Mechanical galvanized steels

Therefore, this type of coating is not sensitive to defects, pinlroles or mechanical damage during service. A typical example is galvanized steel (Zn layer on steel). 

Fitzpatrick et al. [41] used small-spot XPS to determine the failure mechanism of adhesively bonded, phosphated hot-dipped galvanized steel (HDGS) upon exposure to a humid environment. Substrates were prepared by applying a phosphate conversion coating and then a chromate rinse to HDGS. Lap joints were prepared from substrates having dimensions of 110 x 20 x 1.2 mm using a polybutadiene (PBD) adhesive with a bond line thickness of 250 p,m. The Joints were exposed to 95% RH at 35 C for 12 months and then pulled to failure. 

Fitzpatrick and Watts [57] also applied imaging TOF-SIMS to deteiTnine the failure mechanisms of adhesively bonded, phosphated hot-dipped galvanized steel... 

The anodic dissolution of zinc [233, 264] was investigated in solution H3BO3 + NH4CI + Na2S04 at pH 4.4 using electrochemical impedance spectroscopy and EQCM. In the same solution, zinc anodic dissolution of different galvanized steel sheets of zinc [265] was studied. The postulated [41, 266] mechanism of Zn oxidation in acidic solution corresponds to two consecutive monoelectronic transfers. 

Mechanical equipment supports of galvanized structural steel shall be supplied to properly mount the fan, gear and motor assemblies. Each framework shall form an integral unit and be laterally supported by galvanized steel members bolted to the tower posts. 

During exposure, galvanized steel and weathering steel are expected to corrode by forming a protective surface film that retards corrosion. The rate of corrosion would then be diffusion controlled and depend upon the thickness of the film. Many of the corrosion products, particularly the carbonates, hydroxides, etc. within the film are soluble in acid solutions. In environments where increased acidity is present, dissolution of the protective film is a competing mechanism that accelerates the rate of corrosion of metals. 

Surface finish of the test coupon Various manufacturing processes can change the physical form of the metal s initial surface or produce surface films, either of which may influence the eharacteristies of the corrosion deposit that is developed when in contact with water. These effeets may influence or change the mechanism controlling the level of eontamination. The standard sit-and-soak test defines a machined smface that will not be representative of a cast surface, for example. In the first set of eonormative tests, aetual galvanized steel pipe was used to overcome precisely this sort of problem. 

Strom, M., et al. (1992). Mechanism of underfilm corrosion propagation in painted automotive galvanized steels during exposure in the new Volvo high performance chamber. Galvatech 92, Verlag Stahleisen, Dusseldorf, Germany, pp. 521-527. 

Potentiodynamic polarization measurements are quite appropriate for determination of the pitting susceptibility of aluminum coatings, and/or the corrosion current density/ corrosion rate of coated steel products in general. ASTM G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements, describes the calculation of corrosion rates and other information from electrochemical measurements. Another example of the use of DC electrochemical methods to examine the corrosion performance of coated sheet materials is a study by D. A. Jones et al. [48]. The study used polarization resistance measurements to examine the mechanism of steel and coated sheet degradation under conditions of alternate immersion. Jones compared the polarization resistance of samples of low-carbon steel, unpainted galvanized, aluminum-coated, and Zn-Ni alloy coated steel during continuous immersion and alternate immersion. Alternate immersion cyclic exposure produced a thick oxide that led to significant underfilm attack. Jones found that phosphate pretreatment tends to increase the resistance of these materials to underfilm attack. This study is an excellent example of the way electrochemical measurements can be used as a complement to other techniques to elucidate mechanistic information. 

---