Chromium-free chemical conversion treatment method for magnesium alloy surface

A chemical conversion treatment and surface pretreatment technology, applied in the direction of metal material coating process, etc., can solve the problem that the corrosion resistance and self-healing ability of the conversion film have not fully met the requirements for use, the corrosion resistance is not as good as chromate treatment, phosphorus There are many problems in the composition of the chemical liquid, so as to achieve the effect of convenient industrial application, low cost, and expansion of production and application.

Inactive Publication Date: 2015-09-23
SOUTH CHINA UNIV OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Among them, chromate conversion coating technology is more studied in chemical treatment, but the hexavalent chromium produced in this process is more toxic, and phosphate conversion coating technology is a kind of chromium-free conversion coating technology.
[0004] At present, there are two main problems in the chromium-free phosphating treatment process of magnesium alloys: on the one hand, the phosphating treatment technology contains a large amount of heavy metals and carcinogens, which cannot meet the requirements of environmental protection; on the other hand, the composition of the phosphating solution There are many substances, the influencing factors are complex, and the corrosion resistance is not as good as chromate treatment
So far, the corrosion resistance and self-healing ability of the conversion coatings produced by the phosphate conversion treatment of magnesium alloys reported at home and abroad have not fully met the requirements for use.

Method used

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  • Chromium-free chemical conversion treatment method for magnesium alloy surface
  • Chromium-free chemical conversion treatment method for magnesium alloy surface
  • Chromium-free chemical conversion treatment method for magnesium alloy surface

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0023] The magnesium flakes are processed into a size of 60mm×30mm×1mm and then polished, put into a potassium carbonate solution with a mass fraction of 5% to wash and remove oil for 7 minutes, then take it out and wash it with distilled water, and put it into a solution with a mass fraction of 3% hydrogen fluoride pickling in acid for 30s, then take it out and wash it with distilled water, then put it into the -1 Sodium dihydrogen phosphate, 50 g·L -1 Calcium hypophosphite, 8 g L -1 Hexamethylenetetramine, in the 100ml phosphating solution, the phosphating time is 20min, the temperature is 30°C, adjust the pH to 4.6, take it out after the film is formed, wash it with distilled water, dry it with hot air and put it in a sealed bag Sealed. See the result figure 1 and figure 2 ,Compared figure 1 and figure 2 It can be seen that after phosphating treatment, a uniform and dense phosphating film is formed on the surface of the magnesium alloy.

Embodiment 2

[0025] The magnesium flakes are processed into a size of 60mm×30mm×1mm and then polished, put in an 8% sodium hydroxide solution for alkali washing and degreasing for 8 minutes, then take it out and wash it with distilled water, and put it in 4% nitric acid pickling in medium for 20s, then take it out and wash it with distilled water, and then put it into 40 g·L -1 Sodium dihydrogen phosphate, 40 g·L -1 Calcium hypophosphite, 4 g L -1 In the 100ml phosphating solution composed of hexamethylenetetramine, the phosphating time is 18min, the temperature is 20°C, adjust the pH to 3.0 with water, take it out after the film is formed, wash it with distilled water, dry it with hot air and put it in a sealed bag Sealed. Its SEM image can refer to figure 1 and figure 2 .

Embodiment 3

[0027] The magnesium flakes are processed into a size of 60mm×30mm×1mm and then polished, put in a potassium hydroxide solution with a mass fraction of 6% to wash and remove oil for 8 minutes, then take it out and wash it with distilled water, and put in a phosphoric acid with a mass fraction of 7% pickling in medium for 15s, then take it out and wash it with distilled water, and then put it into 20 g·L -1 Sodium dihydrogen phosphate, 60 g·L -1 Calcium hypophosphite, 6g·L -1 In the 100ml phosphating solution composed of hexamethylenetetramine, the phosphating time is 25min, the temperature is 15°C, and the pH is adjusted to 2.9. After the film is formed, take it out, wash it with distilled water, dry it with hot air, put it in a sealed bag and seal it deal with. Its SEM image can refer to figure 1 and figure 2 . image 3 The polarization curves of the magnesium sheet (a) curve and the conversion coating (b) curve prepared in Example 3 in 3.5% NaCl solution. Depend on ...

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Abstract

The invention relates to a chromium-free chemical conversion treatment method for a magnesium alloy surface. The chromium-free chemical conversion treatment method for the magnesium alloy surface comprises the steps of surface pretreatment, alkaline washing for oil removing, water washing, acid pickling, water washing, phosphorization and water washing. Treating fluid used for phosphorization is composed of 20-80 g.L<-1> of sodium dihydrogen phosphate, 1-167 g.L<-1> of calcium hypophosphite and 0.1-10 g.L<-1> of hexamethylenetetramine. The phosphorization treatment temperature is 10-60 DEG C, the pH value is 2.8-7.0, and the phosphorization time is 1-50 minutes. A phosphating film surface prepared through the method is uniform, compact and high in corrosion resistance and can be used independently or serve as the bottom layer of a coating film, and the adhesive force of the coating film to a base body is improved. The reaction temperature is low, the condition is mild, the elements of a phosphating solution are simple, and the technique universality is high; no special requirements exist for equipment and the technique, and industrialized application is facilitated; production cost is reduced; meanwhile, energy resources are saved.

Description

technical field [0001] The invention belongs to the technical field of magnesium alloy surface anticorrosion treatment, and in particular relates to a chromium-free chemical conversion treatment method on the surface of magnesium alloy. Background technique [0002] Magnesium alloy has the advantages of small specific gravity, high specific strength and specific stiffness, good electrical and thermal conductivity, casting performance, machining performance and damping performance, and recyclability. It is increasingly used in aerospace, automobile, machinery, electronics, military and other fields. It is widely used and is known as the "green engineering material" of the 21st century. However, magnesium has a very low electrode potential (-2.37 V) and is chemically active. In addition, the PB ratio of the oxide film of magnesium (the ratio of the volume of the metal oxide film formed when the metal is oxidized to the volume of the metal consumed to form these oxide films) i...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C23C22/07C23C22/68
Inventor 李建三陈艳琴孙佳伟郑营才王春晓钟惠婷
Owner SOUTH CHINA UNIV OF TECH
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