CN100447301C - Phosphate Surface Modification Treatment Method of Magnesium Alloy - Google Patents

Abstract

The invention relates to a magnesium alloy phosphate surface modification treatment method, so as to achieve the purpose of protecting and beautifying magnesium alloy products. It includes degreasing, pickling activation, alkali washing, chemical modification and sealing processes, including water washing and drying processes. The modified solutions used include phosphoric acid, barium hydroxide, sodium fluoride, zinc phosphate, etc. Advantages of the present invention are: 1, this technique is to be the treatment solution of main body with phosphate, does not use chromic acid or cyanide, pollution-free; Compared with the anodizing process, under the same conditions, the cost can be reduced by about 60.5%; 3. The technology is simple and easy to form an automated production line without large investment in equipment; 4. The chemical conversion film formed by this process has greatly improved the adhesion and corrosion resistance of magnesium alloy parts; 5. Mastered the optimal control of the solution ratio, heating temperature and treatment time in the treatment process, overcoming the The medium solution is unstable, the conversion coating layer is uneven, easy to fall off and other problems.

Description

Phosphate Surface Modification Treatment Method of Magnesium Alloy

technical field

The invention relates to a surface modification treatment method of magnesium alloy phosphate.

Background technique

With various application equipment becoming lighter, thinner and shorter and higher requirements are put forward for its heat dissipation and electromagnetic shielding performance, magnesium alloy has good thermal conductivity, electromagnetic shielding and vibration damping properties due to its small specific gravity, high specific strength and specific stiffness. As well as the advantages of green and environmental protection, it has become an ideal alternative material for electronic product housings and light vehicles in the 21st century, and has broad application prospects in industrial fields such as automobiles, computers, and aerospace. However, since magnesium is an extremely active metal, the standard electrode potential is -2.36V, and its corrosion resistance is extremely poor, which restricts the use of magnesium alloys. Therefore, when magnesium alloys are used as structural materials, proper surface treatment must be carried out to improve their corrosion resistance, which has important practical significance for the performance advantages of magnesium and magnesium alloys. At present, according to the film-forming conditions, the surface treatment technologies of magnesium alloys can be classified into two categories: chemical film-forming and anodic oxidation film-forming. Effectiveness and the stability of the treatment liquid temperature and other issues, so it is difficult to promote the use. The chemical conversion process requires simple equipment, less investment, easy operation, and low cost. It is generally used as the bottom layer of the coating to enhance the adhesion of the coating. Since the power supply is not used in the film forming process, there is no disadvantage of uneven film thickness caused by uneven distribution of electric force lines and the inability to deposit film at deep holes. As long as the electrolyte can reach the surface, the thickness can be obtained. Uniform conversion coating. Usually, the chemical surface treatment of magnesium alloys uses chromium series element reagents, such as U.S. Patent No. 4676842 and the chemical modification No. Chemical modification is carried out to form a dense protective film to prevent the metal from being corroded. However, the formed film contains Cr ³⁺ , a highly polluting chemical substance prohibited by the Versailles Convention, which will cause difficulties in the recovery of magnesium alloys in the future. In addition, the poisonous gas volatilized by the solution containing Cr ³⁺ in the treatment tank will pose a threat to the health of the operators, and the discharge of the solution in the treatment tank also needs to be treated with wastewater, but Cr ³⁺ is not easy to settle, which will cause The cost of wastewater treatment increases. In conclusion, the chromate chemical surface treatment of magnesium alloys has different degrees of harm to the human body and the environment. With the increasing demand for magnesium alloy products, the development of technologies and treatment fluids that are harmless to the environment and operators, and the realization of "green surface treatment" will be the main development direction in the future. So far, many scholars at home and abroad are also studying chromium-free chemical surface treatment methods. For example, Japanese scholar Umehara Hiroyuki has done a lot of work on the chromium-free conversion coating of potassium permanganate system; David Hawke has performed phosphate-high A conversion film was obtained on the surface of magnesium alloy through manganate treatment. The study found that the color and thickness of the film were very sensitive to the treatment time; MAGonzalez et al. studied the low-cost, light-pollution stannate conversion film, and solidified the ZC71 magnesium alloy. After dissolving, water quenching and tempering, pickling and other pretreatments, and then immersing the sample in stannate, a chemical conversion film of 2-5 μm can be formed on the surface; adding rare earth elements can also form a protective film, AL Rudd et al. The film-forming characteristics of lanthanum and praseodymium nitrates on WE43 magnesium alloy; AKSharma studied the process of direct electroless nickel plating on magnesium without zinc dipping; Yin Jianjun of Gansu University of Technology studied zinc plating directly on the surface of magnesium alloy; Dai Changsong , Huo Hongwei of the Chinese Academy of Sciences and others have studied electroless nickel plating on magnesium, but the substrate bonding force is poor, so galvanizing is added in the middle. The chemical conversion coatings produced by these chromium-free treatment methods are relatively thin, and have low corrosion resistance and adhesion. Magnesium and magnesium alloy surface treatment technology with commercial value and energy saving.

