| The application for magnesium alloys in the automotive, electronics and communication industries has been expanding at a high rate due to their low density, high strength-to-weigh, rigidity-to-weigh ratio, good damping capacity and good electromagnetic shielding properties.In this thesis, the effect of combined electromagnetic stirring and Ce,Sr,Ca on microstructure and corrosion performance for AZ91 magnesium alloy, which is the most widely used magnesium alloy, was studied. In addition, grain refinement mechanism was discussed. Microstructures of alloys were observed and studied by means of optical microscope(OM),scanning electron microscope(SEM),differential thermal analyzer(DTA) and X-ray diffract analyzer(XRD)and so on. Grain size and alloy hardness was measured, the linear relation was presented between grain size and hardness by regression analysis. The experimental results showed that the effect of combined electromagnetic stirring and Ce,Sr,Ca could all refine grain size. When electromagnetic stirring voltage is 100V, 0.2%～0.8%Ce added to AZ91, 0.8%Ce addition could get the finest grain and maximum hardness value. 0.1%～0.3%Sr addition to AZ91 could refine grains too. 0.2%Sr addition could get the finest grain and maximum hardness value. 0.1%～0.3%Ca addition to AZ91 could also refine grains. 0.2%Ca added to AZ91 could get the finest grain. Regression analysis showed that the relationship between grain size and hardness is in agreement with Hall-petch expression. Besides, grain refinement mechanism of combined electromagnetic stirring and Ce,Sr,Ca on AZ91 was discussed by differential thermal analyzer.The effect of combined electromagnetic stirring and Ce,Sr,Ca on the corrosion property and corrosion mechanism in 3.5%NaCl solution were studied by means of static weight-loss test and X-ray diffract analyzer. The experimental results showed that electromagnetic stirring and 0.2%～0.8%Ce could reduce corrosion rate remarkably. When electromagnetic stirring voltage is 100V, 0.5%Ce addition could get the minimum corrosion rate. Electromagnetic stirring and 0.1%～0.3%Sr could improve corrosion property too, but the effect is inferior to Ce. 0.1%～0.3%Ca... |
PDF Full Text Request