超声冲击处理冷轧钢板缝焊接头的疲劳性能

用窄搭接电阻缝焊机对汽车用SPCC（冷轧低碳普通钢板）进行焊接，采用超声冲击仪对缝焊接头进行处理；通过拉压疲劳试验、X射线应力分析仪、OM、SEM对处理和未处理的缝焊接头疲劳性能和组织进行测试和观察分析对比.结果表明，未经超声冲击处理的缝焊接头经5×104次交变载荷作用即在焊趾区萌生裂纹，裂纹与载荷方向呈45°；经超声冲击处理过的缝焊接头经1.88×106次交变载荷作用未发生断裂；超声冲击处理使缝焊接头表层晶粒细化并形成塑性变形层，降低了其表面的微裂纹缺陷造成的应力集中，使表面残余拉应力变为了压应力，有利于改善缝焊接头的疲劳性能.

Fatigue performance improvement of SPCC steel resistance seam welding by ultrasonic impact treatment

SPCC(steel plate cold common)of cars was welded by Narrow lap resistance seam welder. By using ultrasonic impact treatment technology, the joint of resistance seam welding was treated with the ultrasonic impact. The organization and mechanical properties of treated and untreated seam welded joint were tested and analyzed through tension and compression fatigue test, X-ray diffraction stress measuring instrument, metallographic test and scanning electron microscopy. The results showed that the joint of resistance seam welding, without ultrasonic impact treatment, had big changes in the frequency and cracks under cyclic loading of 5×10⁴ times. The cracks occurred in the weld toe area, and the load direction was a 45-degree angle. The joint of resistance seam welding, with ultrasonic impact treatment, had no changes in the frequency and cracks under cyclic loading of 1.88×10⁶ times. The joint of resistance seam welding of ultrasonic impact treatment was refined in the surface grain and formed the plastic deformation layer, reducing the stress concentration caused by weld defects, such as micro crack of the seam welded joint and the surface of weld toe area. And it is which could improve significantly the fatigue performance of steel plate welded joint.