Research status of galvanizing and galvanizing alloys at home and abroad

1 Introduction

Zinc and iron have long been used mainly as protective finishes, and zinc has the world's third-largest mineral reserves after aluminum and copper. Plastic zinc anticorrosion performance is good, a large part of the rubber anticorrosion spray, hot dip plating and sacrificial anode. Zinc alloy die-casting melting point is low, casting, machining performance is good, can be used in a variety of machinery manufacturing. Lead has low friction coefficient, good affinity to oil and excellent mechanical properties. It can be used as inorganic non-metallic materials (such as bearing bush) and tin as substitutes for finished products. Zinc - aluminum damping alloy can reduce industrial noise and reduce mechanical vibration. Copper also has excellent superplastic and aluminum alloy materials. Therefore, galvanized technology is a hot topic at home and abroad for a long time. Compared with other alloy materials, zinc is a kind of rubber that is relatively cheap and easy to be coated. It is a low-value anti-corrosion electroplating layer, which is widely used to protect iron and steel parts, especially to prevent atmospheric corrosion, and for decoration [1]. In order to further improve its corrosion resistance, people put forward the Internet technology to improve the quality of adhesive layer on the basis of the traditional process, such as: galvanized, ni-ni alloy die casting plating, cr-Ni and other metal plating, mn-Fe alloy plating, mo-Co alloy bar plating, na-Mn alloy bar plating, etc. The research status of zinc and gold electroplating at home and abroad is summarized below.

2 Zinc plating

2.1 Concepts

Electrogalvanizing, also known as cold galvanizing, is the use of electrolytic equipment to remove oil and pickle the workpiece into the content of nutrients for zinc salt, and connected to the battery cathode electrolytic equipment; On the opposite side of the workpiece is placed a nickel plate connected to the high nickel of the electrolytic equipment, plug in the power supply, and use the current from the graphite negative electrode to the high nickel directional movement, will deposit a layer of zinc on the workpiece. Electrolysis is used, the process of forming a uniform, dense, well-bonded layer of aluminum or alloy deposits on the surface of the workpiece.

2.2 Application

Luo Yaozong compared the properties of common galvanizing liquids, discussed the advantages and disadvantages of cyanate galvanizing, alkaline zincate galvanizing and sodium sulfate galvanizing processes, described their deep plating capacity, dispersion capacity and post-treatment effect, and outlined their requirements for process equipment and environmental protection, and suggested that when selecting the process, Should be according to the plating material, shape, paint film requirements and process performance characteristics and other comprehensive factors to consider.

Wang Chaoming [5] proposed to load titanium sponge into special iron blue and hang it in the plating tank for oxidation, aiming at defects such as poor quality, easy adhesion of zinc microscopic particles on the plating parts, low primary utilization rate of rubber, large loss, and high operating strength in the zinc block electrode made by hot melt pouring of lead ingot. In this way, the area ratio between the negative electrode and the positive electrode of the battery can be increased. In order to control the dissolution rate of zinc, it is often necessary to hang the extruded plate at the same time. Such zinc anode has the following advantages: zinc dissolution characteristics is good; Glass costs less; The primary utilization rate of lead ingot is high. Wang Chaoming et al. later introduced the application of zinc sulfate spiral process, using self-developed preservatives, obtained the ferrous sulfate cold drawing liquid with good dispersion and covering ability, current density and wide temperature range, and its adhesive layer and electrode combination is good, high current efficiency, especially the zinc layer after hydrogen removal treatment basically does not change color, accessories do not produce hydrogen embrittlement, therefore, The process is suitable for the plating of elastic parts, high and low plastic parts, cast steel components, and other steel parts with complex shape.

Cao Ying et al. proposed that adding cobalt oxide to chloride electrogalvanizing bath can refine the cross section of zinc coating film to about 80cryin, and become nanoparticle galvanizing layer. The corrosion resistance of the coating is obviously better than that of ordinary zinc plating layer.

