Crossover aluminium alloys have recently been introduced as a new class of coarse-grained age-hardenable alloys. Here

we study the evolution of precipitation of the T-phase — Mg32(Zn

Al)49-phase — in a 5xxx/7xxx crossover alloy with coarse- and ultrafined microstructures. Both alloys were examined using differential scanning calorimetry

X

-ray diffraction and

in situ

transmission electron microscopy. The ultrafine-grained alloy revealed significant different and accelerated precipitation behaviour due to grain boundaries acting as fast diffusion paths. Additionally

the ultrafine-grained alloy revealed high resistance to grain growth upon heating

an effect primarily attributed to inter-granular precipitation synergistically with trans-granular precipitation of T-phase.