Contents of the invention

The purpose of the present invention is to provide a phosphate surface modification treatment method for magnesium alloys, which can not only meet the requirements of environmental protection, but also improve the performance of corrosion resistance and adhesion of magnesium alloys, and save energy.

The present invention is achieved in this way, and its operating steps are: (1) firstly, the magnesium alloy is polished and loaded; (2) the pretreatment process is carried out: the product is immersed in a degreasing tank containing 5% to 10% sodium hydroxide , heated to 80-98°C for 20-30 minutes by ultrasonic waves, then enter the first distilled water washing tank, use ultrasonic waves for 20-50 seconds at room temperature, take it out and dry it with hot air; In the pickling tank of acid and ethylene glycol solution, use ultrasonic waves at room temperature for 1 to 2.5 minutes. After pickling, enter the second distilled water washing tank. Also use ultrasonic waves at room temperature for 20 to 50 seconds. (4) then immerse in an alkali washing tank with 20% to 30% sodium hydroxide, and use ultrasonic waves at room temperature for 25 to 30 minutes, then immerse in the third distilled water washing tank, and ultrasonically clean at room temperature for 20 to 50 seconds , take it out and dry it with hot air; (5) Carry out chemical film forming process: put the product into a tank filled with phosphoric acid, barium hydroxide, sodium fluoride, zinc phosphate, sodium chlorate modification treatment solution, heat to 80~ 100°C, use ultrasonic waves for 10-30 minutes, then put them into the fourth distilled water washing tank for ultrasonic vibration cleaning, take out hot air and dry them; (6) immerse in sodium silicate aqueous solution at 50-65°C for sealing treatment for 25-35 Minutes, take it out and dry it with hot air immediately and unload it.

By adopting the method and formula of the present invention, the main characteristics of the chemical conversion coating obtained by taking the AZ91D magnesium alloy material as an example are as follows:

Appearance of chemical conversion coating layer: uniform white, delicate and smooth;

Thickness of chemical conversion film layer: 80～110um;

Adhesion of chemical conversion coating: 40.33kg/cm ² ; adhesion of magnesium alloy substrate is 17.5kg/cm ² , it can be seen that phosphate chemical conversion coating can significantly improve the adhesion of magnesium alloy;

Salt spray resistance of the chemical conversion coating: Corrosion occurs only after 33 hours. The magnesium alloy substrate, galvanized, and nickel-plated conversion coatings are fully corroded within 8 hours. It can be seen that the phosphate chemical conversion coating greatly improves the corrosion resistance of magnesium alloy parts. Anti-salt spray performance;

Moisture resistance of the chemical conversion coating: Corrosion occurs only after 60 hours, and comprehensive corrosion occurs after 7 hours for the magnesium alloy substrate. It can be seen that the coating layer greatly improves the moisture resistance of the magnesium alloy parts.

The advantages of the present invention are: 1. This process is a treatment solution based on phosphate, does not use chromic acid or cyanide, has no pollution, and meets the requirements of environmental protection and sustainable development in actual production; solves the old treatment process The chromium or heavy non-ferrous metal elements contained in the chromate treatment solution have different degrees of harm to the environment and the human body; 2. The solution of the whole process can be reused in the case of additional loss, which greatly saves resources and reduces Compared with the anodic oxidation process, the production cost can be reduced by about 60.5% under the same conditions; 3. The technology is simple and easy to form an automated production line without large investment in equipment, and the production capacity is short and can be Adapt to the needs of competition in today's society and improve the competitiveness of enterprises; 4. The chemical conversion coating formed by this process greatly improves the adhesion and corrosion resistance of magnesium alloy parts. Compared with other chemical coating methods without chromium (such as galvanizing , nickel plating, potassium permanganate and stannate, etc.), phosphate chemical film formation can improve the corrosion resistance of magnesium alloys; 5. Master the optimization of solution ratio, heating temperature and treatment time in the treatment process control, overcame the instability of the solution in the process of treatment, uneven conversion coating layer, easy to fall off and other problems.

Detailed ways

The present invention will be further described below in conjunction with embodiment: material is magnesium alloy hand electric drill head shell

First prepare the solution: place 80 grams of sodium hydroxide accurately in a beaker with an electronic analytical balance at room temperature, add a small amount of distilled water to the beaker and stir to fully dissolve the drug, then pour it into a 1000 ml measuring bottle, and add distilled water to the standard line to prepare 1 liter of degreasing solution. In addition, accurately weigh 80 grams of 50% hydrofluoric acid and 32 grams of ethylene glycol with an electronic analytical balance and place them in a beaker, add a small amount of distilled water to stir in the beaker to fully dissolve the medicine, and then pour it into a 1000 ml measuring bottle. Add distilled water to the mark to prepare 1 liter of pickling activation solution. Then use the same method to weigh 100-180 grams of sodium hydroxide to prepare 1 liter of alkali washing solution. Then weigh 60-100 grams of phosphoric acid, 40-60 grams of barium hydroxide, 1-4 grams of sodium fluoride, 2-6 grams of zinc phosphate, and 3-8 grams of sodium chlorate to prepare 1 liter of solution, and finally weigh Sodium silicate 18 grams to prepare 1 liter of solution.

