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In this paper, the effect of alternating longitudinal electromagnetic fields on the microstructure, composition segregation and solid solubility of solute elements in aluminium alloy weld beads is studied. The results show that the X-ray diffraction peaks of the deposited aluminium alloy layer under the external magnetic field are much less intense than those for the alloy prepared without the external magnetic field. The diffraction peak intensities from different crystallographic planes in the structure slightly differ under the action of different magnetic field frequencies. As the excitation current increases, the increase in Mg segregation is obvious. With an increase in the magnetic field frequency and excitation current, the external magnetic field promotes the solid solubility of solute Mg in Al.

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In this paper, a capacitance parameters of high-precision digital measuring instrument was designed, based on the VI (virtual instruments), using LabVIEW software platform and applying current comparison measuring principle. This system possesses current comparison based on Magnetic Potential Balance Principle, PC subject, the integrated data acquisition modules and I/O control module. Magnetic potential balance has been achieved by controlling coil turns. With the function of PC, accurate test results have been gained. Because of using the closed-loop control and the successive approximation method to control relay, the system achieves equilibrium sharply. This system has been used to test the capacitance of capacitor, dielectric loss value and the inductance of reactor, which has advantages to more accuracy and stability, convenient operation, and adjusting quickly and a wide range of uses.