AZ91D镁合金电火花堆焊组织及腐蚀性能

Research on microstructure and corrosion resistance of electro-spark overlaying of AZ91D magnesium alloy

采用与母材同质的电极材料,在AZ91D镁合金母材上进行电火花堆焊,研究了焊缝的组织、界面特征及腐蚀性能.结果表明,通过优化的工艺参数可以获得组织均匀、致密的电火花堆焊焊缝.焊缝组织晶粒尺寸在1~5μm之间,由过饱和的α-Mg相、Mg17Al12相以及亚稳态Al Mg相所组成;焊缝与母材之间为冶金结合,形成超薄层熔化互扩散结晶型结合界面,母材一侧没有形成明显热影响区,焊缝保持电极原有的成分;焊缝耐蚀性能优于母材,细化的晶粒组织提高腐蚀的均匀性,过饱和的α-Mg相和晶界上网状连续分布的β相降低腐蚀速率,是其耐蚀性能提高的主要因素.

The overlaying welding was produced on the surface of AZ91 D magnesium alloy by electro-spark welding( ESW) technique using an electrode which is as same as the base metal. The microstructure,bonding interface and corrosion resistance of the layer were investigated. The results showed that the ESW process can produce a uniform and dense weld with proper process parameters. The weld microstructure consisted of supersaturated α-Mg solid solution with size of 1-5 μm,Mg17Al12 phase and metastable AlM g phase. The weld was metallurgically bonded to the base metal and a thin layer formed by interdiffusion,crystallization was formed at the interface between the weld and base metal. There is no obvious heat affected zone on the side of the base metal and original composition of the electrode material was retained in the weld. The corrosion resistance of weld was better than the base metal. The grain refinement of the weld can improve the uniformity of the corrosion,meanwhile,the supersaturated α-Mg solid solution and β phase that was continuously distributed at the grain boundaries with the a netlike morphology can decrease the corrosion rate,which are the main factors leading to a high corrosion resistance of the weld.