Definition of Aluminized Zinc Products

　　Hot-dip galvanized aluminum-zinc steel sheet is a coated steel sheet obtained by hot-dip coating both sides of cold-rolled steel with an aluminum-zinc alloy coating, with the coating alloy composition consisting of 55% Al, 43.5% Zn, and 1.5% Si by mass percentage.

　　Excellent corrosion resistance

　　Physical separation of the aluminum-zinc coating, electrochemical protection, and the role of trivalent aluminum ions impregnation contribute to the excellent corrosion resistance of the aluminum-zinc coated steel plate.

　　In the same environment, aluminum-zinc coated steel sheet has a lifespan 2-6 times longer than standard galvanized steel sheet.

　　1) The U.S. atmospheric exposure test results indicate:

　　In 3 different regions, the corrosion resistance of aluminum-zinc coated steel is 3-6 times that of hot-dipped galvanized steel.

　　2) Australian atmospheric exposure test results indicate

　　The corrosion resistance of aluminum-zinc coated steel is 1.6-4.6 times that of hot-dipped galvanized steel.

　　3) Salt Spray Test Results

　　Test Method: ASTM B-117 test results indicate the time of red rust appearance

　　Aluminized zinc develops red rust 18 times faster than hot-dipped zinc.

　　4) Recirculating Steam Test Results

　　Test Method: Steam Jacket (55℃)

　　1 cycle = 22 hours of moisture and vapor + 2 hours of drying.

　　3. Excellent heat resistance

　　Excellent heat resistance of aluminum-zinc plated material allows for long-term use at high temperatures.

　　4. Good heat reflection properties

　　Its reflectance coefficient is double that of galvanized steel, which can reduce indoor temperature in summer and lower air conditioning energy consumption.

　　6. Large ton steel unfolded area

　　Various thicknesses of hot-dipped galvanized, aluminum-zinc coated expanded area

　　The unfolded area of steel increases by approximately 4%-5%.

　　Introduction: In the previous article "What is Hot-Dip Aluzinc? What Are Its Advantages?", the superior qualities of the hot-dip aluzinc products were introduced. Today, we will briefly discuss their application areas and usage in the construction industry.

　　One. Applications of Hot-Dip Aluzinc Products

　　1. Building Materials: Wall Panels, Roofing Sheets, Pipes, Fencing, Louvers, Window Frames

　　2. Automotive: mufflers, doors, oil filters,

　　3. Appliances: Explosion-proof Belts, Ovens, Vending Machines, Car Audio Systems, Refrigerator Back Panels, Rice Cookers, Electrical Components

　　4. Other: Steel furniture, containers, mailboxes, sewing machines

　　Section 2: Applications of Hot-Dip Galvanized Aluminum Zinc in the Construction Industry

　　Hot-dip galvanized aluminum zinc products are primarily used in the construction industry after being processed into color coated panels, and are widely applied to the roofs and walls of buildings.

　　The surface of the aluminum-zinc (55% Al, 43.5% Zn, and 1.5% Si) substrate is first subjected to a chemical conversion treatment, followed by the application of a very thin (5um) special primer. Then, a color coating with good durability and processing properties, approximately 20um thick, is applied according to customer specifications.

　　Product substrates include SGLCC, G345, G300, G550, etc., with coating thicknesses such as AZ150, AZ165, featuring a smooth, small zinc flower structure. Paint types include PE, PVDF, SMP, HDP, etc. Coating structures are available in double-sided double-coating and single-sided double-coating with the other side being single-coated, with coating colors tailored to customer requirements.

　　III. Application Precautions

　　1. Design Usage Precautions

　　Use aluminum-zinc coated steel sheets with caution in alkaline medium conditions.

　　Avoid direct contact between other unprotected conductive materials and the aluminum-zinc coated color steel plate.

　　Do not allow wet wood or concrete to come into prolonged contact with the galvanized aluminum zinc coated panels.

　　If the roof pitch is low, it is recommended to use galvanized aluminum zinc sheeting.

　　The use of matching components (insulators, seals, and fasteners) should consider their corrosion-resistant aluminum-zinc coated paint simultaneously.

