A rationalization of factors affecting strength, ductility and toughness of AA6061-type Al–Mg–Si–(Cu) alloys

The tensile properties and toughness of AA6061-type alloys (nominally Al–1.0% Mg–0.6% Si–0.3% Cu–0.2% Cr) were characterized in terms of the alloy system’s solubility relationships at the solutionizing temperature. The best combination of strength and ductility is achieved in materials with high soluble Mg2Si and excess silicon concentrations. Enhanced ductility at a given strength level is associated with high work hardening rates (n values), whereas toughness is related to intergranular (IG) fracture tendencies. Toughness is therefore negatively impacted by compositional and processing factors that promote IG precipitation: excess silicon, low solutionizing temperatures, slack quench rates and low dispersoid (Cr/Mn) levels.