Aluminum alloy surface treatment process
Product surface treatment: it is through mechanical and chemical methods of treatment, can form a layer of protection on the surface of the product to protect the body of the protective layer. In the natural world can reach a stable state, increase the corrosion resistance of the body and increase the beauty of the product, thus enhancing the value of the product. The selection of the type of surface treatment should be made firstly from the point of view of using environment, service life and human appreciation, of course, the economic value is also the core of consideration.
The process of surface treatment includes pre-treatment, film forming, post-film treatment. Packaging, warehousing. Shipments and other processes, including pre-treatment of mechanical treatment, chemical treatment. Mechanical treatment includes sandblasting, shot blasting, sanding, polishing, waxing and other processes, the purpose of the product surface to eliminate unevenness, remedying the surface of other bad appearance. Chemical treatment makes the product surface oil stains and rust removal, and the formation of a layer of film-forming substances can make a better combination or into the active metal body, to ensure that the plating layer has a stable state, increase the binding force of the protective layer, so as to achieve the role of protecting the body.
Aluminum common surface treatment, chemical treatment of chroming, painting, plating, anodic oxidation, electrophoresis and other processes. Among the mechanical treatment are drawing, polishing, sandblasting, sanding and other processes.
Aluminum alloy plates can be divided into two categories according to the surface treatment: non-painted products and painted products.
1) Non-painted products
(1) Can be divided into hammered aluminum plate (irregular pattern), embossed plate (regular pattern) and pre-passivation, anodic oxidation aluminum surface treatment plate.
(2) This kind of product does not do paint treatment on the surface of the plate, which does not have high requirements on the appearance of the surface, and the price is also lower.
2) Painted products
(1) Classification: according to the coating process can be divided into: spraying board products and pre-roller coating board; according to the type of paint can be divided into: polyester, polyurethane, polyamide, modified silicone, epoxy resin, fluorocarbon and so on.
(2) A variety of coatings, the main difference in performance is the resistance to sunlight ultraviolet, which in the front of the most commonly used coating for fluorocarbon paint (PVDF), its resistance to ultraviolet rays of the ability to be stronger; the back of the choice of polyester or epoxy resin coatings as a protective varnish.
Classification of daily surface treatment processes
1 Anodizing
Anodic oxidation, mainly of aluminum, is the use of electrochemical principles to generate a layer of Al2O3 aluminum oxide film on the surface of aluminum and aluminum alloys. This oxide film has special characteristics such as protective, decorative, insulating and wear-resistant.
Process:
Single color, gradient color: polishing/sandblasting/drawing→degreasing→anodic oxidation→neutralization→dyeing→sealing→drying
Two-color: ①polishing/sandblasting/drawing→degreasing→masking→anodizing1→anodizing2 →sealing→drying
②Polishing/sandblasting/drawing→degreasing→anodizing1 →radium engraving→anodizing2→sealing→drying
Technical features:
1、Improve the strength;
2、Achieve any color except white;
3, realize nickel-free sealing hole, meet the requirements of Europe, the United States and other countries on nickel-free.
Technical difficulties and key points for improvement:
The yield level of anodizing is related to the cost of the final product, the focus of improving the oxidation yield lies in the suitable amount of oxidizing agent, suitable temperature and current density, which requires structural parts manufacturers to explore and seek breakthroughs in the production process.
2 Electrophoresis
Used for stainless steel, aluminum alloy, etc., it can make the product show various colors and keep the metallic luster, meanwhile, it can enhance the surface performance and have better anti-corrosion performance.
Process flow: pretreatment → electrophoresis → drying
Technical characteristics:
Advantages:
1, rich color;
2、No metallic texture, can be matched with sandblasting, polishing, brushing, etc.;
3、Processing in liquid environment, can realize the surface treatment of complex structure;
4, the process is mature, can be mass production.
Disadvantages:
The ability to cover defects is general, die casting to do electrophoresis requires high pretreatment.
3 Micro-arc oxidation
In the electrolyte solution (generally weak alkaline solution) to apply high voltage to generate the ceramicized surface film layer of the process, the process is a physical discharge and electrochemical oxidation synergistic effect of the results.
Process flow: pretreatment → hot water washing → MAO → drying
Technical Characteristics:
Advantages:
1, ceramic texture, dull appearance, no high-gloss products, delicate feel, anti-fingerprint;
2、Wide range of substrates: Al, Ti, Zn, Zr, Mg, Nb and their alloys, etc;
3, simple pre-treatment, excellent product corrosion resistance, weather resistance, good heat dissipation performance.
