Threaded hole corrosion failure analysis

2020 - threaded hole corrosion failure analysis 02 - 22 Zeng Zhiwei Wang Junzhao ( Shenzhen mation testing technology co. , LTD. ) Abstract: the failure parts for galvanized sheet threaded hole. Finally through visual inspection, SEM, EDS and other characterization methods, the failure reasons of threaded hole is determined. Key words: galvanized sheet, Threaded hole; Failure analysis diagram 1 product appearance pictures 1 case background SECC galvanized sheet after cutting punch forming, and then to drill a bottom hole plate, crowded teeth tapping ( Uninterrupted filling) Is made after finished product, finished product rust began to appear in the thread hole for 20 days. 2 analysis method will fail products along the screw thread hole cut open, and found the thread surface has been covered with rusty spot, and the distribution regularity, certain are far away from the surface of the two ring threaded corrosion. For failure and normal products threaded hole section slices, respectively do the normal product of thread surface have no obvious corrosion phenomenon; Failure products have obvious corrosion phenomenon of corrosion products do EDS analysis, the results show that there is a small amount of Cl. At the same time, the ICP results show that the galvanized sheet accord with the requirement of the material. In order to further determine the introduction of Cl element, tapping oil in FTIR analysis, found the main components in the mineral base oil. After drying of the tapping oil EDS testing, the results show that S and Cl content in oil of tapping are above 3%. Figure 2 threaded hole test result picture 3 outcome therefore threaded hole is the root cause of rust tapping oil contains element S and Cl. Threaded hole base material directly exposed and exposure to air, after the Cl imbibe formation of electrolyte, produce the Cl ion autocatalytic electrochemical corrosion, and the corrosion reaction of Cl is not consumption, prompting deep corrosion to find development.