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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%Na Cl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。
Laser surface melting technology is one of the surface modification methods of magnesium alloy. In order to further improve the surface properties of magnesium alloy, a method combining liquid nitrogen assisted cooling and laser melting was proposed. The surface properties of magnesium alloy were improved by changing the temperature of magnesium alloy substrate and accelerating the solidification rate of modified layer. The results show that under the condition of argon protection at room temperature, a thin layer of modified layer is formed on the surface of magnesium alloy under the condition of liquid nitrogen aided cooling, the grains are remarkably refined and a large number of “worms” Like nanocrystals. A small amount of amorphous structure is also found locally, with a microhardness of HV 90-148, which is about 40% higher than that under room temperature argon protection (HV 60-105). The results of electrochemical tests show that the corrosion resistance of the modified layer is significantly improved under the condition of liquid nitrogen aided cooling, which is mainly due to the grain refinement in the rapid solidification process, Redistribution of Mg17Al12 and the result of local amorphous structure.