Method for preparing manganese phosphate conversion coating

Abstract

The invention relates to a method for preparing a manganese phosphate conversion film. According to the method disclosed by the invention, the nanoscale molybdenum disulfide particles are introduced into the surface conditioning agent, and then the manganese phosphate conversion film is further formed, so that the friction coefficient is remarkably reduced, and the lubricating property of the manganese phosphate conversion film is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a method for preparing a manganese phosphate conversion film on the surface of a metal substrate. Background Art

[0002] Friction and wear are the most common and largest failure modes in machines. Relevant studies have shown that mechanical failures caused by friction and wear account for more than 80% of the total mechanical losses. The mainstream method to solve friction and wear is to introduce lubricating substances on the surface of objects in relative motion. These substances can be divided into gas lubricants, greases and solid lubricants according to their physical states. In actual work, gear sets often use a combination of grease and solid lubricants to achieve the best working condition.

[0003] At present, solid lubricants have a layered structure in most cases, such as graphite, molybdenum disulfide and talc, and also use substances such as tetraboron nitride. In recent years, research on solid lubricants as lubricant additives has been reported, because their special physical and chemical properties have a significant effect on lubricant. However, these solid lubricants are prone to problems such as debris, vibration and noise.

[0004] Phosphate coating treatment is a common surface lubrication treatment method. By applying a phosphate conversion film on the surface of the gear, the gear surface can be made soft, so that it has good lubrication performance and can effectively prevent bonding and damage to the surface of the gear pair. However, the lubrication effect of the phosphate conversion film of the prior art is still relatively limited, so it is usually necessary to further apply an additional solid lubricant layer. However, due to the need to form a dual lubrication system of a phosphate conversion film and a solid lubricant layer, the process is more complicated and the cost is significantly increased; in addition, the presence of a solid lubricant layer will lead to disadvantages in vibration and noise. Therefore, a phosphate conversion film with significantly improved lubrication performance and a preparation method thereof are still desired in the art. Summary of the invention

[0005] The present invention aims to provide a method for preparing a manganese phosphate conversion film with high lubricity, which can reduce friction and wear by improving the lubricity of the conversion film on the surface of the device, thereby increasing the service life of the mechanical equipment.

[0006] The technical solution adopted by the present invention is: by optimizing the formula of the phosphating treatment agent, nano-scale molybdenum disulfide particles are introduced on the surface of the substrate. These nano-scale molybdenum disulfide can serve as a nucleation substrate for the growth of manganese phosphate, so that manganese phosphate can rapidly nucleate and grow in a non-uniform nucleation manner. In addition, molybdenum disulfide itself has good lubrication properties, and can refine the grain size of manganese phosphate crystals while improving the lubrication properties of the film layer itself, thereby further improving the lubrication properties of the manganese phosphate conversion film.

[0007] The present invention provides a method for preparing a manganese phosphate conversion film, the method comprising the following steps:

[0008] (1) Provide metal parts and use a degreasing agent to clean the surface of the metal parts to remove metal chips, oil stains and other impurities on the surface of the metal parts;

[0009] (2) washing the metal parts after the treatment in step (1);

[0010] (3) drying the metal parts after being treated in step (2);

[0011] (4) preparing a surface conditioning liquid, adding nano molybdenum disulfide (MoS2), a surfactant and a surface conditioning agent to water and mixing them thoroughly to obtain a surface conditioning liquid in the form of a suspension;

[0012] (5) surface conditioning treatment, using the surface conditioning liquid obtained in step (4) to perform surface conditioning treatment on the metal parts;

[0013] (6) using a manganese-based phosphating treatment solution to perform a phosphating conversion treatment on the metal parts treated in step (5), thereby forming a manganese phosphate conversion film on the surface of the metal parts;

[0014] (7) The parts after the phosphating conversion treatment in step (6) are thoroughly washed in water.

[0015] (8) placing the metal parts treated in step (7) at room temperature to dry so that the manganese phosphate conversion film is fully stable;

[0016] In a preferred embodiment, the metal parts in the above step (1) are metal parts used in the automotive field, more preferably steel parts or aluminum alloy parts.

[0017] In a preferred embodiment, the degreasing agent used in the above step (1) is a commercially available acidic degreasing agent or alkaline degreasing agent. The acidic degreasing agent can be an aqueous solution containing an inorganic acid and / or an organic acid, wherein an oxidant is optionally added; the inorganic acid is preferably sulfuric acid, nitric acid, hydrochloric acid or a mixture thereof; the organic acid is preferably acetic acid, propionic acid, citric acid or a mixture thereof. The alkaline degreasing agent is an aqueous solution containing an alkaline substance, and optionally contains other additives; the alkaline substance is preferably selected from sodium hydroxide, sodium carbonate, sodium phosphate, sodium pyrophosphate and sodium tripolyphosphate.