　　2. Processing Precautions

　　Ensure the plate surface is not damaged during rolling forming.

　　Veneer boards should be checked for depth and sharpness to ensure durability.

　　Protect or do not expose various trimmed edges.

　　No metal shavings should remain on the surface during cutting and welding.

　　Avoid sagging when handling long boards; stack them on wood blocks and maintain an angle for drainage. Aluminum-zinc coated paint.

　　3. Maintenance and Care Precautions

　　The construction should be thoroughly cleaned after completion (with water).

　　Generally, cleaning should be performed every 6 months; more frequent cleaning is required in coastal and industrial pollution areas.

　　Do not use degreasing powder or industrial detergents (as they may damage the coating). Use domestic dishwashing liquid and conduct a small area test.

　　Damaged coatings can be repaired; those that are not visibly damaged do not require repair. Clean off oil stains and the like before repairing, and avoid extensive repairs.

　　Galvanized

　　The Little-Known Hot-Dip Galvanized Zinc Flower – A Read-It-and-Brag Article

　　What is zinc whiskers

　　A beautiful zinc flower is a major feature of traditional hot-dipped galvanized steel sheets. The complete form of zinc crystals is similar to snowflakes or hexagonal stars, so the zinc crystals formed on the surface of the strip steel through condensation during the hot-dipping process may take on the shape of snowflakes or hexagonal stars.

　　Actually, zinc flower is merely ornamental with no practical use. Conversely, zinc flower is not very resistant to corrosion, and its surface coating appears uneven. Therefore, the appliance and automotive industries tend to opt for small zinc flower (or no zinc flower) products, while the beautifully looking zinc flower products still have a certain usage in the construction industry.

　　High purity zinc liquid cannot solidify into zinc flowers upon cooling due to the lack of necessary crystalline nuclei. To obtain typical zinc flowers, the prerequisite is to add in the zinc liquid an appropriate amount of two types of alloy elements with different properties. One type of alloy element is completely soluble in the zinc liquid but almost completely immiscible in solid zinc, such as lead and titanium; the other type has solubility in both liquid and solid zinc, such as aluminum, tin, antimony, etc. If only one type of alloy element is added, although the surface state of the zinc layer will change after solidification, it is still not sufficient to form typical zinc flowers.

　　Methods for forming zinc flower

　　The method to form zinc flowers involves generating a large number of crystal nuclei early on, reducing the solidification temperature of the zinc liquid to extend the growth time of the zinc flower crystals, making it easier for the zinc flowers to grow larger.

　　(1) Add other elements to the zinc melt

　　After adding a certain alloy element to the zinc melt, it can prolong the crystallization process, so the surface zinc melt will not solidify before reaching its eutectic temperature.

　　Pure zinc solidifies at 419.5°C; when tin (less than 0.5%) is added, the tin-zinc eutectic alloy won't solidify until it drops below 198°C. Adding cadmium prevents the cadmium-zinc eutectic alloy from solidifying until it cools to below 264°C. Similarly, if antimony (less than 0.3%) is included, the antimony-zinc eutectic alloy won't solidify until it falls below 409°C. Lead, when added, causes the lead-zinc eutectic alloy to remain liquid until it cools to below 317°C.

　　Therefore, adding alloy to reduce the melting point of zinc liquid extends the solidification time to varying degrees compared to pure zinc, significantly prolonging the growth time of zinc flower crystals, facilitating the growth of zinc flowers, thus allowing for larger zinc flowers to be obtained.

　　(2) Surface Blowing Gas Method

　　As the zinc coating begins to solidify, blowing a steam or air stream over its surface facilitates the growth of zinc flower crystals, resulting in a larger pattern. Another purpose of the blowing air stream is to form a dense oxide film, thereby enhancing the zinc coating's corrosion resistance.

　　(3) Wire Mesh Method

　　This method is applicable only to galvanized thin plates, where it achieves the purpose by using magnetic rollers to bring the steel wire mesh into contact with the zinc layer's surface. As the contact points of the steel wire mesh nodes are cooled first, solid particles form crystalline nuclei there, becoming the starting points for crystallization. The remaining un-solidified zinc liquid then crystallizes outwards from these nuclei, forming zinc flowers.

