AZ31B镁合金/镀锌钢板电阻点焊接头熔核化合物分析

Analysis of Compounds in Joint Core by Resistance Spot of AZ31B Magnesium Alloy and SPHC Galvanized Steel

镁合金具有质量轻、拉伸强度高和减振能力强的优点,钢一直在制造业中占主导地位。镁钢异种材料的连接,可以实现汽车构件的轻量化设计,对节能减排有着重要的积极意义。采用KDWJ-17型三相次级整流电阻焊机对2.0 mm厚的AZ31B镁合金和1.0 mm厚的SPHC镀锌钢板进行电阻点焊焊接试验,利用QUANTA200型扫描电子显微镜(SEM)分析接头各区域的组织结构和成分分布,并对接头化合物做热力学分析,研究AZ31B镁合金和SPHC镀锌钢点焊接头中心界面化合物的形成机制。研究结果表明:接头处Fe_2Al_5化合物是形成高强度镁合金与镀锌钢板电阻点焊接头的主要原因;结合Fe-Al二元相图和热力学分析计算,在镁合金和镀锌钢板电阻点焊接头中,Fe_2Al_5在可直接生成的Fe-Al系化合物中为接头相结构的最有利生成相;Fe_2Al_5的结构单元总成键能力在Fe-Al系化合物中其化合物保持自身结构稳定性的能力最强。

Magnesium alloy has the advantages of light weight, high tensile strength and strong damping ability. Steel has the domi- nant position in the manufacturing industry. The connecting of magnesium and steel has positive significance in lightweight design of automotive components and energy conservation. 2.0 mm thick of AZ31B and 1.0 mm thick of SPHC were welded by KDWJ-17 three- phase secondary rectification resistance welding machine for welding test. Scanning electron microscopy （SEM） was used to analyze or- ganizational structure and distribution of composition of the joints, and the thermodynamics of compounds were analyzed to research the mechanism of formation of the compounds. The results showed that Fe2A15 compound at the interface was the main reason to form a high-strength welding joints of magnesium alloy and galvanized steel by resistance spot. Combined with binary phase diagram and calcu- lation of thermodynamic of Fe-A1, Fe2 Als was the most favorable phase to generate in the compounds of Fe-A1 in resistance spot welding joint of magnesium alloy and galvanized steel. Fe2 A15 had the strongest ability to maintain its structural stability in compounds of Fe-A1.