Surface pretreatment

No matter what method is used to process aluminum materials and products, there will be dirt and defects on the surface to varying degrees, such as dust, metal oxides (natural or aluminum oxide films formed at high temperatures), residual oil, asphalt marks, artificial Carrying mudra (the main components are fatty acids and nitrogenous

1. Oxalic acid anodizing

Most of the factors that affect sulfuric acid anodization also apply to oxalic acid anodization, which can use direct current, alternating current, or superposition of alternating current and direct current. Under the same conditions, the film obtained by alternating current oxidation is softer and less elastic; direct current oxidation is prone to pitting corrosion, but alternating current oxidation can prevent it. With the increase of alternating current components, the corrosion resistance of the film increases, but the color deepens , the coloring property is worse than that of sulfuric acid film. The concentration of free oxalic acid in the electrolyte is 3%-10%, generally 3%-5%. During the oxidation process, each A. h consumes about 0.13-0.14g, while each A. h There is 0.08-0.09g of aluminum dissolved in the electrolyte to generate aluminum oxalate, which needs to consume 5 times the amount of oxalic acid. The aluminum ion concentration in the solution is controlled below 20g/L, and when it contains 30g/L aluminum, the solution will fail. Oxalic acid electrolyte is very sensitive to chloride. When anodizing pure aluminum or aluminum alloy, the chloride content should not exceed 0.04-0.02g/L, respectively. The solution is best prepared with pure water. As the temperature of the electrolyte increases, the film becomes thinner. To obtain thick films, the pH of the solution should be raised. Direct current anodizing uses lead, graphite or stainless steel as the cathode, and its area ratio to the anode is between (1:2)-(1:1). Oxalic acid is a weak acid with low solubility. When aluminum is oxidized, the product and electrolyte must be cooled. The thickness and color of the oxalic acid film vary according to the composition of the alloy. The film thickness of pure aluminum is pale yellow or silvery white, while the film thickness of the alloy is as deep as yellow and brass. After oxidation, the film layer is cleaned. If it is not dyed, it can be sealed with steam with a pressure of 3.43×10 4 Pa ​​pressure for 30-60 minutes.

2. Chromic acid anodizing

The chromic acid anodizing process is shown in Table-4. Concentration analysis should be carried out frequently during the oxidation process, and chromic anhydride should be added in time. The cathode materials for electrolysis can be lead, iron, stainless steel, and the best area ratio of anode to cathode is (5:1)-(10:1). When there are many trivalent chromium ions in the solution, they can be oxidized to hexavalent chromium ions by electrolysis. If the sulfate content in the solution exceeds 0.5%, the anodic oxidation effect is not good. When the sulfate ion is long, barium hydroxide or barium carbonate can be added to form barium sulfate precipitation. The chloride content in the solution should not exceed 0.2g/L. When the chromium content in the solution exceeds 70g/L, the solution should be diluted or replaced. There are two kinds of chromic acid anodizing method, the anodizing method of voltage cycle change or the constant voltage anodizing method (rapid chromic acid method).

3. Hard (thick film) anodizing

Hard anodizing is a process method for forming a thick and hard oxide film on the surface of aluminum and aluminum alloys. The maximum thickness of the hard film can reach 250μm, the microhardness of the film formed on pure aluminum is 12000-15000MPa, and the alloy is generally 4000-6000MPa, which is almost the same as that of the hard chrome coating, and they have excellent wear resistance at low conformity. , the porosity of the hard film is about 20%, which is lower than that of the conventional sulfuric acid film. Some hard anodizing processes are shown in Table-7.
Table-7 Hard anodizing process

No. Electrolyte temperature/degree current density/(A/dm2) Start and end voltage/V Time/min Film thickness/μm

start voltage end voltage

1 15% sulfuric acid+14-+4.4 2-2.1 26 120 90 50
2 15% boric acid, 4%Na2HC6H5O7 +60-+70 0.4-0.6 100 300 240 200
3 10% sulfuric acid+10 250W/dm2 15-25 80 60 10-130
4 15% Sulfuric acid-1-+4.5 2-2.5 25-30 40-60 60-240 28-150
5 10% Sulfuric acid+8-+10 25 60 60 25-60
6 10%-15% Sulfuric acid0 -+4 5 AC 10-12 60-70
DC 20-24 120-140
7 6%-8% oxalic acid dihydrate Conditions vary depending on the alloy
8 6%-7% sulfuric acid+3%-6% organic additive+ 4.5-+18+4.5-+18 1.3-2 10 150 40 65
9 10%-20% Sulfuric acid-6-+10 30 280 160 115-150
10 10%-15% Sulfuric acid+8 4 20-25 60 60 55 -80
11 5.5% formic acid, 8% oxalic acid dihydrate +15-+25 3-6 45 90 100-250

