二次焊接对Q&P980点焊接头性能的影响

Effect of Secondary Welding on Performance of Q&P980 Spot Welding Joint

研究了二次焊接对Q&P980钢点焊接头微观组织和力学性能的影响。研究发现,一次焊接后进行6 kA电流的二次焊接,可以使Q&P980钢一次焊接组织重熔,形成二次焊核、细化焊核马氏体组织、减少组织中的缩孔缺陷,二次焊核的硬度明显高于一次焊核的,所得到的二次焊接接头的剪切载荷、剥离载荷和吸能性能也有明显提升。但5 kA二次电流焊接仅能使一次焊核马氏体组织发生回火,使接头的硬度、强度和吸能性能反而低于一次焊接接头的。而7k A二次电流焊接易于产生过热,使二次焊接组织中重新出现缩孔,尽管其硬度、强度和吸能性能高于一次焊接接头,但较6 kA二次焊接接头有所下降。因此,要改善Q&P980钢的点焊接头强度,关键在于采用适当的二次焊接电流。

The influence of secondary welding on the microstructure and mechanical properties of Q&P980 steel spot welding joints was investigated. It is found that the 6 kA secondary current welding after primary spot welding remelts the primary welding microstructure of Q&P980 steel, restructures the secondary welding core, refines the martensite structure and decreases the shrinkage cavities in the secondary weld core. Hence, the hardness of secondary welding core, shear load, peel load and energy absorption performance of spot welding joints are obviously improved compared with those of primary spot welding joint. However, 5 kA secondary current welding only tempers the martensite structure of primary welding core, so that the hardness, strength and energy absorption performance of the welding joints are lower than those of primary spot welding joint. Meanwhile, the 7 kA secondary current welding is easy to produce overheating, which causes the shrinkage hole reappeared in the secondary welding microstructure. Although its hardness, strength and energy absorption performance are higher than those of the primary welding joint, it is lower than that of the 6 kA secondary welding joint. Therefore, in order to improve the mechanical properties of Q&P980 steel spot welding joints, the key is to adopt proper secondary welding current.