Zhenjun Peng

Corrosion behaviour of plasma electrolytic oxidation coated AZ91 Mg alloy: influence of laser surface melting pretreatment

Plasma electrolytic oxidation (PEO) was performed on a laser surface melting (LSM) modified AZ91 Mg alloy. The effect of LSM pre-treatment on the long-term corrosion resistance of the PEO coated AZ91 alloy was evaluated. Results showed that the LSM pretreatment had a negligible effect on the phase composition and microstructure of the PEO coatings. However, after LSM pretreatment, the long-term corrosion resistance of the PEO coated AZ91 alloy revealed a large enhancement. This was mainly ascribed to the improved corrosion resistance of the substrate resulting from the change of microstructure characteristics induced by the LSM treatment. This provided an alternative approach to improve the long-term corrosion resistance of the PEO coated Mg alloy by appropriate surface modified pretreatment of substrates.

One-step electrochemical fabrication of bilayered MgO/polymer coating on magnesium alloy

This research demonstrates a novel one-step electrochemical method to fabricate thick bilayer coatings on magnesium alloy in acid phosphate electrolyte containing aniline monomer and styrene-acrylic emulsion (SAE) with pulsed DC voltage. The morphologies, XRD and FTIR results show that the bilayer coating consists of an inner oxide layer and an outer polyaniline (PANI)/SAE composite layer. It is believed that the bilayered structure achieved results from a hybrid process combining electropolymerization (EPM) of aniline, electrophoretic deposition (EPD) of SAE and plasma electrolyte oxidation (PEO) of magnesium alloy substrate. Electrochemical corrosion tests indicate that the bilayer coating can provide superior corrosion protection to the magnesium alloy substrate in 3.5 wt.% NaCl solution.

A comparative study of characterisation of plasma electrolytic oxidation coatings on carbon steel prepared from aluminate and silicate electrolytes

ABSTRACT Two kinds of PEO coatings were prepared on low carbon steel from aluminate electrolyte and silicate electrolyte, respectively. The coating surface and cross-section morphologies were observed by scanning electron microscope. The elemental and phase compositions were investigated by energy-dispersive spectrometer and X-ray diffraction, correspondingly. The scratch test was employed to examine the adhesion of the PEO coating. The electrochemical tests were used to evaluate the anti-corrosion property of PEO coatings. It was found that more substrate was oxidised during PEO process under the same constant voltage for the same length of time in silicate electrolyte than that in aluminate electrolyte. Besides, the silicate PEO coating grew faster than aluminate PEO coating. Compared with the uniform distribution of elements in aluminate PEO coating, silicate PEO coating exhibited a two-layered structure. The two-layered structure of the silicate PEO coating led to a negative effect on the adhesion. The aluminate PEO coating showed a better anti-corrosion property because of its denser structure.

Proton irradiation effects on the structural and tribological properties of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was irradiated with protons in a ground-based simulation facility to study the effects of proton irradiation on the structural and tribological properties of PTFE. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (ATR-FTIR), while the tribological properties were evaluated by friction and wear tests. It was found that proton irradiation induced the degradation of PTFE molecular chains, resulting in the increase of C concentration and the decrease in F concentration on the sample surfaces, and the surface chemical structure and morphology of the samples changed, which affected the friction coefficient and decreased the wear rate of the specimens as the friction and wear tests revealed.