Q：How does mechanical treatment deal with surface coating?
A:1. Grinding/Shot blasting
Applicable scenarios: Removal of local coating (such as before welding), elimination of surface burrs or slight oxide layer.
Steps: Use an angle grinder, sandpaper or shot blasting equipment to grind the coating surface.
The grinding area should exceed the target range (such as 20-30mm on both sides of the welding area) to ensure that the coating is completely removed.
2. Sandblasting
Applicable scenarios: roughening of large-area coating surfaces to enhance the adhesion of subsequent coatings (such as paint).
Steps: Use quartz sand or steel sand, control the air pressure at 0.6-0.8MPa, and spray the surface evenly.
The surface roughness after sandblasting is recommended to reach Ra 3.2-6.3μm.
Q:How do chemical treatments treat surface coatings?
A:1. Pickling passivation
Applicable scenarios: Remove slight white rust or surface oxides to restore the activity of the coating.
Steps: Soak or wipe with dilute hydrochloric acid (5%-10%) or citric acid solution to dissolve zinc oxide/aluminum.
After rinsing with clean water, apply chromate or silane passivation solution to form a protective film.
2. Deplating treatment
Applicable scenarios: The coating needs to be completely removed (such as local repair or substrate recovery).
Steps: Soak the aluminum-zinc plate in a strong alkaline solution (such as NaOH 50-100g/L, heated to 60-80℃).
React until the coating is completely dissolved (aluminum-zinc reacts with alkali to form aluminate and zincate).
Acid wash to neutralize the residual alkali solution, rinse with clean water and dry.
Q:How does heat treatment treat surface coatings?
A:Diffusion annealing
Applicable scenarios: Improve the bonding strength between the coating and the substrate and reduce the brittleness of the coating.
Steps: Heat to 300-400℃ under inert gas protection and keep warm for 1-2 hours.
Slowly cool to promote the diffusion of aluminum and zinc elements into the substrate to form an alloy transition layer.
Q:What is the coating repair method?
A:1. Cold spraying of zinc and aluminum
Applicable scenarios: repair of local coating damage (such as scratches and bumps).
Steps: Use sandblasting to clean the damaged area to Sa2.5 cleanliness.
Use cold spraying equipment to spray zinc and aluminum powder onto the surface at high speed to form a dense repair layer.
2. Electrophoresis re-plating
Applicable scenarios: Repair the uniformity of the coating on precision parts.
Steps: Immerse the workpiece in the electrophoresis solution containing zinc and aluminum ions, and ion directional deposition after power is turned on.
Adjust the voltage (10-30V) and time (1-5 minutes) to control the coating thickness.
Q:What should be paid attention to after plating treatment?
A:Compatibility test: The treated coating needs to be compatible with subsequent processes (such as welding and painting). It is recommended to conduct a small sample test first.
Environmental control: Chemical treatment needs to be equipped with ventilation and waste liquid recovery systems to avoid pollution.
Standard compliance: Select the treatment method in accordance with standards such as GB/T 14978 (continuous hot-dip aluminum-zinc alloy steel plate).