Relations between microstructure, precipitation, age-formability and damage tolerance of Al–Cu–Mg–Li (Mn, Zr, Sc) alloys for age forming

Age forming of Al based alloys for damage tolerant applications requires an alloy with good age formability and good post-forming mechanical properties. To investigate optimisation of this balance, several newly designed Al–Cu–Mg–Li (Mn, Zr, Sc) alloys were subjected to artificial ageing representative of age forming. It was seen that combinations of yield strength and fatigue crack growth resistance could be achieved that are at least comparable to the incumbent damage tolerant material for such applications, whilst creep rates at the ageing temperatures applied were better than those achieved in commercially applied age forming processes of heat treatable Al based alloys. Coarse grain structure and high Li content are associated with good fatigue crack growth resistance but reduce age formability. The underlying physical aspects responsible for the balance between creep rates and resulting properties are discussed. The metallurgical and micromechanical mechanisms analysed and discussed provide a framework for optimisation of composition and forming conditions for age forming of damage tolerant parts.