Different approaches to prevent solidification cracking in laser beam welding stainless steel-copper dissimilar joints
International Congress on Applications of Lasers & Electro Optics (ICALEO)
Fusion joining of stainless steel to copper without filler material for instance for pipe processing proves itself to be challenging due to the very different material properties of the joining partners and very heterogenous characteristics in the weld metal due to different mixing ratios. One of the most common weld defects for this material combination is solidification cracking in the weld metal due to liquid copper accumulation between the stainless steel grain boundaries, which cannot withstand the tensile tensions while cooling down. Consequently, these cracks can reduce the mechanical properties, lead to leakages or cause faster corrosion. To prevent cracking, a precise control of the melting and mixing ratio of stainless steel and copper is needed. Laser beam welding offers many capabilities to influence the resulting weld metal shape and size as well as the mixing ratios with different approaches like parameter optimization, inline process control or the use of different beam shapes. This work shows different weld configurations and applications using sheets with thicknesses in the area of 1 mm and pipe samples. Main focus are different solutions to influence the copper dilution and the weld metal geometry for solidification crack prevention. Therefore, a design of experiment approach and inline weld depth control using optical coherence tomography data are used for the lap weld configuration to limit the copper dilution below 10 wt.\% in steel dominated weld metals. Moreover the benefits of adjustable intensity profiles for the butt weld configuration to control the shape and dimensions of the weld metal and mixing behaviour with different power distributions in the laser beam welding spot are shown. The overall results indicate that solidification cracking in steel-copper joints can be influenced through the different process approaches.