　　(4) Spray Mist Method

　　During the non-solidification of pure zinc liquid on galvanized steel parts, applying a mist (a mixture of water and steam or water and air) creates crystalline nuclei. The zinc liquid then expands from this point, forming zinc flowers.

　　(5) Other Methods

　　In addition to the aforementioned methods, achieving a smooth surface on the plated parts, a relatively thin zinc coating, uniform temperature decrease, and sufficient air cooling time can also result in larger zinc flowers.

　　Zinc flower shape

　　The shape of zinc flower depends on the type of alloy added to the zinc liquid, such as adding lead or antimony results in a peacock tail-like zinc flower; while adding lead and tin yields a fern-like zinc flower, and so on.

　　The crystalline orientation of zinc flowers on the coated surface varies due to their different appearances, affecting processing characteristics. For instance, in processes like simple stretching and deep drawing, the processing of feather-like zinc flowers is good, followed by fern-like and leaf-like zinc flowers, which are less suitable. In bending and tension processing, the processing of leaf-like zinc flowers is good, followed by feather-like and fern-like zinc flowers, which are less suitable.

　　Zinc Flower Size

　　In accordance with the European standard EN 10346:2015, the dimensions of hot-dip galvanized zinc flowers can be categorized as normal spangle and minimized spangle.

　　Regular zinc flower refers to the size and shape of zinc crystals formed after the normal solidification of zinc liquid, while zinc-free flower (also known as small zinc flower) is the size and shape of zinc crystals obtained through special control of the zinc solidification process. If the customer requires specific sizes of zinc flower, it must be negotiated at the time of order.

　　Many factors influence the size of zinc flowers. When the zinc liquid composition meets the conditions for zinc flower formation, the following factors affect the size of the zinc flowers:

　　Raw Material: The thicker the raw steel plate, the smaller the surface roughness, and the larger the zinc flower.

　　(2) Cooling Rate: The faster the cooling rate, the shorter the crystal growth time, and the smaller the zinc flower.

　　(3) Number of Crystal Nuclei: The size of zinc flowers is closely related to the number of crystal nuclei. When the steel base surface is rough or the cleanliness is poor, the zinc flowers are relatively smaller. Zinc crystals form on the steel base, and the more crystal nuclei, the smaller the zinc flowers. The production process of small zinc flowers, using the spray mist method, takes advantage of this principle.

　　(4) Other Factors (Production Environment, etc.)

　　To achieve fine zinc flowers, during galvanizing, immediately spray water droplets with a diameter less than 0.1mm onto the galvanized sheet surface as the zinc liquid approaches its solidification temperature, forming tiny and uniform crystalline nuclei. For smooth zinc flowers, further flatten the zinc with a reduction of less than 1%. Fine zinc flowers are suitable for painting, while smooth zinc flowers are ideal for deep drawing.

　　Zinc coating adhesion

　　As the heated steel strip passes through the molten zinc bath (zinc pot), an iron-zinc alloy layer first forms on the substrate, covered by a layer of pure zinc. The thickness of the iron-zinc alloy layer is uneven, relatively loose, brittle, with poor ductility, and prone to cracking.

　　If the steel plate surface has a certain amount of iron-based salts prior to galvanizing, the resulting iron-zinc alloy has poor adhesion, low ductility, and is prone to flaking. When the pure zinc coating contains harmful impurities such as zinc oxide, zinc slag, cadmium, and lead, it can result in large zinc flowers or disrupt the continuity of the zinc layer, making small cracks in the pure zinc layer more likely to occur.

　　When the galvanized layer is too thick, its bendability also worsens. Adding aluminum to the zinc melt causes a reaction between the aluminum in the melt and the substrate, initially forming Fe2Al5 or Fe2Al3, which thins the iron-zinc alloy coating and improves the adhesion of the zinc layer.

　　Inconsistent zinc flower and influencing factors

　　The uneven zinc flower on the coated surface is a common surface defect in hot-dip galvanized products. Although it doesn't significantly affect the majority of product uses, it impacts the product's appearance and limits its application in certain market sectors. Some products with uneven zinc flower also exhibit poor adhesion of the zinc layer, directly affecting their usability.

