The Effect of Long-Term Thermal Cycles on The Mechanical and Tribological Properties of Hot-Dip Galvanized and Galvalume Coatings

In this study, the mechanical properties and tribological behavior of galvanized and galvalume coatings produced by hot dip method have been evaluated and compared. In addition, due to the high application of these types of sheets at high temperatures, the effect of long-term thermal cycles on the properties of these sheets was studied. For this purpose, samples of carbon steel plate with galvanized coating and galvalume with the same thickness were prepared. Then, structural and surface morphology was studied by scanning electron microscope and Elemental analysis, phase composition and crystalline texture were determined by X-ray diffraction. The mechanical properties of the coatings were evaluated by using Vickers hardness test and tensile test. The tribological properties of the coatings were investigated by pins on the disk test. Laboratory findings showed that overall the strength of galvanized sheet are greater than the Galvalume sheet, while it has a relatively less long elongation. while Galvalume has a weaker abrasive behavior than galvanized. In the case of galvanized sheet heat up to 300 ° C, the iron penetration from the steel substrate to the surface of the coating occurs and it forms brittle intermetallic phases that have a negative effect on the galvanized abrasion behavior. In other side, oxide layers also form on the surface of the coating and due to a better abrasive behavior. By heating the galvalume sheet at temperatures up to 400 ° C, the surface of the cover is dark, and bulges appear on it which indicates the formation of intermetallic phases and the presence of oxide on the surface of the coating. According to the results of this research in applications that friction coefficient is important, it is not recommended to heat galvanized and galvalume coatings at temperatures, respectively, above 300 ° C and 400° C.