Omzeilen van het sandelin-effect: Onderzoek naar de lasbaarheid van een laag siliciumhoudende lasdraad (ZINQWeld)

Omzeilen van het sandelin-effectOnderzoek naar de lasbaarheid van een laag siliciumhoudende lasdraad (ZINQWeld) Hot dip galvanized welded steel structures, when made of sensitive steels, often show abnormalities inthe coating layer, particularly on the weld surface. The aspect of the coating layer, with an increasedthickness over the welds in comparison with the normal layer, shows a dull grey look and isaesthetically less appealing. This is known as the sandelin-effect. The scope of this master thesis aimsto avoid this phenomenon by investigating the weldability of a low silicon consumable (ZINQWeld)for the MAG-welding process.The problem originates from the increased silicon content in the weld metal used, due to the highersilicon content in the consumable in comparison with the base material. If the Silicon level is withinspecific ranges, the sandelin-effect will occur.Tests show that the problem disappears when a welding consumable with low Silicon content(ZINQWeld) is used. For ZINQWeld the Silicion content is 0.14%, compared to a standard weldingwire with 0.7% and unfortunately yielding an increased viscosity and a higher risk of porosities in theweld metal. To reduce these secondary problems, the influence of the welding parameters, thecomposition of the shielding gas and the welding power source used have been studied. A visualevaluation shows that each shielding gas and type of power source used has its own scope. In otherwords, there isn’t an optimal over all combination of shielding gas and power source to be chosen thatproduces satisfactory results for each weld shape and material thickness. However, an acceptable levelof quality is achieved with ZINQWeld according to ISO 5817.This study shows that in a dilution range between approximately 10 to 50% a satisfactory zinc coatingthickness is found with ZINQWeld. This implicates that the increase in thickness of the zinc layer onthe weld is not excessive and that the layer meets the minimum thickness according to ISO 1461.When no increased growth in coating thickness occurs, it is assumed that there is a good adhesionbetween the zinc layer and the base material.Two welding wires with identical chemical composition are used. Using the 1.2 mm ZINQWeldwelding wire, experiments show no clear qualitative preference for the shielding gas. The 1.0 mmwelding wire on the other hand, only yields a good result when using the shielding gas Arcal 12.Despite the welding wires identical chemical composition, it can be argued that the 1.2 mm weldingwire shows a better weldability.The main conclusion of this study is that the ZINQWeld consumable provides a solution related to theSandelin-effect for any future welding application in comparison with a standard welding wire. This isdemonstrated with different Preliminary Welding Procedures Specifications (pWPSs) that are drawnup based on test pieces from customers. Keywords: Galvanizing, Sandelin-effect, ZINQWeld, Silicon