　　The unevenness of the zinc flower on the surface of hot-dip galvanized plates can be categorized into the following types:

　　(1) One side has zinc flowers, the other does not. The diameter of the zinc flowers on the side with them is approximately 6mm.

　　(2) Along the longitudinal direction of the steel strip, the zinc flower size exhibits a regular fluctuation.

　　(3) One side of the steel strip has larger zinc flowers, while the other side has smaller zinc flowers.

　　(4) Steel strip with small zinc flower at the edges and larger in the middle.

　　Key factors affecting the unevenness of zinc flowers include: the ratio of two types of alloy elements in the zinc liquid, gas knife control process, strip temperature, impurity content in coal gas and combustion air, cleanliness of the strip surface, and the reduction state inside the furnace, buildup on furnace rolls, strip scratches, and oxidation scale on the raw material surface, the temperature of the strip entering the zinc pot, zinc liquid temperature, and cooling temperature after plating, etc.

　　Measurement of Hot-Dip Galvanized Coating Thickness

　　In accordance with the requirements of GB/T4596-1985, the main method for measuring coating thickness is the magnetic thickness measurement method, which does not damage the surface of the product being measured, is easy to use, and is currently widely applied. However, attention should be paid to the following points:

　　1. Select a stable-performance magnetic thickness gauge.

　　2. Thickness gauges should be calibrated regularly, and it is recommended to use standard sheets with a metallic coating or standard foil, the latter being less accurate and having a shorter shelf life.

　　3. When measuring galvanized workpieces, the side should be in a horizontal position. If it's necessary to measure in a vertical direction or upside down from bottom up, calibration should be performed in accordance with the above positions separately.

　　4. Different measurement results can be obtained based on the position of the plated parts in the hot-dip galvanizing pot and their order of exit from the zinc bath. It is essential to ensure that the thickness of the hot-dip galvanized parts at all positions is not less than the specified minimum value.

　　Another method for measuring the thickness of hot-dip galvanized coatings is the weighing method. This involves dissolving the galvanized coating in a stripping solution by selecting a test sample, then measuring the weight change before and after dissolution to calculate the coating thickness.

　　This method is rather cumbersome, thus it is used less frequently. It is only employed as an arbitration measure when the user disputes the results of the magnetic method.

　　Galvanized Steel from Japan

　　4.0mm, 275g/m2 SGspan40 hot-rolled non-galvanized product, due to its high production difficulty and technical content, there is little domestic experience to draw upon. Based on numerous discussions and experiments, the R&D team at Rizhao Iron & Steel has successfully developed this product. Its surface quality, mechanical properties, thickness accuracy, and zinc adhesion all meet customer requirements, making it another star product of Rizhao Iron & Steel.

　　"Build up soil to form a mountain, accumulate water to create a sea." Rizhao Iron & Steel is steadily advancing the upgrading of its industrial structure, actively developing new technologies, products, and processes. Always adhering to the important speeches by Xi Jinping General Secretary, such as "core technologies are the heavy weapons of a country, and being subject to others for core technologies is a hidden danger; core technologies cannot be obtained through begging," it dares to innovate and overcomes difficulties. It is leading the way domestically in the hot-rolled non-flakey zinc-coated products.

　　Steel environmental compliance-related REACH, RoHS, and SGS

　　REACH

　　REACH is the abbreviation for the EU Regulation concerning the Registration, Evaluation, Authorization and Restriction of Chemicals, which came into effect on June 1, 2007.

　　REACH aims to enhance protection of human health and the environment by better and earlier identification of the intrinsic properties of chemicals, which is achieved through four processes: the registration, evaluation, authorization, and restriction of chemicals.

　　One of the main reasons for developing and adopting the REACH Regulation is that a large number of substances have been manufactured and placed on the market in Europe for many years, often in high quantities, but insufficient information on their hazards poses a threat to human health and the environment. Therefore, it is necessary to fill these information gaps to ensure that the industry can assess the hazards and risks of substances, determine, and implement risk management measures to protect humans and the environment.

