Design Fabrication And Shielding Mechanisms Of Iron-Aluminum Gradient Alloy Plate And Multi-Layer Structure

To adapt the complex electromagnetic environment and meet the requirement of high shielding effectiveness, gradient alloy plate and physical multi-layer structure (alloy plate/medium layer/alloy plate) shielding materials were designed in this paper. Hot dipping aluminium plating and diffusion alloying were used to form Fe-Al soft magnetic alloy on the surface of DT4E, layered Iron-Aluminum gradient alloy plate was prepared. Optical microscope, scanning electron microcopy, X-ray diffract meter, soft magnetic properties measurement system, coaxial cable method, vector magnetometer were used to investigate microstructure, soft magnetic properties, shielding effectiveness. And the relation between microstructure and properties was investigated; the shielding mechanisms of gradient alloy plate and physical multi-layer structure were analyzed.The Hot dipping aluminum plating coated included aluminum layer and iron-aluminum alloy layer. The iron-aluminum alloy layer zigzag dipped into pure iron matrix, the basis was columnar crystals Fe2Al5. The thickness of alloy layer increased with the rise of hot dipping aluminum temperature. After diffusing heat treatment, iron-aluminum gradient alloy plates were prepared which had two sides with Fe-Al soft magnetic alloy layer and the centre with pure iron matrix. The aluminum content was the highest on the surface, decreased from surface to center, and showed graded distribution.The coercive force of gradient iron-aluminum alloy plate was about 40A/m, corresponded with pure iron. There was a larger hot mismatch stress between Fe-Al iron layer and pure layer, which was the main reason of leading to magnetic properties decreased. The geomagnetic shielding coefficient of gradient iron-aluminum alloy plate was about 26, 8 times as high as pure iron. The gradient iron-aluminum alloy plate produced by 700℃dipping aluminum had the best shielding effectiveness. The structure of gradient alloy plate was two Fe-Al soft magnetic alloy layers, and a pure iron matrix in the middle. The geomagnetic shielding depended on the three layers'role of parallel shunt. The shielding coefficient was influenced by the structure factor the, increased with the size of square shielding tube increasing. Electromagnetic shielding testing showed that the gradient iron-aluminum alloy plate with 700℃dipping aluminum have the highest shielding effectiveness, which was decreased with the dipping aluminum temperature increased. The impedance of each layer showed graded distribution in the gradient alloy, which would reduce the electromagnetic wave reflectance of alloy plate, lead the shielding effect getting worse.The shielding effectiveness of physical multi-layer structure was investigated. Compared with gradient iron-aluminum alloy plate, the geomagnetic shielding coefficient had a 10times increased, reached to 258. Physical multi-layer structure had two magnetic layers and a non magnetic in the middle. The shunting magnetic field action would be occurred two times, more effectively shielding geomagnetic field, increasing shielding effectiveness. But this multi-layer structure couldn't improve electromagnetic shielding effectiveness, lower than gradient iron-aluminum alloy plate. The electromagnetic shielding of modified physical multi-layer structure (electrical conductor/dielectric medium/electrical conductor) was very good. Compared with monolayer material, there is a large improvement.