The causes and control methods of gas pores in laser welding seams

I. Introduction

Laser welding offers advantages such as high energy density, a small heat-affected zone, good weld formation, and low distortion. It is widely used in sheet metal fabrication, consumer electronics, battery manufacturing, medical devices, and the automotive industry. However, in practical welding applications, porosity defects frequently occur inside or on the surface of welds due to combined effects of material, equipment, and process factors. These defects negatively affect weld strength, density, and appearance quality. Therefore, it is necessary to analyze the mechanisms of porosity formation and propose effective control measures to improve welding stability and product quality.

II. Main Causes of Weld Porosity

Porosity in welding is typically caused by entrapped gas, dissolved gas precipitation, or material vaporization. The major causes include:

1. Surface Contamination of Materials

When weld surfaces contain oil, moisture, rust, or coatings, they decompose under high temperatures and generate gases that enter the molten pool. For example:

Oil contamination → generates hydrocarbon gases

Moisture → generates H₂ and O₂

Coatings → decompose into organic or inorganic gases

If the molten pool solidifies quickly, these gases cannot escape in time and form pores.

2. High Gas Content in Materials

Certain materials contain higher levels of hydrogen, oxygen, nitrogen, or inclusions, which may precipitate and form bubbles during melting. For example:

Aluminum alloys are sensitive to hydrogen

Steels are sensitive to oxygen

Copper alloys are sensitive to nitrogen

If molten pool time is insufficient or cooling is too rapid, the gases remain trapped and form pores.

3. Insufficient or Unstable Laser Energy Input

If the energy density is insufficient, the molten pool becomes shallow with poor fluidity, making it difficult for gases to escape. Energy fluctuations can also cause inconsistent molten pool sealing, leading to bubble entrapment.

Common manifestations include:

Laser power fluctuations

Focal deviation leading to reduced power density

Excessively high welding speed causing incomplete penetration

4. Improper Shielding Gas Coverage

Insufficient shielding or incorrect shielding direction allows air to enter the molten pool and produce gas reactions. Excessive gas flow may produce turbulence or air entrainment.

Common issues include:

Excessive argon flow causing vortex formation

Gas misalignment leading to incomplete shielding

Nozzle contamination causing disturbed flow fields

5. Mismatch Between Filler Material and Base Metal

In filler wire welding, if the filler wire composition, gas content, or cleanliness is poor, additional gas or inclusions may be introduced.

Examples include:

Moist or hygroscopic welding wire

Poor storage conditions

Insufficient wire cleaning

III. Main Hazards of Weld Porosity

Porosity defects affect product quality mainly through:

Reduced weld strength and fatigue life

Impaired sealing and barrier performance

Degraded appearance quality

Reduced reliability in critical applications

Industries such as battery enclosures, medical devices, and gas-tight structures may reject products entirely due to porosity defects.

IV. Control Methods for Weld Porosity Defects

To improve laser welding quality, optimization must be carried out across materials, equipment, processes, and environments.

1. Implement Proper Surface Pretreatment

Weld surface cleaning significantly reduces porosity risks. Common methods include:

Mechanical cleaning (grinding, brushing)

Solvent cleaning (alcohol, acetone)

Laser cleaning (suitable for mass production)

Drying and dehumidification (especially for aluminum alloys)

Key areas include the weld zone and internal contact areas of lap joints.

2. Control Material Quality and Storage Conditions

Based on material gas absorption characteristics:

Aluminum alloys should be kept dry to prevent moisture absorption

Copper parts should be protected from oxidation by gas or coating

Steel should avoid severe rust and contaminants

In filler wire welding, the wire must remain dry and clean.

3. Optimize Laser Energy Parameters

Proper process matching is critical for gas escape. Optimization directions include:

Increasing power density → improves penetration and fluidity

Reducing welding speed → increases molten pool open time

Adjusting focal position → enhances molten pool stability

Stabilizing laser output → avoids energy fluctuations

In deep penetration welding, negative defocus may enhance penetration and flow behavior.

4. Improve Shielding Gas Systems

Shielding gas optimization includes:

Selecting appropriate gases (e.g., argon for aluminum welding)

Controlling proper flow rates (avoid turbulence)

Optimizing nozzle angle and standoff distance

Increasing protection coverage to prevent air entrainment

For aluminum welding, dual-gas or enclosure shielding is often used to reduce porosity.

5. Optimize Joint Design and Welding Configuration

Joint design influences gas escape behavior:

Prefer butt joints over lap joints when possible

Provide venting paths for lap joints if unavoidable

Avoid contained structures that trap gas during rapid cooling

Proper structural design reduces stress and improves gas escape efficiency.

V. Conclusion

Laser welding porosity is a typical defect resulting from the combined effects of materials, processes, and environmental conditions. Its formation mechanism is highly coupled with multiple factors. By improving material cleanliness, optimizing laser and shielding gas parameters, and adopting proper joint designs, weld formation quality and performance can be significantly enhanced. In production environments, integrating online monitoring and closed-loop quality control systems can further stabilize welding quality and support broader industrial adoption of laser welding technology.