Abstract
A novel means of producing copper-based powder metallurgy wire containing sufficient iron in particulate form to impart useful magnetic properties has been investigated. The method, which involves encapsulating a powder mixture within a copper tube prior to rolling and die-drawing operations, has been successfully used to produce composite wire of diameter range 1.8-0.4 mm. Particular attention has been paid to the effect of composition, processing strain, heat treatment and iron particle size on the electrical, mechanical and magnetic properties of the wire. Microscopy studies have also been carried out to determine structural changes in the material during processing.
It was found that the good conductivity and ductility of solid copper wire was not greatly reduced provided (a) the iron content of the composite wire was kept fairly low (<6 per cent) and (b) the annealing temperature was not sufficiently high for significant alloying to take place (650°C maximum). Saturation magnetization values increased with increasing process strain, as did the magnetic hardness. The latter, however, could be minimized by fully annealing the iron after processing the wire. The magnetic properties were undoubtedly influenced by the size and shape of the iron particles, smaller particles being more easily elongated and tending to give greater magnetic hardness.