[0018] In a preferred embodiment, the water washing temperature in the above step (2) is 5 to 50° C., and the water washing time is 0.5 to 20 minutes.

[0019] In a preferred embodiment, the drying process in the above step (3) is carried out at a temperature of 5 to 50°C and a drying time of 2 to 30 minutes. Preferably, the drying process is carried out in an oven at a temperature of 30 to 50°C.

[0020] In a preferred embodiment, the surface conditioner used in the above step (4) is a commercially available surface conditioner for manganese-based phosphating treatment, preferably a titanate surface conditioner, such as zinc titanate surface conditioner, ammonium titanate surface conditioner and colloidal sodium titanium phosphate.

[0021] In a preferred embodiment, the surfactant described in step (4) above is selected from polyethylene glycol, sodium pyrophosphate, polyethylene or a combination thereof, and these surfactants help to evenly disperse the nano-MoS2 particles in the surface conditioning liquid.

[0022] In a preferred embodiment, the particle size of the nano-molybdenum disulfide in the above step (4) is 1 nm to 100 nm.

[0023] In a preferred embodiment, the manganese phosphating solution in the above step (6) comprises: 100 to 500 g / L of Malvern salt (Mn(H2PO4)2·2H2O), 10 to 50 g / L of manganese nitrate, 15 to 40 ml / L of phosphoric acid, 0.5 to 5 g / L of sodium nitrite and the remainder of water.

[0024] The present invention also relates to a metal part, on the surface of which there is a manganese phosphate conversion film prepared by the method.

[0025] The principle of the present invention is: using nano molybdenum disulfide as an additive in the surface conditioning treatment will form nano deposits of molybdenum disulfide on the surface of the metal substrate; in the subsequent phosphating conversion treatment, these nano deposits will serve as the nucleation substrate for the heterogeneous nucleation of manganese phosphate crystals, thereby accelerating the rapid film formation of manganese phosphate and refining the manganese phosphate grains. Such refined manganese phosphate grains have better lubrication properties. In addition, molybdenum disulfide itself has good lubrication properties and corrosion resistance, and after participating in the film-forming reaction, it will further increase the lubrication properties and corrosion resistance of the manganese phosphate conversion film. After the manganese phosphate conversion film is formed on the surface of the metal part by the method of the present invention, a surface friction coefficient of less than 0.35 can be achieved.

[0026] The process of the invention is simple and feasible, and can accelerate the film-forming reaction and shorten the reaction time while increasing the lubrication performance of the manganese phosphate conversion film. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the manganese phosphate conversion film prepared in Comparative Example 1.

[0028] Figure 2is a SEM picture of the manganese phosphate conversion film prepared in Example 1. DETAILED DESCRIPTION

[0029] The preparation method of the manganese phosphate conversion film of the present invention further optimizes the composition of the surface conditioning agent without changing the original conversion treatment process. By introducing nano molybdenum disulfide (MoS2) at the interface between the manganese phosphate conversion film layer and the metal substrate, the initial improvement of lubricity can be achieved. On the other hand, the introduction of nano molybdenum disulfide particles can refine the grain size of the manganese phosphate conversion film, and the lubricity of these refined manganese phosphate grains is more prominent, thereby achieving a manganese phosphate conversion film with significantly improved lubricity.

[0030] The technical solution of the present invention is illustrated below by means of specific embodiments.

[0031] The friction coefficient in the embodiment of the present invention is measured by a UMT friction and wear tester, and the load used in the measurement is 100g and the rotation speed is 100r / min. Specific related operations are performed in accordance with the requirements of ISO 8295:1995 (JIS K 7125:1999).

[0032] The metal parts used in the embodiments of the present invention are made of 35# steel.

[0033] Comparative Example 1

[0034] (1) A metal part is provided, and an alkaline degreasing agent (which is an aqueous solution containing the following components: Na4P2O7 6 g / L, Na2CO3 4 g / L and NaF 4 g / L) is used to clean the surface of the metal part to remove metal chips, oil stains and other impurities on the surface of the part.

[0035] (2) The metal parts treated in step (1) are washed with water at a temperature of 25° C. for 2 min.

[0036] (3) Drying the metal parts treated in step (2) at a temperature of 20° C. for 10 min.

[0037] (4) Prepare a surface conditioning solution by adding 0.5 g of a surfactant (sodium hexametaphosphate) and 2 g of zinc titanate (surface conditioning agent) into 1 L of deionized water to obtain a suspension. Place the above-prepared suspension in an ultrasonic cleaner and perform ultrasonic treatment for 120 min to uniformly disperse the components in the prepared solution.

