2023 年 62 巻 1 号 p. 128-133
90° W–bending tests were conducted for Cu–9wt%Ni–6wt%Sn–0.25wt%Mn (base) alloys with or without small amounts of Si, Ti, Zr, or Co, solution–treated at 750, 800 and 850℃ and then under–aged at 345°C for 2 to 4 h. The width of the precipitate–free zone (PFZ) formed by aging was an important factor affecting the bend formability (BF) of the alloys with or without 0.08Si, 0.08Ti, 0.08Zr, and 0.3Co when solution–treated at 850 and 800°C. Among the five alloys, the 0.3Co–added alloy with the smallest amount of sliding on grain boundaries due to the narrowest PFZ width exhibited the best BF. When solution–treated at 750°C, the base alloy and 0.08Ti– and 0.08Zr–added alloys exhibited the best BF among the alloy specimens prepared in this study and the 0.08Si–added alloy exhibited the worst BF. Although both the former group of alloys and the latter alloy had the narrowest PFZ widths, the former group of alloys had much lower densities of coarse D03 particles remaining after solution–treating at 750°C than the latter alloy, resulting in the best BF. The solvus temperature of the D03 phase in the base alloy was measured to be 745°C and increased with the addition of 0.08Ti, 0.08Zr, 0.3Co, and especially 0.08Si. Changing the solution treatment temperature (Tst) from 750°C by ±20°C affected the BF of each alloy, depending on the solvus temperature of each alloy. It may be industrially unsuitable to adopt a temperature around 750°C as the Tst.
