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

Abstract

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 CrCu 2 (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 Cu 4 Zr. This phase precipitates both as discrete particles on the grain boundaries and as thin ('" 5 nm) continuous intergranular films. MST/89

Magnesium addition in copper‐chromium alloys: The refinement of aging precipitates and improvement on mechanical properties

“…Compared to the short aging and peak aging state alloy, the 4 h aging resulted in two types of precipitated phases, Heusler phase and body-centered cubic chromium phase, confirmed by the calibrated selected area electron diffraction patterns, Figure 5. This result is in good agreement with the previously published literature [10,13,14].…”

“…Furthermore, the previous reports have demonstrated that magnesium addition influences the aging behavior of the alloys. For instance, the presence of magnesium and zirconium elements in copper-chromium alloy results in nano-precipitated Heusler phase [13]. The Heusler phase have also been observed in magnesium-containing copperchromium-zirconium alloys and shows the favorable effects of the precipitated phase on performance [10,14,15].…”

“…Herein, we report the addition of magnesium element into the copper-chromium alloy, which can result in the formation of Magnesium oxide, in the presence of oxygen, and exhibits a deoxidizing effect on the melt, preventing the oxidation of active elements. Therefore, the magnesium elements are commonly added, in the copper-chromium-zirconium alloy, to enhance the zirconium yield and refine the aging precipitation process [13,14,17]. Hence, the analysis of the refinement effect of magnesium element, on the precipitated phase, is inevitably disturbed by the presence of zirconium elements.…”

Cr cluster characterization in Cu-Cr-Zr alloy after ECAP processing and aging using SANS and HAADF-STEM

“…The high conductivity of these alloys is mainly attributed to the low solubility of Cr and Zr in Cu at room temperature [2], whereas their strength is due to the precipitation of Cr clusters and Cu x Zr y phases in Cu matrices [3,4]. However, many authors have reported antagonist findings of the sequence and nature of precipitates that can appear during annealing after conventional or severe plastic deformation (SPD) of Cu-Cr-Zr alloys [5][6][7][8][9][10][11][12][13][14][15][16]. Besides Cr clusters, different Cu x Zr y phases have been found in Cu-Cr-Zr alloys: orthorhombic Cu 4 Zr phase [10,17] and Cu 51 Zr 14 (believed to be Cu 3 Zr) phase [11].…”

“…However, many authors have reported antagonist findings of the sequence and nature of precipitates that can appear during annealing after conventional or severe plastic deformation (SPD) of Cu-Cr-Zr alloys [5][6][7][8][9][10][11][12][13][14][15][16]. Besides Cr clusters, different Cu x Zr y phases have been found in Cu-Cr-Zr alloys: orthorhombic Cu 4 Zr phase [10,17] and Cu 51 Zr 14 (believed to be Cu 3 Zr) phase [11]. More complicated phases, such as Cu 7 Cr 3 ZrSi and CrCu 2 (Zr, Mg) Heusler phases have also been ob-*Corresponding author: e-mail address: abib khadidja@yahoo.com served [18][19][20].…”