Effect of Helium-Argon Shielding Gas Mixture Ratio on Iron Dilution in Copper-on-Steel TIG Weld Overlay
1. Definition and Technical Context
In bimetallic cladding manufacturing, copper-on-steel TIG (Tungsten Inert Gas) weld overlay is a critical technology used to deposit a corrosion-resistant or electrically conductive copper layer onto carbon steel or low-alloy steel substrates. The fundamental metallurgical challenge in this process is controlling the iron dilution ratio—the proportion of base metal (iron from the steel substrate) that melts and mixes into the deposited copper weld metal. Excessive iron dilution degrades the electrical conductivity, corrosion resistance, and electrochemical compatibility of the copper overlay, while insufficient dilution compromises metallurgical bonding and interfacial strength.
The use of helium-argon (He-Ar) mixed shielding gas in TIG welding is a well-established technique to modulate arc energy density, heat input, and penetration characteristics. Unlike pure argon, helium has a lower atomic mass and higher ionization potential, producing a hotter, more concentrated arc with deeper penetration. By varying the helium-to-argon ratio, the welder can precisely control the thermal profile, thereby managing the degree of base metal melting and, consequently, the iron dilution in the copper overlay.
This technical study—titled "Effect of Helium-Argon Mixture Ratio on Iron Dilution in Copper-Steel TIG Weld Overlay"—represents a systematic experimental investigation and knowledge consolidation effort that directly informs process parameter optimization, WPS (Welding Procedure Specification) development, and qualification of copper-on-steel cladding operations.
2. Category and Business Positioning
This technical entry falls squarely within the TIG/MIG Weld Overlay technology route of Cladding Technology Shanxi Co., Ltd., specifically addressing the process science underlying copper-on-steel cladding. Within the company's three-pronged technology portfolio—TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding—the TIG weld overlay route serves applications requiring:
- Thin copper overlays (0.5–5.0 mm) on complex geometries where explosive methods are impractical
- Repair and retrofit cladding of existing steel equipment
- High-precision overlay with controlled dilution for electrochemical and electrical applications
- Small-batch, multi-variety production where process flexibility is paramount
The helium-argon ratio optimization study is a foundational process development activity that directly supports WPS qualification, welder certification, and product quality assurance for copper-on-steel TIG overlay products.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- Quantify the relationship between He-Ar mixture ratio and iron dilution percentage in copper-on-steel TIG weld overlay
- Establish optimal parameter windows that achieve target dilution levels (typically 5–15% iron for high-conductivity applications; 15–25% for enhanced metallurgical bonding)
- Develop a predictive model linking shielding gas composition to weld geometry, thermal profile, and dilution behavior
- Support WPS qualification by providing documented experimental data for procedure validation under applicable standards
3.2 Value to Product Delivery
Optimized helium-argon ratio selection enables the company to deliver copper-on-steel cladding products with predictable and repeatable dilution characteristics. This translates directly to:
- Electrical conductivity assurance: For applications such as electrical contact plates, busbar cladding, and copper-bonded steel components, maintaining iron dilution below 10% ensures conductivity within ASTM B751 / GB/T 4730 acceptable ranges
- Corrosion resistance reliability: For marine, chemical, and power generation applications, controlled dilution ensures the copper overlay maintains its galvanic protection capability against steel substrate
- Metallurgical bonding integrity: For mechanical cladding applications, sufficient dilution (15–25%) creates a proper intermetallic bond layer that meets peel test and shear test requirements
- Process repeatability: Documented parameter windows enable consistent production across shifts, operators, and equipment
4. Key Process and Implementation Points
4.1 Helium-Argon Mixture Ratio and Its Effects on Arc Characteristics
The helium-argon mixture ratio fundamentally alters the TIG arc's thermal behavior. The following table summarizes the key characteristics at different ratios:
| He-Ar Ratio | Arc Temperature (°C) | Penetration Depth (mm) | Weld Width (mm) | Iron Dilution (%) | Typical Application |
|---|---|---|---|---|---|
| 100% Ar | ~6,000 | 0.3–0.8 | 4.0–6.0 | 3–8 | Low-dilution high-conductivity overlay |
| 75% Ar / 25% He | ~6,500 | 0.5–1.2 | 3.5–5.0 | 5–12 | General-purpose overlay |
| 50% Ar / 50% He | ~7,000 | 0.8–1.8 | 3.0–4.5 | 8–18 | Balanced dilution and bonding |
| 25% Ar / 75% He | ~7,500 | 1.2–2.5 | 2.5–4.0 | 12–25 | High-bonding strength overlay |
| 100% He | ~8,000 | 1.5–3.0 | 2.0–3.5 | 18–35 | Deep penetration, high dilution |
Note: Values are approximate and depend on additional parameters including current, travel speed, filler wire diameter, and base metal thickness. The data above represents typical ranges observed in copper-on-carbon-steel TIG overlay under controlled conditions.
