A magnesium alloy surface anticorrosion treatment method and metal anticorrosion coating

Abstract

The present invention discloses a method for treating the surface of a magnesium alloy and a metal anticorrosion coating, wherein the method comprises the following steps: performing, on the surface of a substrate, (1) degreasing treatment, (2) pickling treatment, (3) surface conditioning treatment, (4) zinc layer conversion treatment, (5) low nickel treatment, (6) electroplating copper treatment, and (7) nickel surface modification treatment. The present invention aims to obtain a metal anticorrosion coating having high bonding strength and high corrosion resistance on the surface of the substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy surface treatment, and in particular to a magnesium alloy surface anti-corrosion treatment method and a metal anti-corrosion coating. Background Art

[0002] Currently, magnesium alloys are the lightest metal structural materials used in practical applications, enjoying increasing popularity in areas such as automotive, aerospace, and consumer electronics. However, their low electrode potential and susceptibility to corrosion severely restrict their application. Consequently, corrosion prevention methods for magnesium alloys primarily include electroplating and electroless plating, micro-arc oxidation, chemical conversion coatings, organic coatings, physical / chemical vapor deposition, and laser surface alloying.

[0003] Among these, electroplating / electroless plating, and chemical conversion coating are the primary surface treatment methods used in industry. Chemical conversion coatings for magnesium alloys primarily utilize chemical methods to form an oxide film or passivation film on the surface of the magnesium alloy, which can improve corrosion resistance to a certain extent. However, these methods place high demands on the magnesium alloy substrate and can easily lead to uneven film formation or localized excessive corrosion on the substrate surface. This can cause localized corrosion of magnesium alloy components in the operating environment, even in air, severely impacting their service life. Furthermore, different chemical conversion processes are required for different magnesium alloy grades, making them incompatible. Furthermore, electroplating / electroless plating of magnesium alloys primarily involves nickel plating, which is relatively complex and difficult compared to nickel plating on other substrates, such as steel, aluminum alloys, and copper alloys. This is primarily due to the highly active nature of magnesium alloys, making them susceptible to corrosion from various solutions and prone to intense substitution with metal ions in the solution. Furthermore, magnesium alloys rapidly form an oxide film in air, all of which significantly impact the quality of the nickel layer. During the nickel plating process, magnesium's chemical activity and affinity for oxygen instantly form an oxide film on its surface. This oxide film prevents the bonding between the metals during nickel plating, resulting in poor coating adhesion and prone to undesirable phenomena such as bubbles and peeling. Localized nickel layer damage will seriously affect the overall protective effect of the workpiece and fail to achieve surface strengthening. Therefore, a surface treatment method for magnesium alloys with good bonding and corrosion resistance is urgently needed. Summary of the Invention

[0004] The main purpose of the present invention is to provide a magnesium alloy surface anti-corrosion treatment method and a metal anti-corrosion coating, aiming to solve the technical problem that the corrosion protection performance of the existing magnesium alloy with an anti-corrosion coating is not strong.

[0005] To achieve the above object, the present invention provides a method for anti-corrosion treatment of the surface of a magnesium alloy, the method comprising the following steps:

[0006] (1) Degreasing treatment: Soak the substrate in a degreasing solution at 60-80°C for 1-2 minutes to remove oil stains on the substrate surface. 1L of the degreasing solution contains 20-40g of corrosion inhibitor.

