What is a possible cause of porosity in welds?

Porosity in welds is primarily caused by the entrapment of gas bubbles during the solidification process of the weld metal. The presence of contaminants such as moisture, paint, oil, and grease on the base material can lead to the formation of vapor when the weld is heated. This vapor can become trapped in the weld as it solidifies, resulting in small holes or pockets known as porosity.

Moisture is particularly critical because when water vaporizes at high temperatures, it can produce significant gas that the molten weld metal cannot escape from quickly enough. Similarly, oil, grease, and paint can release gases as they burn away due to the intense heat of the welding process, contributing to this defect.

While aspects like high voltage, low temperature, and fast travel speed can impact weld quality, they are not directly associated with the specific chemical and physical processes that lead to porosity in the same way that contaminants are. Therefore, the focus on various forms of contamination as a major cause effectively highlights the importance of proper surface preparation and material cleanliness in welding practices.