Effect of Surface Modification on the Microwave Absorption Properties of Iron-based Amorphous Alloys
The work aims to regulate the microwave absorption performance of iron-based amorphous alloy (IAA) powder composite materials. The magnetron sputtering was used to partially cover an aluminum film on the surface of iron-based amorphous alloy powder, and then KH560 silane coupling agent was adopted to insulate and coat the powder. The powder was characterized by XRD, SEM, and FT-IR, and the electromagnetic properties of the samples were tested by VSM and transmission reflection methods. The real part of the complex dielectric constant ε′ of iron-based amorphous alloy powder after aluminum plating increased by 56.1％, and the imaginary part of the complex dielectric constant εʺ increased by 132.4％. The ε'of iron-based amorphous alloy powder after insulation coating decreased and was 32.6％ of that of iron-based amorphous alloy and εʺ was 25.1％ of that of iron-based amorphous alloy. The ε′ and εʺ of iron-based amorphous alloy powder plated with aluminum and coated with KH560 were 43.5％ and 36.6％ of those of iron-based amorphous alloy, respectively. The real and imaginary parts of the complex dielectric constant were lower than those of the sample after aluminum plating, and higher than those of the sample after pure KH560 coating, showing that aluminum plating could compensate for the decrease in dielectric loss caused by KH560 insulation coating, which was beneficial for adjusting the electromagnetic properties of the KH560 insulation coated powder material. The insulation coating of iron-based amorphous alloy powder improves the high-frequency absorption performance of the corresponding material, but sacrifices its low-frequency absorption performance. To make up for this deficiency, it is proposed to cover the surface of iron-based amorphous alloy powder with aluminum film locally, and then conduct insulation coating. It is expected that after insulation coating, the powder still has high dielectric loss ability, achieving the goal of regulating the low-frequency electromagnetic wave absorption ability of the material. The simulated reflectance curve of the sample shows that when the sample thickness is 2-3 mm, the lowest peak corresponding frequency of the iron-based amorphous alloy/Al/KH560 sample is lower than the corresponding peak position of the iron-based amorphous alloy/KH560. Aluminum plating on the surface of the iron-based amorphous alloy powder can significantly improve the low-frequency microwave absorption characteristics of its composite material. When the thickness is 1.5 mm, the RLmin of IAA, IAA/Al, IAA/KH560, and IAA/Al/KH560 are −7.69 dB (3.80 GHz), −6.83 dB (3.03 GHz), −10.81 dB (15 GHz), and −7.84 dB (10 GHz), respectively. From Figure 7a, it can be seen that the frequency corresponding to the minimum reflection peak of IAA/Al/KH560 is lower than that of IAA/KH560, indicating that aluminum plating is beneficial for improving the low-frequency absorption performance of the sample. When the thickness is 2 mm, the RLmin of IAA, IAA/Al, IAA/KH560, and IAA/Al/KH560 are −9.65 dB (2.70 GHz), −7.82 dB (2.25 GHz), −10.65 dB (6.53 GHz), and −9.37 dB (5.45 GHz), respectively. The lowest peak corresponding frequency of IAA/Al/KH560 sample is 1.08 GHz lower than the corresponding peak position of IAA/KH560, and aluminum coating can significantly improve the low-frequency absorption performance of the sample. When the thickness is 3 mm, the RLmin of IAA, IAA/Al, IAA/KH560, and IAA/Al/KH560 are −14.96 dB (1.80 GHz), −10.08 dB (1.49 GHz), −19.46 dB (4.19 GHz), and −15.00 dB (3.51 GHz), respectively. Compared with the lowest absorption peak of IAA/KH560, the lowest peak of IAA/Al/KH560 sample shifts 0.68 GHz to the left. The lowest absorption peaks of IAA/Al/KH560 are exactly between the frequencies corresponding to the RLmin of IAA and IAA/KH560, which compensates for the disadvantage of using KH560 coating to improve the low-frequency absorption performance of the sample.
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