Residual Stresses in Galvanizing

Abstract

Zinc coating is formed by heterogeneous assembly of phases in which mechanical properties greatly differ. In the galvanizing process the great difference between the linear thermal expansion of the iron substrate and the Zn has proven to be the source of important residual stresses. The primary objective of this paper is to determine the residual stresses which promote crack formation and deterioration of corrosion resistance. Because direct determination by x-ray diffraction has been difficult, three other methods are proposed. The first one led us to calculate an average stress by measuring the variation of crack length with applied load resulting from a Vickers small indentation. The second is an application of the Timoshenko's bimetallic strip method based on the difference in thermal expansion coefficients. The third is deduced from the variation of the curvature of one-face galvanized specimens. These results are compared and the homogeneous value of residual stresses are shown.