Investigation of electromagnetic effects in materials processing.

摘要

A new contactless inductive technique has been developed to evaluate both thermophysical and rheological properties of metals in solid and molten states. This is based on the theory that when a conductor moves in a magnetic field, circulating eddy currents are induced and the opposing mechanical torque created is directly proportional to the electrical conductivity and size of the sample. It was determined that the damping torque T, produced by rotating a sample in a magnetic field, is $T=23swLR4\; B2$, where $s$ is the electrical conductivity of the sample, $w$ is the angular velocity of the crucible, L and R are the length and radius of the sample, respectively, and B represents the strength of the magnetic induction. The technique was applied to a series of materials, including both pure metals and alloys. The results are in excellent agreement with existing data, and new data for several alloys are presented.; The technique can also be used in characterization of microstructural condition for various metals, depending on specific applications. The continuous monitoring of electrical resistivity during heat treatment is sensitive to slight modifications in the metal's microscopic structure like solute content, precipitation hardening, and increasing dislocation densities. Isothermal transformation C-curves for 3024 aluminum-copper alloy were determined based on the electrical resistivity measurements. The C-curves were supplemented with hardness and x-ray diffraction measurements. The results obtained in this investigation were in very good agreement with published literature data.; In addition, an electromagnetic-based permanent-magnet probe was designed and tested for monitoring velocity (as well as the temperature) in molten metals. It is shown that, when rotating a molten metal in a DC magnetic field, the azimuthal velocity in the vicinity of the crucible is significantly different from the one in the center, which is evidence of secondary flow induced by the DC magnetic field.