[0007] (2) Pickling treatment: Immerse the substrate after the degreasing treatment in step (1) in a pickling solution for 20 to 40 seconds, wherein 1L of the pickling solution includes 10 to 30mL of nitric acid with a mass concentration of 68% and the rest is water;

[0008] (3) Surface conditioning: Immerse the substrate after the acid treatment in step (2) in a surface conditioning solution for 1 to 3 minutes, wherein 1 L of the surface conditioning solution includes 200 to 400 mL of 68% nitric acid, 100 to 200 mL of hydrofluoric acid, and the remainder is water;

[0009] (4) zinc layer conversion treatment: immerse the substrate after the surface conditioning treatment in step (3) in a conversion solution at 50-60° C. for 1-2 minutes to obtain a substrate with a dense zinc layer on the surface, wherein 1 L of the conversion solution includes 10-20 g of zinc oxide, 30-50 mL of HEDP, 20-35 g of sodium hydroxide, 30-50 g of a cyanide additive, and the remainder is water;

[0010] (5) Low nickel treatment: immersing the substrate having a dense zinc layer on the surface in step (4) in a nickel plating solution at 85 to 92° C. for 45 to 60 minutes to obtain a substrate having a nickel layer uniformly distributed on the surface of the zinc layer;

[0011] (6) Electroplating copper treatment: Immerse the substrate after nickel plating in step (5) into an electroplating copper solution for 45 to 60 minutes at a current density of 1 to 3 A / dm 2 , obtaining a substrate with a copper layer uniformly distributed on the surface of the nickel layer;

[0012] (7) Nickel surface modification treatment: Immerse the substrate after the copper electroplating treatment in step (6) in a chemical nickel solution at 85 to 92° C. for 30 to 80 minutes.

[0013] Optionally, the method further comprises: (8) passivation treatment, immersing the substrate after the nickel surface modification treatment in step (7) into a passivation solution for 5 to 10 minutes, wherein 1L of the passivation solution comprises 10 to 75g of chromic anhydride and the rest is water.

[0014] Optionally, in step (1), 1L of the degreasing solution further comprises 20-35g of sodium phosphate, 5-15g of sodium hydroxide, 20-30g of sodium silicate, and the remainder is water.

[0015] Optionally, the corrosion inhibitor includes at least one of sodium fluoride and potassium fluoride.

[0016] Optionally, in step (4), the cyanide additive is sodium cyanide or potassium cyanide.

[0017] Optionally, in step (5), 1L of the nickel plating solution includes 20-35g of nickel sulfate, 20-45g of sodium hypophosphite, 20-35mL of lactic acid, 30-75g of potassium fluoride, 10-35g of potassium hydroxide, and the rest is water.

[0018] Optionally, in step (6), 1 L of the copper electroplating solution includes 20-35 g of cuprous cyanide, 20-30 g of potassium cyanide, and the rest is water.

[0019] Optionally, in step (7), 1L of the chemical nickel solution includes 20-35g of nickel sulfate, 20-35g of sodium hypophosphite, 20-30mL of lactic acid, 30-75g of potassium fluoride, 10-25g of potassium hydroxide, and 20-30g of glycine.

[0020] Optionally, the method further comprises: (9) baking treatment, baking the passivated substrate in an environment of 30 to 60° C. for 10 to 30 minutes.

[0021] In addition, the present invention also provides a metal anti-corrosion coating, which is prepared by using any of the above-mentioned magnesium alloy surface anti-corrosion treatment methods.

[0022] Beneficial effects of the present invention:

[0023] The present invention proposes a magnesium alloy surface anti-corrosion treatment method and a metal anti-corrosion coating, which comprises the following steps: (1) degreasing treatment → (2) pickling treatment → (3) surface conditioning treatment → (4) zinc layer conversion treatment → (5) low nickel treatment → (6) electroplating copper treatment → (7) nickel surface modification treatment on the surface of the substrate, wherein in (1) degreasing treatment, a fluoride film layer is generated on the surface of the substrate by adding a fluoride corrosion inhibitor to the solution, thereby having a certain corrosion inhibition effect on the internal substrate, thereby effectively reducing the corrosion of the degreasing solution on the substrate; in (2) pickling treatment, a fluoride film layer is generated by adding a fluoride corrosion inhibitor to the solution, thereby having a certain corrosion inhibition effect on the internal substrate, thereby effectively reducing the corrosion of the substrate by the degreasing solution; in (3) In the washing treatment, dilute nitric acid is used to soak the substrate surface to effectively remove the passivation film and intermetallic segregation compounds on the substrate surface, thereby obtaining a clean and rough substrate surface; in the surface conditioning treatment (3), a higher concentration of acid treatment is used to further remove the impurity elements on the surface of the magnesium alloy, leaving only magnesium elements on the substrate surface, thereby facilitating the subsequent formation of layered metal protective layers on the substrate surface. Therefore, the treatment methods of steps (1) to (3) effectively improve the surface state and cleanliness of the magnesium and magnesium alloy substrates, thereby ensuring the quality of the film layer after the magnesium alloy strengthening treatment.

