Xianyong Zhu

Characterization and property of microarc oxidation coatings on open-cell aluminum foams

The ceramic coatings were prepared on open-cell aluminum foams by microarc oxidation (MAO) treatment in an alkaline-silicon electrolyte. The morphology, microstructure, elemental distribution, and phase composition of the MAO coatings were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, respectively. The corrosion behaviors of the coated and uncoated foams were evaluated by electrochemical polarization measurement. The results show that the MAO coatings cover the surface of open-cell aluminum foams. The coatings were composed of an external porous layer and an internal dense layer. The main phase of the MAO coating phase is γ-Al2O3. The coated aluminum foams exhibit more positive corrosion potential and lower corrosion current density compared with the uncoated aluminum foams.

Influence of Sulfate-Reducing Bacteria on the Corrosion Residual Strength of an AZ91D Magnesium Alloy

In this paper, the corrosion residual strength of the AZ91D magnesium alloy in the presence of sulfate-reducing bacteria is studied. In the experiments, the chemical composition of corrosion film was analyzed by a scanning electron microscope with energy dispersive X-ray spectroscopy. In addition, a series of instruments, such as scanning electronic microscope, pH-meter and an AG-10TA materials test machine, were applied to test and record the morphology of the corrosion product, fracture texture and mechanical properties of the AZ91D magnesium alloy. The experiments show that the sulfate-reducing bacteria (SRB) play an important role in the corrosion process of the AZ91D magnesium alloy. Pitting corrosion was enhanced by sulfate-reducing bacteria. Corrosion pits are important defects that could lead to a significant stress concentration in the tensile process. As a result, sulfate-reducing bacteria influence the corrosion residual strength of the AZ91D magnesium alloy by accelerating pitting corrosion.

Sound Absorption Characteristics of Aluminum Foams Treated by Plasma Electrolytic Oxidation

Open-celled aluminum foams with different pore sizes were fabricated. A plasma electrolytic oxidation (PEO) treatment was applied on the aluminum foams to create a layer of ceramic coating. The sound absorption coefficients of the foams were measured by an impedance tube and they were calculated by a transfer function method. The experimental results show that the sound absorption coefficient of the foam increases gradually with the decrease of pore size. Additionally, when the porosity of the foam increases, the sound absorption coefficient also increases. The PEO coating surface is rough and porous, which is beneficial for improvement in sound absorption. After PEO treatment, the maximum sound absorption of the foam is improved to some extent.

Compressive Properties of Open-Cell Al Hybrid Foams at Different Temperatures

Hybrid Ni/Al foams were fabricated by depositing electroless Ni–P (EN) coatings on open-cell Al foam substrate to obtain enhanced mechanical properties. The microstructure, chemical components and phases of the hybrid foams were observed and analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The mechanical properties of the foams were studied by compressive tests at different temperatures. The experiment results show that the coating is mainly composed of Ni and P elements. There was neither defect at the interface nor crack in the coatings, indicating that the EN coatings had fine adhesion to the Al substrate. The compressive strengths and energy absorption capacities of the as-received foam and hybrid foams decrease with the increasing testing temperatures, but the hybrid foams exhibit a lower decrement rate than the as-received foam. This might be attributed to the different failure mechanisms at different testing temperatures, which is conformed by fractography observation.