The enhancement of strength of a Cu 1.4 massNi 0.25 massP 0.1 massZr alloy, in which the Ni and P contents are about twice larger than those in commercial Cu Ni P alloys, has been tried by means of combining accumulative roll bonding (ARB) process by 7 cycles and aging treatment at 350 to 450°C. For the sake of comparison, the mechanical properties of the alloy conventionally cold rolled to a reduction of 50 and 90 and aged at 350 to 450°C have also been examined. The grain sizes of the Cu Ni P Zr specimens deformed by 7 cycle ARB process and 90 cold rolling were refined down to about 0.4 mm and 4 mm, respectively, and the fractions of high angle grain boundaries in the specimens were nearly the same, about 45. Initial aging, subsequent ARB process or 90 cold rolling and re aging at 400°C produced the Cu Ni P Zr alloy highly strengthened. The alloy, initially aged, then ARB processed and re aged, had a tensile strength of 780 MPa, an elongation of 6 up to failure and an electrical conductivity of 56 IACS. The differences in yield strength among the re aged specimens after 50 and 90 cold rolling and ARB process are explained by the differences among the dislocation density, grain size and inter precipitate spacing. (Received December 20, 2010; Accepted June 3, 2011) Keywords: copper nickel phosphorus alloy, accumulative roll bonding process, tensile property, grain refinement strengthening, precipitation strengthening, dislocation strengthening
The effects of addition of 0.1 massMg and 0.1 massFe on the strength and stress relaxation property of a precipitation hardenable Cu 0.52 massNi 0.19 massP alloy aged at 450°C have been investigated. Precipitation of Ni 2 P, Ni 12 P 5 , both Ni 2 P and Ni 5 P 4 , and both Ni 12 P 5 and Ni 5 P 4 phases was observed to occur on aging the Cu Ni P, Cu Ni P Fe, Cu Ni P Mg, and Cu Ni P Fe Mg alloys, respectively. The needle like Ni 5 P 4 phase was first found to be precipitated in the Cu matrix. In the peak aging stage, the yield strength of the four alloys is controlled by the Orowan mechanism. The addition of Mg to the Cu Ni P alloy enhanced the strength of the alloy, but the Fe addition did not significantly affect the strength. The strength of the Cu Ni P Mg alloy was nearly identical to that of the Cu Ni P Fe Mg alloy. The increase in strength by the addition of Mg is ascribed to the decrease in inter precipitate spacing of precipitates. The Cu Ni P Fe alloy exhibited better stress relaxation property than the Cu Ni P alloy, probably because atoms caused by pairs of Fe and P chemical bonding are dragged by moving dislocations. Adding Mg to the Cu Ni P alloys did not essentially change the stress relaxation property. This may be as a result of the combination of the increase in stress relaxation resistance caused by the Mg atom drag effect on dislocation motion and of the decrease in that due to the decrease in the amount of P atoms in the Cu matrix by adding Mg. (Received November 5, 2009; Accepted February 9, 2010) Keywords: copper nickel phosphorus alloy, alloying element addition, Ni 2 P precipitate, Ni 12 P 5 precipitate, Ni 5 P 4 precipitate, precipitation strengthening, stress relaxation property
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