Study On Combined Magnetic Field Annealing And Wire-connecting Of Nickle Electro-plating Basis For Co-based Amorphous Wires

Based on Co-based amorphous wires with diameterφ40μm, the thesis studied the influence of combined magnetic field annealing on the GMI effect. Moreover, also studied Ni electroplating technique of melt-extracted amorphous microwires, analyzed the solderability and wettability of amorphous wire with nickle electro-plated two-end, even including the effect of Ni electroplating wire-connecting on GMI stability.Experiments results of GMI effect show that combined magnetic field annealing treatment can effectively improve the GMI effect of amorphous wires by comparing with as-cast and conventional vacuum annealing amorphous wires, then increase magnetic field response sensitivity as the magnetic field increases. It is concluded that optimized annealing process parameters as follow:pre-annealed at 300℃for 20m in, follow ing by transverse m agnetic field annealing (α=90°) at 400℃for 10min. At the working frequency of 10MHz, the maximum value of GMI ratio reaches to 310.7% and the sensitivity reaches to 30.91%/Oe. In addition, properly readjusting of the angle between transverse magnetic field and axis of amorphous wire can increase circumferential magnetic anisotropy, also can result in the GMI variation curve from single peak (SP) to double peaks (DPs).The character of GMI viaration exhibits the asymmetry giant magneto- impedance (AGMI) effect as the microwires are annealed by transverse magnetic field treatment. It is the reason that during the transverse combined magnetic field annealing, atomic ordered region formed in the amorphous wires hinder magnetic moment rotation, thus leading to the asymmetrically circumferential magnetization and AGMI effect occurs.The optimized Ni electroplating process is using watts nickel solution electroplated at 55℃, 4A /dm 2 for 3.8min. The average diameter of nickle particle and the thickness of Ni electroplating layer are around 0.361μm, 2.53μm respectively. In contrast to the conventional wire-connecting, after Ni electroplating in the wire-end of amorphous wires, the solderability and wettability of amorphous wires are distinctly enhanced, the wetting angle between solder and CoFeSiB substrate decreases from 85.5°to 56.3°. Meanwhile, It can be obtained stable and reliable spot weld by the Ni electroplating wire-connecting, and the GMI stability was improved effectively in some extent.