The introduction of aluminum surface treatment
Time: 2018-03-31 Reads: 2610 Edit: Admin

Surface treatment:It can form a protective layer on the surface after processing mechanically and chemically.Bing able to keep stably in the nature and increase the value of the products by enhancing the resistance of corrosion and increasing the beauty of the products.The choice of surface treatment is on the basis of the using environment,service life and aesthetic,and furthermore,economic value is also the core of the consideration.

The process of the surface treatment include process of pre-processing,film,Membrane post-processing,packing,put in storage,out of storage,etc,and pre-processing include mechamical processing and chemical processing.

Machanical processing:abrasive blasting,shot blasting,polishing,wax,etc.
The purpose of machamical processing is to remove the bumps,remedy other problem of poor appearance on the surface.The mechamical processing remove the oil and rust on the surface and the formation of a layer of industrial aluminum can make the membrane material better combine or become active metal body,and ensure a stable status of coating,increase the combination of protective layer,so that it could protect the engine body.


Aluminum surface treatment

The common chemical processing of aluminum are chromizing,abraasive blasting,electropalting,anodizing and electrophoresis,etc.And mechamical processing have deep wiredrawing,buffing,abrasive blasting and polishing,etc.

一. Chromizing
The chromium will cause a layer of chemical conversion film on the surface of the product, and the film thickness is 0.5-4um, which is good adsorption of the film, mainly as the coating substrate.The color of the appearance are gold,aluminum and green,etc.Such conversion film has good conductivity and is the best choice of electronic products,like Cell phone battery inner conductive bar,magnetoelectric equipment,etc.And such film apply to all aluminum and aluminum alloy products.But it’s soft,not wear resistant,so it’s not good to be used as external products.

Chromizing technological process:
Degrease-Redeluminum-Chromizing-packing-put in storage
Chromizing apply to aluminum and aluminum alloy,magnesium and magnesium alloy products.

Requiement of quality:
①Uniform color,delicate film,scrap and touch with hands,coarse,dust are not allowed
②The thickness of film is 0.3-4um.

二.Anodizing
Anodizing:The surface of the product can be formed into a uniform layer of oxide layer(AL203,6H20 ae also be called corumdum,which can make the surface hardness of the product reach (200HV-300HV),If special products can be made of hard anodic oxidation,then the surface hardness of the product can reach 400-1200hv, so hard anodic oxidation is an indispensable surface treatment technology of oil cylinder and transmission.

In addition, the product has good wear resistance,which can be a necessary technology of the relevant products of aviation and airspace.The difference between anodizing and hard anodizing is:Anodizing can color the workbench,decoration technique is better than that of hard anodizing.The key point of contruction:Anodizing is very strict with the material,the surface of different material have different decorative effect,the commonly used matrial is 6061,6037,7075,2024,etc.among them,the effect of 2024 is a little less than others,and hard anodizing 7075 appears yellow as the content of CU in the material is different.What’s more,6061,6063 looks like brown,but ordinary anodizing 6061,6063 and 7075 are not much different,but 2024 is tend to get gold stain.

1.Common process
The common anodizing process are the original color of wiredrawing fog face,original color of wiredrawing glossy face,wiredrawing glossy dyeing,wiredrawing fog face dyeing(can be dye into any color).Original color of polishing glossy face,original color of polishing fog face,polishing fog face dyeing.Original color of brasive blasting glossy face,original abrasive blasting fog face,abrasive,abrasive blasting dyeing.All of the coating above can be used for lamp decoration equipment.

2.Anodizing technology
Degreasing--Alkali corrosion--Turn left--Neutralization--Lidi-Neutralization
Anodizing--Dyeing--Hole sealing--Hot wash--Drying

3.Common quality abnormal ajudgment
①Spots on the surface.This anomaly is usually due to poor metal transfer or poor material.
   Handling method:Do heat treatment again or change material.
②Iridescence on the surface,which is usually caused by anodizing,it would loose when racking and result in poor deductivity.
   Handling method:Anodize again.
③The surface is bruised and badly scratched.This abnormality is usually caused by the carelessness of the operation during transportation or processing.
④White spot appears on the surface when dyeing,which is usually caused by other impurities or there’s oil in the water when anodizing.

