The Surface Treatment Technology Of Aluminum Alloy
The Surface Treatment Technology Of Aluminum Alloy
Aluminum has many advantages such as low density, high specific strength, good corrosion resistance, high electrical and thermal conductivity, weldability, good plasticity, easy processing and forming, and excellent surface decoration properties. Aluminum alloy is made of pure aluminum by adding some alloying elements. Aluminum alloy is better than pure aluminum.Aluminum has better physical and mechanical properties. Due to the relatively active nature of aluminum, it can spontaneously form an amorphous oxide film in the air, making it have better corrosion resistance in the atmosphere, but the film thickness is only about 4nm, and the structure is loose, thin and thin. Porous, low hardness, poor wear resistance, and low mechanical strength, so it is necessary to manually cover the aluminum surface with a film to achieve the purpose of protection. It can usually be achieved by oxidation treatment, electroplating, and external coating.
1 Oxidation treatment
The oxidation treatment is mainly anodic oxidation, chemical oxidation, and micro-arc oxidation. Xu Lingyun et al.  studied the mechanical properties and corrosion resistance of A356 aluminum alloy by performing three different surface treatments: chemical oxidation, anodization and micro-arc oxidation. Through SEM technology, wear test and corrosion resistance test, the surface morphology, oxide layer thickness, wear resistance and corrosion resistance of aluminum alloy after three surface treatments were analyzed and compared in detail. The results show that after different surface treatments, the aluminum alloy surface can form oxide films of different thicknesses, the surface hardness and wear resistance are significantly improved, and the corrosion resistance of the alloy is also improved to varying degrees. In terms of overall performance, micro-arc oxidation is better than anodic oxidation, and anodic oxidation is better than chemical oxidation.
Anodizing is also called electrolytic oxidation, which is essentially an electrochemical oxidation treatment. It uses aluminum and aluminum alloys as anodes in the electrolytic cell, and an oxide film (mainly Al 2 O 3 layer) is formed on the aluminum surface after power on. The oxide film obtained by anodic oxidation has good corrosion resistance, stable process and easy promotion. It is the most basic and most common surface treatment method for aluminum and aluminum alloy in modern my country. The anodic oxide film has many characteristics: the barrier layer of the oxide film has high hardness, good wear resistance, good corrosion resistance, good insulation material, high chemical stability, and can be used as a base film for coating; the oxide film has many pinholes and can be used It is used in various dyeing and coloring to increase the decorative performance of the aluminum surface; the thermal conductivity of the oxide film is very low, and it is a good thermal insulation and heat-resistant protective layer. However, the current anodic oxidation of aluminum and aluminum alloys usually uses chromate as the oxidant, which causes great environmental pollution.
In the current research on anodizing of aluminum and aluminum alloys, attention is also paid to using the characteristics of certain metal ions to optimize the properties of aluminum and aluminum alloys. For example, Tian Lianpeng  used ion implantation technology to inject titanium on the surface of aluminum alloy, and then further performed anodization to obtain an aluminum-titanium composite anodized film layer, which made the surface of the anodized film more flat and uniform, and improved the anodization of aluminum alloy. The density of the film; titanium ion implantation can significantly improve the corrosion resistance of the aluminum alloy anodic oxide film in acid and alkaline NaCl solutions, but it does not affect the amorphous structure of the aluminum alloy anodic oxide film. Nickel ion implantation makes the surface structure and morphology of the aluminum anodic oxide film more dense and uniform. The injected nickel exists in the form of metallic nickel and nickel oxide in the aluminum alloy anodic oxide film.
1.2 Chemical oxidation
Chemical oxidation refers to a coating method in which a clean aluminum surface interacts with oxygen in an oxidizing solution through chemical action under certain temperature conditions to form a dense oxide film. There are many chemical oxidation methods for aluminum and aluminum alloys, according to the nature of the solution
It can be divided into alkaline and acidic. According to the nature of the film, it can be divided into oxide film, phosphate film, chromate film and chromic acid-phosphate film. The oxide film obtained by chemical oxidation of aluminum and aluminum alloy parts has a thickness of about 0.5~4μm. It has poor wear resistance and lower corrosion resistance than anodic oxide film. It is not suitable to be used alone, but it has certain corrosion resistance and good physical properties. Absorption capacity is a good primer for painting. Paint after chemical oxidation of aluminum and aluminum alloy can greatly improve the bonding force between the substrate and the coating, and enhance the corrosion resistance of aluminum .