Disadvantages:
At present, the color is limited, only black, gray and other more mature, bright colors are currently difficult to achieve; the cost is mainly affected by high power consumption, is one of the highest cost in surface treatment.
4 PVD vacuum coating
Physical vapor deposition (Physical vapor deposition, PVD): is an industrial manufacturing process, is the main use of physical processes to deposit film technology.
Process flow: PVD pre-cleaning → into the furnace vacuum → washing target and ion cleaning → coating → coating end, cooling out → post-processing (polishing, AFP)
Technical characteristics:
PVD (Physical Vapor Deposition, Physical Vapor Deposition) can be coated on the metal surface of the metal ceramic decorative coating with high hard plating, high wear resistance.
5 Electroplating
Electroplating is a technology that utilizes electrolysis to attach a metal film to the surface of the metal to prevent corrosion, improve abrasion resistance, electrical conductivity, reflectivity, and enhance aesthetics.
Process: Pre-treatment → cyanide-free alkaline copper → cyanide-free white copper tin → chrome plating
Technical Characteristics:
Advantages:
1, high gloss plating, high quality metal appearance;
2, the base material is SUS, Al, Zn, Mg, etc., the cost is relatively low compared to PVD.
Disadvantages:
Poor environmental protection, higher risk of environmental pollution.
6 Powder Coating
Powder spraying equipment (electrostatic spraying machine) to spray powder coating to the surface of the workpiece, under the action of static electricity, the powder will be uniformly adsorbed on the surface of the workpiece to form a powder coating; powder coating after high-temperature baking and leveling and curing, into the effect of the final coating of the different types of effects (powder coating effect).
Process flow: loading → electrostatic dusting → spraying → low temperature leveling → baking
Technical characteristics:
1, rich color, high gloss, matte optional;
2、Lower cost, suitable for construction furniture products and the shell of heat sinks, etc;
3, high utilization rate, 100% utilization, environmental protection;
4、Strong ability to mask defects;
5, can be imitated wood grain effect.
7 Drawing
It is a kind of surface treatment means to form a line pattern on the surface of the workpiece through grinding products and play a decorative effect. According to the different patterns after drawing can be divided into: straight drawing, messy drawing, ripple, spinning.
Technical characteristics:
Drawing treatment can make the metal surface to obtain non-mirror-like metal luster, at the same time, drawing treatment can also eliminate the subtle defects on the metal surface.
8 Sandblasting
Is the use of compressed air as a driving force, in order to form a high-speed jet beam will be sprayed at high speed to the surface of the workpiece to be processed, so that the surface of the workpiece surface of the external surface of the appearance or shape of the change, to obtain a certain degree of cleanliness and a different degree of roughness of a process.
Technical features:
1、To realize different reflective or matte.
2、It can clean the tiny burrs on the surface of the workpiece and make the surface of the workpiece smoother, eliminating the harm of burrs and improving the grade of the workpiece.
3、Clean up the residual dirt left in the pre-treatment, improve the finish of the workpiece, can make the workpiece reveal the uniform and consistent metal color, make the appearance of the workpiece more beautiful and good-looking.
9 Polishing
The surface of a workpiece is finished with flexible polishing tools and abrasive particles or other polishing media. For different polishing processes: rough polishing (basic polishing process), medium polishing (finishing process) and fine polishing (polishing process), the selection of the appropriate polishing wheel can achieve the best polishing results, while improving the polishing efficiency.
Improve the dimensional accuracy or geometric precision of the workpiece, get a smooth surface or mirror luster, but also can eliminate the luster.
10 Etching
Usually referred to as etching, also known as photochemical etching, refers to the exposure of the plate, after developing, to be etched in the area of the removal of the protective film, in contact with chemical solutions in etching, to achieve the role of dissolution and corrosion, the formation of a concave-convex or skeletonized molding effect.
Process flow:
Exposure method: the project according to the graphic opening out the size of the material preparation – material preparation – material cleaning – drying → film or coating → drying → exposure → development → drying – etching → remove the film → OK
Screen printing method: open material → cleaning plate (stainless steel and other metal materials) → screen printing → etching → de-filming → OK
Technical characteristics:
Advantages:
1, can carry out the metal surface fine processing;
2, give the metal surface special effects.
Disadvantages:
Most of the corrosive liquids (acid, alkali, etc.) used in etching are hazardous to the environment.
