Surface pretreatment process for improving film quality of magnesium alloy conversion film

Abstract

The magnesium alloy surface was treated by using glyoxylic acid and ammonium bifluoride as pickling solution and hydrochloric acid and hydrofluoric acid as pickling solution, and the two cases were compared. A large number of black spots can be found on the surface treated by hydrochloric acid and hydrofluoric acid, which cannot meet the surface quality requirements of the sample in the film forming process. Using glyoxylic acid and ammonium bifluoride as pickling solution can effectively reduce the corrosion pits on the sample surface and the junction between the second phase and the matrix. Using glyoxylic acid and ammonium bifluoride as pickling solution can achieve good surface treatment effect and greatly improve the surface quality. The film forming quality of magnesium alloy conversion film is improved.

Description

Technical Field

[0001] This invention relates to a surface pretreatment process for improving the film quality of magnesium alloy conversion films. Background Technology

[0002] Magnesium alloys possess advantages such as being lightweight, having high specific strength and stiffness, and exhibiting good impact and compressive strength. The density of magnesium is 1.74 g / cm³. 3 It is 2 / 3 the weight of aluminum, 1 / 4 the weight of zinc, and 1 / 5 the weight of steel, making it the lightest metal structural material currently available. [1, 2]. With the increasing severity of environmental problems such as the greenhouse effect, people's demand for lightweight structural materials is constantly rising. Moreover, my country is one of the countries with the richest magnesium resources in the world and has good development potential. Due to environmental factors and strategic deployment considerations, the development of the magnesium alloy industry is of great significance. However, magnesium alloys have poor corrosion resistance. Magnesium has high chemical activity and a very low equilibrium potential. When in contact with different types of metals, it is prone to galvanic corrosion and acts as an anode. At room temperature, the magnesium surface reacts with oxygen in the air to form a magnesium oxide film. However, due to the loose and porous nature of the magnesium oxide film, its density coefficient is only 0.79, meaning that the volume of magnesium oxide generated after magnesium oxidation is reduced, and it cannot effectively protect the magnesium substrate. Magnesium alloy surface conversion film is one of the main methods to solve the corrosion problem of magnesium alloy substrates. However, acid and alkali pretreatment causes great damage to the surface and seriously affects the film quality. The preparation of magnesium alloy conversion film and the subsequent film quality are closely related to the surface state of the metal substrate [3]. Therefore, a suitable surface pretreatment process for magnesium alloys is particularly important for improving the corrosion resistance of the surface conversion film.

[0003] References

[0004] [1] Ding Wenjiang, Wu Yujuan, Peng Liming, Zeng Xiaoqin, Lin Dongliang, Chen Bin. New progress in the research and application of high-performance magnesium alloys [J]. Progress in Materials, 2010, 29(08):37-45+36.

[0005] [2] Zhang Gaohui, Zhang Pingze, Pan Junde. Research status and progress of magnesium and magnesium alloys [J]. World Science and Technology Research and Development, 2003(01):72-78.

[0006] [3]Rong H, Su Y, Liu Y, et al. Deposition Process and Properties ofElectroless Ni-P-Al2O3 Composite Coatings on Magnesium Alloy[J].NanoscaleResearch Letters, 2018,13(1):198. Summary of the Invention

[0007] This invention relates to a surface pretreatment process for improving the film quality of magnesium alloy conversion films. It uses glyoxylic acid and ammonium fluoride as pickling solutions to improve the surface treatment effect of magnesium alloys, thereby achieving the goal of improving the film quality of magnesium alloy conversion films.

[0008] This invention relates to a surface pretreatment process for improving the quality of magnesium alloy conversion films. The process uses glyoxylic acid (1–10 g / L) and ammonium hydrofluoride (5–15 g / L) as pickling solutions to enhance the surface pretreatment effect. Experiments were conducted by comparing the use of glyoxylic acid and ammonium hydrofluoride as pickling solutions with those using hydrochloric acid and hydrofluoric acid. EDS results showed no significant difference in elemental distribution near the secondary phase particles after treatment by both methods. Scanning electron microscopy results indicated that after surface pretreatment, the use of hydrochloric acid and hydrofluoric acid as pickling solutions resulted in numerous corrosion pits on the sample surface, failing to meet the surface quality requirements for magnesium alloy during film formation. Treatment with glyoxylic acid and ammonium hydrofluoride as pickling solutions significantly reduced corrosion pits on the sample surface and at the interface between the secondary phase and the substrate, achieving a superior surface treatment effect and greatly improving surface quality.

[0009] Comparative analysis shows that adding glyoxylic acid and ammonium fluoride as pickling solutions can effectively improve the surface pretreatment effect, improve the quality of the conversion film on the magnesium alloy surface, and thus improve the corrosion resistance of the magnesium alloy surface.

[0010] The present invention has the following advantages:

[0011] (1) The preparation process is simple and easy to operate. Glyoxylic acid and ammonium fluoride are cheap and readily available, and their concentrations are easy to control.

[0012] (2) The present invention uses glyoxylic acid and ammonium fluoride as pickling solution to achieve a good surface treatment effect and greatly improve the surface quality, thereby improving the film quality of magnesium alloy conversion film. Attached Figure Description

[0013] Figure 1 (a)(b) Scanning electron micrographs. (c) EDS line scan analysis results of O, Al, Mg and Zn in pretreated magnesium alloy.

[0014] Figure 2 The results are as follows: magnesium alloy surface treated with hydrochloric acid and hydrofluoric acid as pickling solutions, and EDS analysis results. Detailed Implementation

[0015] The surface pretreatment process involves grinding and polishing the magnesium alloy with 800, 1200, and 2000# sandpaper, then ultrasonically cleaning it in anhydrous ethanol for 10 minutes. Next, it is alkaline washed at 40–75°C for 5–15 minutes using a 5–15 g / L NaOH + 5 g / L Na2CO3 solution as the alkaline washing solution. Finally, it is acid-washed at room temperature for 5–15 seconds using 5–15 g / L NH4HF2 + 1–10 g / L C2H2O3·H2O. The final step is activation with 10–30 wt.% NaOH at room temperature for 400–800 seconds.

Claims

1. A surface pretreatment process for improving the film quality of magnesium alloy conversion coatings, the specific operation of which is as follows: After grinding and polishing the magnesium alloy with 800, 1200, and 2000# sandpaper, it was ultrasonically cleaned in anhydrous ethanol for 10 min, then alkaline washed at 40-75℃ for 5-15 min with 5-15 g / L NaOH + 5 g / L Na2CO3 solution, then acid washed at room temperature with 5-15 g / L NH4HF2 + 1-10 g / L glyoxylic acid for 5-15 s, and finally activated with 10-30 wt.% NaOH at room temperature for 400-800 s.

2. The surface pretreatment process for improving the film quality of magnesium alloy conversion films as described in claim 1, characterized in that, An activated film is generated on the surface of magnesium alloy by alkaline washing followed by acid washing and then alkaline washing. This process inhibits the generation of H2 bubbles on the surface of the magnesium alloy during film formation and improves the quality of the conversion film.

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