Hot-dip aluminum-zinc plate is a kind of pre-coated steel plate which is prepared by hot-dip coating of al-zn on both sides with cold-rolled steel plate of various strength and thickness specifications as the base material.
It combines the physical protection and high durability of AI with the electrochemical protection characteristics of Zn.
Sometimes the surface layer has a high decorative bright silver gray and regular pattern, and a sense of buoyancy.
Just as sunscreen protects skin, aluminum and zinc coatings provide good protection to steel plates.An electrochemical reaction of semolboda occurred at the defect
As can be seen from the above introduction, the biggest advantage of hot dip aluminum zinc is corrosion resistance, than the same thickness of hot dip galvanized steel corrosion resistance is much higher, the service life is also high.
Heat resistance is also a major advantage: ordinary hot-dip galvanized products, the use temperature is generally not more than 230°C, aluminum zinc plate can be used in 315 degrees high temperature for a long time.
Some oven liners also use hot – dip aluminum – zinc plates
High reflectivity: the ability to reflect light and heat is twice that of hot-dip galvanized steel, so it is often used as an energy-saving building material.
Formability: can meet the general car press, bending and other processing requirements.
Use restrictions
1, in the alkaline environment, be careful to use hot aluminum zinc plating;
2, to avoid directly cutting hot aluminum zinc plating on the site, the best use of edge plate;
3, the construction of aluminum zinc materials to pay attention to drainage to prevent corrosion;
4. Avoid direct contact with wet cement, wood, lead, copper, graphite, etc.;
5, processing, stacking to prevent moisture and high temperature caused by resistance to fingerprint film black.
Application of hot aluminum zinc plating in the field of architecture
The application of hot aluminum zinc plating products in the field of architecture is basically the late processing into color coated plate widely used in the roof and wall of buildings.
In the aluminum zinc (55% AI, 43.5% Zn and 1.5% Si) substrate surface first do a layer of chemical conversion treatment, then spray extremely thin (5um) special primer, finally according to customer requirements coated with about 20um durability and processing of good color coating.
The product substrate has SGLCC, G345, G300, G550, coating thickness has AZ150, coating structure for light whole small zinc flower, coating varieties have PE, PVDF, SMP, HDP, coating structure has double-sided double coating and one side double coating and one side single coating, coating color according to customer demand.
Application considerations
1. Precautions for design and use
Aluminum – zinc plate should be used with caution under alkaline condition.
Avoid direct contact with other conductive materials for protection;
Wet wood and concrete also do not contact long aluminum zinc color plate;
Small roof slope suggested to use aluminum zinc plate;
The use of accessories (insulation, sealing and fasteners) should be considered simultaneously with the corrosion resistance of aluminum zinc coating.
2. Processing matters needing attention
The surface of the plate should not be damaged in rolling forming.
Embossed plate should pay attention to its depth and sharpness to ensure durability;
All cut edges shall be properly protected or not exposed;
No metal chips should be left on the plate when cutting and welding.
Long plate handling should avoid sagging board, should be stacked on the pad wood, and have a certain Angle to drain aluminum zinc coating.
3. Matters needing attention for maintenance
Complete cleaning (water) after construction;Under normal circumstances, the cleaning should be carried out once every 6 months, and the cleaning of the seaside and industrial polluted areas should be more frequent
In the atmosphere, zinc is much more resistant to corrosion than steel, usually several times more resistant than steel.
1) physical effects:
The zinc coating on the surface of the steel plate blocks the contact between the steel plate and the corrosion medium, so that the steel plate can avoid the corrosion effect of the corrosion medium.
2) electrochemical action:
When the substrate of galvanized steel and the zinc layer are exposed to the corrosive medium at the same time (such as the scratch and incision of the zinc layer), because the electrode potential of zinc is lower than the electrode potential of iron, zinc gives priority to corrosion and protects the substrate.