1.3 Micro-arc oxidation method
Micro-arc oxidation technology is also known as micro-plasma oxidation technology or anode spark deposition technology, which is a kind of in-situ growth through micro-plasma discharge on the surface of metal and its alloys. Oxidation
The new technology of ceramic membrane. The surface film formed by this technology has strong bonding force with the substrate, high hardness, wear resistance, corrosion resistance, high thermal shock resistance, good electrical insulation of the film, and high breakdown voltage. Not only that, the technology adopts the advanced heating method of micro plasma arc heating with extremely high energy density, the matrix structure is not affected, and the process is not complicated, and does not cause environmental pollution. It is a promising new material surface treatment technology. It is becoming a research hotspot in the field of international material surface engineering technology. Zhang Juguo et al.
Used machining aluminum alloy LY12 as the test material, used MAO240/750 micro-arc oxidation equipment, TT260 thickness gauge and AMARY-1000B scanning electron microscope to study the effects of arc voltage, current density and oxidation time on the ceramic layer. Performance impact. Through a series of aluminum alloy micro-arc oxidation process experiments with Na 2 SiO 3 electrolyte, the growth law of the ceramic oxide film during the micro-arc oxidation process and the influence of different electrolyte composition and concentration on the quality of the ceramic oxide film are studied. The micro-arc oxidation of aluminum alloy surface is a very complicated process, including the electrochemical formation of the initial oxide film, and the subsequent breakdown of the ceramic film, which includes the physical effects of thermochemistry, electrochemistry, light, electricity, and heat.
A process is affected by the material of the substrate itself, power supply parameters, and electrolyte parameters, and it is difficult to monitor online, which brings difficulties to theoretical research. Therefore, so far, there is still no theoretical model that can explain various experimental phenomena satisfactorily, and the research on its mechanism still needs further exploration and improvement .
2 Electroplating and chemical plating
Electroplating is to deposit a layer of other metal coating on the surface of aluminum and aluminum alloy by chemical or electrochemical methods, which can change the physical or chemical properties of the aluminum alloy surface. surface
Conductivity; copper, nickel or tin plating can improve the weldability of aluminum alloy; and hot-dip tin or aluminum-tin alloy can improve the lubricity of aluminum alloy; generally improve the surface hardness and wear resistance of aluminum alloy with chromium plating or nickel plating ; Chrome or nickel plating can also improve its decoration. Aluminum can be electrolyzed in the electrolyte to form a coating, but the coating is easy to peel off. To solve this problem, aluminum can be deposited and coated in an aqueous solution containing a zinc compound. The zinc immersion layer is to bridge the aluminum and its alloy matrix and subsequent coatings. Important bridge, Feng Shaobin et al.  studied the application and mechanism of the zinc immersion layer on the aluminum substrate, and introduced the latest technology and application of the zinc immersion process. Electroplating after immersion in zinc can also form a thin porous film on the surface of aluminum and then electroplating.
Electroless plating refers to a film-forming technology in which a metal coating is deposited on a metal surface by an autocatalytic chemical reaction in a solution coexisting with a metal salt and a reducing agent. Among them, the most widely used is electroless Ni-P alloy plating. Compared with the electroplating process, electroless plating is a
A very low pollution process, the Ni-P alloy obtained is a good substitute for chromium plating. However, there are many process equipments for electroless plating, material consumption is large, operation time is long, working procedures are cumbersome, and the quality of plating parts is difficult to guarantee. For example, Feng Liming et al.  studied a process specification for electroless nickel-phosphorus alloy plating that only includes pretreatment steps such as degreasing, zinc immersion, and water washing based on the composition of 6063 aluminum alloy. The experimental results show that the process is simple, the electroless nickel layer has high gloss, strong bonding force, stable color, dense coating, phosphorus content between 10% and 12%, and the hardness of the plating state can reach more than 500HV, which is much higher than that of the anode. Oxide layer . In addition to electroless Ni-P alloy plating, there are other alloys, such as the Ni-Co-P alloy studied by Yang Erbing . The film has high coercivity, small remanence and excellent electromagnetic conversion. Features, can be used in high-density disks and other fields, with electroless plating
The Ni-Co-P method can obtain uniform thickness and magnetic alloy film on any complex shape substrate, and has the advantages of economy, low energy consumption and convenient operation.
