1.What are the plating related defects?
Uneven coating thickness: Symptoms include significant variations in zinc coating thickness across the plate surface (measured with a thickness gauge, the deviation on the same plate surface may exceed the standard ±10%). Thin areas are prone to rust, while thick areas may affect welding or painting.
Missing galvanizing (exposed iron)
Symptoms: Ungalvanized areas appear on the surface, such as dots, strips, or flakes, exposing the underlying steel sheet and making it susceptible to rust.
Zinc particles (zinc slag)
Symptoms: Tiny, raised particles (formed by zinc slag or impurities in the zinc solution) are distributed on the surface, creating a rough feel that can scratch subsequent coatings or affect stamping.
Plating shedding: Symptoms: The zinc layer has poor adhesion to the substrate, causing the zinc layer to flake off when the tape is removed or bent.
2.What types of surface defects are there?
White rust (zinc rust)
Symptoms: A white or off-white powdery substance (primarily composed of zinc oxide and zinc hydroxide) appears on the surface. In severe cases, it becomes spongy and gradually erodes the zinc layer, reducing corrosion resistance.
Black Spots/Black Discoloration
Symptoms: Black spots or streaks appear on the surface, often located along edges or bends, affecting the appearance.
Scratches/Indentations
Symptoms: Linear scratches or indentations of varying depths appear on the surface. These are usually caused by mechanical damage and can penetrate the zinc layer to expose the substrate in severe cases.
Passivation layer defects: Symptoms: The passivation layer (the thin film that improves corrosion resistance) on the surface of the electro-galvanized steel sheet becomes smudged, yellowed, or peels off, losing its protective effect.
3.What are the types of mechanical properties and processing defects?
Stamping Cracking/Wrinkling
Symptoms: During stamping (e.g., bending or stretching), cracks may appear in the zinc layer or the base steel sheet, or the surface may wrinkle due to uneven stress.
Welding defects: Porosity, lack of fusion, or severe zinc burnout at the weld edge, resulting in a localized decrease in corrosion resistance.
Dimensional deviation: Exceeding tolerances in sheet thickness, width, and flatness (such as camber and warping) can affect subsequent processing (such as cutting and assembly).
4.What are the other hidden defects?
Internal Inclusions
Symptoms: Non-metallic inclusions (such as sulfides and oxides) are present within the steel plate. These inclusions are difficult to detect with the naked eye, but they reduce the plate's toughness and can easily cause cracking at the inclusions during stamping.
Causes: Incomplete deoxidation during steelmaking or the introduction of impurities during the continuous casting process.
Hydrogen Embrittlement
Symptoms: High-strength galvanized steel sheets (such as those used in structural parts) can suddenly fracture during use, often at locations of stress concentration.
Causes: During the electrogalvanizing process, hydrogen atoms penetrate the substrate and, under stress, aggregate to form hydrogen bubbles, causing material embrittlement.
5.What are the core impacts of quality issues?
Reduced corrosion resistance (e.g., plating defects, white rust, and plating peeling) shortens service life.
Processability failures (e.g., cracking, wrinkling, and poor welding) lead to production losses.
Appearance defects (e.g., scratches and black spots) affect product aesthetics and added value.