The main process of galvanizing
Hot plating and electroplating are the two main processes of galvanized, now we mainly say hot dip galvanized
Hot dip galvanizing: the melting point of steel and zinc is quite different. The melting point of pure iron is 1534°C, while the melting point of zinc is only 1534°C
At 419°C, the process of galvanizing treated steel by dipping it directly into molten zinc is called hot plating
Product classification and features
Classification: according to the coating types, it is divided into GI (pure zinc coating), GA (zinc ferroalloy coating), 55% ai-zn (aluminum zinc coating, GALVALUM E), 5% ai-zn (GALFAN), Aluminizing (aluminum plating), zn-5ai-3mg (zinc aluminum alloy coating).
Hot-dip galvanized products (GI)
Features: beautiful surface, good corrosion resistance, good processing.
Hot-dip galvanized alloy products (GA)
Features: zinc-iron alloy coated steel plate has good adhesion, good corrosion resistance and good weldability after painting.
Hot aluminized zinc products (GALVALUME)
Features: good corrosion resistance, 2-6 times of hot dip galvanized, this is the sample exposure in different environments for more than 15 years, and galvanized steel plate comparison;Good temperature resistance, no discoloration at 300°C, up to 700°C if discoloration is allowed.Excellent thermal reflective surface.
According to the European standard EN 10346:2015, the size of hot-dip galvanized zinc spangles can be divided into ordinary spangles and small spangles.
Conventional zinc spangles refers to the size and morphology of zinc grain formed after normal solidification of zinc solution, while the absence of zinc spangles(also known as small zinc flower) is the size and morphology of zinc grain obtained through special control of the solidification process of zinc.If the user needs to specify the size of the zinc spangles, it needs to be negotiated at the time of ordering.
There are many factors that affect the size of the zinc spangles. When the composition of the zinc liquid has the conditions for the formation of the zinc spangles, the following factors affect the size of the zinc spangles:
Raw material: raw material plate thickness, surface roughness is smaller, zinc spanglesis larger.
(2) cooling speed: the faster the cooling speed, the shorter the crystal growth time and the smaller the zinc spangles.
(3) number of crystal nuclei: the size of zinc spanglesis closely related to the number of crystal nuclei of zinc spangles.When the surface of steel base is rough or the surface cleanliness is poor, the zinc spanglesis relatively small.Zinc grain is formed on steel base, the more nucleus, the smaller zinc spangles.
(4) other factors (production environment, etc.).
In order to obtain small zinc spangles, when zinc solution is near the solidification temperature, water droplets with a diameter of less than 0.1mm are immediately sprayed on the surface of galvanized sheet to form a fine and uniform crystal nucleus.In order to obtain smooth zinc spangles, less than 1 % of the press to carry out rolling.Small zinc flower is suitable for painting, light whole zinc flower is suitable for deep stamping.
Big spangles
Normal spangles
Mini spanglesZinc layer adhesion
When the heated steel strip passes through the molten zinc solution (zinc tank), it first forms an iron-zinc alloy layer on the substrate and covers the pure zinc layer outside the alloy layer.The layer thickness of fe-zn alloy is uneven, loose, brittle, poor ductility and easy to crack.
If a certain amount of iron base salt is left on the surface of the steel plate before galvanizing, the resulting iron-zinc alloy will have poor adhesion, poor ductility and easy spalling.When the pure zinc coating contains harmful impurities, such as zinc oxide, zinc slag, cadmium and lead, the formation of large zinc flower, or destroy the continuity of zinc layer, easy to hairline zinc layer small crack.
When the zinc coating is too thick, its bendability is also poor.When aluminum is added to the zinc solution, the aluminum in the zinc solution reacts with the substrate, first forming Fe2AI5 or Fe 2AI3, which thins the iron-zinc bonding layer and improves the adhesion of the zinc layer.
Uneven zinc flower and its influencing factors
Uneven coating surface zinc flower, is a kind of surface defects of hot dip galvanized products, although the use of most products will not produce a great impact, but affect its surface beauty, resulting in the product in the market in some areas of application is limited.Some products with uneven zinc flower also have poor adhesion of zinc layer, which directly affects the use of the product.