[0024] And further through step (4) zinc layer conversion treatment and (5) low nickel treatment, the principle is that the magnesium alloy electrode potential is very low and very active. Direct nickel plating on the surface of the magnesium alloy substrate will cause corrosion of the substrate. Therefore, it is necessary to first deposit a zinc layer on the substrate surface and then perform the nickel plating step. Due to the principle mechanism of chemical nickel plating, the gas (H2, etc.) generated during the chemical nickel plating process will cause the chemical nickel plating layer to inevitably have pore defects, seriously affecting the corrosion resistance of the nickel plating layer. Then, the magnesium alloy nickel plating layer is obtained by combining steps (4) to (5), thereby overcoming the porous defects of the single-layer chemical nickel. Moreover, on the basis of the original nickel plating structure, the step (6) electroplating copper treatment and (7) nickel surface modification treatment are further combined to obtain a nickel-copper-nickel three-layer composite coating structure, which can greatly improve the corrosion resistance of the coating, and the final protective layers have a strong bonding force, which enhances the corrosion protection of the substrate; and through further passivation treatment, further protection of the metal protective layer is achieved, thereby improving the corrosion protection performance of the magnesium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic flow chart of an embodiment of a magnesium alloy surface anti-corrosion treatment process according to the present invention;

[0026] Figure 2 Shown is a microscopic image of the cross section of nickel-plated magnesium alloy.

[0027] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0028] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] like Figure 1 As shown, the present invention proposes a method for anti-corrosion treatment of magnesium alloy surface, and the specific steps are as follows:

[0030] Step (1) degreasing treatment: soak the substrate in a degreasing solution at 60-80°C for 1-2 minutes, wherein 1L of the degreasing solution includes 20-35g of sodium phosphate, 5-15g of sodium hydroxide, 20-30g of sodium silicate, 20-40g of a corrosion inhibitor, and the rest is water; specifically, the substrate in this embodiment is a magnesium alloy substrate, preferably a magnesium-aluminum alloy substrate, and the corrosion inhibitor includes at least one of sodium fluoride and potassium fluoride, and the addition of the corrosion inhibitor to the degreasing solution can form a fluoride film layer on the surface of the substrate, thereby having a certain corrosion inhibition effect on the internal substrate, thereby effectively reducing the corrosion of the degreasing solution on the substrate, and further significantly reducing the corrosion of the substrate by chloride ions in the subsequent solution. Preferably, 1L of the degreasing solution includes 30g of sodium phosphate; more preferably, 1L of the degreasing solution includes 10g of sodium hydroxide; more preferably, 1L of the degreasing solution includes 25g of sodium silicate; more preferably, 1L of the degreasing solution includes 30g of corrosion inhibitor; more preferably, the degreasing temperature in step (1) is 70°C; more preferably, the degreasing reaction time in step (1) is 1.5min.

