Effects of aging treatments on low-cycle fatigue behavior of extruded AZ80 for automobile wheel disks

Abstract

The effect of precipitates on the strain-controlled fatigue of automobile wheel disks made of extruded AZ80 magnesium alloy was investigated via T5 and T6 peak aging. The age-hardening behavior, stress–strain response, fatigue fracture morphology, and fatigue crack path of the AZ80 wheel disks were characterized to determine their monotonic and cyclic deformation behaviors. The T5 and T6 peak-aging treatments significantly enhanced their hardness and monotonic strengths via precipitation hardening; as the precipitate amount increased, the twinning–detwinning behavior in the initial stage of cyclic deformation weakened accompany the strain hardening in the half-life cycle. According to the crack growth analysis, the propagation pattern was related to the coalescence of voids in the cyclic plastic zone. Compared with the extruded and T6-peak-aged counterparts, the highly dense lamellar phases in the T5 peak-aged sample suppressed the cyclic plastic deformation at the crack tip, deflecting the cracks and resulting in longer fatigue life at certain strain amplitudes. Thus, the T5 peak-aged sample exhibited excellent fatigue life at intermediate strain amplitudes (0.3%–0.8%).