7N01铝合金脉冲MIG焊与直流CMT焊多次补焊试验

高速列车用7N01铝合金有较大热裂纹倾向,而补焊时该问题更突出.分别采用脉冲MIG焊和低热输入直流CMT焊对4 mm厚7N01铝合金对接接头进行1次、2次、3次补焊,分析了补焊焊接接头的宏观成形、微观组织和硬度.结果表明,脉冲MIG补焊时下塌量和熔宽均大于直流CMT补焊,脉冲MIG补焊焊道与先焊焊缝微观组织界面明显,先焊焊缝晶粒粗大且晶界发生重熔,熔合区变宽,而直流CMT补焊焊道界面不明显,焊缝微观组织晶粒细小,熔合区无明显变化;脉冲MIG焊3次补焊后软化现象较直流CMT补焊严重.采用直流CMT焊进行7N01铝合金补焊,可有效降低热裂纹倾向并缓解接头性能下降.

Multiple repair welding of 7N01 aluminum alloy with pulsed MIG and DC CMT welding

The 7N01 aluminum alloy for high speed trains is sensitive to hot crack and it is more serious during multiple repair welding. Pulsed MIG and DC CMT welding with low heat input were conducted to repair welding 4 mm thick 7N01 aluminum alloy butt joints for one time, two times and three times. The macroscopic forming, microstructure and microhardness were analyzed for the repaired weld. The experimental results show that the sinking and width of the repaired weld by pulsed MIG welding were larger than those by DC CMT welding. When the joints were repaired by pulsed MIG welding, the interface between the repaired weld and the pre-weld section was distinct, the grains in the pre-weld section grew coarse, and the fusion zone was enlarged. While the microstructure of the joints repaired by DC CMT welding showed that no such obvious interface existed, the grains in the pre-weld section remained fine and the fusion zone didn''t change significantly. The softening shown in the microhardness curves by DC CMT welding was weaker than that by pulsed MIG welding. The results show that using DC CMT welding to repair 7N01 aluminum alloy can effectively reduce the hot cracking sensitivity and alleviate the degradation of the joint performance.