Precipitation and aging in high-conductivity Cu–Cr alloys with additions of zirconium and magnesium

The precipitation reactions responsible for age hardening in a high-conductivity Cu–Cr–Zr–Mg alloy have been investigated by analytical transmission electron microscopy and compared briefly with the processes that occur in simpler Cu–Cr and Cu–Cr–Mg alloys. Aging at low temperatures (400°C) results in the formation of Guinier–Preston zones. Peak hardness, obtained by aging for 24 h at 450°C, is found to be a result of the fine scale precipitation of an ordered compound, possibly of the Heusler type, with the suggested composition CrCu2(Zr, Mg). Overaging results in the formation of coarse precipitates of Cr and CU4Zr. The intergranular precipitate which forms in the Cu–Cr–Zr–Mg alloy is Cu4Zr. This phase precipitates both as discrete particles on the grain boundaries and as thin ( ~ 5 nm) continuous intergranular films.MST/89