Failure Analysis of Friction Weld (FRW) in Truck Axle Application

Abstract

A section of a fractured spindle from an axle housing was metallurgically examined. The axle fractured at the friction weld (FRW) interface and was from a truck with only about 8,000 miles of service. SEM and metallographic examinations of the weld fracture revealed that a ferritic band existed at the weld interface. A significant amount of oxides and some micro-porosity was observed in the ferrite. The existence of this type of microstructure compromised the strength of the weld and resulted in the overload fracture of the axle. FRW is supposed to be a solid-state process; however, melting-solidification was evident in this case, as suggested by the band of oxides caused by liquid phase oxidation of the molten layer at the interface and micro-shrinkage porosity formed during solidification of the liquid film. Process conditions that resulted in high heat input and liquidizing of the weld interface before the upsetting stage of the friction welding process should be mitigated.