　　"No data, no market." REACH regulations impose industry responsibility for managing chemical risks and providing safety information on substances. Manufacturers and importers must gather information on the properties of their chemicals, ensure their safe handling, and register this information in the European Chemicals Agency's (ECHA) central database for coordinated in-depth assessment of suspect chemicals and to establish a public database for consumers and personnel to access hazard information.

　　Principally, REACH applies to all chemicals, not just those used in industrial processes but also those integral to our daily lives, such as in cleaning products, paints, and items like clothing, furniture, and appliances. REACH places the burden of proof on companies, requiring them to identify and manage risks associated with substances they produce and sell in the EU. They must demonstrate to the European Chemicals Agency (ECHA) how the substances can be safely used and must communicate risk management measures to users. If risks cannot be managed, local authorities can restrict the use of the substance in various ways.

　　The REACH regulation also requires the progressive substitution of hazardous chemicals (referred to as "Substances of Very High Concern" or SVHC) with suitable alternatives. SVHCs, abbreviated as SVHCs, are a category of harmful substances stipulated in REACH, generally possessing one or more hazards, such as those with carcinogenic, mutagenic, or reproductive toxicity (classified as Category 1 or 2), or substances with persistence, bioaccumulation, and toxicity, or highly persistent and highly bioaccumulative substances. There is also evidence of substances with similar hazards, such as endocrine disruptors. REACH stipulates that companies have an obligation to report SVHCs in their products. SVHCs in the EU are typically updated in June and December each year. To date, there are 181 types of SVHCs, and the European Chemicals Agency and Member States are currently generating or evaluating new data for 750 substances.

　　Note: A special regulation on the management of new chemical substances, promulgated by the Ministry of Environmental Protection of China on February 1, 2010, came into effect on October 15, 2010. As the "Measures" is similar to the EU REACH Regulation, it is also known as the "China REACH." According to the "Measures," the registration of new chemical substances is a prerequisite for the approval of environmental impact assessment documents for construction projects involving the production or processing of new chemical substances, which means enterprises have to assume more obligations and responsibilities for chemical safety assessments.

　　Many exporters to the EU are now required to provide information on SVHCs in their products, with companies violating regulations facing product recalls, fines, and even imprisonment.

　　RoHS

　　RoHS is the abbreviation for "The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment," which is an EU directive. The RoHS directive stipulates that as of July 1, 2006, electronic and electrical products containing more than the prescribed limit levels of lead (Pb), cadmium (Cd), mercury (Hg), hexavalent chromium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE) — a total of six hazardous substances — are prohibited from entering the EU. Controlled electronic and electrical products

　　On July 21, 2011, the European Parliament and the Council issued Directive 2011/65/EU (RoHS 2.0) on the EU Official Journal to replace 2002/95/EC (RoHS 1.0). RoHS 2.0 adds four phthalates (DEHP, BBP, DBP, DIBP) to the list of restricted substances, and the allowable content of these four substances in homogeneous materials is 0.1% (by weight).

　　Note: On January 21, 2016, the Ministry of Industry and Information Technology of China officially released the new "Regulations on the Restriction of the Use of Hazardous Substances in Electrical and Electronic Products" (also known as China RoHS 2.0), which came into effect on July 1, 2016, replacing the previous "Regulations on Pollution Control of Electronic Information Products" (ACPEIP or China RoHS 1.0). China RoHS 2.0 expands the scope of applicable products from the "Electronic Information Products" (EIP) under China RoHS 1.0 to "Electrical and Electronic Products" (EEP).

　　China's RoHS 2.0 requires all applicable electrical and electronic products to affix one of the two marks specified in the China Standard SJ/T11364-2014, indicating the electrical and electronic products. The specific mark to be used depends on whether the product contains harmful substances exceeding the corresponding thresholds.

　　SGS

　　SGS is an international company that offers inspection, verification, testing, and certification services globally, with its headquarters in Geneva. Their services span across various industries, including industrial, agricultural, and chemical sectors. Most domestic steel mills entrust SGS to conduct REACH and RoHS testing reports. In trade, some people are accustomed to calling such environmental compliance reports "SGS reports" (but that's not quite correct). Below is a Chinese version example of an EU RoHS testing report commissioned by a steel mill from SGS.