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

c無氧銅（Oxygen-free copper）為電動機（Electric motor）的轉子（Rotor）主要結構材料之一。由於，銅轉子接合的溫度過高，電磁鋼片（Electrical steels）會產生再結晶反應而造成鐵損增加，導致能源轉換效率降低。因此，本研究以低溫之半固態真空硬銲技術來完成無氧銅間的精密接合，又能保持高的能源轉換效率。實驗採Cu-15Ag-5P為填充金屬，持溫溫度以填充金屬之液-固相共存的673℃~793℃及液相的823℃、真空度<10-5Torr為測試條件。實驗結果發現：經由DSC熱分析，填充金屬在643℃的低熔點三元共晶組織開始熔融。673℃時，填充金屬對無氧銅（C101）有潤濕角39.22°、鋪展面積7.6㎜2；液相之823℃時，相對於673℃的潤濕角減少了90%（3.78°），鋪展面積則成長了192%（22.16㎜2）。然而，潤濕角皆小於90°，顯示填充金屬對C101的潤濕性皆良好。由SEM/EDX分析，銲道基底（Matrix）為黑色銅磷固溶體，成分為Cu與P原子百分比以3:1組成，研判應為Cu3P相，其使銲道硬度值高於兩側母材。半固態溫度硬銲的銲道硬度皆大於液相的接合，其中673℃的最大硬度值達157.05Hv，為母材的192%；823℃則為最小硬度值94.81，僅為母材的80%。電阻量測結果評估，C101受到填充金屬的擴散影響，皆使電阻值上升0.05~0.07mΩ，顯示硬銲溫度對C101間的導電效應影響不大。模擬真空硬銲製程的電磁鋼片，在半固態733℃的電阻值與原狀態僅降低0.29mΩ（0.03%），而液相823℃則有最大差異1.79mΩ（20%），顯示接合溫度確實會造成電磁鋼片在電性特性的影響。最後，拉伸剪應力試驗採1㎜厚試片，無論接合長度為2T或4T，其破斷位置均在母材，顯示以填充金屬Cu-Ag-P之液-固相共存的低溫真空硬銲製程，其銲件在接合剪切強度皆能滿足需求。

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 mm2. 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 mm2）. However, the wetting angles were below 90°, indicating good wettability of the filler metal with respect to C101. Based on SEM/EDX analysis, the weldbase （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.