Last winter, our quality inspector came to see me with some X-ray films. A batch of welded parts for automotive modifications had a porosity rate of 8%, whereas the customer required ≤2%. The welder had been in the trade for over a decade; the welding parameters were correct, the shielding gas flow was normal, and the ambient humidity met the standards. So where was the problem?

After three weeks of investigation, the answer was unexpected: it wasn’t the welders, nor the equipment; it was that the gas supplier had changed batches, and the argon purity had dropped from 99.999% to 99.99%. Just one extra ‘9’ after the decimal point caused the porosity rate to quadruple.

In this article, I wish to share the three hidden root causes of porosity issues, and how we replaced a technical mindset with a supply chain mindset to stabilise the porosity rate from 8% to 0.3%.

Root Cause 1: Shielding Gas – The Purity Trap

Misconception: Argon is just argon; buy the cheapest one.

Reality: Aluminium alloys are extremely sensitive to hydrogen. A drop in argon purity from 99.999% to 99.99%, or an increase in oxygen content from 10 ppm to 100 ppm, is sufficient to cause porosity rates to skyrocket. More insidiously, a supplier’s ‘high-purity argon’ may be a mixed batch sourced from different gas suppliers.

Our lesson: Three consecutive batches met specifications, but the fourth suddenly exceeded limits. Upon investigation, we discovered that the supplier had sourced gas from a different source at short notice to meet a deadline, without informing us.

Countermeasures:

Specify a single gas source; refuse mixed batches

Request third-party test reports (oxygen, nitrogen and water content) for every batch

Maintain a 15-day gas inventory for critical orders to avoid emergency sourcing

Root Cause 2: Base Material – The Time Bomb of the Oxide Film

Misconception: Aluminium materials are used immediately upon arrival; if the surface is shiny, there is no issue.

Reality: The oxide film (Al₂O₃) on the surface of aluminium has a melting point of 2050°C, far higher than the 660°C melting point of the aluminium matrix. During welding, the oxide film does not melt, forming inclusions; moisture adsorbed on the surface decomposes into hydrogen at high temperatures, creating porosity.

We once had a batch of welded components that passed inspection in the morning, only for the porosity rate to surge in the afternoon. Upon investigation, we discovered that the aluminium stock used in the morning had been freshly unpacked, whilst that used in the afternoon had been exposed to the workshop air for four hours—at 65% humidity—allowing the oxide film to absorb sufficient moisture.

Countermeasures:

Use aluminium stock within 24 hours of unpacking; return or re-clean any stock exceeding this timeframe

Perform laser cleaning or mechanical grinding prior to welding to remove the oxide film

Establish a material exposure tracking log rather than relying on experience

Root Cause 3: Ambient Humidity — The Overlooked Seasonal Variable

Misconception: The workshop has dehumidifiers, so humidity control is not an issue.

Reality: Dehumidifiers may be set to 50%, but localised humidity at welding stations can reach as high as 70% — particularly in winter when windows and doors are tightly closed and there is little foot traffic. For every 10% increase in humidity, the porosity rate rises by approximately 15%.

Our analysis of two years’ data shows that from December to February each year, the porosity rate is on average 40% higher than in other months. This is not due to fluctuations in welder skill, but rather to poor ventilation and localised humidity build-up in winter.

Countermeasures:

Install localised dehumidification at welding stations, rather than relying on the workshop’s centralised system

When humidity exceeds 60%, initiate pre-welding preheating (80–120°C) to drive out moisture absorbed by the material

Schedule winter orders in advance to avoid peak humidity periods

Results

After 6 weeks, porosity stabilised at 0.3%

Client audit passed; moved to mass production

Unexpectedly, welder efficiency improved by 15% – no more repeated rework

Key shift in mindset: It is not about finding ‘better welders’, but enabling ordinary welders to consistently produce合格 products in a stable material and environmental setting.

Final Thoughts

Porosity in aluminium alloy welding appears to be a technical parameter issue on the surface, but at its core lies a problem of supply chain stability. Fluctuations in gas purity, base material condition and ambient humidity have a far greater impact than the welder’s technique.

Our experience: manage suppliers as if they were workstations within the workshop. Incoming material inspection, batch traceability and environmental monitoring—these ‘non-welding’ factors determine the upper limit of welding quality.