What are the best and necessary steps in order to achieve a good sample preperation of steel-aluminum welds/joints? I have an S355 steel and 6xxx Al-alloy weld and I am trying to prep my samples for optical microscopy and SEM.
well, It's better to prepare sample from one base to another. because whenever you want to see on microscope you should discover what happen in whole weld zone and after that focus on special region, and don't forget to grind enough and correct specially before SEM test. the etching reagent is also so important because there is some intermetallic precipitations in weld zone which only can be observed by specific reagent.
As per ASTM standards of polishing you should follow the following steps:
The samples should be grinded using 100, 200, 400, 600, 800, 1000,1200,1500, 2000 grit silicon carbide paper one after the other in the mentioned order. Each phase of the sample preparation must be executed cautiously and surface free of scratch can be obtained by engaging a sequence of consecutively finer abrasives grades. Special care must be taken to apply uniform pressure during manual grinding.
After grinding, the samples should be polished using polishing cloth laden with some suitable abrasive i.e. SiC . Diamond paste generally of 0.1- 0.5 µm particle size with desired lubricant, can be employed for obtaining mirror finish surface.
For optical microscopy:- After polishing etching should be done with desired etchant. You should also identify different etchants for the dissimilar materials. You might need to perform separate etching for both materials.
For SEM:- After polishing the samples should be free of any type of mould.
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