[0038] (5) Surface conditioning treatment: using the surface conditioning liquid prepared in step (4) to perform surface conditioning treatment on the metal parts.

[0039] (6) Phosphate conversion treatment: a manganese-based phosphating treatment solution is used to perform phosphating film treatment on metal parts. The manganese-based phosphating treatment solution contains 100 g / L of Marfu salt (Mn(H2PO4)2·2H2O), 20 g / L of manganese nitrate, 20 ml / L of phosphoric acid, 1.5 g / L of sodium nitrite and the balance of water. The phosphating solution treatment temperature is 50°C, and the phosphating treatment time is 4 minutes. After the metal parts are left to stand in the conversion solution for 30 seconds, the parts are slowly moved to ensure that the manganese phosphate crystals can grow evenly.

[0040] (7) Cleaning: the metal parts after the phosphating treatment in step (6) are thoroughly cleaned in water.

[0041] (8) The metal parts treated in step (7) are placed at room temperature for 5 hours to allow the manganese phosphate conversion film to be fully stabilized.

[0042] (9) The metal parts treated in step (7) are placed in packaging to prevent collision and damage to the manganese phosphate conversion film.

[0043] According to the requirements of ISO 8295:1995 (JIS K 7125:1999), the friction coefficient of the metal part surface with manganese phosphate conversion film was tested, and the friction coefficient was 0.44.

[0044] (1) A metal part is provided, and an alkaline degreasing agent (which is an aqueous solution containing the following components: Na4P2O7 6 g / L, Na2CO3 4 g / L and NaF 4 g / L) is used to clean the surface of the metal part to remove metal chips, oil stains and other impurities on the surface of the part.

[0045] (2) The metal parts treated in step (1) are washed with water at a temperature of 25° C. for 2 min.

[0046] (3) Drying the metal parts treated in step (2) at a temperature of 20° C. for 10 min.

[0047] (4) Prepare a surface conditioning solution, add 0.8 g of nano molybdenum disulfide MoS2, 0.5 g of surfactant (sodium hexametaphosphate) and 2 g of zinc titanate (surface conditioning agent) into 1 L of deionized water to obtain a suspension. Place the above-prepared suspension in an ultrasonic cleaner and perform ultrasonic treatment for 120 min to uniformly disperse the components in the prepared solution.

[0048] (5) Surface conditioning treatment: using the surface conditioning liquid prepared in step (4) to perform surface conditioning treatment on the metal parts.

[0049] (6) Phosphate conversion treatment, using manganese phosphating treatment liquid to perform phosphating film treatment on metal parts. The manganese phosphating treatment liquid contains 100g / L of Marfu salt (Mn(H2PO4)2·2H2O), 20g / L manganese nitrate, 20ml / L phosphoric acid, 1.5g / L sodium nitrite and the balance of water. The phosphating liquid treatment temperature is 50°C, and the phosphating treatment time is 4min. It should be noted that when placing metal parts into the phosphating conversion liquid, the operation needs to be slow to avoid washing away small MoS2 particles adhering to the surface. After the metal parts are left to stand in the conversion liquid for 15-60s, the parts are slowly moved to ensure that the manganese phosphate crystals can grow evenly.

[0050] (7) Cleaning: the metal parts after the phosphating treatment in step (6) are thoroughly cleaned in water.

[0051] (8) The metal parts treated in step (7) are placed at room temperature for 5 hours to allow the conversion film to be fully stabilized.

[0052] (9) Place the metal parts treated in step (8) in packaging to prevent collision from damaging the conversion film.

[0053] The friction coefficient of the metal part surface with the manganese phosphate conversion film was tested according to the requirements of ISO 8295:1995 (JIS K 7125:1999), and the friction coefficient was measured to be 0.25.

[0054] Example 2

[0055] (1) A metal part is provided, and an acidic degreasing agent (which is an aqueous solution containing the following components: 35 g / L sulfuric acid, 6 g / L ammonium bifluoride, 4 g / L citric acid and dipropylene glycol) is used to clean the surface of the metal part to remove impurities such as metal chips and oil stains on the surface of the part.

[0056] (2) The metal parts treated in step (1) are washed with water at a temperature of 25° C. for 2 min.

[0057] (3) Drying the metal parts treated in step (2) at a temperature of 20° C. for 10 min.

[0058] (4) Prepare a surface conditioning solution, add 5 g of nano molybdenum disulfide MoS2, 0.5 g of surfactant (sodium hexametaphosphate) and 1.5 g of surface conditioning agent (colloidal sodium titanium phosphate) into 1 L of deionized water to obtain a suspension. Place the above-prepared suspension in an ultrasonic cleaner and perform ultrasonic treatment for 120 min to uniformly disperse the components in the prepared solution.

[0059] (5) Surface conditioning treatment: using the surface conditioning liquid prepared in step (4) to perform surface conditioning treatment on the metal parts.

