| Along with the more and more magnesium alloys used in the industrial production and daily life, The property of magnesium alloys have been pay more attention to. Many countries are investing whopping on research. The research emphasis on two points, one is plastic improvement and another one is enhance the corrosion resistance by scholars at home and abroad. The key points of research are focus on atmospheric corrosion and immersion erosion. The major study of immersion test is the corrosion mechanism of magnesium alloy in different solutions, and the report about corrosion mechanism of magnesium alloy in severe environment such as salt spray test is little. The most applied magnesium alloy is AZ series alloy at present so we should have to understand its corrosion behavior in salt spray environment.β-Mg17Al12 is the most important second phase in AZ series alloy which volume fraction, morphology and distribution situation in the alloy that play an important role affect the corrosion behavior. The research on the single phaseβ-Mg17Al12 will be a beneficial assistance for understanding the corrosion mechanism of magnesium alloy. Magnesium alloy has low corrosion resistance, surface coating was used to improve the corrosion resistance of thin-walled die cast AZ91D magnesium alloy in this paper. The aim is to explore a simple composition organic coating. The property of specimen was characterized by XRD, SEM, DSC , Electrochemical workstation, etc, and analyzed the relationship between them. The following results were obtained:1. In the 48 hours'test range ,the weight loss rates sequence of three cast alloy as follow: AZ91D>AZ61A>AZ31B2. Different aluminum content result in the difference corrosion morphology. Micro-galvanic consists ofβphase andαphase is the main force in the corrosion process.βphase can change the direction of corrosion take place but the retardation effect on corrosion process is weak.3. The main corrosion product is Mg(OH)2. Magnesium-aluminum hydrate was detected after 48h corrosion process, XRD test show the hydrate is Mg6Al2(OH)18·5H2O.4. The density of single phase Mg17Al12 is low at 2.0/cm3 and the hardness is high more than 220HV.5. The corrosion potential of single phase Mg17Al12 is -1.0V which higher than all the AZ series alloy.6. The dominant factor of resulted in crack formation of single phase Mg17Al12 in NaCl solutions is hydrogen induced cracking.7. In test range the optimum temperature of phosphating for die cast AZ91D is 50℃and time is 1 min. 8. The impedance measurement show the electrical resistance of organic coating is 109?. The corrosion current density of sample with organic coating is lower 3 orders of magnitude than the bare sample.9. The immersion test show that organic coatings are unchanged after 10 days erosion in 10% H2SO4 , 10% NaOH and acet. The organic coatings unchanged in boiling water after 72h immersion test. The adhesion between coating and substrate is 0 grade through cross cut test.
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