4. Porcelain anodizing

Porcelain anodizing aluminum and aluminum alloys are anodized in titanium salt, zirconium salt or thorium salt solution of oxalic acid, citric acid and boric acid, and the hydroxide of the salt metal in the solution enters the pores of the oxide film, so that the surface of the product shows a Treatment with opaque and dense enamel or plastic-like appearance with a special luster. The process of porcelain anodizing is basically the same as that of conventional sulfuric acid anodizing. The difference is that porcelain anodizing is performed at high DC voltage (115-125V) and high solution temperature (50-60 degrees), and the electrolyte is often stirred. , Often adjust the pH value to make it in the range of 1.6-2.

Dyeing treatment

The chemical coloring method has the advantages of simple process, easy control, high efficiency, low cost, low equipment investment, wide color gamut and bright color. However, large-area products are prone to uneven color, easy to decolorize after cleaning, improper sealing, or mechanical damage. . The chemical coloration of aluminum anodized film is based on the ability of the porous film layer to absorb dyes like textile fibers. Generally, the pore diameter of the anodized film is 0.01-0.03μm, and the dye is separated into single molecules in water, with a diameter of 0.0015-0.0030μm. During coloring, the dye is adsorbed on the surface of the pores and diffuses and accumulates in the pores. The membrane layer is colored by ionic bonding and hydrogen bonding, and the dye is fixed in the pores after sealing.

(1) Dyeing with organic dyes

1. Selection of
dyes There are many kinds of organic dyes , and dyes are selected according to different uses and product grades. For example, soluble vat dyes are expensive and have excellent color fastness, so they are mostly used in the dyeing of high-grade aluminum products such as gold pens, lighters, and hearing aids; alcohol-soluble dyes are used for aluminum foil dyeing; oil-soluble dyes are used for aluminum foil printing. Dissolve in nitrocellulose before use It can be used in varnishes such as plain, vinyl or polyamide resins, or in melamine resins and epoxy resins dissolved in baking varnishes. After printing, a resin film with dyes is formed on the surface of the cleaned aluminum foil. The types of dyes used for dyeing aluminum products include acid dyes, acid complex dyes, acid mordant dyes, direct dyes, weak acid dyes, disperse dyes, soluble vat dyes, reactive dyes, basic dyes, alcohol-soluble dyes, oil-soluble dyes, etc. .

2. Organic dye coloring process and control

(1) Monochromatic dyeing: Dip the anodized and washed aluminum products into a dye solution at a specified temperature. The dyeing time depends on the color depth, and the dye bath volume can be controlled at a ratio of 10 to the product volume: 1.

(2) Multi-color dyeing: If two or more different colors are dyed on aluminum parts, such as landscapes, flowers and birds, tasks, characters, etc., the printing process is mostly used to complete the printing plate. version) and screen version, direct printing method, paint anti-dyeing method, foam dyeing method, etc. can be used. The general practice is that after dyeing the first color, use a pattern to print a protective paint film on the part that needs to leave the color, and remove the remaining color, and the second, third and more colors can be deduced by analogy. The dyeing concentration and process conditions of various organic dyes are shown in Table-9.