[0031] Step (2) pickling treatment: Immerse the substrate after the degreasing treatment in step (1) in a pickling solution at room temperature for 20 to 40 seconds, wherein 1L of the pickling solution includes 10 to 30mL of nitric acid with a mass concentration of 68%, and the rest is water. Specifically, soaking the substrate surface with diluted nitric acid can effectively remove the passivation film and intermetallic segregation compounds on the substrate surface, thereby obtaining a clean and rough substrate surface. Among them, the main components of the passivation film and intermetallic segregation compounds are magnesium oxide, magnesium hydroxide and some intermetallic second phases (such as Mg 17 Al 12 Etc.), the specific reaction equation in this step is as follows:

[0032] MgO+2H + →Mg 2+ +H2O;

[0033] Mg(OH)2+2H + →Mg 2+ +2H2O;

[0034] Mg 17 Al 12 +70H + →17Mg 2+ +12Al 3+ +35H2↑

[0035] Preferably, 1 L of the pickling solution includes 20 mL of nitric acid with a mass concentration of 68%; more preferably, the substrate pickling time is 30 seconds.

[0036] Step (3) Surface conditioning: Immerse the substrate after the low-acid treatment in step (2) in a surface conditioning solution for 1 to 3 minutes, wherein 1L of the surface conditioning solution comprises 200 to 400mL of nitric acid with a mass concentration of 68%, 100 to 200mL of hydrofluoric acid, and the remainder is water. Specifically, after treatment in this step, only magnesium remains on the surface of the substrate, thereby completely removing impurity elements on the surface of the magnesium alloy. Preferably, 1L of the surface conditioning solution comprises 300mL of nitric acid with a mass concentration of 68%; more preferably, 1L of the surface conditioning solution comprises 150mL of hydrofluoric acid; and more preferably, the substrate is immersed in the surface conditioning solution for 2 minutes.

[0037] It can be further seen that the acid treatment in the above-mentioned step (2) is to remove the surface oxide film by pickling to obtain a clean surface; and the addition of hydrofluoric acid in step (3) can, on the one hand, passivate the surface of the substrate, and on the other hand, can also completely remove surface impurities to obtain a uniform surface.

[0038] Step (4) zinc layer conversion treatment: immersing the substrate after the surface conditioning treatment in step (3) in a conversion solution at 50-60° C. for 1-2 minutes to obtain a substrate with a dense zinc layer on the surface, wherein 1L of the conversion solution includes 10-20g of zinc oxide, 30-50mL of HEDP (hydroxyethylidene diphosphonic acid), 20-35g of sodium hydroxide, 30-50g of a cyanide additive, and the rest is water; specifically, this treatment step can deposit a zinc layer on the surface of the substrate as a subsequent nickel layer base layer, and the addition of the additive can reduce the potential difference between zinc and magnesium, which can effectively change and improve the effect of the surface difference of the magnesium alloy on chemical nickel plating, reduce the zinc deposition rate, increase the density of the zinc layer, and thus obtain a high-density zinc layer on the surface of the substrate. Preferably, 1L of the conversion solution includes 15g of zinc oxide; more preferably, 1L of the conversion solution includes 40mL of HEDP; more preferably, 1L of the conversion solution includes 30g of sodium hydroxide; more preferably, 1L of the conversion solution includes 40g of a cyanide additive, wherein the cyanide is sodium cyanide or potassium cyanide; more preferably, the substrate is immersed in the conversion solution for 1.5min; more preferably, the conversion temperature is 55°C.

[0039] Step (5) bottom nickel treatment: immersing the substrate with a dense zinc layer on the surface in step (4) into a bottom nickel solution at 85 to 92° C. for 45 to 60 minutes to obtain a substrate with a nickel layer uniformly distributed on the surface, wherein the nickel layer is distributed on the surface of the zinc layer; wherein 1L bottom nickel solution includes 20 to 35g nickel sulfate, 20 to 45g sodium hypophosphite, 20 to 35mL lactic acid, 30 to 75g potassium fluoride, 10 to 35g potassium hydroxide, and the rest is water; specifically, the following reaction occurs in this step:

[0040] 1 / 2Ni 2+ +H2PO2 -+H2O→1 / 2Ni+H2PO3 - +H + +1 / 2H2;

