Shielding gas effect on the structure of variable polarity GMA weldbrazed joints of galvanised sheets

Abstract

Abstract The article presents the course and results of tests aimed to determine the effect of shielding gas on the shape of a weldbraze and on the structure of weldbrazed joints made of thin galvanised sheets. Test joints were made using innovative VP GMA weldbrazing utilising variable current and voltage waveforms. The tests involved the use of 3 types of shielding gases and mixtures, i.e. Ar, Ar + 1% O2 and Ar + 18% CO2, and required macro and microscopic metallographic examination of overlay brazes and weldbrazed joints. The tests conducted have revealed that the use of mixtures containing active gases, and CO2 in particular, increases the heat input of a weldbrazing process, improves the wettability of sheets and the geometry of weldbrazes, yet it also favours greater coat damage in the joining area and causes partial melting of workpieces.