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Views: 1 Author: SMARTECH-Sini Publish Time: 2026-08-27 Origin: Site
Laser welding is widely used in automotive manufacturing, machinery, electronics, molds, metal fabrication, and other industrial applications because of its high welding speed, concentrated heat input, small heat-affected zone, and excellent weld quality.
However, porosity is one of the most common internal defects in laser welding.
Pores are small cavities trapped inside the weld. Depending on their size, number, and location, they can reduce weld strength, fatigue resistance, sealing performance, and overall reliability.
So, why do pores occur during laser welding?
The answer is usually related to several factors working together:
Keyhole instability
Gas or vapor entrapment
Surface contamination and moisture
Improper welding parameters
Incorrect shielding gas conditions
Poor joint fit-up
Material characteristics
Understanding how pores form is the first step toward preventing them.
During deep-penetration laser welding, the concentrated laser energy rapidly melts and partially vaporizes the metal.
The vapor pressure generated by this intense evaporation creates a narrow, deep cavity known as a keyhole.
The keyhole is continuously changing during welding. When it becomes unstable or partially collapses, metal vapor can become trapped inside the molten pool and form bubbles.
These bubbles may rise toward the surface and escape. However, if the molten metal solidifies before the bubbles can escape, the bubbles become trapped and form pores.
Research using high-speed imaging and X-ray observation has shown that keyhole fluctuations, bubble formation, bubble movement, and subsequent trapping during solidification are important mechanisms behind laser welding porosity.
Keyhole instability → Bubble formation → Bubble migration → Solidification → Porosity
This is why maintaining a stable keyhole and molten pool is essential for high-quality laser welding.
Laser welding porosity does not usually have a single cause. In production, several factors may interact.
The most important causes are discussed below.
The keyhole is the central feature of deep-penetration laser welding.
It is maintained by the interaction between:
Laser energy
Metal vapor pressure
Surface tension
Molten-metal flow
Gravity
Solidification behavior
If this balance becomes unstable, the keyhole can fluctuate or partially collapse.
When the keyhole collapses, vapor can be trapped inside the molten pool and form bubbles.
Strong molten-metal flow can then transport these bubbles toward other regions of the weld.
If the bubbles cannot escape before solidification, pores remain inside the finished weld.
Studies have demonstrated that strong keyhole fluctuations can increase bubble formation, while bubble merging can contribute to the formation of larger pores.
Common factors include:
Incorrect laser power
Excessive or insufficient welding speed
Incorrect focal position
Excessive heat input
Unstable beam oscillation
Large or inconsistent joint gaps
Material thickness variations
Therefore, simply increasing laser power is not necessarily the solution.
The objective is to establish a stable welding process window.
Gas entrapment is another important mechanism of porosity.
During welding, gases may enter the molten pool from several sources, including:
Moisture
Oil and grease
Surface contamination
Material impurities
Atmospheric gases
Welding process vapor
Once gas enters the molten metal, it can form bubbles.
If the bubbles rise quickly enough, they escape.
If the bubbles are trapped by the rapidly solidifying metal, they remain inside the weld as pores.
The formation of porosity can therefore be understood as three basic stages:
Bubble formation → Bubble movement → Bubble capture by the solidification front
This mechanism is particularly important in aluminum laser welding, where hydrogen-related porosity can be significant.
Before laser welding, the workpiece surface should be clean and dry.
Oil, grease, moisture, dust, oxides, coatings, and other contaminants can decompose or react under the extremely high temperature of laser welding.
Some contaminants can introduce gases into the molten pool and increase the possibility of pore formation.
This is particularly important when welding aluminum alloys.
A practical preparation process is:
Cleaning → Contamination Removal → Drying → Welding
Depending on the material and application, cleaning can include:
Industrial metal cleaning agents
Degreasing
Mechanical cleaning
Brushing
Grinding
Suitable chemical cleaning
Alcohol wiping after cleaning when appropriate
The most important point is that the workpiece should be clean and completely dry before welding.
Aluminum alloys can be particularly sensitive to hydrogen-related porosity.
Hydrogen can enter the molten metal through moisture or surface contamination.
As molten aluminum cools and solidifies, hydrogen solubility decreases significantly. Excess hydrogen can therefore form bubbles.
If these bubbles cannot escape before solidification, they become pores.
