Improvement in Mechanical Properties of a Cu–2.0 mass%Ni–0.5 mass%Si–0.1 mass%Zr Alloy by Combining Both Accumulative Roll-Bonding and Cryo-Rolling with Aging
Yusaku Takagawa, Yukinaru Tsujiuchi, Chihiro Watanabe, Ryoichi Monzen, Nobuhiro Tsuji
The enhancement in tensile properties of a Cu–2.0 mass%Ni–0.5 mass%Si–0.1 mass%Zr alloy without reducing its electrical conductivity is attempted by combining both accumulative roll-bonding (ARB) and cryo-rolling with aging treatment. The grain sizes of the alloy pre-aged at 450°C and ARB-processed in six cycles (P-ARB) and of the alloy pre-aged at 450°C and cryo-rolled to a 90% reduction (P-90CR) are refined to about 0.1 and 0.2 µm, respectively. Both six cycles of ARB and 90% cryo-rolling, together with the presence of fine precipitates formed by pre-aging at 450°C, give significant grain refinement. The P-90CR alloy aged at 350°C exhibits a higher 0.2% proof stress of 830 MPa and a higher tensile strength of σu = 900 MPa than the P-ARB alloy aged at 375°C. The aged P-90CR alloy exhibits almost the same elongation of 6% up to failure and the same electrical conductivity of σ = 45% IACS as the aged P-ARB alloy. The higher proof stress of the aged P-90CR alloy than the aged P-ARB alloy is ascribed to the higher dislocation density in the aged P-90CR alloy. The value of σu = 900 MPa for the aged P-90CR alloy is larger than that of σu ≈ 830 MPa for conventional commercial Cu–3.0 mass%Ni–0.65 mass%Si system alloys. The value of σ for the former alloy is nearly identical to σ ≈ 46% IACS for the latter alloys.