Plasma electrolytic oxidation (PEO) process is proved to be an effective technique for forming highly protective oxide film on Mg alloy AZ31. A comparative study has been done to investigate the PEO films deposited from silicate solution with NaF, Al₂O₃ nano-additives. The surface morphology feature, phase composition and elemental composition were examined by field scanning electron microscope, energy dispersive X-ray, X-ray diffraction. Doping of additives showed an obvious effect mainly on the peak of MgO and the thickness of the PEO films. Fluoride has a promising role and its presence considerably resulted in thicker and compacter films with improved corrosion resistance. Vice versa unexpected negative results had been obtained in the presence of alumina additives. It is assumed that fluoride ions enhanced ions conductivity during PEO process therefore promoted the film growth rate. On the other hand, the bulk Al₂O₃ particles hindered the ions movement through the coating deposition leading to thinner less compact films formation.

This paper introduces a novel coating process based on micro-arc oxidation (MAO) for formation of ceramic MgO layer over some newly developed magnesium alloys in an environmentally friendly electrolyte by anodization. Electrochemical corrosion testing showed that the corrosion resistance of bare AMS4429 is much better than that of AZ31HP-O and MZ due to formation of protective Nd-rich oxide layer in AMS4429 compared to less protective Al- and Zn-rich oxide films for AZ31HP-O and MZ respectively. Surprisingly, the corrosion resistance of MAO coated MZ is about 50 times higher than the bare one. The deposition, characterization and electrochemical characteristics of the fine porous MgO protective layer formed due to MAO coatings were investigated in details.

The corrosion resistance of Mg–alloys 3%Zn–0.8%Ca is enhanced by plasma electrolytic oxidation (PEO) through doping two kinds of nano-additives (NaF and Al₂O₃) in the silicate electrolyte. Those additives yielded less roughness-compact films composed of higher intensity of stable MgO phase, consequently corrosion resistance enhancement. Nano-ceramic Al₂O₃ exhibited more isolation than NaF for ZX alloy due to the high tendency to oxidize Mg to MgO through a direct step. On the other side, NaF needs two steps to form MgO passing by an intermediate phase. The mechanism for the additives influence will be discussed in detail on the light of morphological characteristics, XRD and their corrosion behaviour.

In this research, the surface of magnesium alloy AZ31 is modified by friction stir processing (FSP). The modification process consists of synthesis AZ31/ZnO composite by establishing holes at surface which are filled with nano ZnO and FSP was carried out at traverse speed 45 mm/ min. and...