| Magnesium alloys have been increasingly used in the automotive industry,aircraft industry and electronic industry for their high strength-to-weight ratio,good electromagnetic shielding characteristics and good recycling property.However, the insufficient corrosion resistance has been being a seriouslimitation against their wider practical application. A number of possible coatingtechnologies have been used to improve the corrosion resistance of magnesiumand its alloys, but all these technologies have some inevitable disadvantages. Inthis thesis, an aluminized coating was formed on the surface of pure magnesiumto improve its corrosion resistance by vacuum solid diffusion treatment.The effect of the technological parameters (such as the temperature, thetime and the vacuum degree) to the microstructure and property of thealuminized coating was analyzed. The results showed that an ideal aluminizedcoating could be formed when treated at 400～445℃for 60～120min with acacuum level of better than 10-2 Pa.It was indicated by OM, SEM(equiped with EDS) and XRD analysis that the thickness of the aluminized coating varies from 100μm to 600μm accordingto the different diffusion temperature and different diffusion time. Thealuminized coating is uniform and dense, and the bond between the coating andthe matrix is good. The intermetallic compoundβ-Mg17Al12 phase is a maincomponent of the coating. An Al alloy layer is formed on the surface of thesample after treated at 420℃for 90min.The properties of the aluminized coating were analyzed. The microhardnesstesting showed that the aluminized coating has a much higher hardness valuedue to the exist of the intermetallic compounds, and this is meaningful toincrease its wearing resistance. The immersion testing and the electrochemicaltesting showed that the aluminized samples have a better corrosion resistancethan the untreated ones, even better than AZ91D magnesium alloy.The mechanics of the formation and corrosion resistance of the aluminizedcoating and the influences of the main processing parameters were discussed inthis thesis based on the above experimental results.The above results indicate that the corrosion resistance and themicrohardness of pure magnesium can be improved by the vacuum soliddiffusion. These works explore a new way to the surface alloying of magnesiumalloys via vacumm solid diffusion. |