[0041] 3 / 2H2PO2 - +H + →P+1 / 2H2PO3 - +3 / 2H2O;

[0042] Preferably, 1L of bottom nickel solution includes 30g of nickel sulfate; more preferably, 1L of bottom nickel solution includes 35g of sodium hypophosphite; more preferably, 1L of bottom nickel solution includes 25mL of lactic acid; more preferably, 1L of bottom nickel solution includes 55g of potassium fluoride; more preferably, 1L of bottom nickel solution includes 25g of potassium hydroxide; more preferably, the temperature of the bottom nickel solution is 89°C; more preferably, the time of chemical bottom nickel treatment is 55min.

[0043] After the substrate is treated in the above steps (1) to (5), a magnesium alloy nickel plating layer with a certain thickness is formed on the surface of the substrate, thereby enhancing the corrosion protection inside the substrate.

[0044] Step (6) copper electroplating treatment: immerse the substrate after nickel plating in step (5) into a copper electroplating solution for electroplating for 45 to 60 minutes, wherein 1L of copper electroplating solution includes 20 to 35g of cuprous cyanide, 20 to 30g of potassium cyanide, and the rest is water, and the copper electroplating current density is 1 to 3A / dm 2 Preferably, 1L copper electroplating solution includes 25g of cuprous cyanide; more preferably, 1L copper electroplating solution includes 25g of potassium cyanide; more preferably, the copper electroplating current density is 2A / dm 2 ; The electroplating time is 55min.

[0045] Step (7) nickel surface modification treatment: immerse the substrate after the copper electroplating treatment in step (6) in a chemical nickel solution at 85-92°C for 30-80 minutes, wherein 1L of the chemical nickel solution includes 20-35g of nickel sulfate, 20-35g of sodium hypophosphite, 20-30mL of lactic acid, 30-75g of potassium fluoride, 10-25g of potassium hydroxide, and 20-30g of glycine. Preferably, 1L of the chemical nickel solution includes 30g of nickel sulfate; more preferably, 1L of the chemical nickel solution includes 30g of sodium hypophosphite; more preferably, 1L of the chemical nickel solution includes 25mL of lactic acid; more preferably, 1L of the chemical nickel solution includes 55g of potassium fluoride; more preferably, 1L of the chemical nickel solution includes 18g of potassium hydroxide; more preferably, 1L of the chemical nickel solution includes 25g of glycine; more preferably, the temperature of the chemical nickel solution is 89°C; more preferably, the chemical nickel surface modification treatment time is 60min.

[0046] By further treating the substrate in steps (6) and (7), a nickel-copper-nickel three-layer composite coating structure having a certain thickness is formed on its surface, and each metal layer has a strong bonding force, further enhancing the corrosion protection inside the substrate. The bottom nickel treatment in step (5) mainly generates a bottom nickel layer, which plays a role of base and also prepares for enhancing the adhesion of the copper layer. The nickel surface modification treatment in step (7) is used to achieve high hardness and high brightness of the enhanced coating, thereby enhancing the corrosion protection effect inside the substrate.

[0047] Furthermore, after step (7), the method further includes step (8) of passivation treatment, specifically, immersing the substrate after the nickel surface modification treatment in step (7) into a passivation solution at 60 to 80°C for 5 to 10 minutes, wherein 1L of passivation solution includes 10 to 75g of chromic anhydride and the rest is water. Specifically, the passivation treatment can effectively passivate the exposed areas of each metal layer formed on the surface of the substrate, thereby avoiding corrosion inside the substrate. Preferably, 1L of passivation solution includes 45g of chromic anhydride; more preferably, the temperature of the passivation solution is 70°C; more preferably, the passivation time is 8 minutes. Through further passivation treatment, further protection of the metal protective layer is achieved, thereby improving the corrosion protection performance of the magnesium alloy.

[0048] Furthermore, (9) baking treatment is performed, wherein the passivated substrate is baked in an environment of 30 to 60° C. for 10 to 30 minutes to obtain the target metal anti-corrosion coating.

