稀土镁合金铸件表面微观缺陷形成机理及修复技术

Formation Mechanism and Repair Technology of Surface Micro-defects of Rare Earth Magnesium Alloy Castings

VW63Z稀土镁合金铸件表面微观缺陷经过荧光检测的结果表现为“条状荧光”现象,当该缺陷出现在铸件非加工面时,由于无法经过机械加工去除将直接导致铸件报废。本文探究了铸件表面缺陷的微观组织及其形成机理,结果表明微观缺陷主要成分为稀土氧化物的双层氧化膜,其中部分存在夹杂物;金属液汇流导致表面微观缺陷更易形成。应用激光熔凝技术对铸件表面微观缺陷进行处理,当平顶激光束输出功率为800 W时,重熔层组织呈树枝晶形貌特征,晶粒细小并与基体结合良好,重熔层深度约为915μm,控制铸件热影响范围的同时基本可以修复铸件表面缺陷,原缺陷位置荧光检测未见条纹状缺陷。

The micro-defects on the surface of VW63Z rare earth magnesium alloy castings were shown as"stripe fluorescence"as a result of fluorescence detection.The micro-defects which cannot be removed by mechanical processing would directly scrap the castings if it appeared on the non-machined surface of the casting.The microstructure of the surface defects of castings and their formation mechanism were investigated in this paper.Results showed that the main component of the micro defects was the double-layer oxide film of rare earth oxide,some of which contained inclusions;the confluence of the molten metal made the surface micro defects to form more easily.The laser melting technology was used to treat the surface micro-defects of the casting.When the output power of the flat-top laser beam was 800 W,the microstructure of the melted layer presented the dendrite characteristic,had finer grains and good combination with the matrix.The depth of the remelted layer was about 915μm,which could basically repair the surface defects of the casting while controlling the heat-affected range of the casting.The fluorescence detection of the original defect position showed no streak defects.