The shear fracture mechanism in a rapidly-solidified aluminium alloy was investigated using both smooth and circumferentially-notched bars under uniaxial tension in a temperature range of 193-423 K and a strain rate range of 10(-5)-1 s(-1) for the alloy under as-extruded and precipitation-hardened states. An analytical procedure was performed to make corrections on the hydrostatic stresses in the necked region of a smooth specimen. A complete shear fracture occurs only for the as-extruded alloy in plain tension at intermediate temperatures and relatively low strain rates. The interfacial delamination is associated with both the gross shear fracture in plain tension and the local shearing in notch tension. Based on expert mental observations combined with analytical results, a constraint-releasing mechanism is proposed which fairly accounts for the conditions under which the present shear fracture is evident.