Laser beam welding of metal-supported automotive catalytic converters

We performed laser welding tests on 45µm and 95µm thick Fe20Cr5Al foils of Sandvik 0C404 in order to study the welding feasibility of the catalytic converter monolith. In accordance with the contact configurations occurring between the corrugated foil and the flat foil during the coiling process of the honeycomb-structured monolith, several laser welding techniques are selected and tested in pulsed and continuous wave mode. For each technique, processing domains are explored to identify the ranges of usable energetical and optical parameters. Continuous-wave in keyhole mode is selected for offering better compatibility with the other manufacturing operations. Optimized-irradiation conditions in argon protective atmosphere for overlapped-joint welding of 2? 45µm foils correspond to full penetration-depth and fusion zone widths of 120µm and 80µm. Specific clamping tools are used in order to consolidate honeycomb structure prototypes under the optimized-laser beam conditions. We carry out engine-bench durability tests on these laser welded prototypes and on prototypes strengthened by conventional joining processes. The monolith shows higher performances when consolidated with laser welding than with conventional capacity-discharge welding. These demonstrates the feasibility of the laser welding technique. To study the laser weld behaviour under a stress field and an environment representative of service conditions, isothermal oxidation in both ambient and synthetic air (TGAnalysis) and tensile and creep tests at elevated temperatures are performed on samples including large fractions of laser seams. The laser weld differs significantly from the base material in terms of oxidation and thermomechanical behaviors at high temperature. We interpret these differences by the change in grain morphology and in the localization and combination of the reactive elements, carbon and nitrogen during the fast fusion/solidification cycles.