铝合金CMT焊对接接头组织与性能的研究

Study on Microstructure and Properties of CMT Welded Butt Joints of Aluminum Alloy

应用冷金属过渡焊(CMT)对2. 5 mm厚的6082铝合金薄板进行对接拼焊,对比了热输入不同的两种焊接接头1号与2号试样的组织与性能。显微组织观察表明,从焊缝中心到熔合线附近的组织依次为等轴树枝晶、柱状树枝晶及柱状晶。显微硬度结果显示,从母材至焊缝中心,分别在热影响区的过时效区和焊缝中心存在两处"软化"效应。在拉伸试验中,热输入更低的1号试样的断后伸长率优于2号试样。1号试样拉伸断裂在热影响区的过时效区,主要由于焊接热循环导致了热影响区内强化相的粗化所致; 2号试样的断口则在熔合线附近,主要由于热输入较大导致的焊缝余高较高,残余应力较大,易产生应力集中,导致断后伸长率较低。

The butt joints of 2.5 mm-thick 6082 aluminum alloy sheet were welded by the cold metal transfer(CMT)method.Microstructure and mechanical properties of the two kinds of samples with different heat inputs(sample No.1 and No.2)were compared.The metallographic observation showed that from the weld center to the fusion line,the grain shape changed from equiaxed dendrites to columnar dendrites and then to columnar crystals.The micro-hardness results showed that there are two softening effect zones from the base metal to weld center.One is over ageing zone in the heat affected zone(HAZ),and the other is in the weld center.Tensile test results revealed that the elongation of the sample No.1 with lower heat input was better than that of sample No.2.The tensile fracture position of sample No.1 was in the over ageing zone of HAZ mainly due to coarsening of strengthening phase in the HAZ,while the tensile fracture position of the sample No.2 was near the fusion line,mainly because the surplus height of seam of sample No.2 was higher due to the larger heat input,and resulting in the smaller elongation with higher residual stress.