Thermal Effects of TIG Welding Thick Copper Plates Under Different Welding Conditions

Literature Overview

This study, published in 2009 by researchers from Bohai Ship Heavy Industry Group and Harbin Institute of Technology, investigates the thermal behavior during TIG welding of thick copper plates under varying welding parameters. Copper, with its exceptionally high thermal conductivity of approximately 390 W/(m·K) at room temperature, presents unique challenges in thick-section welding. The research systematically examines how heat input, travel speed, electrode diameter, and preheating temperature influence the thermal cycle, penetration profile, and dilution behavior in thick copper plate fabrication.

Core Technical Analysis

Copper's thermal conductivity is roughly 8 to 10 times that of carbon steel, which means that during TIG welding, the heat is rapidly conducted away from the weld pool. This results in several critical engineering challenges: shallow penetration, wide heat-affected zone (HAZ), susceptibility to hot cracking, and the need for substantial preheating in thick sections. The researchers employed infrared thermography and thermocouple arrays to capture surface and subsurface temperature distributions, providing quantitative data on thermal gradients under different process windows.

Key Process Parameters and Their Effects

Parameter	Typical Range	Effect on Thick Copper Plate
Welding Current (DCEN)	200–450 A	Higher current increases penetration but widens HAZ
Travel Speed	10–30 cm/min	Lower speed increases heat input and dilution
Electrode Diameter	3.2–6.0 mm	Larger electrode allows higher current capacity
Preheat Temperature	300–600 °C	Reduces thermal gradient, suppresses hot cracking
Shielding Gas Flow	15–25 L/min	Critical for preventing oxide inclusion
Plate Thickness	20–60 mm	Requires multi-pass with interpass temperature control

Heat Input and Penetration Characteristics

The study demonstrates that achieving full penetration in thick copper plates requires heat inputs significantly higher than those for comparable steel sections. The linear heat input range typically extends from 15 to 35 kJ/cm for single-pass welds in plates up to 30 mm thick. For plates exceeding 40 mm, multi-pass welding with controlled interpass temperatures between 350 and 500 °C becomes essential. The thermal cycle analysis reveals peak cooling rates in the HAZ can reach 50 to 120 °C/s depending on the specific parameter combination, which directly influences grain structure evolution and potential cracking susceptibility.

Engineering Practice Implications

In shipbuilding and heavy equipment manufacturing, thick copper plates are used for electrical busbars, cryogenic equipment, and specialized heat exchangers. The thermal management strategies identified in this study—particularly the use of high preheat temperatures and controlled interpass temperatures—are directly transferable to production environments. A critical insight from this work is that the thermal asymmetry between the root and cap passes in multi-layer welding of thick copper creates non-uniform residual stress distributions, which can lead to distortion exceeding acceptable tolerances if not properly managed through backing bars, tacks, and staged welding sequences.

Defect Analysis and Countermeasures

Defect Type	Root Cause	Countermeasure
Hot cracking (hot short)	Cu-Zn or Cu-Al impurities, high thermal gradient	Preheat to 400–600 °C, use pure copper filler
Incomplete penetration	Insufficient heat input, excessive travel speed	Increase current, reduce speed, use larger electrode
Oxide inclusion	Inadequate shielding, surface contamination	Increase gas flow, thorough pre-cleaning
Undercut	Excessive arc force, wrong torch angle	Reduce current, maintain proper torch angle
Porosity	Hydrogen absorption, surface moisture	Preheat, dry filler, controlled environment

Study Insights

The most valuable contribution of this research is the systematic correlation between thermal parameters and weld geometry in thick copper sections. From a practical standpoint, the data confirms that copper welding is fundamentally a thermal management problem rather than a metallurgical one. The material's thermal properties dictate process design, and any deviation from recommended thermal control protocols will manifest as geometric defects or cracking. For engineers involved in copper-clad pressure vessel fabrication or copper-to-steel dissimilar welding, the thermal cycle data presented here provides essential input for prequalification testing and WPS development.