Microstructures and mechanical properties of copper-to-glass laser transmission welding employing a nanosecond pulsed laser

This study focuses on the interfacial characteristics of glass/copper welds achieved through laser transmission welding, utilizing a nanosecond pulsed laser. The investigation explores key processing parameters, specifically laser line energy intensity and total scan numbers, and their impacts on weld performance. Through meticulous analysis covering bond strength, cross-sectional surface morphologies, micro- and nano-structures, phase formations, and elemental compositions, the study systematically addresses the weld formation mechanism. The research elucidates potential reasons for diverse bonding characteristics, emphasizing the formation of Cu^x+-O-Si compounds (primarily Cu⁺-O-Si and Cu²⁺-O-Si) at the glass/copper interfacial region, as revealed by the XPS spectrum and HR-TEM images. These findings highlight redox reactions facilitated by strong intra-mixing through diffusion and convection during welding. The shear force separation test unveils an impressive maximum bond strength of 34.9 MPa, surpassing previously reported results, despite the indication of a brittle fracture in the separated surface morphologies. The correlation between a larger weld zone, abundant eutectic Cu^x+-O-Si compounds, and a uniformly re-solidified glass region is closely linked to the resulting high weld strength. This study underscores the direct relationship between laser irradiating energy and the extent of the weld zone, while the number of repeated scans proved to be an effective approach for regulating the elemental composition and microstructures in the weld. Overall, these findings contribute valuable insights into the weld formation mechanism and offer practical considerations for optimizing glass/copper welds through laser transmission welding.