4.Quality standard
①Thicknesss of the film is 5-25um,Hardness is above 200HV,Sealing hole lab variability is less than 5%.
①Salt spray test should be more than 36 hours and reach to the standard of CNS.
③Appearance can not have bruises, scratches, color clouds and other phenomena like hanging spots, yellowing.

5.Die-casting aluminum,those like A380,A365,A382 couldn’t anodize

三.Aluminum electroplating processing
1.
Advantage of aluminum and aluminum alloy
With good conductivity,fast heat transfer,light proportion,eay to shape,it also have some disadvantage,like low hardness rate,not wear resistant,tend to cause crystal corrosion,not easy to weld,which affact the range of application.So as to stengthen the good points and avoid the shortage,people use electroplating to solve this problem in mordern industry.

2.The advantage of aluminum electroplating
①Improve the decoration
②Increase the surface hardness and wear resistance
③Decrease the friction coefficient and improve lubrication
④Increase ductivity on the surface
⑤Increase wear resistance(Include the combination with other metal)
⑥Easy to weld
⑦Increase the bonding force with rubber whrn hot pressing.
⑧Increase reflective rate
⑨Repair dimensional tolerance

As aluminum is a kind of  relatively active metal, the electroplating material is more active than aluminum.so it should do relative chemical translation,like zinc immersion,zinc-iron alloy,zinc-nickle alloy,to get a good adhesion of the intermediate layer cyanide copper plating layer between zinc and zinc alloy.Die casting aluminum due to the loose structure of the body, when grinding, can not be polished off the surface part of the body, otherwise it would cause the needle hole, acid, peeling and other phenomena.

3.Aluminum electroplating processing:
  
Degreasing--Alkali corrosion--Excitation--Zinc replacement--Excitation--Electroplating(like Nickle,zinc and bronze,etc)--chroming or passivation--Drying

①The common used aluminum electroplating are:
Nickle plating(peal nickle,sand nickle,black nickle),Silver plating(Surface of silver and thick silver),gold plating,zinc plating(colorful zinc,black zinc and bule zinc),copper plating(green copper drum,white tin copper,Alkaline copper,coke copper,acid copper),chromeplate(white chrome and black chrome)etc.

②Usage of common used palting

1)Black plating
Black zinc and black nickle are used for optical electron and medical equipment.

2)Gold plating
  As the best conductivity of electronic products ,silver can increase the high decorative quality of products,but it’s very expensive,usally it would be used for the conductivity of electronic products,like the plating of high precision wire terminal.

3)Copper,nickle and chrome are the most common mixed plating in the modern science area not matter in decoration or corrosion resistance.And it apply to sports equipment,lamp decoration and most electronic industry as its cheap.

4)Among the copper plating,white tin copper is the first choice in jewlry industry,it’s devoloped into environmental plating since 7os and 80s in white and bright.Lead tin copper can make imitation gold,but the prevention of allochroism is poor,so its development is slow.

5)Zinc plating:The surface of zinc plating is bluish white,easy to be soluble in acid and alkali.As the standard potential is negative than iron,it can offer accountable electrochemical protection for steel.

6)Hard chrome:Under certain conditions, the deposited chromium coating has high hardness and wear resistance, and the hardness reaches hv900-1200kg /mm.As the hardest coating among all the common used coating,chrome can strengthen the wear resistence prolong service life of accessories.Like die or fixture.Therefore, the plating is an indispensable treatment method for cylinder, oil pressure and transmission system.

③Common abnormalities and improvement measure

1)Peeling:
a.Zink repplacement is bad,time is too long or too short.
  Improvement measures:Reconfirm the displacement time, the bath temperature, the liquid concentration and other operating parameters.
b.Activation is not enough.
  Improvement measure:Change the activation way
c.Pretreatment is not enough,the workpiece have oil on the surface.
Improvement measure:Strengthen the pretreatment.