[0049] Example 1, using AZ80 substrate as the substrate

[0050] (1) Degreasing treatment: The substrate was immersed in a degreasing solution at 70°C for 1.5 minutes to remove oil stains on the substrate surface. 1 L of the degreasing solution contained 30 g of sodium phosphate, 10 g of sodium hydroxide, 25 g of sodium silicate, 30 g of sodium fluoride, and the remaining components were ultrapure water. The degreasing temperature was 70°C and the degreasing time was 1.5 minutes.

[0051] (2) Pickling treatment: immerse the substrate after the degreasing treatment in step (1) in a pickling solution for 30 seconds, wherein 1L of the pickling solution includes 20mL of nitric acid with a mass concentration of 68%, and the pickling temperature is room temperature.

[0052] (3) Surface conditioning treatment: immerse the substrate after the acid treatment in step (2) in a surface conditioning solution for 2 minutes, wherein 1L of the surface conditioning solution includes 300mL of nitric acid with a mass concentration of 68%, 100mL of hydrofluoric acid, and the rest is water, and the surface conditioning temperature is room temperature.

[0053] (4) Zinc layer conversion treatment. The substrate after the surface conditioning treatment in step (3) was immersed in a conversion solution at 55°C for 1.5 minutes to obtain a substrate with a dense zinc layer on the surface. 1L of the conversion solution contained 15g of zinc oxide, 40mL of HEDP, 30g of sodium hydroxide, 40g of sodium cyanide, and the remainder was water.

[0054] (5) Nickel treatment. The substrate with a dense zinc layer on the surface in step (4) is immersed in a nickel plating solution at 89° C. for 55 minutes to obtain a substrate with a nickel layer uniformly distributed on the surface of the zinc layer, wherein 1 L of the nickel plating solution includes 30 g of nickel sulfate, 35 g of sodium hypophosphite, 30 mL of lactic acid, 55 g of potassium fluoride, 25 g of potassium hydroxide, and the rest is water.

[0055] (6) Electroplating copper treatment: immerse the substrate after nickel plating in step (5) into an electroplating copper solution and electroplate for 55 minutes at a current density of 2A / dm 2 , obtaining a substrate with a copper layer uniformly distributed on the surface of the nickel layer, wherein 1L of the copper electroplating solution includes 30g of cuprous cyanide, 25g of potassium cyanide, and the rest is water.

[0056] (7) Nickel surface modification treatment: The substrate after the copper electroplating treatment in step (6) was immersed in an 89°C chemical nickel solution for 60 minutes. 1L of the chemical nickel solution contained 30g of nickel sulfate, 30g of sodium hypophosphite, 25mL of lactic acid, 55g of potassium fluoride, 18g of potassium hydroxide, and 25g of glycine.

[0057] (8) Passivation treatment: immerse the substrate after the nickel surface modification treatment in step (7) in a passivation solution at 70° C. for 8 minutes, wherein 1 L of the passivation solution includes 45 g of chromic anhydride and the rest is water.

[0058] (9) Drying treatment: bake the substrate after passivation treatment in step (8) at 50°C for 30 minutes. The cross-sectional morphology of the nickel-plated magnesium alloy finally obtained is as follows: Figure 2 As shown, from Figure 2 As shown, a coating layer of more than 20 microns is formed on the surface of the magnesium alloy, which has an effective anti-corrosion effect on the interior of the magnesium alloy.

[0059] Example 2

[0060] The magnesium alloy surface pretreatment steps were the same as those in Example 1, with the only difference being that the amount of sodium fluoride added in step (1) was changed to 40 g. The coating properties are shown in Table 1.

[0061] Example 3

[0062] The magnesium alloy surface pretreatment steps are the same as those in Example 1, with the only difference being that sodium fluoride is replaced by potassium fluoride in step (1). The coating properties are shown in Table 1.

