A Study on Corrosion Resistance and Mechanical Performance of 6061 Aluminium Alloy: Galvanized Mild Steel Electron Beam Welds at Varying Welding Parameters

Dissimilar welds of steel and aluminium alloys have an inherent problem of the vast difference in solid solubility which questions their integrity. The present study elaborates on the mechanical failure and corrosion degradation of 6061 Al—galvanized mild steel lap joints fabricated by electron beam welding as a function of varying parameters such as processing speed, voltage and current. The interfaces of two weld specimens were examined using scanning electron microscopy, phase analysis by micro-area X-ray diffraction and hardness testing by Vickers micro-hardness tester. Results showed the generation of the intermetallic layer at the weld seam–mild steel interface in the specimens. The composition of the Al–Fe intermetallics in the layer was confirmed by micro-XRD analysis. The layer width increased with increased heat input and average width varied between 11 and 16 µm in the specimens. The micro-hardness of the layer was found to increase with a decrease in processing speed during welding. The corrosion resistance and mechanical strength of welds were evaluated as per ASTM G 67-04 and D 1002, respectively. The microstructures at weld interfaces have shown intergranular corrosion after nitric acid exposure for 24 h according to ASTM G 67-04. Weight loss analysis was done after the corrosion test. It was identified that welds fabricated at higher voltage exhibited greater weight loss of 55.9 mg and specimen joined at lower voltage was found to exhibit a weight loss of 41.1 mg, respectively. High intermetallic layer thickness in the welds resulted in failure at the weld seam region during lap shear testing.