Influence of repetitious non-isothermal aging on microstructure and strength of Al-Zn-Mg-Cu alloy

In the present work, the influence of repetitious non-isothermal aging (RNIA) temper on microstructure and strength of Al-Zn-Mg-Cu alloy was investigated by hardness measurements, electrical conductivity, tensile properties tests and transmission electron microscopy (TEM) observation. The results suggested that RNIA temper can acquire satisfactory corrosion resistance with a smaller or no reduction in strength equivalent to the non-isothermal aging temper. The variation of hardness and strength with repetitious times depended on the heating and cooling rates, while the electrical conductivity exhibited a monotonous increase with repetitious times. TEM observation indicated that the coarsening of matrix precipitates during RNIA induced the decrease of strength, while the discontinuous grain boundary precipitates and the increase of solute contents in grain boundary precipitates were beneficial for the improvement of corrosion resistance.