Fracture Failure Analysis of Rear Axle Suspension Control Arm in Automobile

Fracture failure occurred in the control arm of the rear axle suspension of a certain vehicle model. To determine the root cause of the failure, comprehensive analyses were conducted, including macroscopic fracture examination, microscopic fracture analysis, microstructural characterization, and hardness testing. The results indicate that the failure was caused by the combined effects of material defects, improper manufacturing processes, and service loading conditions. The fundamental cause of the fracture lies in the initiation of microcracks at the interface between coarse Al-Fe-Si-Mn inclusions and the matrix under cyclic loading. The presence of a strength gradient induced by local segregation of Si further accelerated crack propagation along the inclusion/matrix interface. Under cyclic stress, the cracks propagated progressively through a fatigue striation mechanism and exhibited intergranular fracture in the precipitation-enriched zones along grain boundaries. Ultimately, these factors led to premature fatigue failure of the control arm.