Study Of Phosphate/Stannate Chemical Surface Treatment Techniques For Magnesium Alloys

Magnesium alloys have a number of desirable features, including low density, high strength-to-weight ratio, good conducts electricity and heat capability, excellent cast capability, good machinability, damping characteristics and reusing, and its use in a variety of applications, particularly in aerospace, automobile, mechanical, electronics components, military industry. Magnesium alloys are recognized as the green materials in 21st century. However, Magnesium is very active and is susceptible to corrosion when exposed in practical application environment because of the oxidation coating is very loosen. The limited use of magnesium alloys in engineering applications results mainly from its poor corrosion resistance.A new phosphate/stannate conversion coating system for the corrosion protection of die-casting AZ91D and extruded AZ31B magnesium alloys was studied in this dissertation. This study presented an investigation of corrosion property and forming mechanism of the phosphate/stannate conversion coating formed on die-casting AZ91D and extruded AZ31B magnesium alloys. During the study of chemical surface modification process, the best technological conditions for the formation of phosphate/stannate conversion coating and subsequence coatings were settled.During the study of phosphate/stannate surface modification process, using mutual trials, the kinds of phosphate/stannate solution, the concentrations of the components in the solution, temperature and operate time were studied. The conversion coatings were checked by many kinds of methods. The phosphate conversion coating conducts little or no electricity, while stannate conversion coating conducts electricity is good, and possess excellent Electro Magnetic Interference. The thickness, surface look, structure and the phase constitution of conversion film were studied by scanning electron microscopy (SEM) and XRD. The results showed that the...