In the aluminum and aluminum alloy on the surface to form amorphous green chromate? Phosphate conversion coating process is called chromium phosphating, containing phosphoric acid, hexavalent chromium and alkaline fluorides composed of acidic solution. The international organization for standardization has developed aluminum and aluminum alloy chromate phosphate conversion film standard?.
1 test section
1.1 test conditions
Material industry pure aluminum L6; temperature 20, time 10min.
Process for removing oil and rust, water washing, pickling, water washing, water washing, drying, chromium phosphating (less than 70 degrees Celsius or dry).
Test the standard reaction (bubble), the strength of the film, the color depth, adhesion, film quality.
1.2 film forming factors
1.2.1 composition
(1) A9g/L Cr composite accelerator, (VI) 2
G/L, H3PO4 in 5 ~ 40ml/L? Range can form excellent adhesion film, powder film H3PO4 = 40ml/L to form a loose.
(2) 25ml/L, Cr fixed H3PO4 (VI) 2g/L composite membrane, accelerating agent A into normal in 1 ~ 9g/L; A 9?
15g/L formation of the powder film; A > 15g/L, the inability of the film and corrosion matrix.
(3) fixed 25ml/L H3PO4: accelerator A
9g / L, Cr (VI) content in 1 ~ 5 g / L, green film color becomes shallow, excellent adhesion of the film that Cr (VI) involved in the film formation process, to enter the film in the form of Cr (III). For Protect environment pollution reduction, Cr (VI) low content selection content is appropriate.
According to the repeated test, the best formula for determining chromium phosphating is:
H3PO4 15 ~ 25ml/L; Cr (VI) from 1.5 to 2 g/L; composite accelerator 6 ~ 9g/L.
Effect of.2.2 temperature
Elevated temperature, speed up the reaction, 8 to 45 DEG C can form excellent green film > 45 DEG C, the temperature increases violent reaction, color film instead of a variable shallow, loose and continue to improve that no film and corrosion of the substrate. It is proved that the chromium phosphating can be processed at room temperature.
The relationship between 1.2.3 time and processing time.
T or 5min to form the rainbow color film, t > 5
The formation of the light green film with the time and the green film with the time, 25 ~ 35min to form a deep green film. When the time is extended to a few hours, the film is rough and porous.
Adaptability of 1.2.4 substrate
Chromium phosphating on aluminum and aluminum alloy processing adaptability is very extensive, of industrial pure aluminum, rust proof aluminum, aluminum and cast aluminum alloy (Al Si alloy) has the same substrate film forming rules, parts of the surface gloss color and roughness of only on the film gloss and color slightly.
2 film properties
Chromium phosphating film is amorphous, and the film is thin, with a rainbow colored light green, slightly thick film is olive green. The thin film has good flexibility, can bear all kinds of deformation processing. Brittleness of thick film. Fresh chromium phosphating film is readily soluble in 1: 1 nitric acid solution. The corrosion resistance of the film was improved after being dried and stored for a period of time, which is not soluble in 1: 1 of the nitric acid, phosphoric acid and sulfuric acid. A year without corrosion, fade in the atmosphere, the film intact.