[0063] Example 4

[0064] The magnesium alloy surface pretreatment steps were the same as those in Example 1, with the only difference being that the amount of hydrofluoric acid added in step (3) was changed to 200 mL. The coating properties are shown in Table 1.

[0065] Example 5

[0066] The magnesium alloy surface pretreatment steps are the same as those in Example 1, with the only difference being that potassium cyanide is used in place of sodium cyanide in step (4). The coating properties are shown in Table 1.

[0067] Example 6

[0068] The magnesium alloy surface pretreatment steps are the same as those in Example 1, with the only difference being that AZ42 is used as the substrate. The coating properties are shown in Table 1.

[0069] Example 7

[0070] The magnesium alloy surface pretreatment steps are the same as those in Example 1, with the only difference being that the substrate is changed to LA103. The coating properties are shown in Table 1.

[0071] Furthermore, the substrates with anti-corrosion layers prepared in the aforementioned Examples 1-7 were subjected to coating appearance, scratch tests, and corrosion tests on the anti-corrosion layers on the substrate surfaces, and the conclusions described in Table 1 were obtained:

[0072] Among them, (1) Evaluation of coating adhesion: The scratch method recommended by GB / T5270-2005 is used for evaluation. A steel knife with a sharp angle of 30° is used to scratch 5 rows of square grids with a length and width of 1 mm on the sample. The coating between the scratches is observed to see if it peels or falls off. The coating in the grid is pulled vertically with a strong tape to observe the peeling of the coating after sticking and pulling, and the strength of the adhesion is compared.

[0073] (2) Evaluation of corrosion resistance of coating: A neutral salt spray test was conducted according to the salt spray corrosion test standard of GJB150.11A-2009, with a test period of 96 hours. Then, the corrosion resistance grade of the coating was evaluated according to the corrosion grade standard recommended by GB5944-86. The specific method is: Cover the test area of the sample with a transparent plastic film or organic glass plate with 5mm×5mm squares, so that the test area of the sample is divided into several squares with a side length of 5mm. Count the total number of squares, assuming it is N. If the squares located at the edge of the sample exceed one-half, they are counted as one square, and if they are less than one-half, they are ignored. After the corrosion test, count the number of squares with substrate corrosion points and coating corrosion points respectively, and set it as n. According to the formula: corrosion rate (%) = 100*n / N, the corrosion rate is calculated, and the corrosion resistance of the coating is divided according to the coating corrosion rate. Among the evaluation levels, level 10 is the best and level 0 is the worst.

[0074] Table 1 - Nickel coating performance test results

[0075] Example No. Coating appearance Adhesion scratch test Salt spray test corrosion level Example 1 bright 〇 10 Example 2 bright 〇 9 Example 3 bright 〇 9 Example 4 bright 〇 9 Example 5 bright 〇 9 Example 6 bright 〇 10 Example 7 bright 〇 10

[0076] In the above-mentioned Examples 1-7, after the scratch test, the bonding strength was divided into three levels according to the peeling condition of the coating, from inferior to excellent: the coating peeled during the scratching process, the coating did not peel during the scratching process but peeled slightly after being pulled with tape, and the coating was good and did not peel either during the scratching process or after being pulled with tape (indicated by "0" in Table 1). It can be seen that the metal anti-corrosion coatings prepared in Examples 1, 6-7 basically meet the practical standard requirements in the coating appearance and scratch test; and when further passed the salt spray test, the metal anti-corrosion coatings of Examples 1, 6-7 still have a strong anti-corrosion effect; although the solution components or amounts in each step are replaced in Examples 2-5, after the salt spray test, the surface ratings are all 9 or above, which shows that the pretreatment steps of the present invention are stable, and the prepared metal anti-corrosion coatings have excellent bonding strength and corrosion resistance. Figure 2 The coating shown is more than 20 μm thick, which effectively prevents corrosion inside the magnesium alloy.

[0077] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or system comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or system. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or system comprising the element.

