1.How does the corrosion intensity of the use environment determine the coating weight?
Highly corrosive environments, such as coastal areas (high salt fog), cold regions (frequent use of snow-melting salt in winter), and industrial areas (sulfide/dust pollution), require a higher zinc coating weight. For example, the chassis and door sills of vehicles in coastal areas typically require a zinc coating weight of ≥100g/m² (both sides, the same applies below). Some extreme environments even require 120-180g/m².
Low-corrosive environments, such as dry inland areas and non-industrial urban areas, have lower corrosion risks and can require thinner coatings; generally, 50-80g/m² is sufficient.
2.Different components have different corrosion risks. How to choose?
High-risk areas: Components directly exposed to the elements or susceptible to mud, water, and salt, such as the chassis (longitudinal beams, crossbeams), wheel arches, door sills, floorboards, and fuel tank brackets. These areas are susceptible to splashing mud, water, snow-melting salt, and sand and gravel, and present the highest corrosion risk. They require thicker coatings (typically 80-150g/m²). In extreme cases (such as commercial vehicle chassis), coatings may exceed 200g/m².
Medium-risk areas: Exterior body panels (doors, hood, roof, etc.). Although exposed to the elements, they are typically painted (primer + topcoat) and present a lower corrosion risk than the chassis. The coating must balance corrosion protection with paint adhesion, typically selecting 60-90g/m² (excessive thickness may affect coating adhesion).
Low-risk areas: Internal structural parts (such as pillars and the inside of crossbeams) and non-exposed parts within the engine compartment. These areas operate in dry environments with minimal exposure to contaminants, and thinner coatings (40-60g/m²) are recommended.
3.How do differences in corrosion resistance between zinc coating types affect weight selection?
Pure zinc coating: Corrosion resistance depends primarily on the thickness of the zinc coating, so increasing the weight can improve protection.
Alloy coating: Because alloying improves corrosion resistance, a lower weight can be used for the same corrosion requirements. For example, zinc-nickel alloy coatings offer 3-5 times the corrosion resistance of pure zinc in salt spray environments. For some high-risk areas, a coating weight of 60-100g/m² can replace the 120g/m² of pure zinc.
4.What are the subsequent processing and painting requirements?
Processability: Excessively thick coatings may cause coating peeling or cracking during stamping and bending. This is especially true for complex formed parts (such as door inner panels). The coating weight should be controlled to ensure processability (typically ≤100g/m²).
Coating compatibility: If the part requires subsequent coating (such as exterior body panels), excessive coating thickness may affect coating adhesion (reducing the interfacial bonding between the zinc layer and the coating). A balance must be established between corrosion resistance and coating performance. A coating weight of 60-90g/m² is generally selected.
5.What is the selection logic?
By environment classification: High corrosion (coastal/industrial areas) → thick coating (100-180g/m²); Low corrosion (inland dry areas) → thin coating (40-80g/m²).
By component risk: High-risk components such as the chassis/sills → thick coating; exterior panels/internal structural components → medium-thin coating.
Combined coating type: Alloy coatings (zinc-nickel/zinc-iron) can reduce weight; pure zinc coatings require a higher weight.
Balance between process and cost: Avoid excessive thickness that may affect processing/painting, while also meeting the minimum corrosion resistance requirements for the design life.