Macropore in weld metal
A macroporosity is a large hole in the weld metal, caused by gas evolution or moisture. It significantly reduces the cross-section of the joint and weakens mechanical strength.
Physico-chemical mechanism of action
A macropore forms when gases like hydrogen or carbon dioxide are not sufficiently removed during welding and collect in the weld. These gases expand when heated and form large cavities in the material.
Metallurgical relevance & welding risks
Macropores severely weaken the mechanical strength of the weld metal because they significantly reduce the effective cross-section of the joint. This leads to an increased risk of cracks and brittleness. Additionally, macropores can accelerate corrosion by acting as anchor points for corrosive agents.
Workshop practice & instructions
To avoid macropores, it's crucial to implement good gas shielding. This can be achieved by using shielding gases like argon or carbon dioxide. Also, minimize moisture on the joint surfaces, e.g., by dry surface treatment or using dehumidifying systems. For gas-heavy welds, a slow cooling rate is essential to give gases time to escape and dissipate.