MIG Welding of Profile Radiators and Busbars in AA6063 Aluminum Alloy

Literature Overview

This paper by Sheng Changyuan, Gao Yongyue, and Zhao Min from the Tianjin Welding Research Institute, published in Welding Technology (1991, Vol. 20, No. 1, pp. 19-21), describes the development and implementation of a MIG welding process for joining AA6063 aluminum alloy profile radiators to busbars. The study covers welding method selection, filler material choice, custom-designed process equipment, and modifications to welding machines and travel carts. The process achieved single-side, single-layer, single-pass automatic welding that met the usage requirements. This early work represents a practical engineering solution to a specific manufacturing challenge in aluminum heat exchanger production.

Core Technical Findings

The study successfully developed a MIG welding process for joining AA6063 aluminum alloy profile radiators to busbars, achieving the following process characteristics:

The paper emphasizes the importance of welding material selection, process equipment design, and machine modifications in achieving satisfactory weld quality for this specific application.

Interpretation of Technical Points

AA6063 is a widely used aluminum alloy for extrusion applications, including heat exchangers, radiators, and structural profiles. The alloy belongs to the 6xxx series (Al-Mg-Si) and is typically supplied in the T5 temper (stress-relieved) or T6 temper (solution heat treated and artificially aged). The welding of AA6063 presents specific challenges due to the alloy's susceptibility to hot cracking, its high thermal conductivity, and the tendency for oxide formation on the weld surface.

The selection of MIG welding for this application is appropriate because of the process's high deposition rate, good penetration characteristics, and suitability for automated production. The single-side, single-layer, single-pass configuration indicates that the joint design and welding parameters were optimized to achieve full penetration from one side without the need for root preparation or back-side welding. This is a significant process achievement for aluminum alloy welding, where achieving full penetration from one side is challenging due to the material's high thermal conductivity and low density.

The filler material selection is critical for aluminum alloy welding. For AA6063, the recommended filler metals according to AWS A5.10 (Specification for aluminum and aluminum-alloy welding electrode and rod) include 4043, 4047, and 5356. The choice of filler metal affects the weld metal composition, mechanical properties, corrosion resistance, and hot cracking susceptibility. The paper's analysis of welding material selection likely considered these factors in the context of the radiator application, where thermal cycling and corrosion resistance are important performance requirements.

The custom-designed process equipment and modifications to the welding machine and travel cart reflect the engineering challenges of automating MIG welding for this specific application. The radiator profile geometry, with its fins and channels, creates access challenges for the welding torch and requires precise torch positioning and travel speed control. The modifications likely addressed issues such as torch alignment, wire feed stability, and travel speed consistency to ensure uniform weld quality along the entire joint length.

Process and Standards Analysis

The welding of aluminum alloy radiators and heat exchangers is governed by standards such as AWS D10.6 (Structural welding code for aluminum), ASME BPV Section IV (Construction and inspection code for heating and cooling surfaces), and EN 1090-4 (Execution of aluminum structures). These standards specify requirements for welding procedure qualification, welder qualification, and weld quality assessment.

The single-side, single-layer, single-pass welding configuration requires careful qualification under these standards. The welding procedure specification (WPS) must define the welding parameters, including current, voltage, travel speed, wire feed speed, shielding gas composition, and preheat temperature, to ensure consistent weld quality. The welder qualification must demonstrate the ability to produce welds that meet the specified mechanical and metallurgical requirements.

The shielding gas composition is critical for MIG welding of aluminum alloys. A mixture of 98% argon and 2% oxygen or a mixture of 90% argon and 10% carbon dioxide is commonly used to improve arc stability and wetting. The shielding gas flow rate must be sufficient to prevent atmospheric contamination of the weld pool, which can lead to porosity and oxidation. The paper's emphasis on process equipment design suggests that achieving consistent shielding gas coverage was a significant challenge in this application.

Integration with Engineering Practice

In the production of aluminum alloy radiators for automotive and industrial applications, the welding of profile radiators to busbars is a critical process step that determines the thermal performance and structural integrity of the heat exchanger. The development of an automatic MIG welding process for this application enables high-volume production with consistent quality, which is essential for meeting the cost and performance requirements of the automotive industry.

The custom-designed process equipment and machine modifications described in the paper represent a practical engineering approach to solving manufacturing challenges. The modifications likely included features such as adjustable torch height, automatic wire feed speed control, and travel speed synchronization to ensure consistent weld quality along the entire joint length. These modifications demonstrate the importance of process engineering in achieving production-ready welding solutions.

The single-side, single-layer, single-pass welding configuration also has implications for production efficiency. By eliminating the need for root preparation and back-side welding, the process reduces the number of operations and the associated labor costs. This is particularly important for high-volume production environments where manufacturing efficiency is a key competitive factor.

Key Questions and Reflections

A significant question is the long-term reliability of the weld joints under thermal cycling conditions. Radiators are subjected to repeated heating and cooling cycles during operation, which can cause thermal fatigue cracking in the weld metal and heat-affected zone. The paper does not address the fatigue performance of the weld joints, which is a critical consideration for the service life of the radiator.

Another consideration is the corrosion resistance of the weld joints. Aluminum alloys are susceptible to corrosion, particularly in the presence of chloride ions, which are common in automotive and industrial environments. The weld metal and HAZ may have different corrosion resistance characteristics compared to the base metal, which could lead to localized corrosion at the weld. The paper's emphasis on meeting usage requirements suggests that corrosion resistance was considered, but the specific corrosion testing methodology and results are not detailed.

The paper also raises the question of whether the process can be adapted for other aluminum alloy profiles and busbar configurations. The success of the process depends on the specific geometry of the joint, the material thickness, and the welding parameters. Adapting the process for different geometries may require additional process development and qualification.

Study Insights and Implications

This paper provides a valuable example of practical engineering problem-solving in aluminum alloy welding. The development of an automatic MIG welding process for joining AA6063 profile radiators to busbars demonstrates the importance of process engineering, equipment design, and parameter optimization in achieving production-ready welding solutions. The single-side, single-layer, single-pass configuration achieved in this study represents a significant process advancement that reduces production costs while maintaining weld quality. For engineers working in aluminum heat exchanger manufacturing, this paper provides a reference for the development of similar automatic welding processes for other profile geometries. The study also underscores the importance of considering the long-term performance of weld joints, including fatigue and corrosion resistance, in the process development and qualification phases. The practical engineering approach demonstrated in this paper—combining welding method selection, filler material choice, and custom equipment design—is a model for solving manufacturing challenges in aluminum alloy welding.