Al-Mn / Al composite coating suitable for magnesium alloy and preparation method of Al-Mn / Al composite coating

Abstract

The invention belongs to the technical field of magnesium alloy surface protection, and discloses an Al-Mn / Al composite coating suitable for a magnesium alloy and a preparation method of the Al-Mn / Al composite coating, the Al-Mn / Al composite coating comprises a magnesium alloy matrix, a transition Al-Mn coating and a metal Al coating, the magnesium alloy matrix is externally provided with the transition Al-Mn coating, and the transition Al-Mn coating is externally provided with the metal Al coating. The pretreatment of the magnesium alloy matrix comprises the steps of polishing, acid pickling, activating, zinc dipping, zinc removing, secondary zinc dipping and electroplating. The method comprises the following steps: firstly, obtaining a uniformly distributed zinc-dipped layer on the premise of optimizing a pretreatment process, and then electroplating the Al-Mn / Al composite coating on the zinc-dipped magnesium alloy by using the ionic liquid. And due to introduction of the compact and flat nanocrystalline aluminum-manganese transition layer, formation of interface defects is avoided, and interface bonding of the plating layer and the magnesium matrix is guaranteed. The magnesium alloy plated with the Al-Mn / Al composite coating can be further subjected to passivation or anodic oxidation treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy surface protection, and in particular relates to an Al-Mn / Al composite coating suitable for magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloy has low density, high specific strength, good electrical and thermal conductivity, and is an ideal structural material for lightweight design in aerospace, 3C electronics and other fields. However, magnesium alloy has poor corrosion resistance, and surface treatment technology is an important way to improve its corrosion resistance. At the same time, with the growing demand for artificial intelligence (AI) and the trend of lightweight and thin products, the use of magnesium alloy in the consumer electronics field (such as AIPC) will continue to increase, which requires higher thermal conductivity and decorative properties on the surface of magnesium products.

[0003] Among the current magnesium alloy surface treatment methods, chemical nickel plating and micro-arc oxidation processes are the most mature. However, chemical nickel plating has high porosity, insufficient corrosion resistance and a single appearance color. The conductivity and heat dissipation capacity of the micro-arc oxidation layer are poor, and the metallic texture of the appearance is poor. Metal Al and its alloy coating materials have excellent corrosion resistance, and their density and electrode potential are closer to magnesium alloys, making them ideal coating materials for magnesium alloys. The Al coating is further passivated or anodized, and the corrosion resistance is significantly improved again. At the same time, the anodized aluminum film also has corrosion resistance, wear resistance, thermal conductivity and a rich color appearance.

[0004] The reduction potential of metallic Al is more positive than that of hydrogen, and it cannot be prepared by electroplating from aqueous solution. Ionic liquids do not contain water, have a wide electrochemical window and high conductivity, and are a new ideal medium for electroplating metallic Al and its alloys. However, it is difficult to electroplate metal directly on the surface of magnesium alloys, because magnesium alloys have high chemical activity and uneven surface microstructures, which are prone to oxidation or corrosion. Therefore, pretreatment before electroplating metal on the surface of magnesium alloys is particularly important. The applicant's research found that the zinc-plated layer obtained by the traditional "degreasing-pickling-activation-zinc-plating" pretreatment is loose and uneven; and direct ionic liquid aluminum plating after zinc-plating will cause interface bonding problems such as bulging of the coating. Summary of the invention

[0005] The object of the present invention is to provide an Al-Mn / Al composite coating suitable for magnesium alloys and a preparation method thereof, so as to solve the above-mentioned technical problems.

[0006] In order to solve the above technical problems, the specific technical scheme of an Al-Mn / Al composite coating suitable for magnesium alloy and a preparation method thereof of the present invention is as follows: An Al-Mn / Al composite coating suitable for magnesium alloys comprises: a magnesium alloy substrate, a transition Al-Mn coating and a metal Al coating, wherein the magnesium alloy substrate has a transition Al-Mn coating outside, and the transition Al-Mn coating has a metal Al coating outside.

[0007] Furthermore, the magnesium alloy matrix includes AZ31B magnesium alloy, AZ91D magnesium alloy, AZ41 magnesium alloy, AM60 magnesium alloy, ZK61M magnesium alloy, ZM5 magnesium alloy or LZ91 magnesium-lithium alloy.

[0008] The invention also discloses a method for preparing an Al-Mn / Al composite coating suitable for magnesium alloys. The pretreatment steps of the magnesium alloy substrate include: polishing, pickling, activation, zinc immersion, zinc stripping, secondary zinc immersion and electroplating.

