Chemical coloring of aluminum and aluminum alloys

( a ) Overview

    Most of the chemical coloring of aluminum and aluminum alloys is performed on anodized films. This is because the anodized film of aluminum is thicker than the chemical film, and the properties of the film such as abrasion resistance, corrosion resistance, coloring durability, and the generality of the color are better than those of the chemical film, but the equipment is simple because of the chemical direct coloring. , No need of power equipment, easy operation, low production cost

With many advantages, chemical direct coloring also has a certain use and market. In particular, some interior decorations, where no sunlight, wind and rain, and less demanding products, use chemical direct coloring methods. In addition, chemical coloring is also used as a background color, and then spray and brush transparent paint to protect the decoration.

( B ) Aluminum chemical coloring process

    A black aluminum chemistry solution formulation and process conditions shown in Table 3-28, Table 3-29 the solution formulation and process conditions for the other colors aluminum chemistry.

Table 3-28 Aluminous Chemical Black Formulation and Process Conditions

    Solution composition and process conditions

1

2

3

4

5

Ammonium molybdate [(NH4)2M004] / (g / L)

Ammonium chloride (NH4C1) / (g / L)

Boric acid (HsB03) / (g / L)

Potassium nitrate (KN03) / (g / L)

Chromium anhydride (Cr03) / (g / L)

Sodium Chromate (Na2Cr04) / (g / L)

Potassium carbonate (K2C03) / (g / L)

Copper sulphate (cuS04 · 5Hzo) / (g / L)

Nickel sulphate (NiS04 · 7H00) / (g / L)

Sodium Nitrate (NaN03) / (g / L)

Sodium Cyanide ENazsi (CN) 6] / (g / L)

Sodium hydroxide (NaOH) / (g / L)

Sodium carbonate (Na2C03) / (g / L)

Potassium Permanganate (KMn04) / (g / L)

Nitric acid (HN03) / (mL / L)

Copper nitrate ECu(N03)2] / (g / L)

Solution temperature/°C

Processing time / min

15

30

8

8

82

  appropriate

    -

    -

    -

    -

10

25

25

25

    -

    -

    -

    -

    -

    -

    -

    -

70 — 80

20 to 30

    -

    -

     -

    -

    -

    -

    -

    -

2

10

1.5

    -

    -

    -

    -

    -

70 to 100

20 to 30

15 to 18

150

50 to 60

40 to 60

25 to 35

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

5 to 10

2 to 4

20 to 25

80 to 90

5 to 15

Table 3-29 Aluminium chemistry with other color solution formulations and process conditions

    Solution composition and process conditions

    gray

  red

  blue

1

2

3

4

5

Manganese nitrate [-Mn(N03)2] / (g / L)

Ammonium phosphate [(NH4)3P04] / (g / L)

Sodium carbonate / (g / L)

Potassium chromate (K2Cr04) / (g / L)

Potassium carbonate (KzC03) / (g / L)

Selenite (H2Se03) / (g / L)

5

100

   

   

1

   

   

20

5

   

 

25

10

25

   

10 to 30

      

10 to 30

Solution composition and process conditions

gray

red

blue

1

2

3

4

5

Ferric chloride (FeCl3) / (g / L)

Potassium ferricyanide [K3Fe(CN)6] / (g / L)

Solution temperature/°C

Processing time / min

Note

50

10 to 15

Color film corrosion resistance

80 to 100

10 to 30

Potassium chromate can not be more

80 to 100

30 to 50

Add a small amount of alum, filming fast

50 to 60

10 to 20

Red selenium precipitates

60 to 70

appropriate

( III ) Chemical coloring process of aluminum alloy

    Aluminum alloy chemical coloring and aluminum chemical coloring are quite different, mainly aluminum does not contain other alloying elements, even if there is a very small amount, and aluminum alloy is composed of several additive elements, so the coloring varies with the type and amount of alloy content , but there are also some coloring formulas that can be made with a variety of aluminum alloys, as well as a variety of colors. See Table 3-30 for formulas and technological conditions for the chemical coloring solution of aluminum alloys.

Table 3-30 Aluminum Alloy Chemical Coloring Solution Formula and Process Conditions

Solution composition and process conditions

1

2

3

4

Potassium nitrate (KN03) / (g / L)

Nickel sulphate (NiS04 · 7H20) / (g / L)

Sodium Fluorosilicate (Na2SiF6) / (g / L)

Sodium Molybdate (Na2M004) / (g / L)

Water (H20) / L

Sodium carbonate (Na2C03) / (g / L)

Disodium hydrogen phosphate (Na2 HP04) / %

Sodium dichromate (Na2Crz07) / (g / L)

Zinc Fluoride (ZnF2) / (g / L)

Solution temperature/°C

Processing time / min

Applicable alloy type

25

10

10 % solution

1mL

4

60 to 70

All aluminum

alloy

margin

2 %

0.2

90 to 100

10 to 20

A1-Si.A-Mg , Al-Mg-Si, Al-CU-Si

0.5 to 2.6

0.1 to 1.0

80 to 100

10 to 20 ,

Al-Si, A1-Mg , A1-Zn , A1-Ni, A1-Cu-Si.A1-Cu-Mg

16

4

twenty four

60 to 70

2 to 10

A1-Cu-Si . A1.Cu-Mg , Al-CU-Ni

Solution composition and process conditions

1

2

3

4

Color type

Yellow, bronze, brown, red, etc.

