Effect of Zr addition on hot workability of Cu-6Ni-2Mn-2Sn-2Al alloy
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HAN, Senior Researcher, MANSIK KONG, Researcher, and CHANGJOO KIM, Principal Researcher, are with Materials Engineering Department, Korea Institute of Machinery and Materials, Changwon, Korea. SANGSHIK KIM, Associate Professor, is with the Division of Materials Science and Engineering, Engineering Research Center, Gyeongsang National University, Chinju, Korea. Manuscript submitted March 26, 2001. 3298—VOLUME 33A, OCTOBER 2002
Fig. 1—Macroscopic views of (a) 90 pct hot-swaged Cu-6Ni-2Mn-2Sn2Al alloy and (b) 10 pct hot-swaged Cu-9Ni-6Sn alloy.
Fig. 2—SEM micrographs of cracked areas in 90 pct hot-swaged Cu-6Ni2Mn-2Sn-2Al alloys (a) without and (b) with 0.3 pct Zr addition and (c) 10 pct hot-swaged Cu-9Ni-6Sn alloy. METALLURGICAL AND MATERIALS TRANSACTIONS A
Fig. 3—Macroscopic views of 80 pct hot-rolled Cu-6Ni-2Mn-2Sn-2Al alloy sheets (a) without and (b) with 0.3 pct Zr addition.
microscope were used for the documentation of microstructure. For micrographic examinations, the specimens were etched with 50 mL NH4OH ⫹ 25 mL H2O2 ⫹ 6 mL HNO3 solution, and subsequently cleaned with supersaturated NaOH solution. Figure 1 shows the macrographs of 90 pct hot-swaged Cu-6Ni-2Mn-2Sn-2Al alloy and 10 pct hot-swaged Cu9Ni-6Sn alloy. Cu-9Ni-6Sn alloy showed a severe cracking with 10 pct swaging and further swaging was unsuccessful. Compared to Cu-9Ni-6Sn alloy, Cu-6Ni-2Mn-2Sn-2Al alloy showed significantly improved hot workability. Ninety percent swaging was readily obtained for Cu-6Ni2Mn-2Sn-2Al alloy. For non-Zr containing Cu-6Ni-2Mn2Sn-2Al alloys, however, some intergranular cracks began to occur at the edge of the bar with 90 pct swaging. For 0.3 pct Zr added counterparts, on the other hand, any intergranular cracks were hardly observed. Figure 2 shows the high-magnification SEM micrographs of cracked areas in Figure 1. Both 10 pct swaged Cu-9Ni-6Sn and 90 pct swaged Cu-6Ni-2Mn-2Sn-2Al alloys apparently showed intergranular cracks. In 0.3 pct Zr added Cu-6Ni-2Mn-2Sn2Al alloys, the number of cracks was extremely reduced and the observed cracks were mostly transgranular type. Figure 3 represents the macroscopic views of 80 pct hotrolled Cu-6Ni-2Mn-2Sn-2Al alloy sheets (a) without and (b) with 0.3 pct Zr addition. Again, Cu-6Ni-2Mn-2Sn-2Al alloys could be readily rolled down to 1 mm at 850 ⬚C, which was impracticable for Cu-9Ni-6Sn alloys. The beneficial effect of Zr addition on hot workability of Cu-6Ni2Mn-2Sn-2Al alloys was also noticed in the figure. A considerable amount of edge cracks were observed in the nonZr added Cu-6Ni-2Mn-2Sn-2Al alloys at a rolling rate of 80 pct. With Zr addition, the frequency of the occurrence of edge cracks was greatly reduced. From Figures 1 through 3, the beneficial effect of Zr addition on the hot workability of Cu-6Ni-2Mn-2Sn-2Al alloys was demonstrated. To understand the improved hot workability with Zr addition, the microstructure of as-cast alloys were examined. Figure 4 shows the SEM micrographs of as-cast (a) Cu-6Ni-2Mn-2Sn-2Al, (b) Cu-6Ni2Mn-2Sn-2Al-0.3Zr, and (c) Cu-9Ni-6Sn alloy. A s
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