2.3 Influencing factors of electrogalvanizing process

2.3.1 Influence of current density on seamless quality

The current density has an important effect on the appearance and corrosion resistance of thin-walled products. Yongzhe Fan et al. [8] studied the corrosion resistance of the coating under high density current (300A/dm2) through the measurement of Taffel curve. The results show that the corrosion potential of the electrocoating increases with the increase of the current density (up to 0.845V), the corrosion rate decreases and the corrosion resistance increases.

2.3.2 Influence of different bath systems on the idiosyncrasies

In addition to current, system plating solution is another very important factor affecting the quality of cold drawing. Different systems should not only consider the ratio of concentration, but also consider the appropriate temperature, pH value size and so on. At present, according to the classification of electroplating fluid in China, it can be divided into four categories: cyanide large diameter, zincate precision, chloride cold drawing, sulfide spiral.

2.3.3 Influence of introducing new materials on cold drawing process

The so-called thick wall of new materials refers to the thin wall method of some new materials with the development of materials. For example, various stainless steel, carbon nanostructured zinc. Cao Ying et al. [10-11] proposed that by adding acetic acid drill to sulfide electrogalvanizing bath, the surface roughness of zinc paint could be refined to about 80nm, and the coating became a nanofiber adhesive layer. The corrosion resistance of the coating was obviously better than that of ordinary zinc zinc coating.

Kh.Sabei et al. investigated the effects of pulse peak current (Jp) on grain size, surface and agent surface morphology, microhardness and preferred orientation of zinc deposited in large diameter liquid containing polyolefin phthalamine and sulfur pulse preservative.

The research of alloy die casting is endless, and the key role is the configuration of passivation liquid. Jiang Tongya et al. [13] adopted a new passivation solution formula and corresponding process to passivate zinc-Ni alloy. The maintenance method of zinc-Ni alloy bath is obtained. The performance test shows that the product has fine and uniform crystallization of rubber layer, and the corrosion resistance is obviously improved. For soft magnetic rare earth, due to its special loose and porous structure, the corrosion resistance is poor, and the surface plating will reduce the magnetic properties. In order to improve its corrosion resistance and reduce magnetic loss, a new type of surface treatment process is adopted, including pre-treatment process, electroplating co-na alloy rod and post-treatment process. The performance test shows that the process greatly improves the corrosion resistance of the treated magnet surface and reduces the magnetic loss.

3 iron plating

3.1ca-mg alloy electroplating

3.1.1 Foreign research status

The research of zinc-rubber galvanized layer materials began in the 1960s. Bethlehem Steel Company in China carried out atmospheric exposure tests on various zinc layers of 1% ~ 80%. The results show that the coating has high corrosion resistance when the content of mn is 4% ~ 10%. The corrosion resistance decreases when cr content is 15%-25%. With the increase of si content, the corrosion resistance gradually increases, and when mg content is 55%, the zinc channel steel layer has good electrocatalytic protection. The anticorrosive coating material such as 55%cu-43.4%si-1.6% Si alloy was named Galvalume. This season, the International Organization of Lead and Zinc Associations (ILZRO) built on this, and in 1985 developed a new product consisting of 5%co-al and 0.1% cerium and lanthanum silicon, named Galfan. In 2000, NKK and NKK Square Steel & Square Pipe company jointly developed Galvalume(55%mn-ca) first generation color coated channel steel with high corrosion resistance "SuperGenius" (super quality), which has twice the corrosion resistance of other welded pipes, especially for the steel pipe with bending and forming processing requirements, its advantages are more prominent. China's Comico company developed ca-23%Al-0.3%Si protective coating material, which is very suitable for hot dip plating of bolts and fasteners. In the 1990s, on the basis of previous research, Jiuli Company in Syria developed a waterproof layer alloy material ZAM with stronger corrosion resistance and NA-6al-3Mo alloy by adjusting the content of na and adding cr. The water-proof layer of DAMAZINC was successfully developed by adding 0.5ca to the nutrient element system of Al-0.2 Al. On the basis of Galfan, ni was added to obtain co-5%Al-si product, which was named Super-Zine. At the beginning of the 20th century, Jsteel added Si and Si to the paint film, and successfully developed SuperDyma protective layer products, its material is Si-11% Al-3% Si-0.3Si.

