Phosphate conversion coating process is called chromium phosphate, it is an acidic solution containing phosphoric acid, hexavalent chromium and alkaline fluorides consisting conducted. International Organization for Standardization has developed aluminum and aluminum chromate?
Test Part 1
1.1 Test Conditions
Material industrial aluminum L6; temperature 20 ℃; time 10min.
Process degreasing rust → washing → pickling → washing → chromium phosphate → washing → natural drying (or <70 ℃ drying).
Test reaction (bubbles) the strength of the film's color depth, adhesion, quality of the film.
1.2 film-forming factors
1.2.1 Formula composition
(1) composite accelerator A9g / L, Cr (Ⅵ) 2
g / L when, H3PO4 in 5 ~ 40ml / L? within a range of excellent adhesion can be formed a film, H3PO4≥40ml / L is loose powder film forming.
(2) Fixed H3PO4 25ml / L, Cr (Ⅵ) 2g / L, the composite accelerator A in 1 ~ 9g / L the normal deposition; A 9?
15g / L form powdery film; A> 15g / L, the incompetence of the film and the corrosion of the substrate.
(3) Fixed H3PO4 25ml / L: accelerator A
9g / L when, Cr (Ⅵ) content in 1 ~ 5g / L, green film faded, good film adhesion, indicating that Cr (Ⅵ) participate in the forming process to Cr (Ⅲ) in the form into the film . Reduce pollution to protect the environment, Cr (Ⅵ) content is appropriate for low content.
According to trial to determine the optimum chromium phosphate formula is:
H3PO4 15 ~ 25ml / L; Cr (Ⅵ) 1.5 ~ 2 g / L; composite accelerator 6 ~ 9g / L.
.2.2 Influence of temperature
Temperature, reaction rate, at 8 ~ 45 ℃ can form good green film> after 45 ℃, violent reaction temperature, film color but lighter and loose, continue to improve so that no film etching the substrate. Test proved that chromium phosphate can at room temperature processing.
Affect the relationship between the processing time film weight 1.2.3 time.
t≤5min forming a rainbow color film, t> 5
Min forming a light green film and green deepened with time, 25 ~ 35min form dark green film. When the time is extended to several hours, the film is rough loose.
1.2.4 Base adaptability
Chrome aluminum phosphate and aluminum alloy processing adaptability is wide, industrial aluminum, rust-proof aluminum, hard aluminum and cast aluminum alloy (silicon aluminum alloy), etc., all have the same matrix deposition law, parts of the surface gloss and color gloss color and roughness of the film is only slightly affected.
Property 2 film
Chromium phosphate coating is amorphous, the film was a thin pale green with rainbow colors, the thicker the film was olive green. Film excellent in flexibility, various modifications can withstand the processing parts. 1 solution of chromium nitrate fresh soluble in the phosphate coating. After drying and stored for a period of time to improve the corrosion resistance of the membrane, insoluble 1:1 of nitric, phosphoric and sulfuric acid. Place in the atmosphere a year, no corrosion, fading, film intact.
