Study of intergrown L and Q′ precipitates in Al–Mg–Si–Cu alloys

Intergrown Q′ and L precipitates formed in an overaged Al–Mg–Si–Cu alloy were studied by transmission electron microscopy and atom probe tomography. The composition of the ordered Q′ phase was measured to be Al3.8Mg8.6Si7.0Cu1.0, while less Mg was found in the disordered L phase. Compared to the equilibrium Q phase, Q′ contained less Cu and more Al. Similar Si concentrations were found in the Q′ and L precipitates, consistent with the presence of a common Si arrangement in both structures.

Research highlights
► APT and HRTEM study of intergrown precipitate particles in an overaged Al–Mg–Si–Cu (6xxx) alloy.
► The particles are shown to contain the structures of both the Q′ and L hardening phases.
► A more accurate structure and composition is reported for the Q′ phase.
► The L and Q′ phases are shown to be connected by a common underlying Si arrangement present in both structures.