Liang Zhong

(Fe/C)/ABS resin electromagnetic metamaterials were fabricated via 3D printing, and the effect of iron salt loading (0, 1, 2, and 3 g) in the Fe/C filler on the microwave absorption performance of the resulting composites was systematically investigated. The results demonstrate that, with increasing iron salt content, the microwave absorption bandwidth of the samples exhibits a trend of initial significant broadening followed by saturation. At an iron salt loading of 1 g, the (Fe/C)/ABS resin composite achieves an effective absorption bandwidth (EAB) of 6.2 GHz at a matching thickness of 10 mm, representing an approximately 48% enhancement over that of the pure C/ABS resin composite (4.2 GHz). The incorporation of iron salts not only endows the material with magnetic loss capability but also promotes the formation of an sp²-hybridized carbon framework within the carbon matrix during Fe/C composite preparation, concurrently introducing abundant defect sites that augment the dielectric loss capacity. Under the synergistic magneto-dielectric loss mechanism, the microwave attenuation coefficient of the material is markedly enhanced, and the effective absorption bandwidth is substantially broadened, all at a filler loading of merely 2.5 wt%. This study elucidates the influence of iron salt loading on the microwave absorption performance of (Fe/C)/ABS resin composites, while the 3D printing-based fabrication approach employed herein offers a promising technical pathway for the development of novel microwave-absorbing materials.

Nowadays, there are many surface treatment methods for aluminium alloys; the most commonly used of these is the chemical dip galvanizing process, which is complicated due to its use of large quantities of corrosive drugs. In order to simplify the process, this paper proposes a new electromagnetic induction heating activation method instead of the zinc dipping process. The method works as follows: The substrate is first degreased and then activated. The activation process starts by soaking the degreased substrate in an activation solution, taking it out after ten minutes, and placing it into an induction heating unit. The activation solution is sprayed onto the surface of the substrate while heating, using the energy generated by high temperatures to complete the activation reaction. The surface of the activated substrate forms a nanoscale film of nickel, which is finally utilised as a catalytic centre for ENP (an advanced surface treatment process that deposits a very uniform layer). The optimisation of important parameters of the non-destructive activation process was determined using the L9 Taguchi method. The main parameters ranged from 0.15 L/min to 0.25 L/min for spray rate, 200 °C to 400 °C for heat treatment temperature, and 1:4, 1:5, and 1:6 for Ni²⁺ and H₂PO₄⁻ ion concentration ratios. The above data were derived from a single variable and were analysed using Minitab 20 software. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy spectrometry (EDS), and ultrasonic experiments were used to characterize and analyse the surface morphology, composition, and bond strength of the coatings. The results show that the nanoscale nickel particles can completely cover the surface of the substrate, forming a layer of nano-film. After activation and ultrasonic cleaning for 30 s at an ultrasonic frequency of 40 KHz and a power of 80 W, the surface nano-film was not destroyed, which proves that it had a high bonding strength. After the application of the plating, the plated surface had a compact microstructure, and the continuity was good. Therefore, compared with the currently commonly used zinc dipping process, this process has the advantages of being a low-cost, simple operation, and non-destructive and environmentally friendly activation process for the substrate.

A new high efficient and non-destructive mental activation process of electroless composite plating was proposed. The process utilized electromagnetic induction equipment to heat the titanium alloy substrate and used its energy to complete the activation process, which could successfully attach the nickel nanoparticles firmly to the surface of the titanium alloy; at the same time, the process pre-activated Al₂O₃ nanoparticles and added the activated nanoparticles to the plating solution. In the process of plating, the activated titanium substrate was used as the catalytic center of electroless nickel plating (ENP) for electroless composite plating. The new activation process avoided complicated traditional processes such as acid etching and zinc dipping. Such traditional processes require huge doses of chemicals, including various strong acids, so improper waste liquid treatment will cause harm to the environment. The important parameters of the process were optimized by orthogonal experiments. A scanning electron microscope (SEM), an X-ray photoelectron spectroscopy (XPS), an energy dispersive spectrometer (EDS), thermal shock experiments and friction and wear experiments were used to characterize and analyze the surface morphology, composition, binding force and friction coefficient of the coating, and analyze the coating quality by measuring the plating rate and the thickness of the coating. The results showed that the rate of electroless composite plating increased with the increase in Al₂O₃ nanoparticle concentration. When the concentration of Al₂O₃ nanoparticles reached 1.5 g/L, the ENP rate decreased with the increase in Al₂O₃ nanoparticle concentration. The adhesion of the sample was evaluated by the scratch test, which showed that the binding grade of the sample was 0, and the Vickers hardness was 688.5 HV. Results showed that the coating produced by this new process has excellent performance. Therefore, the process is an environmentally friendly and fast activation composite plating process.

To address the issue of poor corrosion resistance of the Mg–Li alloy, electroless Ni–P plating was used to create a protective coating. However, there were significant differences between the upper and lower surface coatings, which were summarized as follows: (1) compared with the lower surface, the longitudinal differences between different areas of the upper surface coating were larger; and (2) the denseness of the upper surface coating was insufficient in areas where the insoluble phase was concentrated, resulting in significantly lower corrosion resistance of the upper surface coating than the lower surface. Resolving these differences could compensate for the defects of the upper surface coating so as to improve the overall corrosion resistance of the material. Therefore, in this paper, the deposition process of Ni–P was observed and speculated, and the reasons for these differences were analyzed in combination with experimental phenomena. Based on these, two optimization measures were proposed. The SEM observation results showed that the differences between the upper and lower surface coatings were significantly reduced after optimization. The results of potentiodynamic polarization tests and EIS tests showed that the optimized upper surface coating had good corrosion resistance similar to the lower surface coating.

A new non-destructive activation process before electroless nickel plating (ENP) is proposed, which reduces the use of strong corrosive drugs and noble metals, and is environmentally friendly without damaging the surface of alumina ceramics. The process successfully attaches nickel nanoparticles firmly to the alumina ceramic surface and uses the nickel nanoparticles as a catalytic center of ENP for electroless plating. The important parameters of the non-destructive activation process were optimized by orthogonal experiments. And a scanning electron microscope (SEM), an X-ray photoelectron spectroscopy (XPS), an energy dispersive spectrometer (EDS) and thermal shock tests were used to characterize and analyze the surface morphology, microstructure, composition and binding force of the coating, and measure the plating speed and conductivity so as to analyze the coating quality. The rate of ENP reduces with the decrease of ion concentration. When the plating time is 30 minutes, the average plating rate is 10.93μm/h, and when the plating time is 90 minutes, the plating rate reduces to 8.76μm/h. The difference of coating resistivity of different samples is in proximity to each other, which directly reflects the good uniformity of coating. When plating for 90 minutes, the coating resistivity is about 103 × 10 -8 Ω·cm, which meets the international standard of Ni coating containing P. Therefore, the process has advantages of simple operation and low cost, and it is a nondestructive and environmentally friendly activation process for substrates.