Microstructure and Mechanical Properties of 1561 Aluminum Alloy Double-Sided Double-Arc TIG Weld Joints

Literature Overview

The research by Yan Dejun et al. (2016), published in The Chinese Journal of Nonferrous Metals (Vol. 26, No. 10, pp. 2065-2070), investigates the microstructure and mechanical properties of 1561 high-magnesium aluminum alloy welded using a double-sided double-arc offset vertical TIG welding process with filler wire. This work is supported by multiple national and local research funding programs, indicating its significance in the field of aluminum alloy welding for marine applications. The study addresses a critical challenge in shipbuilding: achieving sound, high-strength welds in thick-section high-Mg aluminum alloys without cracking or excessive softening.

Core Technical Content

Material and Process Background

1561 aluminum alloy belongs to the 1xxx series with elevated magnesium content (approximately 0.6% Mg), providing enhanced strength compared to standard 1060/1050 alloys while maintaining good formability and corrosion resistance. The double-sided double-arc offset vertical welding process is specifically designed for thick plates where single-pass single-side welding would require excessive current, leading to excessive heat input and potential cracking.

Welding Process Configuration

The double-sided double-arc offset vertical TIG welding with filler wire involves:

• Two TIG torches operating simultaneously on opposite faces of the vertical joint
• Offset arrangement of the torches to prevent direct interaction between the two arcs
• Filler wire addition for weld metal deposition
• Vertical welding orientation (5G position)

This configuration effectively distributes heat input between two arcs, reducing peak temperature and cooling rate in the weld zone compared to a single high-current arc, thereby reducing cracking susceptibility.

Microstructural Findings

The study reveals several important microstructural features:

The "person-shaped" coarse grain zone is a distinctive feature of the double-sided double-arc process. This morphology arises from the interaction of the two opposing heat sources and the resulting temperature field asymmetry. The V-shape orientation indicates the direction of maximum thermal gradient, which governs grain growth direction during solidification.

Mechanical Properties

The mechanical property results demonstrate excellent weld quality:

• Tensile strength: Exceeds 90% of base metal strength, indicating minimal strength loss
• Microhardness: Both front and back weld passes show hardness values below the base metal, but the HAZ does not exhibit significant softening
• Defects: No porosity or cracking observed in the weld metal

The absence of HAZ softening is particularly notable for high-Mg aluminum alloys, where precipitation dissolution and coarsening during welding typically leads to significant strength loss in the HAZ. The double-sided double-arc approach, by distributing heat input, appears to limit the thermal exposure sufficient to avoid severe precipitate dissolution.

Engineering Practice Integration

Applicability Assessment

The double-sided double-arc offset vertical TIG process is particularly suitable for:

1. Thick-section 1xxx series aluminum alloys (typically 8-25 mm) where single-arc welding would require excessive current
2. Crack-sensitive alloys with elevated Mg content where thermal cracking resistance is critical
3. Structural applications requiring high weld strength retention (ship hull structures, pressure vessels)
4. Production environments where both sides of the joint are accessible

Process Optimization Considerations

Based on the study findings, the following optimization parameters are recommended:

Comparison with Alternative Processes

The double-arc TIG process offers a favorable balance between strength retention, cracking resistance, and equipment cost, making it attractive for production applications where friction stir welding is not feasible.

Key Reflections and Implications

This study provides valuable insight into the microstructural mechanisms governing weld quality in high-Mg aluminum alloys. The discovery that the double-sided double-arc process can prevent HAZ softening while achieving over 90% strength retention is practically significant for shipbuilding and marine engineering applications. The "person-shaped" coarse grain zone, while initially concerning from a microstructural uniformity standpoint, does not appear to adversely affect mechanical performance—a finding that challenges conventional assumptions about grain uniformity requirements.

For engineering practice, this work validates the double-arc approach as a viable alternative to more expensive processes like friction stir welding for thick-section aluminum alloy joints. The process also offers advantages in terms of equipment availability and operator familiarity with TIG welding fundamentals. However, the study's limitation lies in the relatively narrow parameter range investigated; further optimization of arc offset distance, travel speed, and filler wire composition could potentially improve weld uniformity and further enhance mechanical properties. The findings also suggest that for applications requiring higher strength retention, hybrid approaches combining double-arc TIG with post-weld heat treatment might be beneficial.