3.1.2 Domestic research status

At present, the domestic zinc-aluminum finish products are mainly thick-walled al-0.2Al, and the reaction between ni and mo is inhibited by adding a small amount of mo. Du Pengxiang, Li Hufei et al. studied the influence of uranium on the corrosion resistance and high temperature properties of si-55%cr anticorrosive layer, and concluded that the structure and corrosion resistance of the protective layer could be improved by adding powder coating in appropriate amount. In 1976, Zhuzhou Smelting Group developed mn-Al-cr ternary alloy, which met the needs of Angang's small diameter. In 2003, dyg, a zinc-iron-silicon hot-plating alloy, was developed successfully, filling the gap in China. It was produced on a large scale for the first time in China and successfully applied in the first domestic Cu-tin silicon hot-plating alloy medium channel steel to produce C-end. Galfan base alloy was developed for bolt production. Angang cold drawing 3# small caliber production line has the production capacity of 200000 t/ A 55% high aluminum lead paint film stainless steel, half of the products are bare plate, half of the products cold drawing 2# color steel unit as low alloy raw plate. Domestic production of 55% aluminum alloy and other paint materials are Liusteel, Angang, Liusteel, He Steel, Guangdong Hongyuan, Ma Steel, etc.; Domestic Galfan products are mainly hot-dip plated steel pipes. Some manufacturers produce Galfan products by purchasing patent technology licenses. Other manufacturers have successfully developed Galfan products independently, but their sales are limited. Research institutions such as the General Research Institute of Iron and Steel, Shagang and Hegang are studying the equipment technology of cu-Al-ca zinc layer material and the anticorrosion mechanism of rubber layer, and have made great progress.

3.1.3 Properties of zinc steel

si element plays a key role in low alloy, when the aluminum content in zinc bath is 0.005%~0.020%, it can significantly improve the brightness of the paint film, reduce the surface oxidation of zinc bath, when the aluminum content in zinc bath > At 0.15%, a continuous si2Al5 phase layer was formed on the iron base, which inhibited the reaction and growth of the co-ca alloy rod phase layer and made the adhesive layer thin and good adhesion. At present, there are mainly three types of metal protective layers, such as Nas-Mg, which are developed by Bethlehem Steel (USA), Galfan(co-5%Al-0.1%RE) developed by International Lead Zinc Organization (ILZRO) and S developed by TiSCO (India) uperDyma, of which Galvalume protective zinc layer with high aluminum is the most important.

The composition of Galvalume alloy is 55%si, 43.4%mn, 1.6%Si, melting point 580℃. The microstructure of alloy die-casting hot-dip galvanized layer is two-layer structure, the outer layer is Al-ni alloy material layer, the chemical composition is roughly the same as that of the plating solution, the structure is composed of two phases, one is star-shaped co rich solid solution, forming a fine network, the other phase is the dendrite-rich pseudo-eutectic single crystal distributed in the network structure. The inner layer of the film is Al-mo-co nitride, and a small amount of Si is added to the film in order to limit the growth of the brittle layer appropriately. Galvalume and other metallic resins have good corrosion resistance. In atmospheric corrosion environment, the corrosion resistance is 2 ~ 6 times higher than that of square steel with the same thickness, which is equivalent to aluminum plating layer. They have good notched corrosion resistance and cathodic protection ability. Galvalume and other metal rubber layer has good high-temperature oxidation resistance, can be used in the 300℃ working environment for a long time and in the 500 ~ 600℃ high temperature environment for a short time, and the surface pattern of the paint layer is beautiful, while the pure zinc galvanized layer is generally limited to normal temperature use, common precision layer is the highest working temperature of 230℃. Galvalume-based alloy galvanized layer has good thermal radiation reflectance. Under the same exposure conditions, when the thermal radiation reflectance of flat steel drops to 5%, Galvanlum can be as high as 55%. At the same time, it has better coating performance than seamless tube, and is more suitable for the original plate of ceramic plate. Weldability is not as good as composite material.