Add chromium sulfate green, add copper nitrate

Red blue

White, white brown

Multiple shades: yellow, black, brown, green, bronze, red green, etc.

( four ) black examples of aluminum alloy

1 . Overview

    Black is an important common color of aluminum alloy products. It can be used as a surface decoration in everyday life, with elegant and elegant features. Thermal materials, optical materials, and many parts in industrial products require black color. The black color of the aluminum alloy mainly adopts the traditional electrolytic coloring and hard anodic oxidation method. The product quality is high, but the power consumption is large. It requires special equipment and fixtures. The investment is large. It is only suitable for large-scale aluminum products production plants. Suitable for the manufacture of small parts and complex structures. The use of chemical coloring can also be obtained with good bonding strength, corrosion resistance, color and beautiful aluminum alloy black products.

2 . Aluminum alloy with black process flow

    Aluminum alloy workpieces → degrease degreasing → washing → alkali etching → washing → light → washing → chemical oxidation → washing → chemical blacking → washing → sealing → washing → drying → finished products.

3 . Chemical coloring pretreatment    

(1) After the chemical degreasing and degreasing aluminum alloy parts have been processed in various ways, the surface is stained with various oil stains, and the following steps must be processed to remove the oil stains. The degreasing formula and process conditions are as follows:

Sodium hydroxide (NaOH)

5 ~ 8g / L

Surfactant

0 . 5 ~ 1.5g / L

Sodium carbonate (Na 2 C0 3 )

22 to 27g / L

Solution temperature

60 to 68°C

Sodium phosphate (Na 3 P0 4 ·12H 2 0)

2 to 16g / L

Processing time

2 to 3min

(2) Alkali-etched oxide film Alkaline-etching to remove the old oxide film on the surface of the aluminum alloy. The solution formulation and process conditions are as follows:

Sodium hydroxide (N 8 0H)

40 ~ 50g / L

Solution temperature

55 to 65°C

Ammonium citrate

5 ~ 10g / L

Processing time

l ~ 2min

(3) Acid etching   The acid etching is to neutralize the residual lye on the surface of the aluminum alloy, and at the same time to dissolve the corrosion products after the alkali etching to expose the surface of the aluminum alloy to a bright gray and white color. The light solution formulation and process conditions are as follows:

Sulfuric acid (H 2 S0 4 )

15 to 20 mL / L

Solution temperature

20 to 30°C

Nitric acid (HN0 3 )

4 to 10 mL / L

Light time

l ~ 2min

4 . Chemical oxidation and chemical black

(1) Chemical Oxidation The surface of the aluminum alloy that has been pre-treated is very active, and it is very easy to oxidize in the air to produce a natural oxide film after acidic emission. Therefore, chemical oxidation must be performed immediately. Generally, a traditional chemical oxidation process can be used, and its solution formulation and process conditions are as follows:

Sodium chromate (Na 2 Cr0 4 )

15 to 20g / L

Sodium phosphate (Na 3 P0 4 )

5 ~ 10g / L

Sodium carbonate (Na 2 C0 3 )

40 ~ 50g / L

Solution temperature

60 to 70°C

Sodium hydroxide (NaOH)

3 ~ 6g / L

Dipping time

8 to 12 minutes

(2) Chemical black   According to Deng Liyuan et al., the chemical coloring of aluminum alloys is based on the use of a transition metal compound A as a colorant, together with an oxidizing agent, a catalyst, and the like, and the pH of the solution is adjusted with HNO 3 . Its solution formulation and process conditions are as follows:

Colorant A

L6 ~ 18g / L

Solution pH

4 . 5 to 5 . 0

KMn0 4

8 ~ 10g / L

Solution temperature

80 to 85 %

NiS0 4

2g / L

Coloring time

8 to 10min

5 . Sealing of coloring film

    The use of hydrolyzed salt method to seal pores mainly produces hydroxide precipitation in pores of blackened membranes, blocking pores. Sealing can improve the film's hardness, wear resistance, corrosion resistance and anti-pollution properties. Solution formulation and process conditions are as follows:

Nickel sulfate (NiS0 4 · 2H 2 O)

4 ~ 5g / L

Boric acid (H 3 B0 3 )

4 ~ 5g / L

Sodium Acetate (NaAc·3H z 0)

4 ~ 6g / L

Solution pH

4 . 5 to 5 . 0

Cobalt sulfate (CoS0 4 ·7H 2 0)

0.5 to 0.8g / L

Solution temperature

8 . 0 to 8 . 5

Closed time

8 to 10min

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