For this reason, when laser welding aluminum alloys, particular attention should be paid to:
Surface cleanliness
Moisture control
Material storage conditions
Filler material cleanliness
Shielding gas quality
Welding parameter stability
Recent X-ray tomographic observations of laser welding have also shown that bubbles can form near the keyhole, move through the molten region, and become trapped at the liquid-solid interface.
Even when the material surface is clean, unsuitable welding parameters can still cause porosity.
The main parameters include:
Laser power
Welding speed
Focus position
Defocus
Beam diameter
Oscillation width
Oscillation frequency
Material thickness
Joint gap
These parameters work together to determine the stability of the keyhole and molten pool.
If laser power is too low, the keyhole may not remain stable enough to achieve consistent penetration.
If laser power is excessively high, vaporization and molten-metal flow can become more intense, potentially increasing keyhole instability.
Therefore:
Higher laser power does not automatically mean fewer pores.
The correct laser power must be matched with welding speed, focal position, material thickness, and other process parameters.
Welding speed directly affects heat input and molten-pool behavior.
If the welding speed is too high, insufficient energy may be delivered to the material, potentially resulting in unstable penetration.
If the welding speed is too low, excessive heat input may produce an overly large or unstable molten pool.
Therefore, the goal is not simply to "weld slower."
The goal is to find the optimal combination of laser power and welding speed for a stable process.
Research has shown that welding speed and laser power can significantly affect pore number, pore size, and overall porosity characteristics.
The focal position influences energy density and penetration.
An incorrect focus position can change:
Keyhole depth
Weld width
Penetration
Molten-pool stability
Heat distribution
If porosity appears after changing the focus position, the focus should be checked together with laser power and welding speed rather than adjusted independently.
Shielding gas protects the molten pool from atmospheric contamination and influences the welding environment.
Common shielding gases include:
Argon (Ar)
Helium (He)
The type, flow rate, direction, and nozzle position of shielding gas can all influence the welding process.
A stable gas shield helps protect the molten pool and maintain consistent welding conditions.
There is no single shielding gas that is best for every laser welding application.
Argon is widely used because it is:
Chemically inert
Relatively economical
Readily available
Dense enough to provide effective coverage
Suitable for many common welding applications
Helium has different thermal and plasma characteristics from argon.
It can be beneficial in certain high-power and deep-penetration applications, but its lower density means that gas delivery must be carefully controlled.
Material
Material thickness
Laser power
Welding speed
Joint design
Welding environment
Required weld quality
Therefore, shielding gas should be optimized together with the welding parameters instead of selecting gas based on flow rate alone.
If the gas flow is insufficient, the molten pool may not receive adequate protection.
Possible consequences include:
Increased oxidation
Unstable welding conditions
Atmospheric contamination
Poor weld appearance
Increased risk of welding defects
Workshop airflow can also affect shielding.
For example, strong ventilation or air-conditioning outlets may disturb the protective gas layer even when the flow rate displayed on the regulator appears correct.
More shielding gas does not always mean better protection.
Excessive gas flow can create turbulence around the welding zone.
Under certain conditions, turbulent gas flow may disturb the molten pool and contribute to gas entrainment.
Therefore, the objective should be:
Stable and uniform shielding — not maximum gas flow.
The optimum flow rate depends on:
Laser power
Material
Nozzle design
Nozzle-to-workpiece distance
Gas delivery direction
Welding environment
For this reason, values such as 15 L/min should be considered a reference starting point rather than a universal standard.
The condition of the joint itself should not be overlooked.
An excessive or inconsistent gap between workpieces can change molten-metal flow and keyhole behavior.
Before welding, check:
Joint gap
Workpiece alignment
Edge condition
Material thickness
Surface cleanliness
A stable and consistent joint helps create a more predictable welding process.
For production applications, the most effective approach is to control several factors simultaneously.
Remove:
Oil
Grease
Dust
Moisture
Oxides
Paint
Surface coatings
Always ensure that the surface is completely dry before welding.
Optimize:
Laser Power + Welding Speed + Focus Position + Beam Oscillation
Do not adjust only one parameter without considering the others.
The goal is to establish a stable process window with:
Stable keyhole
Stable molten pool
Consistent penetration
Smooth weld formation
Sufficient bubble escape time
Select an appropriate shielding gas according to the material and welding application.
