The cracking of zinc spangles on hot-dipped galvanized steel

The cracking of zinc spangles on hot dipped galvanized sheet steel was studied under controlled conditions. It was confirmed that there are two major modes of failure—boundary cracking and intragranular basal cleavage. There are four types of surface topographiesviz “mirror-like”, “feathery”, “dimpled” and “ridged”. Of these only the last type, “ridged”, was found to have its basal planes lying at an angle to the plane of the sheet. These spangles also tended to fracture most readily when strained. Hence a relationship between surface topography, crystallographic orientation and fracture behavior has been established. The implications of these findings for paint adherence is discussed. Formerly Senior Lecturer, University of Newcastle.