I am studying oxidation behavior of magnesium alloys containing neodymium (0.78%Nd) wherein effect of super saturated solid solution treatment in regards to microstructural changes is to be observed and furthermore the oxidation rate is to be evaluated and compared with as cast samples.
The samples are cut in equal size, heat treated to 525 degree C for 10hrs ground and polished for SEM analysis.
0.9%Nacl solution is used for studying the oxidation.
SEM micrographs of both as cast and heat treated samples after they are submerged in salt solution for 24hrs are attached below.
I need some inputs on microstructural observations in regards to both heat treated and as cast forms for comparison.
I don't understand how to link the photo and the backstory of the sample.
Dear Akshat Pravin Kulkarni
Is the SEM micrographs (Mg-05Nd+Exp-SE-10000x_001.tif) belongs the as cast or heat treated sample. Your answer will be very helpful to follow the case study.
Best regards,
Dear Akshat Pravin Kulkarni
The solubility of Nd in the Mg matrix is not too much that can make the potential difference between the Mg matrix and the Mg-Nb second phases as small as can reduce the whole microgalvanic corrosion. Now if this is the case with the as cast state, then the high temperature annealing will increase the solubility of Nd and so new distribution map for the second phases will got within the matrix. In other words, grain size change during the annealing process and second phase's migration from the grain boundaries to the Mg matrix in addition to the new structure forms of the second phases all of these will affect the corrosion resistance. As a result there is a competitive process as;
The microstructure with larger grain size involves a lower number of grain boundaries which result in decreasing the corrosion resistance.
The diversity of the possible second phase as reported as Mg12Nd, Mg41Nd5 and Mg24Nd is the reason of the poor corrosion resistance of the Mg-Nd alloy by providing more cathodic phases and causing more dissolution of the Mg matrix.
The positive effective role of Nd element is to produce a microstructure that can reduce the hydration of the corrosion product film of Mg-Nd specimens and then improve the protective performance of the corrosion product.
This means that the mount of second phases and grain size are well directed by the annealing process resulting in a much change in microstructure homogeneity which will change the microgalvanic corrosion amount.
Now, looking at the SEM micrographs of both as cast and heat treated samples after they are submerged in salt solution for 24hrs, you can see the difference in the role of Nd element in reducing the hydration of the corrosion product film which means that there are quite change in their microstructure as cleared in above.
Best regards,
@Mohammed Hussein j. H. Al'Atia Thanks a lot Sir for your much detailed inputs.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Coating