Then process operation:

1. Load the shell of the electric drill head.

2. Put it in a degreasing tank at 80-98°C, and use ultrasonic waves for 20-30 minutes to make the oil, alkaline solution and surface active substances undergo saponification and emulsification reactions and dissolve in water to achieve the purpose of degreasing, which can be clearly seen The surface of the part becomes bright. The effect of the ultrasonic waves used in each process in this method is to vibrate the particles of the solution to make them fully chemically react with the metal surface; on the other hand, to make the particles in the solution vibrate with the surface of the metal parts, and the particles vibrate and impact the metal surface The impurity particles on the surface make it detached from the metal surface by shear force, so as to achieve the purpose of cleaning the surface of metal parts. Put it into the first water washing tank, and remove the alkaline solution and grease molecules remaining on the surface of the magnesium alloy by ultrasonic cleaning at room temperature for 20 to 50 seconds, take it out and dry it with hot air.

3. Immerse in the tank containing the previously prepared acidic activation solution, and use ultrasonic waves at room temperature for 1 to 2.5 minutes to micro-etch the metal surface to remove the oxides generated on the surface of the product. alkaline substances on the Enter the second water washing tank, and use ultrasonic cleaning at room temperature for 20 to 50 seconds to remove the acidic solution and oxide particles remaining on the surface of the magnesium alloy, take it out and dry it with hot air.

4. Immerse in an alkali washing tank filled with sodium hydroxide, and use ultrasonic waves at room temperature for 25 to 30 minutes to neutralize the acidic substances remaining on the surface of the magnesium alloy product. Enter the third washing tank, and use hot air to dry for the same time.

5. Heat the previously prepared modification solution to 80-100°C, put the magnesium alloy parts in, and form a layer of dense protective chemical conversion film on the surface of the parts through ultrasonication for 10-30 minutes. After modification, immerse in the fourth water washing tank, remove the residual chemical reagents on the surface of the part by ultrasonic cleaning at room temperature for 20-50 seconds, and take out the hot air to dry.

6. Finally, immerse in 50-65°C sodium silicate aqueous solution for sealing treatment for 25-35 minutes, so that the formed phosphate conversion film is uniform and dense, take it out and immediately dry it with hot air and unload it.

Claims (4)

1, a kind of magnesium alloy phosphate surface modified treatment process is characterized in that operation steps is: (1) is at first with magnesium alloy polishing, material loading; (2) carry out pretreatment technology: product is immersed be equipped with in the degreasing tank of 5%～10% sodium hydroxide, be heated to 80～98 ℃ of temperature, after 20～30 minutes, enter in the first distilled water washing bath by the ultrasonic wave effect, at room temperature, take out and use hot blast drying with ultrasonic wave effect 20～50 seconds; (3) immersion fills in the pickling tank of hydrofluoric acid, ethylene glycol solution, at room temperature with ultrasonic wave effect 1～2.5 minute, enters after the pickling in the after-fractionating water washing bath, equally at room temperature with ultrasonic wave effect 20～50 seconds, takes out and uses hot blast drying; (4) immersion is equipped with in the alkaline bath of 20%～30% sodium hydroxide, at room temperature with ultrasonic wave effect 25～30 minutes, immerses then in the triply distilled water washing bath, and room temperature ultrasonic cleaned 20～50 seconds, takes out and uses hot blast drying; (5) carry out chemical membrane technology: product is put into the groove that fills the modification treatment soln, the concentration of modification treatment solution is phosphoric acid 60～100 grams in 1 liter of solution, hydrated barta 40～60 grams, Sodium Fluoride 1～4 gram, zinc phosphate 2～6 grams, sodium chlorate 3～8 grams, be heated to 80～100 ℃, with ultrasonic wave effect 10～30 minutes, put into the 4th distilled water washing bath cleaned by ultrasonic vibration, take out hot blast drying; (6) immerse in the sodium silicate aqueous solution of 50～65 ℃ of temperature and carried out sealing treatment 25～35 minutes, water glass solubility is that 1 liter of solution contains 18 gram water glass, takes out at once with hot blast drying and blanking.

2, magnesium alloy phosphate surface modified treatment process according to claim 1 is characterized in that sodium hydroxide 80 grams in 1 liter of skim soln.

3, magnesium alloy phosphate surface modified treatment process according to claim 1 is characterized in that the hydrofluoric acid in the pickling tank, the concentration of ethylene glycol solution are that 1 liter of solution contains 50% hydrofluoric acid 80 grams, ethylene glycol 32 grams.

4, magnesium alloy phosphate surface modified treatment process according to claim 1 is characterized in that sodium hydroxide 100～180 is restrained the soda-wash solution that is mixed with 1 liter.