4.2 Mechanism of Iron Dilution Control
The iron dilution mechanism in copper-on-steel TIG overlay operates through the following sequence:
- Arc heat concentration: Higher helium content increases arc energy density, concentrating heat in a narrower zone and driving deeper penetration into the steel substrate
- Base metal melting: Deeper penetration melts more steel substrate, increasing the volume of iron entering the weld pool
- Weld pool dynamics: The interaction between the copper filler metal and molten steel creates a diffusion zone where iron atoms migrate into the copper-rich weld metal
- Solidification: Upon cooling, the iron-copper mixture forms intermetallic phases (CuFe, Cu₃Fe, Cu₅Fe) that influence the final dilution percentage and metallurgical bond quality
4.3 Recommended Process Parameters for Different Dilution Targets
| Target Dilution | He-Ar Ratio | Current (A) | Travel Speed (mm/min) | Filler Wire (mm) | Preheat (°C) | Application |
|---|---|---|---|---|---|---|
| 3–8% | 100% Ar or 90/10 | 120–180 | 300–500 | 1.6 | 0–50 | Electrical contact cladding |
| 8–15% | 75/25 or 60/40 | 150–220 | 200–400 | 1.6–2.4 | 50–100 | Corrosion protection overlay |
| 15–25% | 50/50 or 25/75 | 180–280 | 150–300 | 2.4–3.2 | 100–150 | Mechanical cladding, repair |
| 25–35% | 75/25 (He/Ar) or 100% He | 220–350 | 100–250 | 3.2–4.0 | 150–250 | Heavy-duty bonding, thick sections |
4.4 Critical Process Controls
- Gas flow rate: Maintain 12–18 L/min for He-Ar mixtures (higher than pure Ar due to helium's lower density); ensure adequate back-of-weld coverage with trailing gas shroud
- Gas lensing: Use a gas lens for concentrated shielding; helium's higher velocity requires careful nozzle-to-workpiece distance control (8–12 mm)
- Tungsten preparation: Use pure tungsten or thoriated tungsten with a 60° grind; maintain clean, undamaged tip to ensure arc stability
- Filler metal selection: Use pure copper (Cu-ETP, GB/T 5586) or oxygen-free copper (GB/T 468) depending on conductivity requirements; pre-clean filler wire to remove oxide
- Base metal preparation: Grind to bare metal with 24–40 grit; degrease with acetone or equivalent; preheat uniformly to prevent cracking and control cooling rate
- Weld sequence: For multi-pass overlays, use a transition layer (e.g., Cu-Ni or 309L stainless steel) to manage dilution and reduce cracking susceptibility
5. Applicable Standards and Acceptance Criteria
5.1 Welding Procedure and Qualification Standards
- GB/T 985.1 — Designation of welding methods and welding positions
- GB/T 985.2 — Designation of welding processes (TIG = 141, MIG = 131)
- NB/T 47014 — Qualification and approval of welding procedures for pressure vessels
- ASME Section IX — Qualification of welding procedures, welders, and welding operators
- ASTM E164 — Standard test method for determining dilution in weld overlay
- ASTM B751 — Standard specification for copper and copper alloys (filler material)
- GB/T 5586 — Copper and copper alloys for welding and brazing
- GB/T 468 — Oxygen-free copper rod and tube
5.2 Inspection and Acceptance Standards
- GB/T 3323 — Radiographic testing of welds in steel, nickel, titanium, and their alloys
- GB/T 11345 — Ultrasonic testing of welds
- GB/T 15055 — Magnetic particle testing of ferromagnetic materials
- ASTM E709 — Magnetic particle examination
- ASTM E165 — Liquid penetrant examination
- GB/T 2651 — Peel test for clad steel plate (bond strength verification)
- GB/T 2652 — Shear test for clad steel plate
- ASTM A490 — Clad steel plate (where applicable for mechanical properties)
5.3 Acceptance Criteria for Copper-on-Steel TIG Overlay
| Test Parameter | Acceptance Criterion | Standard Reference |
|---|---|---|
| Iron dilution (high-conductivity) | ≤ 10% (by mass, cross-section area method) | ASTM E164 |
| Iron dilution (bonding-critical) | 15–30% (by mass, cross-section area method) | ASTM E164 / GB/T 2651 |
| Peel test strength | ≥ 60 MPa (for bonding applications) | GB/T 2651 |
| Shear test strength | ≥ 150 MPa (for mechanical cladding) | GB/T 2652 |
| Electrical conductivity | ≥ 55% IACS (high-conductivity applications) | ASTM B751 / GB/T 468 |
| NDT - Radiographic | No porosity > 0.5 mm; no cracks; no lack of fusion | GB/T 3323 / ASTM E164 |
| NDT - Ultrasonic | No indications exceeding acceptance level per product specification | GB/T 11345 |
| NDT - Magnetic Particle | No linear indications > 1 mm; no cluster indications | GB/T 15055 / ASTM E709 |
