What is a common cause of weld porosity?

What is a common cause of weld porosity?

• A. Clean metal surfaces
• B. Contaminated metal or improper shielding gas flow
• C. Proper shielding gas flow
• D. Rapid cooling

Answer: (B)

Porosity in welds comes from gases getting trapped in the weld metal as it cools. In automotive welding, the two most common causes are contamination and shielding gas problems. If the metal surface has contaminants like oil, grease, paint, rust, or moisture, those substances release gases into the molten pool and form pores as it solidifies. If the shielding gas doesn’t protect the weld properly—due to leaks, incorrect flow rate, or an improper gas mix—air and moisture can enter the weld area and create porosity. That’s why the best practice is to start with clean, dry surfaces and ensure the shielding gas is flowing correctly to prevent porosity. Rapid cooling can lead to other defects, but it isn’t the typical cause of porosity.