[0009] Furthermore, the pickling solution components of the pickling process include chromic acid, phosphoric acid, oxalic acid, hydrochloric acid, acetic acid, hydrofluoric acid, nitric acid, citric acid, and ammonium bifluoride, either alone or in combination; the concentration of the acid solution is 5 g / L ~ 200 g / L, the pickling time is 10s ~ 10 min, and the temperature is room temperature 20 ~ 25 ° C.

[0010] Furthermore, the activation solution components of the activation process include hydrofluoric acid, phosphoric acid, nitric acid, ammonium bifluoride, potassium fluoride, potassium pyrophosphate, sodium fluoride, sodium pyrophosphate, sodium carbonate or a combination thereof, the concentration of each component in the activation solution is 5 g / L~200 g / L, the activation treatment time is 1 min~5 min, and the temperature is room temperature 20~25°C.

[0011] Furthermore, the zinc immersion solution comprises ZnSO4.7H2O, K4P2O7, Na2CO3, and KF, the zinc immersion temperature is 40°C to 80°C, and the zinc immersion time is 1 min to 10 min.

[0012] Furthermore, there are two ways to strip zinc. One is to use activation solution to strip zinc at room temperature for 2 minutes; the other is to use one or more combinations of hydrofluoric acid, ammonium bifluoride and nitric acid to strip zinc at room temperature for 2 minutes, where the concentration of a single reagent is 5 g / L ~200 g / L.

[0013] Furthermore, the electroplating solution in the electroplating process of the transition Al-Mn coating is an Al-Mn electroplating solution, which is prepared from anhydrous manganese chloride and a room temperature ionic liquid, wherein the ionic liquid is prepared from anhydrous aluminum chloride and an imidazole ionic liquid, the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1, the concentration of anhydrous manganese chloride is 0.01 mol / L ~0.2 mol / L, the plating solution temperature is 20°C ~80°C, and the current density is 5 mA / cm 2 ~100 mA / cm 2 The electrodeposition time is 5 min~240 min.

[0014] Furthermore, the electroplating solution in the electroplating process of the metal Al plating layer is a room temperature ionic liquid, and the ionic liquid is prepared from anhydrous aluminum chloride and an imidazole ionic liquid, the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1, the plating solution temperature is 20°C to 80°C, the current density is 5 mA / cm2 to 100 mA / cm2, and the electrodeposition time is 5 min to 240 min.

[0015] Furthermore, sufficient water washing is performed for at least 10 seconds between each two processes.

[0016] The Al-Mn / Al composite coating suitable for magnesium alloys and the preparation method thereof of the present invention have the following advantages: The present invention proposes a new surface treatment process suitable for magnesium alloys, that is, firstly obtaining a uniformly distributed zinc-immersion layer under the premise of optimizing the pretreatment process, and then electroplating the Al-Mn / Al composite coating on the zinc-immersed magnesium alloy with ionic liquid. The introduction of a dense and flat nanocrystalline aluminum-manganese transition layer avoids the formation of interface defects and ensures the interface bonding between the coating and the magnesium substrate. The magnesium alloy coated with the Al-Mn / Al composite coating can be further passivated or anodized, which broadens the application prospects of magnesium alloys in high-requirement fields such as aerospace, 3C electronics, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of an Al-Mn / Al composite coating suitable for magnesium alloys of the present invention Figure 2 This is a surface SEM image (20,000 times) of the zinc-impregnated magnesium alloy in Example 1 of the present invention; Figure 3 This is a surface SEM image (20,000 times) of the zinc-magnesium alloy ionic liquid electroplated Al-Mn in Example 1 of the present invention; Figure 4 This is a surface SEM image (5000 times) of the Al-Mn / Al composite coating after zinc-magnesium alloy ionic liquid electroplating in Example 1 of the present invention; Figure 5a This is a cross-sectional SEM image (2,000 times) of the Al-Mn / Al composite coating after zinc-magnesium alloy ionic liquid electroplating and anodization in Example 1 of the present invention; Figure 5b This is a line scanning EDS spectrum of the Al-Mn / Al composite coating after zinc-magnesium alloy ionic liquid electroplating and anodization in Example 1 of the present invention; Markings in the figure: 1. Magnesium alloy substrate; 2. Transition Al-Mn coating; 3. Metal Al coating. DETAILED DESCRIPTION

[0018] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of an Al-Mn / Al composite coating suitable for magnesium alloys and a preparation method thereof in conjunction with the accompanying drawings.

