The aluminum alloy welding samples exhibited the phenomenon of a rainbow film after being exposed to corrosion and cleaning. The pictures show the aluminum alloy welding samples with the rainbow film, and the surface of the sample re-prepared after vacuum impregnation to fill the pores.
When there are gaps between the sample and the resin (as shown in the figure below), water, alcohol, or corrosive agents will flow out from the gaps and sample pores during the drying process, and the contaminated sample area will be colored, resulting in a “rainbow film” that makes inspection difficult and even makes it impossible to conduct the inspection.
Solution:
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Use edge-protecting epoxy resin and vacuum cold embedding to ensure that the resin fully fills the sample pores and the gaps between the sample and the resin.
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Avoid using compressed air to dry the sample after final polishing because compressed air contains oil or water.
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Clean and dry the sample immediately after each sample preparation process.