Color dye name concentration g/L temperature 0C pH value time min

Aludye Black Black HBK 8-10 50-60 5.5-6 15-30
Black MBK 8-10 50-55 5.0-5.5 5-10
Black MRL 10-12 50-60 5.0-6.0 5-30
Black BBK 10-12 50 -60 5.0-6.0 15-30
Black DG 10 55-60 6.0-7.0 10-30
Black WAL 10-12 50-55 6.0-7.0 15-30
Black MLW 8-12 50-60 4.2-4.8 5-30
Aludye Red Big Red A 2-5 50-60 5-5.5 5-10
Big Red D4BS <25 55-60 6.0-7.0 5-10
Brilliant Red MB 0.5-5 50-55 5.5-6.0 5-15
Red B 2-5 55-60 5.5-6.0 5-15
Red D4B 2 55-60 5.5-6.0 5-10
Red SBR <3 50-55 5.0-6.0 5-10
Red FRB 0.5-5 50-55 5.0-5.5 5-10
Bright Red 3B 1- 2 50-55 5.5-6.0 5-15
Red MBES 1-2 55-60 5.0-5.5 5-10
Big Red MBES 1-2 55-60 5.0-5.5 5-10
Red RBL 2 55-60 4.5-5.0 5-15
Red PBL 2 55-60 5.0-6.0 5-10
Red CFB 0.5-5 50-55 6.0-7.0 5-15
Red FPR High Concentration 0.5-5 50-55 5.0-6.0 5-15
Big Red FAR High Concentration 0.5-5 50-55 6.0-7.0 5-10
Pink BN 0.5-5 50-55 6.0-7.0 5-15
Aludye Purple Violet VB <2 50-55 5.5-6.0 5-10
Purple MFBL <5 50-55 5.5-6.0 5-10
Purple RVB <5 50-55 5.0-6.0 5-15
Purple MBB <5 50-55 5.0-6.0 5-15
Burgundy BL 50-55 5.0-5.5 5-15
Aludye Brown Brown BRL <2 50-60 4.5-5.0 5-15
Brown CFA 0.5-2 55-60 4.5-5.5 5-15
Brown THM 0.5-5 55-60 5.0 -6.0 5-10
Brown BM 0.5-5 55-60 5.5-6.0 5-15
Brown GL 0.5-5 55-60 5.5-6.0 5-15
Brown KBL 1-5 55-60 5.5-6.5 5-15
Red Brown AG 0.1-2 50-55 6.0-7.0 5-10
Yellow Brown ASG 0.2-2 56-60 4.5-5.0 5-10
Aludye Green Green BGLN <2 50-55 5.0-5.5 5-15
Green RGS 1-9 55-60 5.0-5.5 5-15
Green 5GM <2 50-55 5.0-6.0 5-15
Green M6B <2 50-60 5.5-6.0 5-15
Green ABGL <2 50-55 5.5-6.0 5-10
Green DB 0.5-2 55-60 5.0-6.0 5-10
Green A3GM 2-5 55-60 6.0- 7.0 5-15
Aludye Yellow Yellow FD 0.5-5 50-55 5.0-5.5 5-10
Yellow FLY 0.2-5 50-60 5.0-5.5 5-10
Yellow DRL 0.5-2 55-60 6.0-6.5 5-10
Yellow GR 0.2-2 50-55 5.5-6.0 5-10
Yellow DGL 0.2-2 50-55 6.0-7.0 5-10
Yellow 3RF 0.5-5 55-60 4.5-5.5 5-10
Yellow YBL 0.2-2 50-55 5.0 – 5.5 5-15 Yellow
MBES 0.5-2 55-60 5.5-6.5 5-10
Yellow 2GL 1-2 50-55 5.5-6.0 5-15
Yellow GLL <2 50-55 5.5-6.0 5-10
Bright Yellow ALNW 1-2 50-55 6.0-7.0 5-10
Aludye Orange Gold D2GL 0.1-2 55-60 6.0-7.0 5-15
Orange GR 0.1-2 50-55 5.5-6.5 5-10
Gold G 2 27-60 5.5-6.5 1- 10
Orange SRL 2-5 50-55 5.5-6.5 1-10
Orange MBES <2 50-55 4.5-5.5 5-10
Orange GNS 0.5-5 50-55 5.5-6.0 5-10
Aludye Blue Lake Blue AB 1-2 50-55 4.5-5.0 5-15
Blue 2LW 0.5-2 55 5.5-6.0 5-15
Blue GBL 1-2 50-55 4.5-5.5 5-15
Blue 2AL 1-2 50-55 4.5 5-15
Navy Blue NBL 1-2 55 5.8 5-15
Turquoise Blue GB 0.5-2 55-60 5.0-6.0 5-15
Aludye Grey Grey MBL 0.5-2 55-60 6.0-7.0 5-10
Grey BRL 0.5-1 50-55 6.0-7.0 5-10
Grey 2BL 0.1-1 55-60 5.0-6.0 5-10
Grey ABL 0.5-10 55-60 6.0-6.5 5-20
Grey GBL 0.5-2 55-60 5.5-6.0 5-10
Grey VA 0.5-1 50-55 5.0-5.5 5-10
Grey G2RC 1-10 55-60 5.0-6.0 5-15
Grey GR 1-10 50-55 5.0-5.5 5-15
Grey GL 2-5 55-60 6.0-6.5 5-10
Aludye Bronze Bronze 2LW 2-5 55-60 4.0- 5.0 5-10