Zhixiu Wang

Microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy by micro-arc oxidation

Abstract The microstructure and mechanical properties of ceramic coatings formed on 6063 aluminium alloy obtained in silicate-, borate- and aluminate-based electrolyte without and with nanoadditive Al 2 O 3 and TiO 2 by micro-arc oxidation (MAO) were studied by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness and friction–abrasion tests, respectively. SEM results show that coatings with nanoadditive have less porosities than those without nanoadditive. XRD results reveal that nanoadditive-containing coatings contain more oxides compared with nanoadditive-free coatings in all cases, which are consistent with the EDS analysis. Mechanical properties tests show that nanoadditive Al 2 O 3 -containing coatings have higher microhardness values compared with the other coatings obtained in silicate-, borate- and aluminate-based electrolyte. On the other hand, nanoadditive has a positive effect on improving the wearing-resistance of MAO coatings in all cases. Furthermore, the borate-MAO coatings present an inferior anti-wearing property compared with the silicate- and aluminate-MAO coatings for both the nanoadditive-free and nanoadditive-containing coatings.

EFFECT OF STRUCTURAL PARAMETERS ON THE THERMAL STRESS OF A NiFe2O4-BASED CERMET INERT ANODE IN ALUMINUM ELECTROLYSIS

Inert anode has been a hot issue in the aluminum industry for many decades. With the help of FEA (finite element analysis) software ANSYS, a model was developed to simulate the thermal stress distribution working condition of an inert anode. To reduce its thermal stress, the effect of some parameters on the thermal stress distribution was investigated, including the anode height, the anode radius, the hole depth, the hole radius, and the radius of inner chamfer and outer chamfer. The results showed that in the actual working condition of an inert anode, there existed a large axial tensile stress near the tangent interface between the anode and bath, which was the major cause of anode breaking. Increasing the anode height and reducing the hole depth properly seemed to be beneficial for the stress distribution. With the increase of anode radius, the stress distribution became better first and then deteriorated, the reasonable value was between 0.045 to 0.06m. The hole radius had a significant effect on the stress and a smaller radius would reduce the thermal stress. The effect of the radius of the inner chamfer and the outer chamfer was less than other parameters.

Preparation and characterization of ultra-thin Pd-Ag alloy membranes

Ultra-thin Pd-Ag alloy membranes were prepared initially by cold rolling, and it was found that there exist a large number of defects such as pinholes or cracks in the as-rolled membranes. Subsequently, these defects were repaired using electroless plating technique. The morphologies of the membranes have been examined by scanning electron microscopy (SEM). It was observed in some as-repaired membranes that the defects were disappeared. A hydrogen permeation study has demonstrated that the as-repaired Pd-Ag alloy membranes were of high hydrogen permeation flux and hydrogen selectivity.