( A ) rust removal
   The rust of aluminum and aluminum alloys is mainly an oxide film on the surface, and sometimes has a white powder, also called white rust. The method of removal is mainly to remove the alkaline chemical solution. Depending on the type of material and the condition of the surface of the aluminum workpiece, when the surface of the aluminum workpiece is low in oil, the oil can be removed and treated together with the film. If the surface is heavily oily, remove the oil first and then remove the oxide film. Otherwise, the oil removal and film removal will not be completed, which will affect the subsequent process and may reduce the quality of the surface treatment. Table 2-31 and Table 2-32 show the solution formulation and process conditions for the removal of oxide films on aluminum and aluminum alloys by chemical immersion.
Table 2--31 aluminum solution formulation and process conditions of an oxide film Stripping
Formulation and process conditions
1
2
3
4
5
6
Sodium hydroxide / (g / L)
Sodium phosphate / (g / L)
Sodium carbonate / (g / L)
Non-ionic surfactants
Sulfuric acid / %
Chromium anhydride / %
Solution temperature/°C
Operating time / min
Scope of application
30
30
30
-
-
-
40 to 50
3 to 5
Cast aluminum parts
50
-
-
Some
-
-
50 to 60
30 to 60s
Aluminum and aluminum alloys
-
15 to 25
15 to 25
Some
-
-
70 to 80
1 to 3
Aluminum alloy
5 % to 25 %
-
-
-
-
-
50 to 90
20 to 30s
Aluminum alloy
3 % to 8 %
5 % to l0 %
-
-
-
-
Room temperature
Depending on the circumstances
Aluminum alloy
-
-
-
-
3 to 5
2 to 10
60 to 75
30 to 120s
Aluminum alloy
Table 2-32 Solution formula and process conditions for removal of aluminum anodic oxidation film
Formulation and process conditions
1
2
3
4
5
Concentrated sulfuric acid / (mL / L)
Concentrated phosphoric acid / (mL / L)
Concentrated nitric acid/%
Sodium hydroxide / (g / L)
Chromic anhydride / (g / L)
Hydrofluoric acid / (mL / L)
Potassium fluoride / (g / L)
Solution temperature/°C
Operation time
100
-
-
-
-
10
-
Room temperature
Retire
-
35
-
-
20
-
-
boiling
Retire
100
-
-
-
-
-
4
Room temperature
Retire
-
-
27 ( mass fraction )
-
-
2 %
-
Room temperature
Retire
-
-
-
10
-
-
-
90
Prevent over-corrosion
Table 2-33 Rust removal formula and process conditions for aluminum and aluminum alloys
 Formulation components and process conditions
General etching
Bright etching
l
2
3
4
5
6
7
8
9
10
1l
12
13
Nitric acid (HN03.p=1.40 g / mE) / (mL / L)
Sulfuric acid (H2S04 , p =1-849/
mL) / (mL / L)
Hydrochloric acid (HCl.p=1.199 / mL) / (mL / L)
Phosphoric acid (H3P04)/(mL/L)
Chromic anhydride (Cr03)/(g / L)
Hydrofluoric acid (HF , 48 % )/(mL / L)
Hydrogen peroxide (H2O2 , 30 % )
/ (mL / L)
Water (H20) / (mL / L)
Temperature/°C
Time / min
Scope of application
200 ~
270
 Room temperature
3 to 5
Natural oxide film
General aluminum alloy
40 to 50
40 to 50
Room temperature
1 to 3
100
35
70 to 80
3 to 5
Heat treated surface
Forged aluminum with scale
10 % to 30 %
1 % to 3 %
89 % to 67 %
Room temperature
0.1 ~ O. 3
Oxidation
 The skin contains
 Silicon aluminum
 alloy
15 %
80 to 90
2 to 3
Pure aluminum and copper content
High aluminum alloy. A1-MgAt-Mg-Si Alloy Alkali
After the eclipse to the residue
500
500
Room temperature
5 to 15s
Pure aluminum and A1-Mrl alloy
500
500
Room temperature
5 to 15s
Hard aluminum
Most of the gold alkali corrosion
Light treatment
630
320
50
Room temperature
5 ~ 15S
Anti-rust aluminum aluminum
After the light
750
250
Room temperature
3 to 5s
   Silicon content is 10 %
The following silicon aluminum
Gold and heat treated surface oxide
500
500
Room temperature
5 ~ 30s
Silicon content
At 10 %
Above
Silicon aluminum
alloy
700
100
Room temperature
5 to 15s
In heavy metal solution
Treated Silicon
Aluminum alloy
100
50
Room temperature
0.5 to 1
Most aluminum and its
alloy
500
500
Room temperature
Aluminum plate
( II ) Rust removal of aluminum and aluminum alloys
   When aluminum and aluminum alloy parts are rust-removed by pickling, the parts must be thoroughly deoiled to ensure the quality of rust removal. Because if the degreasing is not clean, it will affect the contact and reaction of the acid liquid and the oxide film, resulting in incomplete removal of the rust, or inefficiency, long time, and the like. With rust removing by pickling, the loss of the base material is small and the operation is easy to control. The rust-removed surface is in a semi-bright state and does not require ash removal. It can be colored or anodized directly. However, if electroplating or electroless plating is required, zinc immersion and other processes are required. Aluminium and aluminum alloy pickling rust solution formula and operating process are shown in Table 2-33 .