某变速箱悬置支臂在整车路试中，因过坑时受到冲击载荷而发生断裂。采用宏观分析、断口分析、金相检验、化学成分分析、硬度测试及同批次零件的检查等方法，对变速箱悬置支臂的断裂原因进行了分析。结果表明：该变速箱悬置支臂的断裂是因为其内部存在热态裂纹。热态裂纹的产生与模具温度的上升、芯模背面未喷脱模剂以及脱模时铸件冷却不充分有关。

When the test car passed a pit during the road test, a transmission mounting arm was fractured due to the impact load. The fracture causes of the transmission mounting arm were analyzed by means of macro analysis, fracture analysis, metallographic examination, chemical composition analysis, hardness test and inspection of the same batch of parts. The results show that the fracture of the transmission mounting arm was due to the existence of hot cracks inside the arm. The hot cracks were related to the increase of mold temperature, the absence of mold release agent on the back of core mold and the insufficient cooling of casting during demoulding.