Some observations on deformation-related discontinuous precipitation in an Al-14.6at.%Zn alloy

The discontinuous precipitation (DP) in a supersaturated Al-14.6at.%Zn alloy in relation to different forms of deformation structures has been investigated with optical and electron microscopy. It has been found that intense surface scribing, followed by short-term ageing at 65 °C, resulted in a recrystallized duplex structure with nanoscale equiaxed β-Zn particles and α-Al grains. In the absence of recrystallization and shear banding, moderate surface grinding increased the transformation kinetics of DP on the alloy surface by an order of magnitude compared with that of the undeformed counterpart. The enhanced transformation kinetics is attributed to intragranular nucleation and growth of DP colonies associated plausibly with dislocation cell wall structures induced by the surface strain. In contrast, bulk deformation by means of cold-rolling (13–66% reduction) and in situ stress-ageing (∼1% strain) both suppressed the development of DP in the alloy. The role of deformation bands as nucleation sites of DP and the driving force determining the development of DP colonies in deformed matrices are discussed.

Research highlights▶ Effects of prior strain on discontinuous precipitation (DP) in an Al-Zn alloy. ▶ DP in recrystallized grains enables formation of equiaxed dual-phase nanostructures. ▶ Deformation bands and dislocation cell walls are potential nucleation sites for DP. ▶ Deformation bands contribute to the development of faceted DP cell fronts.