Failure Analysis of Friction Weld in Rear Axle Casing

In this study, Housing and Spindle failed at Friction weld (FRW) interface and sample submitted was from a Passenger vehicle after covering 18410 Kms was considered to address the repeated weld failures reported in Rear Axle Casing. The Metallurgical examinations revealed, chemical composition and hardness found satisfactory whereas Microstructure reveals MnS (Manganese sulfide) Inclusions at the friction weld interface resulting in insufficient friction weld fusion. SEM and Metallographic examinations confirmed the orientation of MnS (Manganese sulfide) along the surface of the Spindle that was subjected to friction welding (FRW), resulting in insufficient weld fusion. Microstructure observation of Spindle shows inclusions of Type A - Thick 2 against the allowable limits in Raw Material Type A - Thick 1. Also, elongated MnS inclusions at the Friction weld (FRW) interface act as initiation sites, "Stress raiser "that is more vulnerable to failure due to comparatively less tensile and impact strength than base metal similar to the effect of flake graphite’s in cast iron. Due to the anisotropy and orientation of the sulfide inclusions, there is a reduction in transverse ductility in reduced area and not much significant effect in the longitudinal direction. Inclusion control by calcium treatment [1] [3] or Electro slag re-melting in spindle raw material will significantly improve the ductility and toughness of friction weldments. This study aims at the effect of sulfide inclusions on weldability, mechanical properties of the weld Interface and role of the fracture initiation site.