Pure copper is an industrially important material with high thermal and electrical conductivity and is widely used in electric vehicle motors and batteries. In recent years, the thickness of pure copper components has increased to improve current-carrying capacity; however, laser welding of thick copper components remains challenging because of their high thermal conductivity and low absorptivity in the near-infrared (NIR) wavelength range. Therefore, the realization of high-efficiency and high-quality deep penetration welding of pure copper is strongly required.

  While blue lasers exhibit significantly higher absorptivity for copper, their output power and brightness are currently limited, thereby restricting their applicability to deep penetration welding. In contrast, NIR lasers provide high power and brightness but suffer from low absorptivity and unstable welding. To overcome these limitations, hybrid laser welding combining blue and NIR lasers has recently attracted attention.

  In this study, the energy conversion efficiency in blue–IR hybrid laser welding of pure copper was quantitatively evaluated using a calorimetric method. The correlation between energy conversion efficiency and weld penetration was systematically investigated. The results demonstrate a clear correlation between energy conversion efficiency and weld penetration depth. These findings indicate that hybrid laser welding is an effective approach for achieving high-efficiency and high-quality welding of pure copper.