| Overlay thickness uniformity | ± 0.5 mm (for thin overlay); ± 1.0 mm (for thick overlay) | Product specification / WPS |
6. Common Risks and Controls
6.1 Excessive Iron Dilution
Risk: Iron dilution exceeding 20–25% significantly degrades electrical conductivity and may introduce brittle intermetallic phases (CuFe, Cu₃Fe) that reduce ductility and crack resistance.
Controls:
- Reduce helium content in shielding gas (shift toward 100% Ar or 90/10 Ar/He)
- Increase travel speed to reduce heat input per unit length
- Use smaller filler wire diameter (1.6 mm) for thinner, faster deposits
- Implement a transition layer (e.g., 309L stainless steel) to act as a dilution barrier
- Reduce current and increase gas flow for more controlled arc shape
6.2 Insufficient Dilution / Poor Metallurgical Bond
Risk: Iron dilution below 5% may result in poor metallurgical bonding, leading to delamination under mechanical or thermal cycling loads.
Controls:
- Increase helium content (shift toward 50/50 or 75/25 He/Ar)
- Reduce travel speed to increase heat input and penetration
- Use larger filler wire (2.4–3.2 mm) for deeper weld pool
- Preheat base metal to 100–150°C to promote substrate melting
- Employ multi-pass welding with controlled interpass temperature
6.3 Arc Instability and Porosity
Risk: Improper He-Ar ratio can cause arc wandering, spatter, or shielding gas breakdown, leading to porosity and incomplete fusion.
Controls:
- Maintain nozzle-to-workpiece distance at 8–12 mm
- Ensure gas flow rate of 12–18 L/min with adequate trailing gas
- Use gas lens for concentrated shielding cone
- Verify gas supply purity (≥ 99.99% for both He and Ar components)
- Check for gas leaks in hose, regulator, and torch connections
6.4 Cracking in High-Dilution Welds
Risk: High iron dilution (>25%) combined with rapid cooling can produce hot cracking due to Cu-Fe intermetallic segregation at grain boundaries.
Controls:
- Preheat base metal to 150–250°C to slow cooling rate
- Apply post-weld heat treatment (PWHT) at 300–400°C for 2–4 hours
- Use a nickel-containing transition layer (e.g., Ni-Cu alloy) to reduce cracking susceptibility
- Control interpass temperature to 150–250°C for multi-pass welds
- Employ pulse TIG welding to modulate heat input and reduce peak temperatures
7. Application Scenarios Across the Company's Three Technology Routes
7.1 TIG/MIG Weld Overlay Route (Primary Application)
The helium-argon ratio optimization study is directly applicable to the company's TIG/MIG weld overlay production line. Key applications include:
- Copper-on-steel electrical contact plates: Using 100% Ar or 90/10 Ar/He to achieve ≤ 8% dilution for maximum conductivity in switchgear, busbar, and transformer components
- Corrosion-resistant copper overlay on marine steel: Using 50/50 He/Ar for balanced dilution (10–18%) providing both corrosion resistance and metallurgical bond strength
- Repair and retrofit cladding: Using 75/25 He/Ar for deep penetration on existing equipment, enabling thicker single-pass deposits with controlled dilution
- Transition layer welding: Optimized He-Ar ratios for 309L stainless steel transition layers between steel substrate and copper overlay to manage dilution and reduce cracking
7.2 Hydraulic Explosive Bonding Route (Complementary Application)
While hydraulic explosive bonding produces copper-steel cladding through high-velocity impact without melting, the helium-argon TIG overlay technology serves as a complementary process for:
- Edge finishing and trimming: TIG welding with optimized He-Ar ratios for precise edge preparation of explosively bonded plates
- Repair of bonding defects: Localized TIG overlay repair of areas where explosive bonding produced insufficient bond quality
- Overlay on complex geometries: Hydraulic explosive bonding is limited to flat or simple curved surfaces; TIG overlay with He-Ar optimization enables cladding of complex shapes (tubes, nozzles, forged components) where explosive methods are impractical
- Multi-layer cladding: Combining explosive bonding for the base layer with TIG overlay (using controlled He-Ar ratios) for additional copper thickness on top
7.3 Explosion Welding Route (Integrated Application)
In explosion welding, copper-steel plates are bonded through detonation-driven collision at supersonic velocities. The helium-argon TIG overlay technology integrates with this route in the following ways:
- Post-explosion finishing welds: TIG welding with optimized He-Ar ratios for seam sealing, edge repair, and surface finishing of explosion-welded assemblies
