Why Argon Is Essential as a Shielding Gas？
To understand why argon is used as a shielding gas, we must first consider the characteristics of aluminum. In ordinary air, aluminum reacts easily with oxygen to form a stable oxide film—aluminum oxide—with a melting point as high as 2050°C. This oxide film has strong adsorption properties, and the moisture it retains can lead to porosity in the weld seam.
In arc welding, removing this oxide film is a complex process achieved through the impact of ionized shielding gas and the electron bombardment from the workpiece to the electrode.
Compared with steel, aluminum exhibits very different physical, chemical, and mechanical properties. It has a much lower melting point (560–660°C) but a high thermal conductivity and heat of fusion, meaning the total heat required for aluminum welding is roughly comparable to that for steel.
During cooling and solidification, aluminum undergoes significant shrinkage and thermal expansion, which can cause distortion, cracking, or residual stress in the welded joint.
Why Inert Gases Are Used for Aluminum Welding
Inert gases such as argon and helium are chemically stable and do not react with molten metal or oxygen, even at high temperatures. Therefore, in arc welding of aluminum and its alloys, inert gases are used as shielding gases. In contrast, active gases such as CO₂—commonly used for welding steel—are unsuitable for aluminum and aluminum alloys.
In most cases, pure argon is used for welding aluminum alloys. However, helium or argon-helium mixtures are also employed, depending on the application.
The shielding gas must have a purity higher than 99.99% and a dew point below –50°C at 1 bar pressure to ensure optimal protection. The primary role of argon or helium is to prevent air from entering the molten pool and to shield the molten metal and high-temperature regions from oxidation. Additionally, these inert gases help stabilize the arc.
At the same welding current, helium provides higher arc power and heat concentration than argon, but argon produces a more stable arc and is easier to ignite. Therefore, for AC tungsten inert gas (TIG) welding, argon or argon-helium mixtures are usually preferred.
Because helium has a lower density than argon, achieving the same shielding effect requires 2.5 to 3 times the helium flow rate compared to argon.
Recommended Shielding Gases for Different Metals in Welding
| Metal / Alloy | Recommended Shielding Gas | Typical Gas Mixture | Main Advantages | Notes / Applications |
|---|---|---|---|---|
| Carbon Steel | CO₂ or Ar+CO₂ | Ar+15–25% CO₂ | Cost-effective, stable arc, good penetration | Suitable for general fabrication and structural steel |
| Stainless Steel | Ar+O₂ or Ar+CO₂ | Ar+1–2% O₂ / Ar+2–5% CO₂ | Smooth weld bead, good wetting, low oxidation | Best for MIG welding of austenitic or ferritic stainless steel |
| Aluminum & Alloys | Pure Ar or Ar+He | Ar+25–75% He (optional) | Clean welds, minimal oxidation, deep penetration | He improves speed and penetration for thick plates |
| Copper & Copper Alloys | Ar or Ar+N₂ | Ar+1–3% N₂ | Lower cost, adequate protection | Slightly more spatter and fume |
| Nickel & Alloys | Ar or Ar+He / Ar+H₂ | Ar+5–10% He / Ar+2% H₂ | Better penetration, higher efficiency | Hydrogen addition enhances productivity |
| Titanium & Alloys | Pure Ar or Ar+He | Ar+25–50% He (optional) | Prevents oxidation, high weld purity | Must avoid O₂, N₂, and H₂ contamination |
Selection and Application of Shielding Gases
(1) Shielding Gas Selection in GTAW (TIG)
Argon (Ar) is widely used in gas tungsten arc welding (GTAW) because it is inert, nonreactive at both low and high temperatures, and provides a stable arc with low ionization potential. Argon ensures clean, aesthetically pleasing welds and offers a cost-effective solution.
Argon is suitable for welding nearly all metals, including carbon steel, stainless steel, aluminum, copper, nickel, titanium, zirconium, and their alloys.
While pure argon delivers excellent weld quality, its lower arc energy can limit penetration and welding speed. To overcome this, mixtures such as Ar+He or Ar+H₂ can be used to enhance arc power and penetration.
(2) Shielding Gas Selection in GMAW for Carbon Steel
For standard carbon steel or structural steel, CO₂ is often used as the shielding gas, known as CO₂ gas metal arc welding (GMAW). It offers high productivity, good weld quality, and low cost. However, CO₂ may contain moisture, which can cause porosity or weld defects, so gas purity must be controlled.
In cases requiring higher weld quality—such as when nondestructive testing or pressure testing is needed—a mixture of Ar+CO₂ can be used. The composition affects arc stability, energy density, and droplet transfer, improving weld appearance, reducing spatter, and enhancing mechanical performance.
(3) Shielding Gas Selection in GMAW for Stainless Steel
The choice of gas for stainless steel GMAW depends on material type, welding position, and desired weld properties. Pure argon is suitable for TIG welding stainless steel but not for MIG welding, as it leads to poor wettability and bead appearance.
Adding 1–2% oxygen to argon reduces surface tension, improving fluidity and producing a smoother weld bead. For austenitic stainless steel, 0–1% O₂ is recommended, while ferritic stainless steel can use up to 2%.
Alternatively, Ar+2–5% CO₂ mixtures can also be used. Despite concerns about carbon pickup, studies show that CO₂ below 5% keeps the carbon content well within acceptable limits while maintaining excellent arc stability and minimal oxidation.
Ternary mixtures such as Ar+5% CO₂+2% O₂ or Ar+He+CO₂ further improve arc focus, weld penetration, and bead formation, making them suitable for high-quality stainless steel applications.
(4) Shielding Gas Selection in GMAW for Aluminum Alloys
In aluminum GMAW, pure argon is commonly used due to its high purity and effectiveness in preventing oxidation. If the shielding gas purity is insufficient, black oxides may appear along the weld, affecting its appearance and integrity.
To achieve deeper penetration and higher welding speed, helium can be mixed with argon. Helium’s higher thermal conductivity increases arc voltage and temperature, making it suitable for thicker aluminum plates and improving productivity. However, excessive helium may cause increased spatter.
(5) Shielding Gas Selection for Other Metals and Alloys
For copper and copper alloys, argon or argon-nitrogen mixtures are used. Adding nitrogen can reduce cost while maintaining adequate protection, though it may slightly increase spatter and fume.
For nickel and nickel alloys, argon, argon-helium, or argon-hydrogen mixtures can improve efficiency.
For titanium and titanium alloys, only pure argon or argon-helium mixtures can be used, as titanium reacts readily with nitrogen, hydrogen, and oxygen.
Conclusion
Shielding gases play a crucial role in gas-shielded welding, directly influencing weld quality, efficiency, and cost. Because different materials require different welding parameters, selecting the right shielding gas involves balancing material characteristics, welding methods, droplet transfer modes, and positional requirements. Proper gas selection ensures optimal weld quality and performance in practical applications.
About Jinhong Gas
Jinhong Gas is a leading industrial and specialty gas supplier in China, providing high-purity argon, helium, hydrogen, nitrogen, oxygen, and customized gas mixtures for industrial welding, electronics, and manufacturing sectors. With advanced purification and distribution systems, Jinhong Gas ensures reliable supply, consistent purity, and tailored gas solutions for every customer.
Our welding-grade argon and helium meet international standards with purities up to 99.999%, ensuring stable arcs, superior weld quality, and enhanced process efficiency. Whether for TIG, MIG, or laser welding applications, Jinhong Gas delivers dependable performance and professional technical support for industries worldwide.
