1.What is the core performance of hot-dip galvanized coil?
The core performance of hot-dip galvanized coil is its long-lasting corrosion resistance, which stems from its unique coating structure and protective mechanism:
Coating structure advantage: The coating formed by hot-dip galvanizing is not a single zinc layer, but a composite structure of an "Fe-Zn alloy layer (inner layer) + a pure zinc layer (outer layer)" (the alloy layer is composed of Fe₃Zn₁₀ or FeZn₇, while the pure zinc layer consists of dense zinc grains). The alloy layer is metallurgically bonded to the steel substrate (rather than simply adhered), resulting in an extremely strong bond (adhesion reaching 70-100 MPa), making it resistant to dislodgement due to external forces (such as bending or impact).
Dual Protection Mechanism:
Barrier Protection: The outer pure zinc layer and any subsequent passivation film (such as chromate/chromium-free passivation film) form a dense "physical barrier" to isolate the steel from corrosive media such as water, oxygen, and salt spray.
Sacrificial Anodic Protection: If the coating is scratched or damaged, the exposed steel substrate forms a galvanic cell with the surrounding zinc layer (zinc has a lower electrode potential than iron). The zinc layer corrodes preferentially ("sacrifices" itself), thus protecting the steel from rust.
2.What is the cold working performance of hot-dip galvanized coil?
It can be stamped, bent, and rolled. For example, when manufacturing appliance housings (refrigerators, washing machines) and automotive parts (door linings, underbody panels), bending angles can reach 90° or even smaller, preventing the coating from cracking or peeling.
It can also be cut and welded. Although the substrate is exposed at the cutout after cutting, the surrounding zinc layer still protects the cutout through a "sacrificial anode," effectively preventing rust in the short term. During welding (with the use of an appropriate welding wire), the corrosion resistance of the weld area can be further enhanced through re-plating or painting.
It is suitable for subsequent coatings. The passivation treatment of the zinc coating improves adhesion to paints and powder coatings, making it suitable as a "primer" for further processing (for example, as a base for color-coated steel sheets), achieving both corrosion protection and appearance requirements.
3.What are the mechanical properties of hot-dip galvanized coils?
Wide strength range: From ordinary low-carbon steel (tensile strength of 300-400 MPa, used in general construction and home appliances) to high-strength steel (such as DX53D and HC340LA, with a tensile strength of 400-600 MPa, used in automotive structural parts and load-bearing brackets), the base material can be selected based on specific needs.
Excellent toughness: Maintains good impact toughness even at low temperatures (e.g., -20°C) and resists brittle cracking, making it suitable for outdoor low-temperature applications (such as steel structure factories and outdoor billboards in northern China).
Moderate surface hardness: The pure zinc layer has a hardness of approximately HV50-80, while the alloy layer has a hardness of approximately HV150-200. This prevents processing cracking caused by excessive hardness while also resisting minor scratches (such as friction during transportation and installation).
4.What is the environmental resistance of hot-dip galvanized coils?
Atmospheric Corrosion Resistance: Remains rust-free for extended periods in humid, rainy, and lightly polluted atmospheres (such as those found in cities other than coastal areas). Even in coastal salt spray environments, increasing the zinc coating thickness (e.g., from 60g/m² to 120g/m²) can extend the service life to 10-15 years.
Weak Acid and Alkali Corrosion Resistance: Excellent resistance to neutral water and weak alkaline solutions (such as rainwater and cooling water with a pH of 6-10), making it suitable for applications such as water tanks, water pipes, and cooling tower casings. However, caution is advised: The zinc coating is intolerant to strong acids and alkalis (such as concentrated hydrochloric acid and strong alkaline solutions), which can rapidly dissolve the zinc coating.
Stable Temperature Resistance: The zinc coating maintains a stable structure within the temperature range of -50°C to 120°C, resisting detachment or performance degradation due to temperature fluctuations. Suitable for applications such as low-temperature cold storage partitions and medium-temperature ventilation ducts.
5.How economical is hot-dip galvanized coil?
Extremely Low Maintenance: Frequent repainting and rust removal are unnecessary during use, requiring only regular cleaning (such as removing surface dust and oil stains), reducing labor and material costs for ongoing maintenance.
Long Replacement Cycle: The service life is 4-6 times that of cold-dip galvanizing and 3-5 times that of conventional painting. This reduces the frequency of replacement due to sheet corrosion and lowers overall project costs. (For example, for outdoor steel structure workshops, hot-dip galvanizing offers "once-coated, lifetime maintenance-free" functionality.)
High Recycling Value: Upon scrapping, the steel base of the galvanized coil is 100% recyclable, and the zinc layer can also be recycled through specialized processes, complying with the requirements of a circular economy and reducing scrap disposal costs.