Zn coating II - Coating defects

Zn coating II - Coating defects

Figure 1: Scanning electron micrographics of areas in the wear tracks of Zn and zinc-iron coatings. (a) and (b) galvanized; (c) and (d) ZnFe.

Figure 2: Micrograph of wear/corrosion products on the wear track of the Zn-Fe sample.

Defect name: Zn coating
Record No.: 1680
Type of defect (Internal/Surface): Surface
Defect classification: Coating defects
Steel name: Steel
Steel composition in weight %: No data.
Note: In fact, when the micrographs of wear tracks are observed it is possible to see that the Zn-Fe surface shows more debris particles when compared to galvanized surface, Figure 1. A spread structure is visualized on the wear track of Zn-Fe surface, Figure 1d. This fact could indicate plastic deformation of the coating or wear particles compacted. Plastic deformation could take off relatively large particles by an adhesive wear mechanism. On the contrary, at the galvanized surface defined grooves were observed on the wear tracks. Some sticking of fragmented abrasive particles could also been observed, Fig 1b. These remarks are indicative that the wear mechanism predominant to galvanized surface was abrasive wear.

Actually, as illustrated in Figure 1a, at the surface of the wear track formed on the Zn-Fe sample, heterogeneous spherical-like agglomerates of wear/corrosion products are observed. These products were not seen on the wear tracks of zinc, which appeared almost free of wear debris. These observations have a two-fold relevance. First the presence of the wear/corrosion products appears to be responsible for the relatively low friction coefficient monitored during the test. But, on the other hand, it indicates that the formation of wear/corrosion debris becomes quite more important in the Zn-Fe samples.
Reference: Not shown in this demonstration version.