Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

• Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT).
• CAT improved mechanical and conductivity of Al alloy than T6 treatment.
• Cooling aging time decreased about 90% than that for T6 treatment.
• Fine GP zone and η′ phase transformed to be larger η′ and η precipitates during CAT.
• Strengthening and precipitation mechanism after cooling aging was discussed.

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.

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