极端冷却条件下AZ31B镁合金激光熔凝层的组织与性能

Microstructure and Properties of Laser Melted Layer of AZ31B Magnesium Alloy at Extreme Cooling Condition

采用固体脉冲Nd：YAG激光器,对AZ31B镁合金进行了液氮极端冷却条件下的表面熔凝试验,并与在空气中冷却的熔凝层和原始镁合金进行了对比。结果表明,液氮冷却熔凝层的晶粒比空气冷却熔凝层晶粒更加细小。液氮冷却熔凝层的显微硬度达到70~77 HV0.05,明显高于原始镁合金的显微硬度（约55 HV0.05）,且高于空气冷却熔凝层的60~67 HV0.05。磨损试验表明,液氮冷却熔凝层的磨损量为1×10-3g,小于空气冷却熔凝层的2×10-3g,说明液氮冷却条件更有利于镁合金表面耐磨性能的提高。在质量分数为3.5%的NaCl溶液中的电化学极化曲线测试结果表明,液氮冷却熔凝层和空气冷却熔凝层的腐蚀电位较原始镁合金分别降低了22 mV和29 mV,阳极腐蚀电流密度分别提高了1倍和2倍,说明激光熔凝使镁合金的耐腐蚀性能有所降低。

Surface of AZ31B magnesium alloy is melted using a pulsed Nd…YAG laser in liquid nitrogen.Then the laser melted layer cooled in liquid nitrogen is compared with that cooled in air and the substrate.The results show that the grain size of the laser melted layer cooled in liquid nitrogen is smaller than that cooled in air.The laser melted layer cooled in liquid nitrogen has higher micro-hardness（70~77 HV0.05） than that cooled in air（60~67 HV0.05） compared with the as-received magnesium alloy（about 55 HV0.05）.The wear mass loss of the laser melted layer cooled in liquid nitrogen（1×10-3 g） is less than that cooled in air（2×10-3 g）.The results indicate that liquid nitrogen is better for the enhancement of wear resistance of the laser melted layer.The experimental results show that the corrosion potential of the laser melted layer cooled in liquid nitrogen and cooled in air decrease by 22 mV and 29 mV than those of the as-received magnesium alloy respectively.This indicates that corrosion resistance of AZ31B magnesium alloys becomes worse by laser surface melting.