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A pretreatment method for homogenizing chromium-free conversion coating on magnesium alloy

A technology of homogenization treatment and chrome-free transformation, which is applied in the direction of superimposed layer plating, metal material coating process, coating, etc., can solve problems such as uneven film formation, achieve uniform film layer, uniform nucleation, and process stable effect

Active Publication Date: 2019-10-22
INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0005] In view of the above problems, the object of the present invention is to provide a pretreatment method for the homogenization of chromium-free conversion coatings on magnesium alloys. The samples processed by this method have more uniform nucleation on the surface of the substrate in the conversion coating solution, and the grain distribution is tighter. Improve the overall corrosion resistance of the film, and solve the problem of uneven initial film formation on the surface of the magnesium alloy due to the influence of the second phase

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  • A pretreatment method for homogenizing chromium-free conversion coating on magnesium alloy
  • A pretreatment method for homogenizing chromium-free conversion coating on magnesium alloy
  • A pretreatment method for homogenizing chromium-free conversion coating on magnesium alloy

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Embodiment 1

[0036] In the present embodiment, the sample is a die-cast WE43 magnesium alloy, and its specific steps are as follows:

[0037] (1) Pretreatment: The pretreatment solution is an aqueous solution of sodium hydroxide 50g / l, sodium fluoride 20g / l, and sodium carbonate 20g / l, at a temperature of 60°C, soaking for 5 minutes;

[0038] (2) Homogenization treatment: the homogenization treatment solution is ammonium phosphate 20g / l, sodium silicate 10g / l, the aqueous solution of hydroxylamine sulfate 20mg / l, soaks 1min at normal temperature;

[0039] (3) Homogenization post-treatment: the homogenization post-treatment solution is 1wt% hydrochloric acid, 50mg / l sodium dodecylsulfonate aqueous solution, soaked at room temperature for 30s. After pretreatment according to this method, the second phase existing on the surface of the sample is completely dissolved, and its morphology can be seen in figure 2 ;

[0040] (4) Film formation: the sample after pretreatment is immersed in the p...

Embodiment 2

[0042] In the present embodiment, the sample is a die-casting GW93 magnesium alloy, and its specific steps are as follows:

[0043] (1) Pre-treatment: the pre-treatment solution is an aqueous solution of potassium hydroxide 40g / l, potassium fluoride 10g / l, and potassium carbonate 25g / l at a temperature of 50°C for 8 minutes;

[0044](2) Homogenization treatment: the homogenization treatment solution is ammonium dihydrogen phosphate 50g / l, sodium silicate 5g / l, the aqueous solution of hydroxylamine hydrochloride 40mg / l, soaks 2min at normal temperature;

[0045] (3) Homogenization post-treatment: the homogenization post-treatment solution is an aqueous solution of 3 wt % citric acid and 100 mg / l tetraethylamine perfluorooctane sulfonate, soaked at room temperature for 30 s.

[0046] (4) Film formation: The sample after pretreatment is soaked in the phosphate solution described in patent ZL02132772.6 to prepare the film layer to form a phosphate conversion film with a thickness ...

Embodiment 3

[0048] In the present embodiment, the sample is a die-casting EW75 magnesium alloy, and its specific steps are as follows:

[0049] (1) Pretreatment: The pretreatment solution is an aqueous solution of sodium hydroxide 100g / l, sodium fluoride 40g / l, and sodium carbonate 20g / l at a temperature of 80°C for 5 minutes;

[0050] (2) homogenization treatment: the homogenization treatment solution is diammonium hydrogen phosphate 25g / l, sodium silicate 20g / l, the aqueous solution of ammonium metavanadate 100mg / l, soaks 2min at normal temperature;

[0051] (3) Homogenization post-treatment: the homogenization post-treatment solution is an aqueous solution of 5 wt % nitric acid and 150 mg / l disodium edetate, soaked at room temperature for 60 s.

[0052] (4) Film formation: the sample after pretreatment is soaked in the phosphate solution described in patent ZL201010125808.4 to prepare the film layer to form a phosphate conversion film with a thickness of 5 μm, and the film layer is uni...

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Abstract

The invention relates to the field of magnesium alloy surface treatment, particularly to a magnesium alloy chromium-free conversion film homogenizing pretreatment method, which mainly comprises pre-treatment, homogenizing treatment and homogenizing post-treatment, wherein the pre-treatment can remove greases and contaminants from the surface of a substrate and forms a layer of a thin protection film on the alpha matrix phase of a magnesium alloy, the homogenizing treatment can preferentially dissolve the large-size second phase on the surface of the substrate, and the subsequent homogenizing post-treatment can remove salt crystal grains and oxide skins remaining on the surface and can provide a certain activation effect. According to the present invention, the sample treated through the method can form the uniform core on the surface of the substrate in the conversion film solution, the grain distribution is compact, the corrosion resistance of the whole film layer is improved, and theproblem that the non-uniform film forming on the surface of the magnesium alloy at the early stage due to the influence of the second phase is solved.

Description

technical field [0001] The invention relates to the field of magnesium alloy surface treatment, in particular to a pretreatment method for homogenizing a chromium-free conversion film of a magnesium alloy. Background technique [0002] The magnesium alloy chemical conversion coating has the advantages of low cost and simple process, and is suitable for industrial application. However, the formation process of the conversion film has high requirements on the state of the substrate itself, such as: corrosion pits, oxide scales, especially the second phase on the surface of the magnesium alloy will lead to uneven microstructure of the alloy, affect the initial deposition and growth of the film, and ultimately affect the film quality. However, magnesium alloys need to add some alloying elements to improve their mechanical properties during the smelting process, and the existence of the second phase is inevitable, resulting in poor uniformity of the conversion coating. If you w...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C23C28/04C23C22/60C23C22/42C23G1/12
Inventor 董凯辉宋影伟单大勇韩恩厚
Owner INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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