Zinc coating is widely used in the corrosion protection of steel.But the difference of zinc coating is very big, so the metallographic sample preparation is a challenge.This application shows the validated and optimized method, these methods will help to sample preparation of zinc coating in a quick and reliable way, so as to get high quality image for structural interpretation.
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Figure 1: aluminum, zinc plating, etching by 1% nitric acid ethanol, 500 x
Figure 2: the surface of hot-dip zinc coating, SEM
Steel continuous by zinc bath.The coating thickness is usually between 7 to 15 (including m, but it is also possible (including 20 m thick.After completion of processing, some hot dip galvanized parts could make a further processing, including heat treatment or static immersion in molten zinc pool.
There are a lot of very specific method of galvanized.You can be inComplete application instructionsThe details about these methods.
Figure 4: the electrodeposited zinc coating, polishing to 1 microns.With pure alcohol for a final cleaning/polishing, 1000 x
Figure 5: after the processing of the zinc coating, the ethanol 0.5% nitric acid etching, at the edge of the substrate metal as gamma phase, zinc base has a large delta cylinder in the body, 200 x
Because of the hardness and thickness of the zinc coating will have differences, so in the process of metallographic sample preparation have different performance.In addition, some of the zinc coating will react with water and makes the sample preparation process difficult.
With the sampleThe challenges in the process of
Galvanized samples with sample can be a challenge, especially in the case of pressed for time.In order to avoid shrinkage clearance, must ensure that the correct adhesion between materials and samples.
Figure 6: between sample and resin shrinkage clearance can cause water damage and alcohol stains, as well as the round corner and grinding debris residues, 200 x
Grinding andpolishingThe challenge of steps
According to the purity of zinc coating, zinc coating will become more soft and more sensitive to water, especially ordinary hot dip plating and electrolytic deposition coating, zinc content is very high.This will make them soft and prone to mechanical deformation.They do not clean with water.
Figure 7: soft coating, grinding and polishing scratches, can be seen 500 x
Figure 8: zinc and lead to change color after reaction with water erosion, 1000 x
Steel plate cutting is relatively simple, can use the appropriate alumina abrasive cutting wheel.With shears or iron to shear could make the steel plate bending seriously, and causes the coating cracks.
Figure 9: after cleaning with water hot dip coating, 500 x
Figure 10: clean with alcohol after hot dip coating, 500 x
Zinc coating is the most commonly used etching agent 0.5 2% nitric acid ethanol.Etching time is short, just a few seconds.Excessive etching is easy to happen, so the etching should be careful.
Figure 11: Galfan coating by 0.5% nitric acid ethanol etching.Primary dendritic structure, 500 x
Figure 12: the same coating as figure 9.Higher magnification, shows the zinc rich solid solution alpha and beta by alpha and rich aluminum phase lamellar eutectic structure, consisting of 1000 x
Figure 13: Galvaneal coating by 1% nitric acid ethanol etching.Between the steel matrix and the zinc coating showed a thin iron rich gamma diffusion layer.Concentration of the coating for zinc iron structure, with the distance of the matrix metal, 1000 x
All images by Danish application specialists Olafur Olafsson provided.
About the details of the zinc coating of the metallographic sample preparation,Please contact our application specialists.
