低碳钢与紫铜搅拌摩擦焊接头显微组织分析

用搅拌摩擦焊焊接了4 mm厚的Q235低碳钢板和T2紫铜板,得到了内部无缺陷、外观成形良好、无变形的对接接头.研究表明,低碳钢紫铜接头的显微组织与其所受到的热和力作用大小有关.在接头钢侧,轴肩挤压区有较大的变形,组织发生动态再结晶后形成了细小的等轴晶铁素体;在探针附近的热影响区,经历的应变较小,组织则由变形的先共析铁素体和侧板条铁素体组成.在接头铜侧热影响区的晶粒受热长大,而热力影响区的铜由于发生了动态再结晶,晶粒细小.在焊核区,上部主要由钢、铜薄层交叠组成;焊核中下部为钢、铜及钢与铜形成的化合物交叠组成的漩涡状条带,其中铜条带的组织为细小的等轴晶,钢条带的组织为细小的等轴晶或先共析铁素体 侧板条铁素体组织.

Microstructural investigation on friction stir welds of dissimilar metals between mild steel and copper

The joining of dissimilar metals,T2 copper and Q235 mild steel plates with 4 mm thickness,was carried out using friction stir welding(FSW) technique.A defect-free weld with good surface appearance has been obtained.The results indicated that the resultant microstructure of the weld is associated with the thermo-mechanical effects during the FSW.In the near-shoulder zone at the steel side,the microstructure of the steel presents fine equiaxed ferrite grains which attributed to dynamic recrystallization due to the large strain and higher temperature,but in the heat-affected zone(HAZ) adjacent to the pin,the microstructure of the steel is composed of pre-eutectic ferrite(PF) and ferrite side plate(FSP),which is same as the original microstructure before welding because of the lower strain and temperature within this region.At the copper side,the grains in the HAZ present coarser due to the welding heat,but in the thermomechanical affected zone the grains become quite small due to the dynamic recrystallization induced by the welding heat and the strain.In the stir zone,the microstructure presents lamella composed of copper and steel plates alternately on the upper part,and vortex-like feature composed of copper,steel and the intermetallics from them alternately on the lower part,in which copper plates present fine equiaxed grains,and the steel plates present fine equiaxed grains or PF FSP intercalation microstructures.