1.What is white rust?
First, it's important to understand the nature of white rust. The main components of white rust are zinc hydroxide and basic zinc carbonate. It's an early product of corrosion occurring in galvanized layers in humid, poorly ventilated environments. You can think of it as a "zinc disease."
2.What are the causes and consequences of welding defects?
Cause: White rust and its attached moisture (water of crystallization) rapidly decompose upon exposure to the high temperatures of welding, producing large amounts of water vapor, hydrogen, and oxygen.
Consequences:
Porosity: These gases, unable to escape from the molten metal, form pores inside and on the surface of the weld. Porosity severely reduces the effective cross-sectional area of the weld, leading to decreased weld strength, plasticity, and density.
Intense Spatter: The rapid expansion of gases causes arc instability and intense metal spatter, affecting weld bead formation and contaminating the welding torch and workpiece surface.
3.What are the causes and consequences of factors affecting arc stability and weld formation?
Cause: The white rust layer is an uneven, unclean, and conductive substance. During welding, it interferes with the stability of the electric arc, causing it to waver.
Consequence: This results in a rough, discontinuous weld, with defects such as undercut and incomplete penetration.
4.What are the causes and consequences of reduced corrosion resistance in welds?
Causes:
During the welding process, the zinc layer in and around the white rust area is damaged. The resulting weld metal itself does not contain zinc, and its corrosion resistance is far lower than that of galvanized steel.
Defects such as porosity and cracks provide pathways for corrosive media, allowing corrosion to begin at these weak points and spread inwards and outwards.
Consequences: The welded joint becomes the first part of the entire structure to rust through, creating a "weakest link" effect and significantly reducing the corrosion resistance advantages of galvanized steel.
5.What are the causes and consequences of welding difficulties and toxic fumes?
Causes: The presence of white rust makes the welding process more unpredictable, requiring welders to frequently adjust parameters, increasing the operational difficulty. Simultaneously, zinc evaporation at high temperatures produces large amounts of zinc vapor, which oxidizes with air to form zinc oxide fumes.
Consequences: Inhaling zinc oxide fumes can lead to "metal fume sickness" in welders, causing symptoms such as fever, chills, and nausea, endangering their health. White rust exacerbates fume production.