The uneven state of zinc flower on the surface of hot galvanized sheet can be summarized as follows:
(1) zinc flower on one side and no zinc flower on the other side.The diameter of the zinc flower with one side of the flower is about 6mm.
(2) along the longitudinal strip, the size of zinc flower fluctuates regularly.
Horizontal along the strip, one side of the zinc flower is large, the other side of the zinc flower is small.
(4) the edge of the strip zinc flower is small, the middle zinc flower is large.
The main factors affecting spangles unevenness of include: the proportion of the two kinds of alloy element in zinc liquid composition, air knife, strip temperature control technology, impurity content in the gas, combustion air, and the strip surface cleanliness and the furnace condition, furnace iron nodules, strip scratches and raw materials on the surface of iron oxide, zinc strip into the pot, most liquid zinc, aiming to have strolled, etc.
With beautiful zinc flower is the main characteristic of traditional hot galvanized sheet.The most complete form of zinc crystal is similar to snowflake or hexagonal star. Therefore, the zinc crystal obtained by condensation on the surface of hot plating process is most likely to form snowflake or hexagonal star zinc flower.
Actually, zinc flower just has ornamental value, no practical value, on the contrary, zinc flower in corrosion resistance is not good, surface coating will appear concave uneven.Therefore, household appliances and automobile industry tend to choose small zinc flower (no zinc flower) products, and looks very beautiful with zinc flower products, there is a certain amount of use in the construction industry.
High purity zinc solution will not solidify to form zinc flower when it is cooled, because there is no necessary crystallization nucleus in the zinc solution.In order to obtain a typical zinc flower, it is necessary to add two kinds of alloying elements with different properties in the zinc solution.Another kind of alloying element is soluble in both liquid and solid zinc, such as aluminum, tin, antimony, etc.If only one kind of alloy element is added, the surface state of the zinc layer will change after solidification, but it is not enough to form a typical zinc flower.
Why have Spangles
The way to form zinc flower is to try to form a large number of crystal nuclei as early as possible, reduce the solidification temperature of zinc liquid, in order to extend the growth time of zinc flower crystal, facilitate the growth of zinc flower.
(1) add other elements to the zinc solution
When an alloying element is added to the zinc solution, the crystallization process can be prolonged, and the surface zinc solution will not solidify until its eutectic temperature is reached.
Pure zinc solidifies at 419.5°C, and if tin (less than 0.5%) is added, the tin-zinc eutectoid alloy will not solidify until it is reduced to 198°C.After adding CD, CD zn eutectoid alloy did not decrease to 264.) does not solidify.If pounds (less than 0.3%) is added, the antimony zinc eutectoid alloy will not solidify until it is reduced to 40 °C.When lead is added, the lead-zinc eutectoid alloy will not coagulate until it is reduced to 317°C.
Therefore, the addition of alloy to reduce the melting point of zinc liquid, than the solidification time of pure zinc have different degrees of extension, make the growth time of zinc flower crystal greatly extended, facilitate the growth of zinc flower, so the taste guide the larger zinc flower.
(2) surface blowing
When the zinc layer on the surface is about to solidify, if the vapor or sulfur dioxide flow through the surface, the zinc flower crystal can be jaded to grow, and a larger pattern can be obtained.Another purpose of blowing sulfur dioxide gas flow is to form a dense oxide film and improve the corrosion resistance of galvanized coating.
(3) wire mesh method
This method can only be used on galvanized sheet, which is achieved by making the wire mesh contact the surface of the zinc layer with a magnetic shaft.Because the junction of the wire mesh is cooled at first, the crystallized solid particles are formed at first to form the crystallized nucleus, and the remaining unsolidified zinc liquid starts to expand to form the zinc flower.
(4) water spraying method
The pure zinc solution on the surface of galvanized steel is sprayed with water mist (water and steam or a mixture of water and air) to form the crystallization nucleus before solidification.The unsolidified zinc liquid was dispersed from this point to form zinc flower.
(5) other methods
In addition to the above method, if the surface of the plating can be achieved smooth, galvanized layer is relatively thin, control temperature uniform drop and enough air cooling time, can also obtain a larger zinc flower.
