Characterization of Cold Lap Defects in Tandem Arc MAG Welding

Paper in proceeding, 2010

Cold laps are small incomplete fusion defects that are located at the weld toe. These defects have recently been shown to have severe influence on the fatigue life of components which undergo vibrations (or cycling loadings) such as automotive components. The small size of the cold laps, i.e. average size 0.05-0.3 mm, makes them difficult to detect with conventional NDT tools. Hence, better understanding of their formation is necessary to be able to avoid their formation. The objective of this study was to classify and characterize cold lap defects. The study consisted of two different parts. In the first part, tandem arc welding experiments were performed on Domex 355 MC using wires of OK Autrod 12.51 and shielding gas composed of Ar 92% + CO2 8%. The observed cold lap defects were classified into three types, namely “spatter induced cold laps”, “overlap induced cold laps”, and “spatter-overlap induced cold laps”. n the second part of the study, optical microscopy and scanning electron microscopy (SEM) have been used to evaluate if spatters can induce cold laps and thus the interface between spatters and base metal was investigated. Oxides, voids and carbon were found to be the main constituents of the incomplete fusion. The oxides contained both silicon and manganese.