交流直流重畳磁場配向法による短繊維アルミナ/マグネシウム合金複合材料の製造

抄録

Unidirectional alignment and high volume of fibers efficiently increase the strength of fiber reinforced MMC. However, it is very difficult in an ordinary process to get a high orientation and volume of short fibers in MMC. This research was done to solve these problem of short fibers. The apparatus, which has superimposed magnetic fields generated by A. C. solenoid coil in the upper part, D. C. solenoid in the lower part and iron core in D. C. solenoid, makes the orientation of ferromagnetic short fibers in uniaxis. The fibrous preform made by this apparatus has less than 10 degrees of fiber orientation angle and 0.35 to 0.45 or higher of volume fraction of fibers. Inorganic fibers coated with ferromagnetic materials also could be aligned in uniaxis by the apparatus with a rather high magnetic flux density of D. C. solenoid. Fine crystallized α alumina fibers, 18 μm in diameter and 2 mm in length, which were coated with ferromagnetic nickel by electroless plating, were aligned uniaxaly in a casting mold. The molten magnesium alloy was sucked up and infiltrated into the mold under a low pressure of the vacuum pump. The Ni-B electroless plating process is effective in preventing the reaction between the nickel layer of fibers and molten magnesium. The thickness of the nickel plated layer needs to be 1 or 0.5 μm. With increasing thickness of the nickel layer, the nickel content in the magnesium matrix increases, and a larger volume of the brittle structure of Mg₂Ni is formed. This decreases the strength of these composites. As an example of the strength of these composites, 1 μm nickel-coated alumina fiber reinforced magnesium alloy composites display a bending strength of 570 MPa in 0.4 volume fraction and 8 degree orientation angle. This is about twice the strength of the matrix.