Effect of magnesium doping on discontinuous precipitation in age-hardenable copper–titanium alloys

One of the most important goals in the development of Cu-based alloys for electrical engineering applications is the realization of materials with both high mechanical strength and electrical conductivity. Cu-Ti alloys are promising alternatives to Cu-Be alloys, which are expensive and can be hazardous to health. Herein, an age-hardenable binary Cu96Ti4 alloy and its Mg-doped analog were compared by advanced electron microscopy techniques. The mechanical properties of the Mg-doped alloy are superior to those of the binary alloy. The effects of Mg-doping on the microstructure are investigated by atomic-scale scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. The Cu96Ti4 (at.%) solid-solution alloy developed lamellar aggregates when subjected to prolonged aging treatment at 450 °C for 100 h owing to discontinuous precipitation (DP) along the grain boundaries. The DP consisted of a face-centered cubic (FCC) Cu solid-solution phase (denoted as α-Cuss) and a stable Cu4Ti intermetallic phase (β-Cu4Ti). Conversely, while the Cu94Ti4Mg2 counterpart had similar lamellar aggregates, the amount of these aggregates was reduced, and no β-Cu4Ti phase was observed. The lamellar in the Cu94Ti4Mg2 counterpart consisted of two distinct FCC Cuss phases with different Ti-solute contents. Accordingly, the possible effects of Mg doping on the local structures of the DP in the Cu-Ti alloy are explained, and the structural characteristics of the DP that may result in improved mechanical properties is discussed.