Distributed Surface Pores
Distributed surface porosity refers to open pores on the weld bead surface caused by gas bubbles during solidification. They indicate contamination of shielding gas or the base material surface.
Physical-Chemical Mechanism of Action
Gas bubbles form when undissolved gas bubbles in the molten pool cannot escape and get trapped in the weld as it solidifies. These bubbles grow with pressure and form pores.
Metallurgical Relevance & Welding Risks
Distributed surface porosity can damage the weld by creating mechanical stress concentrations. It reduces the strength and toughness of the material and increases the susceptibility to cracking and hot cracking. Additionally, pores can become sites for corrosion.
Shop Practice & Action Guidelines
To avoid distributed surface porosity, it is crucial to keep the shielding gas clean and dry. The workpiece surface must be thoroughly cleaned before welding. For heavily contaminated materials, pretreatment with a deoxidizing agent may be necessary. Proper gas supply and an appropriate solidification sequence are also important.