Then optimize:
Gas type
Gas flow rate
Nozzle position
Nozzle angle
Nozzle-to-workpiece distance
Gas purity
Avoid strong airflow around the welding zone.
Check:
Workshop ventilation
Fans
Air-conditioning outlets
Cross-drafts
Gas hose leakage
Keep the joint gap and alignment within the required process tolerance.
Inconsistent gaps can change the molten-pool flow and penetration conditions, making the process more difficult to stabilize.
Porosity Problem | Possible Cause | Recommended Action |
|---|---|---|
Many small pores | Moisture or surface contamination | Clean and thoroughly dry the workpiece |
Large isolated pores | Keyhole instability | Optimize laser power, speed and focus |
Porosity increases after increasing gas flow | Excessive gas turbulence | Reduce and optimize gas flow |
Porosity mainly occurs in aluminum | Hydrogen/moisture contamination | Improve cleaning and moisture control |
Porosity appears intermittently | Unstable process or shielding | Check gas delivery, focus and parameters |
Porosity near the weld root | Keyhole instability or penetration issue | Optimize penetration and process stability |
Porosity appears after material storage | Moisture or contamination | Clean and dry before welding |
Porosity changes with joint gap | Inconsistent fit-up | Improve joint preparation and alignment |
It is difficult to guarantee absolute zero porosity under every material and welding condition.
Porosity is affected by:
Material composition
Material thickness
Surface condition
Moisture
Joint design
Laser power
Welding speed
Focus position
Shielding gas
Keyhole stability
Molten-pool dynamics
Welding environment
Therefore, the practical goal is to minimize porosity and keep it within the quality requirements of the specific application.
For high-reliability applications, additional inspection methods such as X-ray or CT inspection can be used to evaluate internal weld defects.
Before starting production, check the following:
Is the workpiece clean?
Is the workpiece completely dry?
Is there oil or grease on the surface?
Is the joint gap consistent?
Is the laser focus correctly positioned?
Is the laser power appropriate?
Is the welding speed appropriate?
Is the shielding gas pure and sufficient?
Is the gas nozzle correctly positioned?
Is there strong airflow around the welding zone?
Is the keyhole stable?
Is the molten pool stable?
A systematic check is usually more effective than changing one parameter randomly.
Laser welding porosity is a complex defect caused by the interaction of keyhole behavior, molten-pool dynamics, gas formation or entrapment, surface contamination, shielding gas, welding parameters, and joint conditions.
The most effective way to reduce porosity is to control the entire welding process rather than relying on a single parameter.
1. Keep the material surface clean and dry.
2. Maintain a stable keyhole and molten pool.
3. Optimize laser power and welding speed together.
4. Set the correct focus position.
5. Select the appropriate shielding gas.
6. Avoid both insufficient and excessive gas flow.
7. Maintain consistent joint fit-up.
8. Control external airflow around the welding area.
9. Establish a stable parameter window through actual welding tests.
With proper process optimization, laser welding can achieve high-quality, stable, and repeatable welds while significantly reducing the risk of porosity.
Common causes include surface contamination, moisture, unstable keyhole formation, unsuitable laser power or welding speed, poor shielding gas conditions, excessive gas turbulence, and inconsistent joint fit-up.
Aluminum alloys can be sensitive to hydrogen-related porosity. Moisture and surface contamination can introduce hydrogen into the molten pool, while hydrogen solubility decreases significantly as aluminum solidifies.
No. Too little gas can provide inadequate protection, while excessive gas flow can create turbulence and disturb the molten pool. The correct flow rate must be determined according to the specific welding setup.
Neither is universally better. Argon is widely used because of its availability, cost, and effective shielding. Helium has different thermal and plasma characteristics and can be advantageous in certain high-power applications.
Not necessarily under every material and process condition. However, proper surface preparation, stable welding parameters, correct shielding gas, and good joint preparation can significantly reduce porosity.
External visual inspection cannot reliably detect all internal porosity. For critical applications, X-ray or CT inspection can be used to evaluate internal weld defects.
Clean the material. Stabilize the keyhole. Optimize the welding parameters. Control the shielding gas.
These four principles form the foundation for reducing porosity and achieving consistent laser welding quality.
