Sn and Ti influence in bending cracks path in hot dip galvanizing coatings (original) (raw)
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Damaging and crack path in bended galvanized specimens: influence of Pb and Sn contents
International Conference on Crack Paths (CP2009), 2009
Hot-dip galvanizing is one of most important protection technique against corrosion in many environments. In this work damage and crack propagation in intermetallic zinc based coating phases was investigated in order to evaluate chemical influence of Pb and Sn in the bath, comparing not-alloyed zinc bath. Hot dip zinc coated ipersandelin steel specimens were investigated in order to identify the main damaging micromechanisms during bending tests, considering both chemical composition and intermetallic phases distribution influence. Longitudinal sections of bended specimens were observed by means of a LOM (Light Optical Microscope) and main damage micromechanisms were identified as longitudinal and radial cracks. Experimetal results obtained with Zn-Pb and Zn-Sn baths were compared with coatings obtained using Zn bath.
Sn and Ti influences on intermetallic phases damage in hot dip galvanizing
ECF 19 – Europeean Conference on Fracture, 2013
Protection against metallic materials corrosion is one of the most important means to reduce both maintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity of the melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation.
Sn and Ti influences on intermetallic phases damage in hot dip galvanizing.PDF
Protection against metallic materials corrosion is one of the most important means to reduce both maintenance costs and environmental impact. In the last years new studies on chemical baths compositions and fluxes have been performed in order to improve processes, corrosion resistance and mechanical behavior of Zn based coatings. Chemical bath composition is often improved by the Sn addition which increases the fluidity of the melt. Ti addition makes the coatings to change color under appropriate heat treatment. In this work a comparative microstructural analysis, in Zn-Sn and Zn-Ti coatings, is performed to evaluate intermetallic phases formation kinetics and the influence of intermetallic microstructure on coating damage under constant bending deformation.
Cracking mechanisms in a hot-dip zinc coated steel
11th International Conference on Fracture, 2005
Hot-dip galvanizing is one of the most used methods to apply zinc-based coatings on steels in order to provide sacrificial protection against corrosion over all the steel surface. The efficiency of the protection is affected by the coating mechanical response to loading: cracking and coatings delamination during forming and/or during service could decrease the corrosion resistance and could allow the contact between the environment and the substrate (the steel). The aim of this work is the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-standardized bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. Bending tests are performed both on non-coated and on hot dip zinc coated plates, correlating the measured variables (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show that the main damaging mechanisms depend on the different mechanical behaviour of the intermetallic phases and on their thickness. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the Γ phase and propagate up to the ζ−η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ−δ interfaces. As a consequence, the increase of coating thickness implies an increase of the susceptibility to a coating-steel debounding damage mechanism, with a consequent loose of the coating adhesion and a decreasing of the capability of the zinc coating to improve the steel corrosion resistance.
The structure and deformation behavior of hot-dip galvanized coatings
Scripta Materialia, 1996
The material used was a commercial hot-dip galvanized steel with a coating weight of 13Og/m2 (thickness: 182mm) on a 0.35mm thick low carbon cold-rolled steel substrate. Skinpass rolling was applied after coating to diminish buckling (specimen A). Brushing treatment was then performed with a brushing-roll under the conditions shown in . This treatment removed about log/m2 of the coating.
Metallurgical and Materials Engineering, 2014
The purpose of this work is to identify the influence of zinc bath temperature on the morphology, texture and corrosion behavior of hot-dip galvanized coatings. Hot-dip galvanized samples were prepared at temperature in the range of 450-480 °C in steps of 10 °C, which is the conventional galvanizing temperature range in the galvanizing industries. The morphology of coatings was examined with optical microscopy and scanning electron microscopy (SEM). The composition of the coating layers was determined using energy dispersive spectroscopy (EDS) analysis. The texture of the coatings was evaluated using X-ray diffraction. Corrosion behavior was performed using salt spray cabinet test and Tafel extrapolation test. From the experimental results, it was found that increasing the zinc bath temperature affects the morphology of the galvanized coatings provoking the appearance of cracks in the coating structure. These cracks prevent formation of a compact structure. In addition, it was concl...
Characterization of hot-dip galvanized coating on dual phase steels
Surface & Coatings Technology, 2011
This work explored the microstructure of continuous hot-dip galvanized zinc coating on two dual phase steels, focusing on the sample preparation methods for cross-sectional microstructure and Fe-Al intermetallic compound observation. Based on the microstructure revealed by proper method, we established a relationship between the annealing atmosphere and coating microstructure. The experimental results showed that the coating thickness and Fe-Al intermetallic compound's size are relevant to the annealing atmosphere. And the coexistence of Fe-Al intermetallic compound and Fe-Zn phase has proved indirectly that the aluminothermic reduction is working during hot-dip galvanizing.
Pitting Corrosion of Hot-Dip Galvanized Coatings
Materials, 2020
Lead (Pb) addition to hot-dip galvanizing (HDG) baths affects the physical characteristics of zinc coatings and is also useful to protect kettles. The influence of lead additions on both corrosion rate and morphology as well as on structure of zinc coating is less investigated. In this paper, three different additions, (Pb = 0.4–0.8–1.2 w/w) were chosen for three series of steel substrates, plus references without lead. The three steels chosen as substrates contained silicon (Si) = 0.18, 0.028, 0.225 w/w, respectively. The experimental part included both macro- and micro-electrochemical measurements, weight loss vs. time plots, Glow Discharge Optical Emission Spectroscopy (GDOS) and SEM/EDX microanalysis of both surface and cross-section of samples. Lead concentration is responsible for evident bimetallic coupling in the surrounding of lead inclusion with consequent increased dissolution rate, chunk effect, and rougher surface morphology.
Microstructure of zinc hot-dip galvanized coatings used for corrosion protection
Materials Letters, 2006
Low carbon steel substrates were galvanized in molten zinc containing 1 wt.% manganese. The as-cast coatings were examined with optical microscopy, scanning electron microscopy and X-ray diffraction. From the above investigation it was deduced that, although Mn concentration in the coating cross-section is very low (below the EDS sensitivity), Mn-rich crystals are deposited at the lateral surface of the hot-dip galvanized coating. These Mn "islands" are very beneficial with regard to the corrosion performance of the coating, because they act as sacrificial anodes that protect Zn.
Evaluation Of Mechanical Properties In of Double-Dip Galvanized Coatings on Carbon Steel
Little is known about the operational conditions, the microstructure and properties of the coatings manufactured by hot double-dip. The objective of this work is to evaluate the mechanical properties of Zn / Zn-5%Al coatings applied by the hot double-dip technique, varying the immersion times in liquid baths. For the evaluation, Vickers microhardness profiles and bending tests were made. The microhardness profiles for different immersion times show similarities, exhibiting great heterogeneity due to the microstructural characteristics. It is observed that increasing the immersion time decreases the critical angle, and the immersion time does not significantly influence the density of confined and unconfined cracks. It is concluded that the ductility of the coatings is influenced by their total thickness, and possibly by the thickness of the different areas and residual stresses, with the samples being coated for a 60 s immersion time, which present better behavior in the bending test.