Precipitation and decomposition phenomena in a Zn-Al-Cu-Mg alloy

• We observe non-equilibrium ZnxAl1−x (x≥0.7) precipitates in a Zn-Al alloy.
• For the first time we analyse their structure and chemistry by TEM and APT.
• Deformation at elevated temperature causes dissolution of these precipitates.
• Precipitate dissolution contributes to mechanical instability of Zn-Al alloys.
• Future alloy design will build on these results to improve mechanical stability.

We investigate the precipitation and decomposition phenomena in a Zn-Al-Cu-Mg alloy using transmission electron microscopy and atom probe tomography. Uniaxial tensile tests reveal brittle fracture at room temperature and ductile failure after work hardening at 85 °C. For the first time we identify and structurally and chemically characterise precipitates of a non-equilibrium ZnxAl1−x (x≥0.7) transition phase and show that these precipitates dissolve during deformation at 85 °C. We propose that the partial dissolution of these precipitates contributes to the lack of long-term mechanical stability of Zn-Al alloys that currently poses one of the major drawbacks to their application. The presented approach and findings will benefit the design of new Zn-Al alloys with improved mechanical stability.