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

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 degrees 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 degrees C, 80 degrees 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 eta phase were transformed to be larger eta' and eta precipitates. Moreover, continuous eta 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. (C) 2013 Elsevier Ltd. All rights reserved.