Laser surface melting (LSM) is a high-energy surface treatment that allows modification of the microstructure and surface properties of Mg alloys. In the present work, an attempt of LSM on magnesium alloy with liquid nitrogen-assisted cooling (LNSC) was carried out to get the higher cooling rate and improve the surface properties. The experimental results were compared with those of Ar gas protection at room temperature. The samples after LSM with LNSC resulted in a thinner melted layer, a highly homogeneous, refined melted microstructure and formed a lot of worm-like nanocrystals and local amorphous structures. Microhardness of the melted layer with LNAC was improved to HV 90-148 as compared to HV 65-105 of the samples with Ar gas protection. The corrosion resistance of the melted layer in a 3.5% NaCl solution (mass fraction) was improved because of the grain refinement and redistribution ofβ-Mg17Al12 phases following rapid quenching associated with the process.%激光表面熔凝技术是镁合金表面改性方法之一.为了进一步提高镁合金的表面性能,提出了液氮辅助冷却与激光熔凝相结合的方法,通过改变镁合金基体温度,加快改性层的凝固速度来改善镁合金的表面性能.结果表明,与室温氩气保护条件下相比,液氮辅助冷却条件下,镁合金表面形成一层较薄的改性层,晶粒显著细化,并在其上表层形成了大量"蠕虫状"的纳米晶,局部还出现少量的非晶组织,其显微硬度为 HV 90~148,比在室温氩气保护条件下(硬度为 HV 60~105)提高了约40%.在3.5%NaCl溶液中进行电化学测试,结果表明,液氮辅助冷却条件下改性层的耐蚀性显著提高, 其原因主要是由于快速凝固过程中晶粒细化、第二相 β-Mg17Al12的再分配及局部非晶组织综合因素的结果.
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