Fiber Optic Laser-TIG Hybrid Welding of 5083 Aluminum Alloy

Literature Overview

This paper, published in High Power Laser and Particle Beams (2014, Vol. 26, Issue 3, pp. 306-310) by Li Fei, Kong Xiaofang, Wu Shikai, and Xiao Rongshi from the Beijing Institute of Technology Laser Engineering Research Institute, investigates the fiber optic laser-TIG hybrid welding of 4 mm thick 5083-H116 aluminum alloy. The research was supported by the National Natural Science Foundation of China (Project No. 51275013), the National Major Science and Technology Project (2013ZX04001-131), and the Beijing Natural Science Foundation (Project No. 3142006).

Material and Process Background

5083 aluminum alloy is a widely used marine-grade aluminum alloy containing approximately 4.1-4.8% magnesium. The H116 temper designation indicates a strain-hardened condition achieved through cold working, providing a good combination of strength and corrosion resistance. This alloy is extensively used in shipbuilding, automotive, and aerospace applications where corrosion resistance and formability are critical.

The hybrid welding process combines a fiber optic laser (IPG YLS-6000) with a TIG arc (Fronius MagicWave3000job digital welding power source). The laser provides deep penetration through keyhole welding, while the TIG arc contributes additional heat and filler metal deposition. The hybrid arrangement allows the laser to create the initial weld pool while the arc fills and stabilizes the joint.

Key Experimental Parameters

Welding Process Optimization and Results

The study systematically investigated the effects of power source characteristics, current magnitude, and heat source spacing on weld bead morphology. The key findings are:

Weld Bead Morphology

The fiber optic laser-TIG hybrid welding produced weld beads with:

• Bright metallic luster: Indicating good surface quality and minimal oxidation.
• Uniform fish-scale pattern: Suggesting stable metal transfer and consistent heat input.
• No porosity or cracking defects: Demonstrating excellent process stability.
• Slight surface depression: A minor cosmetic imperfection that does not affect mechanical properties.

The combination of laser and TIG arc proved particularly effective when using alternating polarity TIG (AP-TIG). The alternating polarity provides periodic cathodic cleaning action that removes the oxide layer from the aluminum surface, while the laser maintains the weld pool. This synergy results in a cleaner, more stable weld pool compared to either process alone.

Mechanical Properties

The hybrid weld joint achieved a tensile strength of 318 MPa, representing 93% of the base metal strength, with an elongation of 7.6%. The fracture analysis confirmed a ductile fracture mode, indicating good toughness and ductility in the weld joint.

Defect Analysis and Metallurgical Considerations

Aluminum alloy welding is notoriously challenging due to several inherent material characteristics:

• High thermal conductivity: Rapid heat dissipation requires high heat input to maintain the weld pool.
• Oxide formation: A tenacious Al2O3 layer forms immediately on the surface, with a melting point (2050°C) far above the aluminum melting point (660°C).
• Hydrogen porosity: Aluminum readily absorbs hydrogen from moisture, leading to porosity during solidification.
• Hot cracking susceptibility: The wide solidification range and low melting point of eutectic phases promote hot cracking.

The hybrid laser-TIG process addresses these challenges effectively:

• Keyhole effect: The laser creates a deep keyhole that provides deep penetration with relatively low total heat input, reducing distortion.
• Arc cleaning: The TIG arc, particularly in alternating polarity mode, provides cathodic cleaning of the oxide layer.
• Filler metal deposition: The arc contributes filler metal that fills the weld pool, reducing the risk of incomplete fusion and porosity.
• Reduced hot cracking: The combined heat sources produce a more uniform temperature distribution, reducing thermal gradients and residual stresses that promote cracking.

Process Configuration and Heat Source Spacing

The study found that the optimal configuration is with the laser leading and the arc trailing, with a heat source spacing not exceeding 4 mm. This configuration allows the laser to create the keyhole and initiate the weld pool, while the arc follows to fill and stabilize the joint. The spacing of 4 mm or less is critical because:

• If the spacing is too large, the arc may not interact effectively with the laser-created weld pool, resulting in poor fusion and potential porosity.
• If the spacing is too small, the arc may interfere with the laser beam, causing arc instability and inconsistent weld quality.

The arc current of 150 A was found to be optimal for 4 mm thick 5083 aluminum alloy. Higher currents would increase heat input and potentially lead to excessive penetration and burn-through, while lower currents would not provide sufficient filler metal deposition and arc cleaning action.

Engineering Practice and Standards Compliance

For engineering application of fiber optic laser-TIG hybrid welding of 5083 aluminum alloy, several standards and qualification requirements must be considered:

• Welding procedure qualification: Under standards such as AWS D10.9 (Structural Welding Code for Aluminum), ISO 13919, or EN 1090, the welding procedure must be qualified by demonstrating adequate mechanical properties, including tensile strength, elongation, and potentially bend testing.
• Non-destructive testing: The absence of porosity and cracking in the hybrid weld joints is a significant advantage, but formal NDT (radiographic testing or ultrasonic testing) is still required to verify internal quality.
• Corrosion resistance: 5083 aluminum alloy is valued for its marine corrosion resistance, and the welding process must not compromise this property. The weld metal composition and microstructure should be verified for compatibility with the base metal in terms of galvanic corrosion resistance.
• Distortion control: The reduced heat input of hybrid welding compared to conventional TIG welding alone is beneficial for distortion control, particularly in thin-walled structures.

Study Insights and Implications

This research demonstrates that fiber optic laser-TIG hybrid welding is a highly effective process for 5083 aluminum alloy, producing weld joints with excellent mechanical properties (93% of base metal strength), good surface quality, and no porosity or cracking defects. The synergy between the laser and the TIG arc, particularly with alternating polarity, creates a process that is more robust and productive than either process alone.

The findings have significant implications for aluminum alloy fabrication in marine, automotive, and aerospace industries, where 5083 aluminum is widely used. The ability to achieve high-quality welds with reduced heat input and minimal defects is particularly valuable for thin-walled structures and complex geometries.

For pipe and fitting applications, the hybrid process could be adapted for welding aluminum alloy pipes and fittings, provided that the joint geometry and process parameters are appropriately adjusted. The reduced distortion and improved surface quality would be advantageous for applications where dimensional accuracy and aesthetic appearance are important.

In conclusion, this study provides strong evidence that fiber optic laser-TIG hybrid welding is a viable and effective process for 5083 aluminum alloy, achieving excellent mechanical properties and defect-free welds through the synergistic interaction of the laser and alternating polarity TIG arc, and offers a promising pathway for high-quality aluminum alloy fabrication in demanding engineering applications.