冷喷涂改善2219铝合金熔焊接头残余应力新方法

目的采用冷喷涂技术改善2219铝合金变极性钨极氩弧焊(VPTIG)焊接接头残余应力。方法采用冷喷涂技术在8 mm厚2219铝合金VPTIG焊接接头表面进行Cu涂层制备,分析冷喷涂前后接头微观组织、力学性能及残余应力的变化,探究冷喷涂过程中高速碰撞颗粒的"喷丸效应"与加热气体的"热效应"对接头残余应力的改善作用及内在机制。结果冷喷涂前后,接头整体的微观组织无明显变化,但在焊缝表面(Cu涂层与焊缝结合面处)观察到明显的塑性变形。冷喷涂后,焊缝区上表面显微硬度提高,作用深度约2 mm(余高处);接头抗拉强度表观上稍有降低,这是由于涂层对焊缝的拉伸应变局部化改变所致,"喷丸效应"与"热效应"单独作用下,接头抗拉强度无明显变化,所有拉伸试样均从焊趾处沿着熔合区发生断裂。焊态接头残余应力分布总体呈拉应力状态,在焊缝处最大,经过冷喷涂后,焊缝残余拉应力峰值从约200MPa降到约24MPa,大部分区域从拉应力变为压应力,且分布均匀性变好。结论冷喷涂技术可以显著改善VPTIG焊接接头残余应力分布。冷喷涂粒子的"喷丸效应"对基体残余应力的改善作用显著。高温气流的"热效应"虽未能显著降低残余应力,但使应力分布变得均匀。

New Method to Modify the Residual Stress in Variable Polarity TIG Welded 2219 Aluminum Alloy Joints by Cold Spraying

The work aims to modify the residual stress of VPTIG welded 2219 aluminum alloy joints by cold spraying. Cu coating was prepared on the 8 mm thick VPTIG welded 2219 aluminum alloy joint surface by cold spraying (CS) technology. The microstructure, mechanical property and residual stress changes of joints before and after CS were analyzed. The modification effect on the residual stress of joints and its mechanism caused by "shot peening effect" of high-speed colliding particles and "heating effect" of hot gas in CS were explored. There was no significant change in the microstructure of the joint before and after CS. However, the obvious plastic deformation was observed on the joint surface (i. e. the interface between Cu coating and joint fusion zone). After spraying, the microhardness of near-top surface of the weld zone was increased, and the influence depth was about 2 mm (at the weld toe). The tensile strength of the coated joint was slightly reduced, which was caused by the localized change of tensile strain of the joint under the constraint of Cu coating. However, there was no significant change of joint tensile strength after "shot peening effect" or "heating effect" treatment. All specimens fractured along the fusion zone initiating at the weld toe. The distribution of residual stress in welded joints was generally tensile stress, with the maximum at the weld joint. After cold spraying, the residual peak stress of the joint was decreased from about 200 MPa to about 24 MPa, and the stress in most regions of the joint changed from tensile stress to compressive stress, and was distributed more uniformly. Therefore, CS can improve the residual stress of VPTIG welded 2219 joints significantly. The "shot peening effect" of particles can remarkably improve the residual stress of the joint. Although the "heating effect" of high-temperature gas flow cannot significantly reduce the residual stress, the residual stress distribution becomes more uniform.