[0060] (6) Phosphate conversion treatment, using manganese phosphating treatment liquid to perform phosphating film treatment on metal parts. The manganese phosphating treatment liquid contains 100g / L of Marfu salt (Mn(H2PO4)2·2H2O), 20g / L manganese nitrate, 20ml / L phosphoric acid, 1.5g / L sodium nitrite and the balance of water. The phosphating liquid treatment temperature is 50°C, and the phosphating treatment time is 4min. It should be noted that when placing metal parts into the phosphating conversion liquid, the operation needs to be slow to avoid washing away small MoS2 particles adhering to the surface. After the metal parts are left to stand in the conversion liquid for 15-60s, the parts are slowly moved to ensure that the manganese phosphate crystals can grow evenly.

[0061] (7) Cleaning: the metal parts after the phosphating treatment in step (6) are thoroughly cleaned in water.

[0062] (8) The metal parts treated in step (7) are placed at room temperature for 5 hours to allow the conversion film to be fully stabilized.

[0063] (9) Place the metal parts treated in step (8) in packaging to prevent collision from damaging the conversion film.

[0064] The friction coefficient of the metal part surface with the manganese phosphate conversion film was tested according to the requirements of ISO 8295:1995 (JIS K 7125:1999), and the friction coefficient was measured to be 0.33.

[0065] By comparing Examples 1-2 and Comparative Example 1, it can be seen that the method of the present invention forms molybdenum disulfide nano-deposits on the surface of the metal substrate by introducing nano-scale molybdenum disulfide (MoS2) particles in the surface conditioning treatment, and then forms a manganese phosphate conversion film. The manganese phosphate conversion film prepared in this way has a significantly reduced friction coefficient and further improved lubrication performance.

[0066] Figure 1 and Figure 2 The SEM micrographs of the manganese phosphate conversion films obtained in Comparative Example 1 and Example 1 are shown respectively. Figure 1 and Figure 2 It can be clearly seen that by introducing nano-sized molybdenum disulfide (MoS2) particles in the surface conditioning treatment, the grain size of the resulting manganese phosphate conversion film is significantly refined. This significant grain refinement helps to improve the lubrication performance of the manganese phosphate conversion film.

Claims

1. A method for preparing a manganese phosphate conversion film, the method comprising the following steps: (1) Providing metal parts, and using a degreasing agent to clean the surface of the metal parts to remove metal chips, oil stains and other impurities on the surface of the metal parts; (2) washing the metal parts after the treatment in step (1); (3) drying the metal parts after being treated in step (2); (4) adding nano molybdenum disulfide (MoS2), a surfactant and a surface conditioning agent to water and mixing them thoroughly to obtain a surface conditioning agent in the form of a suspension; (5) using the surface conditioning liquid obtained in step (4) to perform surface conditioning treatment on the metal parts; (6) using a manganese-based phosphating treatment solution to perform a phosphating conversion treatment on the metal parts treated in step (5), thereby forming a manganese phosphate conversion film on the surface of the metal parts; (7) washing the parts after the phosphating conversion treatment in step (6) in water; and (8) The metal parts treated in step (7) are placed at room temperature to dry so that the phosphate conversion film is fully stabilized.

2. The method according to claim 1, wherein the degreasing agent used in step (1) is an acidic degreasing agent or an alkaline degreasing agent.

3. The method according to claim 1, wherein the water washing temperature in step (2) is 5 to 50°C and the water washing time is 0.5 to 20 minutes.

4. The method according to claim 1, wherein the drying treatment in step (3) is carried out at a temperature of 5 to 50°C and a drying time of 2 to 30 minutes.

5. The method according to claim 1, wherein the surface conditioner used in step (4) is a titanate surface conditioner, such as zinc titanate surface conditioner, ammonium titanate surface conditioner, etc.

6. The method according to claim 1, wherein the surface conditioning agent used in step (4) is colloidal sodium titanium phosphate.

7. The method according to claim 1, wherein the surfactant used in step (4) is selected from polyethylene glycol, sodium pyrophosphate, polyethylene or a combination thereof.

8. The method according to claim 1, wherein the particle size of the nano-molybdenum disulfide described in step (4) is 1 nm to 100 nm.

9. The method according to claim 1, wherein the manganese phosphating solution in step (6) comprises: 100 to 500 g / L of Malvern salt (Mn(H2PO4)2·2H2O), 10 to 50 g / L of manganese nitrate, 15 to 40 ml / L of phosphoric acid, 0.5 to 5 g / L of sodium nitrite and the remainder of water.

10. A metal part, characterized in that The metal part has a manganese phosphate conversion film on its surface which is prepared by the method according to any one of claims 1 to 9.

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