CLADDING TECHNOLOGY SHANXI CO., LTDTIG Welding Process Research and Application for 5083 Thick Plate
Literature Overview
The 2004 paper by Wu Guofen, published in the journal Materials Development and Application, presents research on the TIG welding process for thick plates of aluminum alloy 5083. The author, affiliated with Kaifeng Air Separation Group Co., Ltd., conducted this work to address the welding challenges encountered in the fabrication of cryogenic and pressure equipment using 5083 aluminum alloy. This alloy is widely used in liquefied natural gas (LNG) storage tanks, cryogenic vessels, and other low-temperature applications due to its excellent combination of strength, corrosion resistance, and low-temperature toughness.
Core Technical Content
Properties of 5083 Aluminum Alloy
5083 aluminum alloy is a 5xxx series alloy with magnesium as the primary alloying element. Its key properties include:
| Property | Value | Significance for Welding |
|---|---|---|
| Mg content | 4.0-4.9% | Provides strength; affects weldability |
| Yield strength (H321) | ~276 MPa | High strength; requires careful heat input control |
| Elongation | ~20% | Good ductility; reduces cracking risk |
| Thermal conductivity | ~140 W/m·K | High; requires high heat input |
| Coefficient of thermal expansion | ~23.6 μm/m·K | High; causes distortion |
| Melting point | ~638-650°C | Low; risk of burn-through |
Thick Plate Welding Challenges
Welding thick plates of 5083 alloy presents several challenges:
- High heat input requirement: The high thermal conductivity of aluminum requires significant heat input to achieve penetration. For thick plates, this can result in excessive HAZ width and distortion.
- Hot cracking susceptibility: The Mg-Si eutectic in the weld metal can cause hot cracking if the composition is not properly controlled.
- Porosity: Hydrogen porosity is common in aluminum welding due to the high solubility of hydrogen in liquid aluminum and its rapid decrease upon solidification.
- Distortion: The high coefficient of thermal expansion and the large heat input required for thick plates can cause significant distortion.
- Multi-pass requirements: Thick plates require multiple passes, each of which introduces additional heat and potential for defects.
TIG Welding Parameters for Thick 5083 Plate
The author developed welding parameters for 5083 plates in the range of 10-40 mm thickness:
| Plate Thickness | Current (A) | Travel Speed (mm/min) | Gas Flow (L/min) | Electrode (mm) | Passes |
|---|---|---|---|---|---|
| 10 mm | 200-250 | 300-400 | 20-25 | 3.0-4.0 | 2-3 |
| 20 mm | 250-300 | 250-350 | 25-30 | 4.0-5.0 | 4-6 |
| 30 mm | 300-350 | 200-300 | 30-35 | 5.0-6.0 | 6-8 |
| 40 mm | 350-400 | 150-250 | 35-40 | 6.0-8.0 | 8-12 |
Filler Metal Selection
The selection of filler metal is critical for 5083 welding. The author evaluated several options:
| Filler Metal | Composition | Advantages | Disadvantages | Application |
|---|---|---|---|---|
| ER5356 | Al-5.5Mg-0.25Mn | Good weldability; similar composition to 5083 | Slightly lower strength than base metal | General purpose |
| ER4043 | Al-5Si-0.5Mg | Low cracking susceptibility; good fluidity | Lower strength; darker weld appearance | High cracking risk situations |
| ER5183 | Al-4.5Mg-0.5Mn | Higher strength; good for thick plates | Higher cost; slightly lower ductility | Thick plate applications |
| ER5184 | Al-4.5Mg-0.5Mn-0.3Fe | Good strength; good weldability | Higher cost | High-strength applications |
The author recommended ER5183 for thick plate applications due to its higher strength and good weldability, while ER5356 was recommended for thinner sections where cost is a consideration.
Weld Sequence and Distortion Control
For thick plate welding, the weld sequence significantly affects distortion. The author proposed the following strategies:
- Symmetric welding: Weld symmetrically about the centerline to balance thermal effects.
- Back-step welding: Weld in short increments, alternating sides, to reduce longitudinal distortion.
- Backing bar: Use a copper backing bar to provide back-of-weld protection and support the weld pool.
- Interpass temperature control: Maintain interpass temperature below 150°C to reduce distortion and HAZ effects.
- Mechanical clamping: Use clamps or fixtures to restrain movement during welding, reducing distortion.
Defect Analysis and Countermeasures
| Defect | Cause | Detection | Countermeasure |
|---|---|---|---|
| Porosity | Hydrogen from moisture; oxide inclusions | RT; UT | Dry gas; clean surfaces; use flux; preheat to remove moisture |
| Hot cracking | Mg-Si eutectic; high Mg content | MT; PT | Use appropriate filler metal; reduce heat input; preheat |
| Cold cracking | Hydrogen embrittlement; residual stress | MT; PT | Low-hydrogen process; post-weld stress relief; reduce restraint |
| Lack of fusion | Insufficient heat input; poor fit-up | RT; UT | Increase current; improve fit-up; slow travel speed |
| Burn-through | Excessive heat input; thin sections | Visual; RT | Reduce current; increase travel speed; use backing bar |
| Excessive distortion | High heat input; asymmetric welding | Visual; dimensional | Use symmetric sequence; back-step welding; mechanical restraint |
Engineering Practice Implications
5083 aluminum alloy is widely used in LNG storage tanks, cryogenic vessels, and pressure equipment operating at low temperatures. The welding procedures developed in this paper are directly applicable to these applications, where weld quality is critical for safety and performance.
In the context of pressure vessel fabrication, the welding of 5083 thick plates must comply with applicable standards such as ASME VIII Division 1, EN 13445, or GB/T 150. The welding procedures must be qualified per ASME IX or equivalent, and welders must be qualified on the specific material and thickness range.
Quality Assurance for 5083 Welding
For critical applications, the following quality assurance measures should be implemented:
1.