The relationship between the fracture toughness and grain boundary characteristics in hot-dip galvanized zinc coatings

Abstract

This publication presents an experimental study on the relation between the grain boundary (GB) characteristics and the intergranular cracking resistance in a hot dip zinc coating. The cracking was studied using in situ tensile tests in a scanning electron microscope on small tensile samples of a hot dip galvanized steel sheet. In situ testing offered a series of advantages like monitoring the kinematical evolution of cracking without unloading, or making micrographs and OIM imaging on the same area of the tensile sample. The grain boundaries were classified into random and special boundaries (respectively Low angle boundaries and Coincidence site lattice-CSL boundaries). These special boundaries which account for 3.5% of the whole boundaries clearly show better cracking resistance than the random boundaries. The only special boundaries which present cracking failure are in an orientation with their normal direction close to the tensile direction, i.e. submitted to a maximum effective stress. The grain boundaries characteristics are obtained from EBSD individual orientation measurements.

Intergranular stress corrosion crack propagation in hot-rolled AZ31 Mg alloy sheet

“…The number of CSL grain boundaries was also relatively low for all materials. This is an inherent characteristic of HCP metals [52,53]. Thus, the potential for improving the resistance of the materials to IG-SCC by grain boundary engineering, as has been proposed for Ni and its alloys [54], is limited.…”

A Review of Recent Developments in Coating Systems for Hot-Dip Galvanized Steel

“…The anticipated galvanizing coating after zinc immersion can be realized when cooperating with a proper type of steel. In fact, the microstructure and mechanical property of prepared galvanized coatings would be significantly influenced by the chemical composition of matrix steel (Breval and Rachlitz, 1988;Lin, 1999;Vourlias et al, 2004;Vincent et al, 2006;Maaß et al, 2011;Schulz and Thiele, 2012;Kania and Liberski, 2014;Pokorny et al, 2016). The content of carbon and silicon in the matrix played a guiding role on the coating properties, meanwhile the component of manganese, phosphorus, and sulfur had relatively little impact on it.…”

Formability of 800 MPa Grade Hot‐Dip Galvanized Steel Sheet

“…For galvanized steel sheets, features of zinc layer during the deformation also need to be considered carefully. There have been many studies on the formability of galvanized steel sheets . The zinc layer is composed of intermetallics including the outer η phase, the subsequent ζ phase, the δ phase, and the inner γ phase .…”

“…And according to the research of Asgari and Vincent, crack propagation is influenced by texture and grain boundary characteristics in the η layer, in which cracks develop inward from the outer zinc layer. Severe macro‐cracks might be developed when microcracks from different directions unite . Song studied the failure of zinc layer on dual‐phase steel sheet during tensile deformation, and he found the pre‐existed microcracks and voids at the zinc grain boundaries propagate along the zinc grain boundaries and form crack nets within the zinc layer under tension .…”