汽车后驱动桥由多个零件焊接而成,在行驶约790 000 km时该零件发生断裂。通过宏观分析、显微组织分析、化学成分分析以及断口形貌分析后认为,该零件断裂性质为疲劳断裂,主要原因为被焊接的两个零件尺寸差异较大,局部形成应力集中,再加上焊接热影响区存在焊接应力和魏氏体组织,并在汽车行进中不断受到颠簸和震动造成该区域产生裂纹源,进而在运行一定时间后发生疲劳断裂。

The automotive rear axle welded by several parts was fractured after 790 000 km running. Macro-examination,microstructure examination,chemical composition analysis,and fracture analysis were carried out on the failure rear axle and the results showed that failure of the rear axle is fatigue fracture. Because of local stress concentration caused by the size difference of the two welded parts,welding stress of the heat-affected zone and the weakness of the Widmanstaten structure,cracking source were produced at the heat-affected zone,which led to the final fatigue fracture of the rear axle when the automobile bumped and shake.