Study On Microbiologically Influenced Corrosion Of AZ91 Magnesium Alloy Based On In-situ Corrosion Method

Magnesium alloys are widely used in recent years due to their remarkable performances. With the development of mechanical products, video, computer and communication, the utilization of magnesium alloy components increases with a rate of 25%. Also, the application of magnesium alloys exhibits an attractive prospect. However, the application of magnesium alloys is restricted due to their bad corrosion resistance. Microbiologically influenced corrosion of metals involves the metabolism of bacteria. Usually, the metabolism of bacteria induced the corrosion of materials. It is easy to observe that a number of structural components were destroyed under the influence of bacteria. As a result of statistic, the corrosion induced by bacteria was more than 20% in general in the corrosion of metals and architecture materials. The loss directly induced by bacteria achieved approximately 300～500×108 dollar per year. Therefore, the research about the microbiologically influenced corrosion of magnesium alloys is very significant.As compared with the immersion corrosion method, in-situ corrosion method involves the addition of agar. The utilization of agar help the bacteria grow on the surface of magnesium alloy originally. The metabolism of bacteria and the effect of the life activity were directly observed with the use of in-situ corrosion method.Although some research productions were acquired, the mechanism involved the microbiologically influenced corrosion of magnesium alloy await an advanced research. So, AZ91 magnesium alloy was adopted in this paper for the study of the microbiologically influenced corrosion about magnesium alloy. The study on the microbiologically influenced corrosion of magnesium alloy was embarked as follows:(1) The standard API culture was adopted and optimized. In one hand, the culture medium should satisfy the growth of sulfate-reducing bacteria. In another hand, the ion concentration should be decreased as possible in order to give prominence to the effect of bacteria.(2) The in-situ corrosion method is an effective method for the study on the microbiologically influenced corrosion of magnesium alloy. The in-situ corrosion method is an original invented corrosion method for the study on the microbiologically influenced corrosion of magnesium alloys.(3) The corrosion behavior of AZ91 magnesium alloy under the sterilized corrosion condition was studied in compared with that under the inoculated condition. Sulfate-reducing bacteria accelerated the corrosion rate of magnesium alloy with a characteristic of pitting corrosion.(4) At the very beginning, biofilm formed on the surface of AZ91 magnesium alloy and restricted the ion diffused to the surface of magnesium alloy. The metabolism of sulfate-reducing bacteria induced the pitting corrosion of magnesium alloy.(5) The addition of rare earth Ce did not change the main components of corrosion film. At the same time, the free corrosion potential shifts to the negative direction due the grain refinement effect of rare earth.(6) Ce improved the corrosion resistance of magnesium alloy by the grain refinement and improving the distribution ofβphase.