New chemical blackening process of the hottest alu

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New chemical blackening process of aluminum alloy Abstract: a new chemical blackening process of aluminum alloy was developed. The optimum process conditions were obtained by orthogonal test. The black oxide film of aluminum alloy with good adhesion, strong corrosion resistance and bright color was obtained by two-step oxidation coloring method

key words: aluminum alloy; Chemical Blackening; Two step oxidation coloring

Chinese Library Classification No.: tgl77 document identification code: B Article No.: X (2004)

1 preface

black is an important common hue in the application of aluminum alloy, which is another example of graphene and related materials moving steadily from laboratory to factory workshop. It can not only be used as a generous and elegant surface decoration color, but also an indispensable color for the preparation of heat absorbing materials, optical materials and parts of aluminum alloys. Aluminum alloy with black color has great market demand. At present, the traditional electrolytic coloring and hard anodic oxidation coloring methods are mostly used for the black coloring of aluminum alloys, which consumes a large amount of power and requires special equipment and fixtures, and is not suitable for ultra small workpieces and workpieces with complex structures. Using a new technology of chemical oxidation and coloring, a black oxide film of aluminum alloy with good adhesion, strong corrosion resistance and bright and beautiful color was obtained by two-step oxidation and coloring

2 experimental part

2.1 experimental process

two-step oxidation blackening process of aluminum alloy:

workpiece → chemical degreasing → alkali corrosion → acid etching light → chemical oxidation → blackening → sealing → drying → finished product

2.1.1 pretreatment

(1) chemical degreasing

use 60 ~ 65 ℃ alkaline chemical degreasing solution to treat the workpiece for about 2 minutes to remove the oil stain on the surface of the workpiece, so as to ensure uniform alkali corrosion and prevent spots on the workpiece. Its degreasing solution formula is as follows:

naoh5 ~ 6 s/l

na2co320 ~ 25 g/l

na3po4 · 12h2o10 ~ 15 g/l

surfactant 1 g/l

(2) alkali corrosion

NaOH at 60 ℃( ρ (NaOH) =40 ~ 50g/l) solution for 1 ~ 2min to remove the residual natural oxide film and modified alloy layer on the workpiece surface, and adjust the substrate surface to make it uniform. In order to reduce the alumina flocs precipitated in the corrosion process, ammonium citrate can be used( ρ= 10g/l) as chelating agent

(3) acid etching light

neutralize the residual alkali with H2SO4 and HNO3 with a volume concentration of 15 ~ 20 ml/l and 3 ~ 5 ml/l respectively, and dissolve the ash attachments at the same time, so that the workpiece exposes a bright and clean active surface

2.1.2 oxidation coloring

oxidation coloring is divided into two steps. In the first step, the traditional chromate oxidation process is used to carry out chemical oxidation on the pretreated workpiece in time to avoid re pollution or the formation of new natural oxide film. The process specification is as follows:

na2cro418 g/l

na2co45 g/l



θ 60 ~ 70 ℃

t10 min

after this step, the oxidation film with basically up to standard corrosion resistance can be obtained

step 2 is to paint the oxidized workpiece black. In this step, a transition metal compound A is used as colorant, KMnO4 as oxidant, NiSO4 as catalyst, and HNO3 is added to adjust the pH value to about 5. The workpiece can be treated at 80 ~ 90 ℃ for about 8min

2.1.3 sealing

hydrolytic salt method can be used for sealing, and hydroxide precipitation will be generated in the pores of the formed blackened membrane to block the micropores. After sealing, the corrosion resistance and gloss can be further improved. The sealing process specification of hydrolytic salt method is as follows:

niso4 4 ~ 5 9/l

naac · 3h2o4 ~ 6g/l

coso4 · 7h2o0.5 ~ 0.8g/l

h3bo34 ~ 5 9/l

ph 4 ~ 6

θ 80 ~ 85 ℃

t15 ~ 20 min

2.2 main performance evaluation indexes of the film

due to the two-step oxidation, the formula can obtain an oxide film with good corrosion resistance within a large test range. Therefore, three indexes of film color, uniformity and adhesion are emphatically selected when determining the orthogonal score and inspection standard (see table 1). In the table, the evenness is observed with a microscope (100 meshes) that all countries in the world, especially developed countries, attach importance to the development of the new material industry, and scored with the number of small pits or protrusions on the inner membrane of the same area; Adhesion is scored by the number of times that the degreased cotton force evenly wipes the film surface to the exposed substrate. The comprehensive score Z is calculated by the formula

3 results and discussion

3.1 the influence of various factors on the coloring effect

through preliminary tests, four main factors affecting the black effect were selected: the mass concentration of colorant a, the mass concentration of KMnO4, the coloring temperature and the coloring time. L9 (34) orthogonal table was used for orthogonal test optimization. The mass concentration of NiSO4 was fixed at 2 g/l, and the pH value of each formula was adjusted to 5 with HNO3)

make range analysis based on the results of orthogonal test and draw range analysis diagram. It can be seen from the figure that the amount of colorant a has a great impact on the chromaticity and adhesion. The large amount of colorant a used in this transaction is conducive to improving the overall performance of the film; The concentration of KMnO4 has an optimal value, but the film indexes decrease when the dosage is too high; The coloring temperature can fluctuate in a large range, which is easy to operate and control

3.2 optimum process conditions

according to the range analysis results of orthogonal test, the optimum process conditions are obtained by combining the results of the standard factor test of material testing in China

colorant a16 ~ 18g/l

kmno48 ~ 10 g/l


θ 80 ~ 85 ℃

ph value 4.5 ~ 5

t8 ~ 10 min

3.3 test results of oxide layer

according to the analysis of the surface electron microscope photos of the film, the surface is obviously amorphous structure with high corrosion resistance, and the film is uniform and dense; It can be seen from the side electron microscope that the film is very uniform, and the two layers of oxide film are well bonded

according to the electronic energy spectrum analysis, the main components of the film are Al2O3, MnO2, NiO and another key coloring component, with mass fractions of 25%, 44.5%, 13.5% and 17% respectively

for the colored workpieces obtained in this test, the file method was used to evaluate their adhesion, and the flat file was 45. File the edges of the coating from the base metal to the coating direction, and the coating is not lifted or fallen off

4 conclusion

by using the New Chemical Blackening Technology of aluminum alloy, the aluminum alloy treated with alkaline chromate oxidation solution is chemically colored, and a black oxide film with bright color, good adhesion, strong corrosion resistance, good decoration and corrosion prevention effect is obtained. The method has the advantages of low power consumption, simple equipment, small investment, simple operation, and is convenient for mass production. It is especially suitable for aluminum alloy workpiece with complex shape with black surface, and has a good application prospect. (end)

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