Thermal Effects of TIG Welding Thick Pure Copper Plates

Literature Overview

Published in Materials Science and Process (2009, Vol. 17, Issue 1), this paper from Bohai Shipbuilding Heavy Industry Group and Harbin Institute of Technology investigates the thermal behavior during TIG welding of thick pure copper (Cu-ETP) plates. Using Marc finite element software, the authors simulated temperature field distributions and analyzed the effects of welding current and preheat temperature on molten pool and heat-affected zone (HAZ) dimensions. The study also compares the thermal performance of different shielding gases (Ar, He, N2) and their interaction with preheat conditions.

Core Technical Findings

The study reveals that both molten pool size and HAZ dimensions increase monotonically with welding current and preheat temperature. A key insight is that different combinations of preheat temperature and welding current can produce identical molten pool dimensions but significantly different HAZ sizes. This means that achieving full penetration does not necessarily require maximum HAZ, which is critical for maintaining the mechanical properties and electrical conductivity of the copper.

The comparison between He and N2 shielding at 20 °C versus Ar at 400 °C preheat is particularly instructive. Both achieve comparable molten pool dimensions, but the He and N2 conditions produce significantly narrower HAZ regions. This is because He has higher thermal conductivity and ionization energy than Ar, resulting in a more concentrated arc and deeper but narrower penetration. N2 introduces some exothermic reaction with the molten copper, providing additional heat input without the broad thermal spread associated with preheating.

Process Analysis and Parameter Selection

Pure copper presents unique welding challenges due to its extremely high thermal conductivity (approximately 401 W/m·K at 20 °C), which rapidly dissipates heat from the weld zone and requires high energy input to achieve adequate penetration. For thick plates (typically >6 mm), conventional TIG welding without preheat often requires currents exceeding 300 A, which can cause excessive HAZ widening and potential distortion.

The study demonstrates that using He as a shielding gas effectively concentrates the arc energy, reducing the thermal spread while maintaining penetration depth. The N2 shielding option, while less common for copper, leverages the exothermic reaction of nitrogen with molten copper (forming Cu3N) to supplement heat input, though this must be carefully controlled to avoid excessive nitride formation that could embrittle the weld metal.

Engineering Practice Implications

For shipbuilding and heavy equipment applications where thick copper plates are used (such as in electrical busbars, heat exchanger headers, and radiation shielding), this study provides a practical framework for welding procedure optimization. The key engineering takeaway is that preheat, while effective for achieving penetration, comes at the cost of a wider HAZ and potentially reduced electrical conductivity in the affected region. Alternative approaches using He shielding or controlled N2 addition can achieve equivalent penetration with narrower HAZ, preserving more of the base material properties.

In production environments, thermocouple monitoring of the HAZ temperature distribution should be implemented to validate simulation predictions and ensure that peak temperatures remain below the threshold for significant grain growth (approximately 700 °C for annealed copper). For multi-pass welding of thick copper plates, interpass temperature control between 150–250 °C is recommended to balance weldability and HAZ limitation.

Study Insights and Reflections

This research highlights the importance of thermal management in welding high-conductivity materials. The finding that molten pool and HAZ dimensions can be decoupled through gas selection offers a powerful tool for process engineers who need to maintain penetration while minimizing thermal damage. The Marc finite element simulation approach, while validated against experimental data, should be supplemented with infrared thermography or high-speed imaging for real-time process monitoring in production settings. The practical implication is clear: for thick copper welding, investing in He shielding infrastructure may yield better long-term component performance than relying solely on high-current Ar welding with extensive preheat.