Liquid Metal Induced Crack Formation in Molten Zinc – a Damage Mechanism Driven by Diffusion and Stress

Abstract

Tests have been performed on hot-dip galvanized four point bend specimens to investigate how different levels of compressive stresses and tensile loads under simultaneous thermal activation below the melting temperature of the zinc coatings affect liquid metal assisted cracking (LMAC). While the material volumes under tensile stress developed intergranular cracking, areas under compressive stress – even using a tin and lead alloyed zinc melt – did show no signs of damage. The flat specimens tested without superimposed loading did only show intergranular edge defects in the order of several grain layers when ageing during several hours in differently alloyed zinc melts. Moreover, in the context of the tests, the dominating effect of the alloying elements lead and tin could be confirmed for the intergranular crack formation. Furthermore, the particular importance of the material condition for the occurrence of the damage by LMAC could be shown by means of the progression of the crack formation in the microstructure.

Change of Mechanical Properties of Zinc Coatings After Heat Treatment

“…Even though the anticorrosion coating belongs to cathodic protection of base metals, microcracks in the coating significantly lower its service life. Microcracks due to higher heat treatment can be eliminated by specific chemical composition of the zinc bath (Körber et al, 2012).…”