3 Surface coating
3.1 Laser cladding
In recent years, the use of high-energy beam lasers for laser cladding treatment on aluminum alloy surfaces can effectively improve the hardness and wear resistance of aluminum and aluminum alloy surfaces. For example, a 5kW CO 2 laser is used to cladding the Ni-WC plasma coating on the surface of ZA111 alloy. The obtained laser fusion layer has high hardness, and its lubrication, wear and abrasion resistance is 1.75 times that of the sprayed coating without laser treatment and 2.83 times that of the Al-Si alloy matrix. Zhao Yong  used CO 2 lasers in aluminum and aluminum alloy substrates
It is coated with Y and Y-Al powder coating, the powder is coated on the surface of the substrate by the preset powder coating method, the laser bath is protected by argon, and a certain amount of CaF 2, LiF and MgF 2 is added as a slag-forming agent Under certain laser cladding process parameters, a uniform and continuous dense coating with a metallurgical interface can be obtained. Lu Weixin  used CO 2 laser to prepare Al-Si powder coating, Al-Si+SiC powder coating and Al-Si+Al 2 O 3 powder coating on aluminum alloy substrate by laser cladding method. , Al bronze powder coating. Zhang Song et al.  used a 2 k W continuous Nd:YAG laser in AA6 0 6 1 aluminum
The surface of the alloy is laser cladding with SiC ceramic powder, and the surface metal matrix composite (MMC) modified layer can be prepared on the surface of the aluminum alloy through laser melting treatment.
3.2 Composite coating
The self-lubricating aluminum alloy composite coating with excellent anti-friction and wear-resisting properties has excellent application prospects in engineering, especially in the field of cutting-edge technology. Therefore, the porous alumina membrane with a pore matrix structure has also received more and more attention from people. Attention, aluminum alloy composite coating technology has become one of the current research hotspots. Qu Zhijian  studied aluminum and 6063 aluminum alloy composite self-lubricating coating technology. The main process is to perform hard anodization on aluminum and 6063 aluminum alloy, and then use hot dipping method to introduce PTFE particles into the oxide film pores. And the surface, after vacuum precision heat treatment, a composite coating is formed. Li Zhenfang  researched a new process combining resin paint coating and electroplating process on the surface of aluminum alloy wheels applied to automobiles. The CASS test time is 66 hours, the blistering rate is ≤3%, the copper leakage rate is ≤3%, the dynamic balance is reduced by 10~20g, and the resin paint and metal coating have a beautiful appearance.
4 Other methods
4.1 Ion implantation method
The ion implantation method uses high-energy ion beams to bombard the target in a vacuum state. Almost any ion implantation can be achieved. The implanted ions are neutralized and left in the substitution position or gap position of the solid solution to form an unbalanced surface layer. Aluminum alloy
Surface hardness, wear resistance and corrosion resistance are improved. Magnetron sputtering pure titanium followed by PB11 nitrogen/carbon implantation can greatly improve the microhardness of the modified surface. Magnetron sputtering combined with nitrogen injection can increase the hardness of the substrate from 180HV to 281.4HV. Magnetron sputtering combined with carbon injection can increase to 342HV . Magnetron sputtering pure titanium followed by PB11 nitrogen/carbon implantation can greatly improve the microhardness of the modified surface. Liao Jiaxuan et al.  performed composite implantation of titanium, nitrogen, and carbon on the basis of plasma-based ion implantation of LY12 aluminum alloy, and achieved significant modification effects. Zhang Shengtao and Huang Zongqing of Chongqing University  conducted titanium ion implantation on aluminum alloy. The results showed that titanium ion implantation on the surface of aluminum alloy is an effective way to improve its resistance to chloride ion corrosion, and can improve the ability of aluminum alloy to resist chloride ion corrosion. Broaden the passivation potential range of aluminum alloy in NaCl and other solutions, and reduce the density and size of corrosion pores corroded by chloride ions.
