Mechanisms for refining precipitation and improving strengthening of annealed Cu-2Ag alloy via La modification.

• The radii of the nanoscale precipitates are dramatically smaller in the annealed Cu-2Ag-0.14La alloy than in the annealed Cu-2Ag alloy. • The grain size of annealed Cu-2Ag-0.14La alloy is always smaller than that of the annealed Cu-2Ag alloy from 400 °C to 650 °C. • Precipitation strengthening of nanoscale precipitates in the matrix and grain-boundary strengthening during grain refinement substantially improve the yield strength of the Cu-2Ag-0.14La alloy. [Display omitted] A new Cu–2Ag–0.14La alloy is developed to enhance the mechanical property and electrical conductivity with inducement of Ag-rich primary phases and finer nanoscale Ag precipitates. The microstructural evolution and mechanical properties of Cu–2Ag–0.14La and Cu–2Ag alloys obtained by drawing and annealing were then summarized and analyzed. The results indicate that both the yielding and ultimate tensile strengths of annealed Cu–2Ag-0.14La alloy were reinforced after La modification. The average grain sizes of two alloys increase during annealing, but the size ratio (R Cu-2Ag-0.14La /R Cu-2Ag) dramatically varies with rising the heat temperature, evolving from 70.48% at 400 °C to 43.78% at 650 °C. Meanwhile, it is found that the refined grains sizes in Cu-2Ag-0.14La alloy are closely related to the nano-scale precipitates (~450 nm), which hinder the formation of subgrain boundaries at 400 °C, and impose a stronger pinning effect on boundary migration of recrystallized grains during annealing (≥ 450 °C). Consequently, higher hardness and electrical conductivity are contributed by grain refinement and dispersion strengthening of the nanosized phases. [ABSTRACT FROM AUTHOR]