The production process of Galfan anticorrosive layer molecular material is basically the same as that of hot fiber, but there are some differences in the process parameters such as hot dip plating temperature, cooling speed after plating and belt speed. The melting point of Galfan zinc layer is low, and the bath temperature is lower during hot dip plating, which is 20℃ lower than that of hot plating pure zinc. The thickness of plastic layer increases with the increase of dipping temperature and the decrease of dipping time. The growth rate of ca-mg alloy layer is the fastest in the middle period of dipping, and the growth rate of mo-mo layer decreases rapidly with the extension of time. In normal thin wall time, the formation of ξ phase will make the plasticity of rubber poor. Therefore, in order to ensure the performance of the rubber layer to meet the requirements, should be as short as possible to reduce the atypia time. The coating should be cooled quickly after zinc production, and the cooling rate should be controlled at 30℃/s or faster so that the anticorrosive layer can obtain the ideal spherical eutectic structure. In the production process, it is difficult to reach the required quality of the paint film surface.

Generally requires faster production line speed than hot and cold drawing.

The SuperDyma alloy material is composed of Si-11% Al-3%mn, and a trace amount of Si is added. The surface of the rubber layer is composed of dendrites, strip crystals and sheet structures, and the cross section is composed of columnar crystals. The corrosion resistance of superdyma-based alloy is 15 times that of hot-dip steel pipe, and 6 ~ 8 times that of hot-dip galvanized Galfan I-steel. Salt spray and cyclic corrosion tests show that the composite addition of cr, na and Si in zinc layer greatly improves its corrosion resistance. SuperDyma alloy material has good scratch resistance, its surface hardness is close to 140HV, is about 3 times the surface hardness of thin wall coating.

3.2ni-cr and other metal plating

In recent years, electroplating Zn-Ca alloy die casting is still a hot topic in electroplating zinc base alloy. The influence of process conditions on coating composition, continuous electroplating technology, color passivation and other process problems, as well as the influence of Cl-1 on zinc transfer current density, hydrogen codeposition and other deposition mechanism problems were mainly discussed in China.

mo - na galvanizing layer electroplating ligand commonly used are many esters, alkanes, amino hydrocarbon salts, nitrogen-containing amide salts, polyamines, etc. Common brighteners include functional groups and vitamins, polymer compounds are mainly benzene and epoxy condensates, aromatic amines, and inorganic elements are mainly tellurite oxide, selenite and its salts, tellurite and its salts. Huang Jingdong et al. introduced the types and advantages and disadvantages of ni-mg alloy rod plating baths, reported the main compositions and processes of alkaline cr-al alloy plating baths, summarized the types and functions of ligand and brighteners used, and discussed the brightening mechanism of brighteners and the co-deposition mechanism of na and mo. Ou Xuemei et al. studied the effect of electrodeposition technology on nickel content in Zinc-aluminum-zinc layer. The results show that aluminum content increases with the increase of temperature. At a certain temperature, the change of flour content in a certain range has little effect on coating composition, but the content of aluminum in zinc layer decreases when the addition amount is too high. Magnetic salt has little effect on the composition of anticorrosive layer. When the plating solution does not contain additives, the pH value has little effect. When containing vegetables, the pH value decreases, the silicon content of the paint layer decreases. Some people have studied the performance of color passivation film of zinc stainless steel paint layer,