- Filler material qualification: The dilution control knowledge from He-Ar TIG studies informs the selection of filler materials for post-explosion welding operations
- Hybrid cladding systems: Explosion welding provides the primary copper-steel bond; TIG overlay with controlled He-Ar ratios adds additional copper thickness for applications requiring > 10 mm copper overlay
- NDT support welding: TIG welds with optimized dilution characteristics serve as reference standards for NDT calibration on explosion-welded products
8. Contribution to Qualification Building and Customer Value
8.1 WPS Qualification Support
The systematic study of helium-argon ratio effects on iron dilution provides the experimental foundation for developing and qualifying Welding Procedure Specifications (WPS) for copper-on-steel TIG overlay. Key contributions include:
- Parameter documentation: Detailed records of He-Ar ratio, current, travel speed, and resulting dilution percentages form the basis of WPS qualification records per NB/T 47014 and ASME Section IX
- Essential variable identification: The study identifies helium-argon ratio as a critical essential variable that must be controlled within specified limits for procedure qualification
- Qualification test data: Peel test, shear test, dilution measurement, and NDT results from the study support the technical basis for WPS approval
- Welder performance qualification: Documented parameter windows enable welder qualification testing under controlled conditions, ensuring consistent dilution control in production
8.2 Customer Value Enhancement
The helium-argon optimization capability directly enhances customer value through:
- Customized dilution control: Ability to tailor iron dilution to specific customer requirements (from ≤ 5% for ultra-high conductivity to 25% for maximum bond strength)
- Reduced rework rates: Optimized process parameters minimize dilution-related defects, reducing rework costs and delivery delays
- Expanded application range: Controlled dilution enables the company to serve applications previously requiring more expensive explosive bonding or specialized processes
- Technical documentation: Comprehensive data packages support customer audits, regulatory compliance, and product certification
- Cost optimization: Selecting the optimal He-Ar ratio balances gas costs (helium is significantly more expensive than argon) with performance requirements, minimizing material costs without compromising quality
8.3 Knowledge Consolidation and Organizational Capability
The "learning reflection" format of this technical entry represents a deliberate knowledge management practice. By documenting the relationship between helium-argon ratio and iron dilution, the company:
- Creates a reference database for process engineers and welders
- Supports training programs for new operators
- Enables rapid troubleshooting of dilution-related quality issues
- Builds institutional expertise that differentiates the company in the bimetallic cladding market
- Provides technical content for customer presentations, bid proposals, and technical publications
9. Conclusion
The systematic study of helium-argon shielding gas mixture ratio effects on iron dilution in copper-on-steel TIG weld overlay represents a critical process development activity that underpins the company's technical capability in bimetallic cladding. By establishing quantitative relationships between shielding gas composition, arc characteristics, and dilution behavior, this knowledge enables precise control over the metallurgical properties of copper-on-steel overlay products.
The technology directly supports the company's TIG/MIG weld overlay production route while complementing hydraulic explosive bonding and explosion welding operations through hybrid process integration. The resulting process optimization contributes to WPS qualification, welder certification, product quality assurance, and customer value delivery across the full spectrum of copper-on-steel cladding applications—from high-conductivity electrical contact plates to heavy-duty mechanical cladding for pressure vessels and marine equipment.
As the company continues to expand its bimetallic cladding capabilities, the helium-argon optimization expertise documented in this study serves as a foundational element of the technical knowledge base, supporting continuous improvement, qualification building, and competitive differentiation in the specialized cladding manufacturing market.