Change in magnetic property of Cu-6.5mass%Co alloy through processing by ECAP

A Cu-6.5 mass%Co alloy containing a fine dispersion of ferromagnetic Co precipitates in the Cu matrix is processed by ECAP and measurements of coercivity are carried out after ECAP with different numbers of passes and different processing routes. Changes in particle size and shape including crystal structures are examined using transmission electron microscopy and X-ray diffraction analysis. It is demonstrated that the application of ECAP for 1 pass leads to an increase in the coercivity by more than twice as much as the as-aged condition without ECAP. Microstructure observation reveals that the increase in the coercivity is due to intense straining by ECAP and fragmentation of the Co particles to finer sizes as 10-30 nm. Magnetic anisotropy is observed when the sample is processed through Route A but it is minor for 4 passes of Route C and very little after 4 passes of Route Bc. The anisotropy appears because Co particles are uniaxially elongated by processing via Route A.