[0078] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0079] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for anti-corrosion treatment of magnesium alloy surface, characterized in that: The method comprises the following steps: (1) Degreasing treatment: Soak the substrate in a degreasing solution at 60-80°C for 1-2 minutes to remove oil stains on the substrate surface. 1L of the degreasing solution contains 20-40g of corrosion inhibitor. (2) Pickling treatment: Immerse the substrate after the degreasing treatment in step (1) in a pickling solution for 20 to 40 seconds, wherein 1L of the pickling solution includes 10 to 30mL of nitric acid with a mass concentration of 68% and the rest is water; (3) Surface conditioning: Immerse the substrate after the acid treatment in step (2) in a surface conditioning solution for 1 to 3 minutes, wherein 1 L of the surface conditioning solution includes 200 to 400 mL of 68% nitric acid, 100 to 200 mL of hydrofluoric acid, and the remainder is water; (4) zinc layer conversion treatment: immerse the substrate after the surface conditioning treatment in step (3) in a conversion solution at 50-60° C. for 1-2 minutes to obtain a substrate with a dense zinc layer on the surface, wherein 1 L of the conversion solution includes 10-20 g of zinc oxide, 30-50 mL of HEDP, 20-35 g of sodium hydroxide, 30-50 g of a cyanide additive, and the remainder is water; (5) Low nickel treatment: immersing the substrate having a dense zinc layer on the surface in step (4) in a nickel plating solution at 85 to 92° C. for 45 to 60 minutes to obtain a substrate having a nickel layer uniformly distributed on the surface of the zinc layer; (6) Electroplating copper treatment: Immerse the substrate after nickel plating in step (5) into an electroplating copper solution for 45 to 60 minutes at a current density of 1 to 3 A / dm 2 , obtaining a substrate with a copper layer uniformly distributed on the surface of the nickel layer; (7) Nickel surface modification treatment: Immerse the substrate after the copper electroplating treatment in step (6) in a chemical nickel solution at 85 to 92° C. for 30 to 80 minutes.

2. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: The method further comprises: (8) passivation treatment, wherein the substrate after the nickel surface modification treatment in step (7) is immersed in a passivation solution at 60 to 80° C. for 5 to 10 minutes, wherein 1 L of the passivation solution comprises 10 to 75 g of chromic anhydride and the rest is water.

3. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: In step (1), 1 L of the degreasing solution further includes 20-35 g of sodium phosphate, 5-15 g of sodium hydroxide, 20-30 g of sodium silicate, and the rest is water.

4. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: The corrosion inhibitor includes at least one of sodium fluoride and potassium fluoride.

5. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: In step (4), the cyanide additive is sodium cyanide or potassium cyanide.

6. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: In step (5), 1L of the nickel plating solution includes 20-35g of nickel sulfate, 20-45g of sodium hypophosphite, 20-35mL of lactic acid, 30-75g of potassium fluoride, 10-35g of potassium hydroxide, and the rest is water.

7. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: In step (6), 1L of the copper electroplating solution includes 20-35g of cuprous cyanide, 20-30g of potassium cyanide, and the rest is water.

8. The method for anti-corrosion treatment of magnesium alloy surface according to claim 1, characterized in that: In step (7), 1L of the chemical nickel solution includes 20-35g of nickel sulfate, 20-35g of sodium hypophosphite, 20-30mL of lactic acid, 30-75g of potassium fluoride, 10-25g of potassium hydroxide, and 20-30g of glycine.

9. The method for anti-corrosion treatment of magnesium alloy surface according to any one of claims 1 to 8, characterized in that: The method further comprises: (9) baking treatment, baking the passivated substrate in an environment of 30 to 60° C. for 10 to 30 minutes.

10. A metal anti-corrosion coating, characterized in that: The metal anti-corrosion coating is prepared by the magnesium alloy surface anti-corrosion treatment method according to any one of claims 1 to 9.

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