Fretting wear in self-piercing riveted aluminium alloy sheet

Fretting wear in aluminium alloy AA5754 joined by self-pierce riveting (SPR), a relatively new fastening technique increasingly used in vehicle structures, has been investigated in this paper. Surface damages have been induced when a joint experienced a sinusoidal cyclic tension-tension load. Various degradation zones have been characterised in the contact surfaces between the aluminium sheets, as well as the rivet and the locked sheet. Subsequent examination of the fretting scars at the contact surfaces and through the cross-section has been carried out using optical and scanning electron microscopies. The fretting patterns in the self-piercing riveted joints have been identified. It was noted that fretting wear was initially patchy and layers of compacted debris were created as fretting continued. An Energy Dispersive X-ray (EDX) analysis of the fretting debris from the interface between the rivet and the aluminium sheet revealed the presence of Al, Fe, Si, C and O so that it is suggested that intimate mixing of debris from the aluminium alloy and the steel rivet had occurred. The effects of testing conditions such as the load magnitude and the number of loading cycles on the fretting wear patterns were also studied. Metallographic examination has shown that these fretting zones are critical with respect to fretting crack nucleation. The test results have shown that joint fracture initiates at these critical zones.