Calculation-experimental study of the aging of casting high-strength Al-Zn-Mg-(Cu)-Ni-Fe aluminum alloys

The effects of natural aging and steplike aging on the hardness and the electrical conductivity of the following high-strength casting aluminum alloys are studied and compared: experimental alloys ATs6N4, ATs7NZh, and ATs6N0.5Zh based on the Al-Zn-Mg-(Cu)-Ni-Fe system (nicalins) and a commercial AM5 alloy based on the Al-Cu system. It is found that, during 3-day natural aging, the hardness of the nicalins increases to HV 1.4–1.55 GPa, which is higher than their hardness in the as-quenched state by a factor of 1.6–1.7. The hardness of the AM5 alloy is almost unchanged during natural aging and is retained at the level of the as-quenched state (HB ∼ 0.8 GPa). After quenching and natural aging for 1 day, the alloys are subjected to steplike aging in the temperature range 100–250°C at a step of 25°C on holding for 3 h at each temperature. Upon steplike aging, hardness HB of the nicalins reaches a maximum (∼2.1 GPa for the ATs7NZh and ∼1.9 GPa for the ATs6N4 and ATs6N0.5Zh alloys) at a temperature of 150°C. The hardness of the AM5 alloy reaches a maximum (HB ∼ 1.3 GPa) at a temperature of 175°C.