2)Rough surface:
a.Electroplating liquid light agent,soft agent,pinhole dose is improper 
  Improvement measure: Readjust the number of auxiliaries.
b.The surface itself is rough,Re-polish it before plating.

3)The surface become yellow,low potential and direction is not striaght.
  Improvement measure:Add proper walk agent.

4)The surface get rough teeth,electoplating liquid is dirty.
  Improvement measure:Do the proper tank liquor processing.

④The requirement of quality

1)There’s no negative phenomenon of yellow surface,pinhole,burrs,blister,bumping,scratch.
2)The film thickness is more than 15Um, and the salt spray test is 48 hours, reaching the level of the US army at level 9 or above, and the electric potential difference of 130-150mv.
3)The binding force can be tested by bending 60 degrees.
4)Products under special environment can be changed accordingly.

⑤Aluminum and aluminum alloy plating operation precautions.

1)Aluminum parts is suitable to be plated with aluminum alloy for hanging fixture.
2)The process of aluminum and aluminum alloy must be done quickly after etching,The shorter the interval between the cabinet aluminum profile, the better it be finished well and not to reoxidize.
3)The second etching should not keep long so as not to cause errosion.
4)Water cleaning should be washed clean.
5)In the process of plating, avoid power cuts.

四.Coating of aluminum
The coating is divided into dip coating, spraying, spray coating, roller coating and brush coating, among them dip coating and spraing coating are the mainly coating,and deep coating is electrophoresis coating,which form a transparent and organic coating in various color by the electrochemical way to depoosit the  colloidal particles of organic resin on the surface of workpiece.Negative electrophorehsis is not only the the main technology but also the new one since 70s with strong wear resistance,anti-allochroism and binding force. Spraying is divided into powder coating and liquid coating, and electrostatic coating is a popular technology in the industry.

1.The working principle of electrostatic
Under the action of the pump, the coating enters the electric field and the paint is negatively charged.Under the action of atomizing air pressure, the coating becomes thinner and uniform, and under the action of the working pressure, the coating is sprayed on the surface of the workpiece uniformly and uniformly under the action of the cup or nozzle.The distance of spray and workpiece is equal on the same vertical plane,and the electric field intensity of the same interface is the same, and the positive and negative charges attract each other,the organic resin coating is coated uniformly on the workpiece surface.Then,he resin meets the state of flow and solidification under the high baking temperature. It is firmly embedded on the surface of the workpiece to protect the workpiece.

2.The technological process of aluminum coating
Mechamical polishing-Degreasing-Remove oxide film-Chromizing-Spray the powder or liqor-Baking-Sagging-Complete inspection-Packing-Put in storage

五.Aluminum chemical plating
1.Electroless plating is the REDOX effect of reducing agent in the same solution when no current is passed,In this way, metal ions are deposited on the surface of parts.Therefore,So chemical plating can be described as a controlled, self-catalyzed chemical reduction process for deposition of metals.

2.The characteristic of chemical plating
With the development of industry,chemical plating have become a promising process technology.,it hs the characteristics as below compared with other plating method:
①Metal can be coated on parts made of various materials, such as metals, semiconductors and non-conductors.
②No matter how complex the geometrical shape of the parts, the uniform thickness of the coating can be obtained from the place where the solution can be reached.
③For self - catalyzed electroless plating, a large thickness can be obtained, and can even be electroplated.
④No current
⑤The coating is compact and less pore
⑥The coating often has special chemical and mechanical properties.

As there’s many advantages of electroless nickle,its development become quick in the industry and electronic industry.The following is an example of electroless nickel plating.
For electroless nickle plating,as sodium hypophosphite is used as reducing agent, so the coating is generally nickel - phosphorus alloy.Depending on the phosphorus content, it can be divided into low phosphorus(1%~4%,medium (4%~10%)and high phosphorus(10%~12%).

Shortage:It’s fragile but the product plasticity can be greatly improved after heat treatment.

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