超声冲击改进地铁车辆焊接裂纹修复质量的探究

Research on Improving Repair Quality of Welding Crack of Metro Vehicle by Ultrasonic Impact

目的针对地铁车辆车体、转向架构架疲劳裂纹频发的问题,探索超声冲击工艺增强焊接结构件疲劳强度的机理和可行性。方法分别利用机械打磨和不同工艺参数的超声冲击处理SMA490BW钢焊接对接接头,借助应力分析仪、金相显微镜、超声疲劳机、扫描电镜等,综合分析试样的应力分布、接头形貌、晶粒组织、疲劳寿命以及断口形貌,以对比不同处理方式的强化效果。结果超声冲击处理可有效改善对接接头的应力集中,细化表层晶粒,并调整表面应力场的分布,将焊接残余拉应力转为较大的残余压应力。在工艺参数1.5 A/10 min的冲击下,试样可获得最高平均寿命3.35×10^(7)周次,是机械打磨试样的3.8倍,是原始试样的10倍,且疲劳断裂失效模式不变。结论超声冲击通过表面改性,显著提高焊接结构的疲劳寿命,且优于机械打磨方法。超声冲击法高度契合车辆裂纹修复的需求,但相关标准、设备、工艺不够完善,建议对超声冲击方法进一步探索,并最终将其纳入地铁车辆裂纹修复工艺。

In order to solve the problem of fatigue crack of metro vehicle body and bogie frame,the mechanism and feasibility of ultrasonic impact technology to enhance the fatigue strength of welded structure were explored.In order to obtain the strengthening effect of different treatment methods,the welded butt joints of SMA490BW steel were treated by mechanical grinding and ultrasonic impact with different process parameters.The stress distribution,joint morphology,grain structure,fracture morphology and fatigue life of the specimens were analyzed by means of stress analyzer,metallographic microscope,ultrasonic fatigue machine and scanning electron microscope.The results show that ultrasonic impact can effectively improve the stress concentration of butt joint,refine the surface grain and adjust the distribution of surface stress field,and transform the welding residual tensile stress into larger residual compressive stress.Under the impact of 1.5 A/10 min process parameters,the maximum average life of the sample is 3.35×10^(7) cycles,which is 3.8 times of the mechanical grinding sample and 10 times of the original sample,and the fatigue fracture failure mode remains unchanged.The results show that ultrasonic peening can significantly improve the fatigue life of welded structure by surface modification,and it is better than mechanical grinding method.The ultrasonic impact method is highly suitable for the needs of vehicle crack repair,but the relevant standards,equipment and technology are not perfect.It is suggested that the ultrasonic impact method be further explored and finally incorporated into the subway vehicle crack repair process.