Properties and microstructure of copper–titanium alloys with magnesium additions

The volume fractions and morphology of precipitates in precipitation-strengthened Cu-Ti alloys, which precipitate mainly as continuous and discontinuous precipitates, are important for the application of the alloy. This study employed hardness and electrical conductivity tests, transmission electron microscopy (TEM), atom probe tomography (APT), and first-principles calculations to demonstrate that the addition of Mg is effective for accelerating nanosized continuous β′-Cu₄Ti precipitation as well as for suppressing the precipitation of coarse lamellar discontinuous β-Cu₄Ti precipitates along the grain boundaries, resulting in Cu-Ti alloys with high yield strength and good electrical conductivity. The results showed that the continuous precipitation of β′-Cu₄Ti was accelerated by the Mg additions, which reduced the supersaturation of the matrix, thereby reducing the chemical driving force for the discontinuous precipitates. On the other hand, Mg additions increased the mismatch between the discontinuous β-Cu₄Ti precipitates and matrix, decreased the nucleation rate of the discontinuous precipitates, and increased the spacing of the discontinuous precipitation layer, resulting in a lower growth rate of the discontinuous precipitates. Therefore, the addition of Mg to Cu-Ti alloys enhances the strength and improves the resistance to over-ageing.