MAGNETIC-PROPERTIES OF 1-PERCENT AL-IRON AND ITS APPLICATIONS

A study was carried out to improve permeability and coercivity of pure iron without decreasing its saturation magnetization. It was found that about 1-wt % addition of aluminum in combination with a high-temperature annealing process greatly increases its permeability (mu-m) up to 60 000, which is close to that of Permalloy B, and reduces its coercivity (H(c)) to 0.2 Oe without decreasing the high-saturation magnetization of pure iron. This marvelous effect of the 1-wt %-Al addition can be attributed to a stabilization of the ferrite phase which enables ferrite grains to coarsen drastically due to abnormal grain growth during the high-temperature annealing. The ferrite stabilization also helps to avoid both residual strain and grain refining due to the austenite-ferrite phase transformation, which are thought to be undesirable for soft magnetic properties. In the present paper, the performance of this Fe-1-wt %-Al soft magnetic alloy, and an example of its practical application to the magnetic shielding, will be described.