Abstract:
The aging response of Al-Zn-Mg alloy type 7020 was systemically studied including natural aging, one-stage aging, and two stages aging. The naturally aged alloy resulted in peak hardness of 113 HB, while one-step aging of the alloy at 120 °C for 28 hr, at 150 °C for 5 hrs, or at 200 °c for 20 min resulted in peak hardness of 109, 93, and 79 HB respectively. The two-stages aging was carried out at 120 °C as a low aging temperature and 150 °C as a high aging temperature and through different aging periods of time. When aging at 150 °C was preceded by a low temperature aging stage at 120 °C for different periods of time, the obtained hardness was increased and attained a peak value of 108 HB after 6 hrs at 120 °C and 8 hrs at 150°C. The analysis of the tensile fracture surface demonstrated dominating ductile dimple fracture modes in the solution treated specimens, while in the peak aged specimens some zones of cleavage brittle fracture were manifested together with the ductile fracture zones.