高速列车车厢用的铝合金板焊接接头的组织与性能

利用光学显微镜和透射电子显微镜研究了国产7020铝合金熔化极惰性气体保护焊(MIG)接头的微观组织结构,并对接头的力学性能进行研究.结果表明,接头的硬度以焊缝中心线为轴呈对称分布,且焊缝中心为接头的最薄弱环节;焊缝区为典型的树枝状晶的铸造组织.在熔合区,焊缝一侧为沿散热方向排列的柱状晶,另一侧为细小的等轴晶组织.热影响区内,仍可见纤维状加工痕迹,部分析出相固溶到基体中;强化相的粗化,是热影响区内出现软化区的主要原因.国产7020铝合金焊接接头强度达到欧洲标准.

Microstructure and Properties of Welded Joints on Al-Alloy Sheets for High-Speed Train Carriges

The microstructure and mechanical properties of the joints welding domestic 7020 Al-alloy sheets together by use of metal inert gas(MIG) were investigated.It was found that the hardness distribution is symmetrical to the center line of welded joint,where is just the weakest zone of the whole joint to which the weld zone presents a typical dendritic casting structure.In the fusion zone,the columnar grains range in the direction of heat dissipation on one side of the joint and fine equiaxed grains on the other side.Fibrous processing marks remain in the heat-affected zone(HAZ) with part of precipitated solid phase solved into the base metal.Precipitate microstructure shows that the growth of precipitates is the main reason to soften the HAZ.The results showed that the tensile strength of the joints welding the 7020 Al-alloy sheets together exceeds the standard DIN EN288-4.