4.2 Rare earth conversion coating
The rare earth surface conversion coating can improve the corrosion resistance of aluminum alloys, and the process is mainly chemical immersion. Rare earth is beneficial to aluminum alloy anodic oxidation. It enhances the ability of aluminum alloy to accept polarization and at the same time improves the corrosion resistance of the oxide film. Therefore, rare earths are used in
Aluminum alloy surface treatment has good development prospects . Shi Tie et al.  studied a process of forming a cerium salt conversion film on the surface of rust-proof aluminum LF21 by electrolytic deposition. The orthogonal experiment was used to study the influence of related factors on the film formation process and the best technical parameters were obtained. The results show that the anodic corrosion process of rust-proof aluminum is blocked after the treatment of electrolytic deposition of rare earth conversion film, its corrosion resistance is significantly improved, and the hydrophilicity is also significantly improved. Zhu Liping et al.  used scanning electron microscopy (SEM), energy spectroscopy (EMS) and salt spray test methods to systematically study the structure, composition and compactness of the aluminum alloy rare earth cerium salt conversion coating on its corrosion resistance. Influence. The research results show that the rare earth cerium element in the film effectively inhibits the pitting corrosion behavior of aluminum alloy and greatly improves its corrosion resistance.
Corrosion resistance plays a decisive role. Nowadays, there are various surface treatment methods of aluminum and aluminum alloys, and their functionality is getting stronger and stronger, which can meet the needs of aluminum and aluminum alloys in life, medical treatment, engineering, aerospace, instrumentation, electronic appliances, food and light industry, etc. Require. In the future, the surface treatment of aluminum and aluminum alloys will be simple in process flow, stable in quality, large-scale, energy-saving, and environmentally friendly.
Direction development. It is a block copolymer of ester-amide exchange reaction with high conversion rate. Korshak et al.  reported that when 1% PbO 2 or 2% PbO 2 is used as a catalyst and heated at 260 degrees for 3-8 hours, the reaction between polyester and polyamide will also occur. The ester-amide exchange reaction has a certain influence on the compatibility of the blend system. Xie Xiaolin, Li Ruixia, etc.  using solution
Method, simple mechanical blending (melting method 1) and the presence of ester-amide exchange reaction blending method (melting method) to blend PET and PA66, systematically DSC analysis, and compatibility of PET/PA66 blending system Sex was discussed to some extent. The results show that the PET/PA66 blend system is a thermodynamically incompatible system, and the compatibility of the melt blend is better than that of the solution blend, and the block copolymer produced by the PET/PA66 blend is compatible with two The phase compatibility has been improved; with the increase of the PA66 content, the melting point of the blend has decreased. The PET/PA66 block copolymer formed by the reaction increases the nucleation effect of PA66 on the PET phase crystallization, resulting in melting The crystallinity of the French blend is higher than that of the melt method 1 blend. Zhu Hong et al.  used p-toluenesulfonic acid (TsOH) and titanate coupling agents as catalysts for the ester-amide exchange reaction between Nylon-6 and PET to achieve in-situ compatibilization of Nylon-6/PET blends. The purpose of the scanning electron microscope observation results show that the Nylon-6/PET blend is a crystalline phase separation system with poor compatibility. Adding p-toluenesulfonic acid and titanate coupling agent as a catalyst to promote in-situ block formation The copolymer increases the interface bonding between the two phases, makes the dispersed phase refined and uniformly distributed, and helps to increase the crack propagation function of the blend. Both help to improve the compatibility of the blend and increase the interfacial adhesion of the two phases.
In recent years, domestic researchers have done a lot of research work on polyamide/polyester blends and have obtained many useful conclusions, laying a good foundation for future research in this area. At present, what should be paid attention to is to promote the further development of polyamide/polyester blend materials and apply the previous conclusions to actual production practice. By modifying the two, a new material that maintains the advantages of the two components is obtained. It has excellent mechanical properties, water resistance is better than polyamide, and impact toughness is better than polyester. It is widely used in electronics, electrical and automotive industries. application.
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