(1) poor passivation, insufficient or uneven passivation film thickness;
The surface is not oiled;
(3) residual water on steel surface;
(4) passivation is not completely dried;
(5) dampness or rain during transportation or storage;
(6) long storage time of finished products;
(7) galvanized sheet and other acid and alkali corrosive media contact.
White rust may develop into black spots, but the spots are not necessarily caused by white rust alone, such as friction spots.
8. The maximum allowable storage time
If oil is applied, packaging and storage are very convenient. Some products can be stored for more than one year, but it is better to use them for three months. If no oil is applied, the storage time is shorter, so as to avoid oxidation caused by long-term storage.
9. Tolerance
The length tolerance is not allowed to be negative, and the maximum is not allowed to be +6mm
10. Classification of spangles
Zinc flower is divided into large spangles, small spangles, no spangles.
11. Protection principle of zinc layer
In the corrosive environment, zinc will be preferred to steel corrosion, so as to protect the steel base, and the zinc layer in corrosion resistance will be due to the line into a certain protective film to prevent too fast oxidation, delay the corrosion speed, and can be in the maintenance of brush zinc paint and other ways to prevent steel corrosion, ensure the mechanical properties of the material and other safety properties.
12. Passivation principle
The passivation film can be formed by chromate passivation treatment of galvanized sheet, the trivalent insoluble in water in solution passivation group plays the role of skeleton, while the hexavalent aluminum in solution is soluble in water, which can play the role of passivation again when the passivation film scratches, and has the healing effect of passivation film.Therefore, within certain limits, passivation film can prevent steam or moist air direct erosion of galvanized sheet, play a protective role.
13. Method of corrosion resistance
There are three methods to test the corrosion resistance of hot galvanized sheet:
(1) salt spray test;(2) moisture test;(3) erosion test.
Hot galvanized sheet is mainly used in automobile, home appliances, construction, machinery, electronics, light industry and other industries.
2. Steel Galvanized Classification
Steel factory galvanized products have galvanized, hot dip galvanized two kinds of methods, and these two kinds of subdivision again, galvanized from the zinc layer thickness is divided into single side, double side and poor thickness coating three kinds, and hot dip galvanized is no single side and poor thickness coating, but hot dip galvanized is divided into galvanized and galvanized ferroalloy, electroplating is no zinc ferroalloy.Plating on the kind of plating coating and extend to the electric galvanized, galvanized iron, galvanized tin, plating, galvanized extension is more, including galvanized, zinc iron, aluminum zinc, zinc aluminum, and zinc aluminum magnesium.
3. Annealing Method
There are two kinds of annealing methods for conventional cold rolling coated products: continuous annealing and cover annealing.
4. Common Steel
Product types: general commercial coil (CQ), deep drawing hot galvanized sheet (DQ), super deep drawing hot galvanized sheet (ddq-eddq /SEDDQ), structure galvanized sheet (HSLA), baking hardened hot galvanized sheet (BH), duplex steel (DP), TRIP steel (phase-change induced plastic steel), and multiphase steel (CP).
5. Defects of hot-dip galvanizing
Zinc layer peeling, scratch, passivation spot, zinc particles, thick edge, air knife striations, air knife scratches, exposed steel, inclusions, mechanical damage, poor steel base performance, wavy edge, bending, size, imprinting, zinc layer thickness, etc.
6. The main reason of zinc layer shedding
The main reason of zinc layer falling off is raw material production and processing mismatching.Raw materials for surface oxidation, silicon compounds, NOF section of high oxygen atmosphere and dew point of shielding gas, air-fuel ratio is not reasonable, hydrogen flow rate is low, the stove aerobic infiltration, into the pot temperature is low, NOF section of furnace temperature is low, oil evaporation is endless, zinc pot aluminum content is low, the unit too fast, inadequate reduction, in zinc liquid residence time is too short and thick coating.Machining mismatches have bending radius, mold wear, scratch, mold gap is too large or too small, less pressing lubricating oil, mold working time is too long without repair and maintenance.
