W/Cu複合型電極によるめっき鋼板のスポット溶接における電極寿命改善機構

摘要

Znめっき鋼板は優れた耐食性を有すことから，住宅 分野をはじめ自動車や家電など様々な分野で使用されて いる。中でも近年開発された溶融Zn-6%Al-3%Mg合金 めっき鋼板（以下，ZAM鋼板と記す）は他のZn系めっ き鋼板よりも優れた耐食性を有しており，加工後に 電気Znめっき，カチオン電着塗装，浸潰めっきなどの 防食を行う使用形態からめっき鋼板を加工したまま使用 する形態への転換が可能な防食材料として，使用が増加 している。%To improve the electrode life in spot welding of hot-dip Zn-6%Al-3%Mg alloy coated steel sheet, the W/Cu hybrid electrode was developed. Electrode life improvement effect and its mechanism was investigated. The results are as follows. (1) W/Cu hybrid electrode can be used for conventional spot welders under common welding conditions. Plating elements of steel sheets does not alloy with W at the electrode tip, the enlargement of electrode tip diameter is suppressed. Accordingly the electrode life is remarkably improved in comparison with the case of l%Cr-Cu electrode. (2) Cracking in the W portion is caused by the thermal and mechanical shock derived from welding, but does not have influence on the welding qualities even after regrinding of electrode tip. (3) In case that plating layer contains reactive metal element to W, electrode life is affected by the reactivity of the element to W. (4) W/Cu hybrid electrode effectively support the formation of nugget by low-heat removal effect due to the low thermal conductivity and heating effect due to high electrode resistance of W.