mg, MgZn2, and MgZn3, with no α-Mn phase. After laser treatment, the diffraction peaks shifted to a higher angle by approximately 0.3° and the peak width increased, indicating grain refinement. In terms of mechanical properties, the microhardness of the melted zone showed a step-like distribution from the surface to the matrix, with a trend of first increasing and then decreasing. The surface hardness at 600 W reached 74HV, which was 32% higher than that of the matrix (56HV), and the hardness gradually decreased with the increase of power (63HV at 1 200 W). In terms of friction and wear properties, the 600 W sample had the lowest friction coefficient (0.218 3), which was 29.82% lower than that of the as-received alloys, and the smallest wear loss (2.9 mg), which was 66% lower than that of the as-received sample (8.6 mg). The wear loss increased with the increase of power (6.5 mg at 1 200 W), and the wear mechanism was mainly fatigue failures. In terms of corrosion resistance, the 1 000 W sample performed the best, with a corrosion potential of -1.168 V, which was 0.553 V positively shifted compared with the as-received sample (-1.721 V), a corrosion current density of 3.52×10-5 A/cm2, and a corrosion rate of 0.779 mm/a, which was 83% lower than that of the as-received alloys (4.592 mm/a). The corrosion morphology showed a dense oxide layer. The 800 W sample had an abnormally high corrosion rate (4.510 mm/a) due to galvanic corrosion caused by the aggregation of the second phase at grain boundaries. Biocompatibility tests showed that the polished LSR-treated samples had the highest relative cell survival rate after 72 hours, no obvious cytotoxicity or high cell adhesion density, while the unpolished samples had lower cell survival rates due to surface residues. Laser surface remelting technology can effectively improve the surface microstructure and properties of Mg-1Mn-2Zn alloys. Low-power (600 W) LSR significantly enhances the hardness and wear resistance of the alloys through grain refinement strengthening and precipitation strengthening; medium-power (1 000 W) treatment can optimize corrosion resistance, attributed to the synergistic effect of fine-grained structure and dense oxide layer; high-power (1 200 W) leads to performance degradation due to grain coarsening and thermal stress. Meanwhile, the polished LSR-treated samples maintain good biocompatibility. In conclusion, through adjusting the laser power (600 W for optimizing wear resistance and hardness, 1 000 W for optimizing corrosion resistance), precise control of the surface properties of medical magnesium alloys can be achieved, provide theoretical and technical support for the clinical application of medical magnesium alloys.
Key words
magnesium alloy /
laser surface remelting /
microstructure /
wear resistance /
corrosion resistance /
biocompatibility
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Funding
Natural Science Foundation of Shandong Province (ZR2023MC140; ZR2023ME077); The Disciplinary Interdisciplinary Convergence Construction Project of University of Jinan in 2024 (XKJC-202406)
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