三元亞共晶填充金屬之半固態溫度對無氧銅真空硬銲研究

Impact of Ternary, Hypoeutectic Filler-Metal Semi-Solid Temperatures on Vacuum Brazing of Oxygen-Free Copper

李義剛(I-Kon Lee) ； 蔡明樺(Ming-Hua Tsai) ； 劉全輝(Chuan-Hwei Liu)

《科學與工程技術期刊》 10卷1期 (2014/03) Pp. 1-10

摘要

Oxygen-free copper is one of the major structural materials of electric motors. Because the bonding temperature of copper rotors is extremely high, recrystallization of electric steel increases iron loss and reduces the efficiency of energy conversion. Therefore, in this study, low-temperature, semi-solid vacuum brazing technology was adopted to achieve precise bonding between oxygen-free copper while maintaining high efficiency of energy conversion. Cu-15Ag-5P was used as the filter metal and the conditions tested were of liquid-solid-coexistence temperatures (between 673°C and 793°C), liquid-phase temperature (823°C), and a vacuum of ＜ 10^(-5) Torr. DSC thermal analysis of the experimental results indicated that the low-melting-point ternary hypoeutectic structure of the filler metal caused it to melt at 643°C. At 673°C, the wetting angle of the filler metal with respect to oxygen-free copper (C101) was 39.22°, with a spreading area of 7.6 mm^2. At 823°C, in the liquid phase, the wetting angle was diminished by 90% (3.78°), compared with that at 673°C, whereas the spreading area grew by 192% (22.16 mm^2). However, the wetting angles were below 90°, indicating good wettability of the filler metal with respect to C101. Based on SEM/EDX analysis, the weld base (matrix) was a black-copper/solid-phosphorus solution with a 3:1 composition ratio between Cu and P atoms, determined to be in Cu3P phase, and the weld hardness was higher than the base material on both sides. The weld hardness of semi-solid-temperature vacuum brazing was higher than the liquid-phase bonding. At 673°C, the maximal hardness reached 157.05 Hv, which was 192% of that of the base material. At 823 °C the minimal hardness was 94.81 Hv, only 80% of that of the base material. Under the impact of diffusion of the filler metal, the resistance of C101 was observed to be increased by 0.05-0.07 mΩ, indicating a minor influence of brazing temperature on the conductivity of C101. Regarding the electrical steel used for simulating the vacuum brazing process, the resistance at the semi-solid phase 733°C, was only 0.29 mΩ (0.03%) less than the original state, whereas the maximal difference in resistance (1.79 mΩ) occurred in the liquid phase 823°C (20%), showing that the bonding temperature affected the electrical property of electrical steels. Lastly, a 1-mm-thick specimen was used for tensile-strength and shear-stress tests, and the breaking positions were all on the base material for bonding lengths of 2T and 4T. This indicates that the bonding-shear strength of welding in the low-temperature vacuum-brazing process in the liquid-solid coexisting phase of the filler metal Cu-Ag-P, can be in line with requirements.

關鍵字

無氧銅 ； 真空硬銲 ； 潤濕性 ； 液－固相共存 ； 剪切強度 ； 半固態

並列摘要

Oxygen-free copper is one of the major structural materials of electric motors. Because the bonding temperature of copper rotors is extremely high, recrystallization of electric steel increases iron loss and reduces the efficiency of energy conversion. Therefore, in this study, low-temperature, semi-solid vacuum brazing technology was adopted to achieve precise bonding between oxygen-free copper while maintaining high efficiency of energy conversion. Cu-15Ag-5P was used as the filter metal and the conditions tested were of liquid-solid-coexistence temperatures (between 673°C and 793°C), liquid-phase temperature (823°C), and a vacuum of ＜ 10^(-5) Torr. DSC thermal analysis of the experimental results indicated that the low-melting-point ternary hypoeutectic structure of the filler metal caused it to melt at 643°C. At 673°C, the wetting angle of the filler metal with respect to oxygen-free copper (C101) was 39.22°, with a spreading area of 7.6 mm^2. At 823°C, in the liquid phase, the wetting angle was diminished by 90% (3.78°), compared with that at 673°C, whereas the spreading area grew by 192% (22.16 mm^2). However, the wetting angles were below 90°, indicating good wettability of the filler metal with respect to C101. Based on SEM/EDX analysis, the weld base (matrix) was a black-copper/solid-phosphorus solution with a 3:1 composition ratio between Cu and P atoms, determined to be in Cu3P phase, and the weld hardness was higher than the base material on both sides. The weld hardness of semi-solid-temperature vacuum brazing was higher than the liquid-phase bonding. At 673°C, the maximal hardness reached 157.05 Hv, which was 192% of that of the base material. At 823 °C the minimal hardness was 94.81 Hv, only 80% of that of the base material. Under the impact of diffusion of the filler metal, the resistance of C101 was observed to be increased by 0.05-0.07 mΩ, indicating a minor influence of brazing temperature on the conductivity of C101. Regarding the electrical steel used for simulating the vacuum brazing process, the resistance at the semi-solid phase 733°C, was only 0.29 mΩ (0.03%) less than the original state, whereas the maximal difference in resistance (1.79 mΩ) occurred in the liquid phase 823°C (20%), showing that the bonding temperature affected the electrical property of electrical steels. Lastly, a 1-mm-thick specimen was used for tensile-strength and shear-stress tests, and the breaking positions were all on the base material for bonding lengths of 2T and 4T. This indicates that the bonding-shear strength of welding in the low-temperature vacuum-brazing process in the liquid-solid coexisting phase of the filler metal Cu-Ag-P, can be in line with requirements.

並列關鍵字

Oxygen-free copper ； Vacuum Brazing ； Wettability ； Liquid-solid phase coexistence ； Shear strength ； Semi-solid