Liquid Metal Assisted Crack Formation in Zinc Melts, Representation of the Damage Pattern Using 3D Computed Tomography

Abstract

Abstract In the past, liquid metal induced galvanizing cracks were either analyzed on the metallographic section in the respective partially ground plane of view, or the exposed main fracture surface was examined in the scanning electron microscope (SEM). Thus, possibly existing secondary cracks remained undetected. Three-dimensional computed tomography (CT) allows for a representation of all cracks including their branchings and ramifications and makes possible an analysis of an overall picture of the network of cracks. Differences in the effect of different zinc melts can be further identified by means of 3D analysis and the load situations that promote the crack initiation during hot-dip galvanizing can be differentiated more clearly using laboratory samples. Key results are the representation of cracks parallel to the direction of the main load (B-cracks) which are oriented with the pearlite bands and apparently penetrate significantly deeper into the base material than the macroscopically visible crack which is orientated perpendicular to the direction of the main load (A-crack). A relationship between the occurrence of B-cracks and the used zinc alloys could only conditionally be shown. Examinations on flat samples, which had been dipped into various metal melts under load-free condition, yielded more or less comparable results, in particular for molten pure tin and molten pure lead. In this case, the pearlite phase is preferentially damaged even without introducing an external load into the samples.