Assessment of the corrosion resistance, properties and the structure of TIG braze welded galvanised steel sheets

The article discusses tests concerning the assessment of the corrosion resistance, properties and the structure of TIG braze welded galvanised steel sheets. Test butt joints were made of 0.9 mm thick galvanised car body steel sheets DC04 (in accordance with EN 10130), using a robotic welding station and a CuSi3Mn1 braze (in accordance with PN-EN 13347:2003) wire having a diameter of 1.0 mm. The research-related tests aimed to optimise braze welding parameters and the width of the brazing gap. The test joints were subjected to visual tests, macro and microscopic metallographic tests, hardness measurements as well as tensile and bend tests. The corrosion resistance of the joints was identified using the galvanostatic method. The tests revealed that it is possible to obtain high quality joints made of galvanised car body steel sheets using the TIG braze welding process, the CuSi3Mn1 braze and a brazing gap, the width of which should be restricted within the range of 0.4 mm to 0.7 mm. In addition, the joints made using the aforesaid parameters are characterised by high mechanical properties. The minimum recommended heat input during process, indispensable for the obtainment of the appropriate spreadability of the weld deposit should be restricted within the range of 50 kJ/mm to 70 kJ/mm. At the same time, the aforesaid heat input ensures the minimum evaporation of zinc. Joints made using the TIG braze welding method are characterised by high resistance to electrochemical corrosion. The galvanostatic tests did not reveal any traces of corrosion in the joint area.