1.5 the bending center diameter of steel plate for coating bending test is specified in the table below. After 180 ° bending, the outer surface of the sample shall be free of coating peeling, but the coating peeling within 6 mm from the edge of the sample is allowed. The width of bending sample shall not be less than 50mm during arbitration
Grand
180 Degrees bending test
Bending diameter
DC51D+AZ
1a
II. Appearance and dimension requirements: 2.1 diagonal length difference is not more than 1.5mm
2.2 thickness deviation:
Grand
Nominal Thickness (mm)
Allowable thickness tolerance(mm)
700-1000mm Width
1000-1250mm Width
DC51D+AZ
0.35-0.4
+-0.05
+-0.06
2.3 tolerance of unevenness: Edge waviness of height: less than 3mm width waviness of height: less than 3mm height warpage: less than 3mm Edge waviness of steepness and slowness: less than 1.0%; width waviness of steepness and slowness: less than 0.5% 2.4 the coating shall be fine and uniform, bright and clean without scratch marks (slight scratch shall not expose the underlying metal), and the thickness of the coating shall be greater than 50um. A kind of
2.5 the coating is not allowed to have blisters , cracks, peeling, pinholes, spongy layer and other defects; the galvanized parts are not allowed to have chromic acid water trace (blue and white phenomenon is allowed).III.Packaging requirements of products
3.1 for the packaging of batch steel plates, two schemes of ordinary packaging or wooden box packaging can be selected.
3.2 the packaging of steel plate shall be rust proof and moisture-proof. A kind of3.3 the sign shall be placed at the obvious place of the package, and the text and pattern of the sign must be printed clearly and neatly. A kind of
3.4 the outer package shall indicate the product name, specification, model, quantity, color card number, production batch number, production date, etc. 4.5 there shall be product inspection certificate in the packing box.
The difference between galvanized steel and galvalumed steel mainly lies in the difference of coating,the surface of galvanized is evenly distributed with a layer of zinc material, which plays the role of anode protection for the base material. That is to say, the substitute corrosion of zinc material protects the use of raw materials. Only when the zinc is completely corroded can the inner raw materials be damaged.
Galvalumed steel the surface of the zinc coating is composed of 55% aluminum, 43.5% of the zinc and small amounts of other elements, aluminum zinc coating under microscopic surface for honeycomb structure, composed of aluminum in the “honeycomb” containing zinc, in this case, Galvalumed steel has anodic protection role, but on the other hand due to the shrinking of zinc content on the one hand, because of the zinc material by aluminum bag not the role of electrolysis anode protection so greatly reduced, so once the Galvalumed steel is cut, the cut off the edge of the protection of basic loss was will soon be under the condition of corrosion, so the plating Galvalumed steel should be cut less as far as possible,Once the edge is protected by anti-rust paint or zinc-rich paint after cutting, the service life of the plate can be extended.
Application
Architecture: roofs, walls, garages, sound barriers, plumbing and modular houses
Home appliances: refrigerator backplate, gas stove, air conditioner, electronic microwave oven, LCD frame, CRT explosion-proof belt, LED backlight, electric cabinet, etc
PPGI Corrugated sheet, also known as: color coated roofing sheet, is the use of color coated steel plate, by rolling cold bending into a variety of wave pressure plate.
It is suitable for industrial and civil buildings, warehouses, special buildings, large span steel structure roof, wall and exterior wall decoration, with light weight, high strength, rich color, construction convenient and fast, seismic, fire prevention, rain prevention, long life, free from maintenance and other characteristics, has been widely promoted and applied.
Specialty
1. A stylish and attractive design,giving the apperance of a traditional roof tile.
2. Resistant to frost,heat,hail and gales;100% waterproof,thanks to the lateral run-off channel on each sheet for several model.
3. Quick and easy to install.
4. On renovation jobs the old roofing won’t,in most circumstances,need to come off.
5. No problem with bad weather conditions during roof-on-roof assembly.
6. Reduces the load to borne by the roof support structure to a minimum(low self-weight:5kg/m2).
7. Longer lasting,thanks to the use of perfectly coated,high grade steel(coating:plastisol).
