Evolution of microstructure and strain field by precipitation during early ageing of Al–Si–Mg–Cu alloy

ABSTRACT The evolution of microstructure and the variation of strain field induced by precipitation in Al–Si–Mg–Cu alloy with high copper content during early ageing is characterised by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and geometric phase analysis (GPA) calculations. The basic building blocks for GP zones and step-shaped edges around subsequent precipitation are characterised. Incorporation of solute atoms, namely Si, Mg and Cu, accounts for the expansion of GP zones with core–shell structure and further precipitation transformation. The induced strain field rises as the ageing time increases and structural transformation proceeds, which results in a hardening of the sample.