Fracture behaviour of an Al–Mg–Si industrial alloy

The tensile fracture behaviour of an Al–0.89 wt.% Mg2Si industrial alloy is studied. It is found that the alloy deforms in a highly localised way only in the underaged (UA) state. In the peak aged (PA) condition the hardening precipitates are often by-passed by an Orowan mechanism, which predominates in the overaged (OA) state. In the UA condition, the stress concentration is shown to be large enough to nucleate cracks at the particle interfaces provided the shear strain has reached the critical value for cutting the precipitates into pieces. In the PA and OA conditions, failure results from coalescence of voids nucleated at large AlFeSi and smaller (Mg+Si) particles. It is shown that none of these particles are responsible alone for fracture. In contrast, ductility and rupture surfaces are consistent with a damage mechanism whose nucleation step is the coalescence of voids nucleated at large AlFeSi and neighbouring (Mg+Si) particles.