[0019] like Figure 1 As shown, an Al-Mn / Al composite coating suitable for magnesium alloys of the present invention comprises: a magnesium alloy substrate 1, a transition Al-Mn coating 2 and a metal Al coating 3, wherein the magnesium alloy substrate 1 has a transition Al-Mn coating 2 outside, and the transition Al-Mn coating 2 has a metal Al coating 3 outside.

[0020] The magnesium alloy matrix 1 includes but is not limited to AZ31B magnesium alloy, AZ91D magnesium alloy, AZ41 magnesium alloy, AM60 magnesium alloy, ZK61M magnesium alloy, ZM5 magnesium alloy and LZ91 magnesium-lithium alloy.

[0021] The pretreatment steps of the magnesium alloy substrate include: polishing, pickling, activation, zinc immersion, zinc stripping, secondary zinc immersion and electroplating.

[0022] The components of the pickling solution include but are not limited to chromic acid, phosphoric acid, oxalic acid, hydrochloric acid, acetic acid, hydrofluoric acid, nitric acid, citric acid, and ammonium bifluoride, either alone or in combination; the concentration of the acid solution is 5 g / L ~ 200 g / L, the pickling time is 10s ~ 10 min, and the temperature is room temperature (20 ~ 25°C).

[0023] The components of the activation solution include, but are not limited to, hydrofluoric acid, phosphoric acid, nitric acid, ammonium bifluoride, potassium fluoride, potassium pyrophosphate, sodium fluoride, sodium pyrophosphate, sodium carbonate or a combination thereof. The concentration of the various components in the activation solution is 5 g / L to 200 g / L, the activation treatment time is 1 min to 5 min, and the temperature is room temperature (20 to 25°C).

[0024] The zinc immersion solution mainly includes ZnSO4.7H2O (30 g / L ~60 g / L), K4P2O7 (120 g / L ~160 g / L), Na2CO3 (5 g / L ~10 g / L), and KF (5 g / L ~10 g / L). The zinc immersion temperature is 40℃~80℃, and the zinc immersion time is 1 min~10 min.

[0025] There are two ways to remove zinc. One is to use activation solution to remove zinc at room temperature for 2 minutes. The other is to use one or more combinations of hydrofluoric acid, ammonium bifluoride and nitric acid to remove zinc at room temperature for 2 minutes. The concentration of a single reagent is 5 g / L ~200 g / L.

[0026] The Al-Mn electroplating solution in the electroplating process of the transition Al-Mn coating 2 is prepared from anhydrous manganese chloride and room temperature ionic liquid. The ionic liquid is prepared from anhydrous aluminum chloride and imidazole ionic liquid (including but not limited to 1-methylimidazolium chloride, 1-methylimidazolium tetrafluoroborate, 1-ethylimidazolium chloride, 1-butylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium chloride), the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1, and the concentration of anhydrous manganese chloride is 0.01 mol / L ~0.2 mol / L. The plating solution temperature is 20℃~80℃, and the current density is 5 mA / cm 2 ~100 mA / cm 2 The electrodeposition time is 5 min~240 min.

[0027] The Al plating solution in the electroplating process of the metal Al plating layer 3 is a room temperature ionic liquid. The ionic liquid is prepared from anhydrous aluminum chloride and imidazole ionic liquid (including but not limited to 1-methylimidazolium chloride, 1-methylimidazolium tetrafluoroborate, 1-ethylimidazolium chloride, 1-butylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium chloride), and the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1. The plating solution temperature is 20°C to 80°C, the current density is 5 mA / cm2 to 100 mA / cm2, and the electrodeposition time is 5 min to 240 min.

[0028] Among them, sufficient water washing for at least 10 seconds is carried out between each two processes. Example

[0029] AZ31B magnesium substrate, 3000 grit sandpaper polishing, citric acid (20 g / L) pickling at room temperature for 10s, ammonium bifluoride (100 g / L) and phosphoric acid (100 mL / L) activation at room temperature for 2 min, zinc immersion at 70℃ for 5min (zinc immersion solution consists of ZnSO4.7H2O (30g / L), K4P2O7 (130g / L), Na2CO3 (5g / L) and KF (6g / L)), dezincification in activation solution for 2min, secondary zinc immersion for 5min. Al-Mn electroplating solution is prepared from anhydrous manganese chloride (0.2 mol / L) and ionic liquid, and the ionic liquid is prepared from anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 1.5:1. The current density of Al-Mn electroplating is 15 mA / cm2, the plating solution temperature is 20℃, the electroplating time is 50 min, and gas stirring is used. The Al electroplating bath was prepared by anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 2:1, with a current density of 20 mA / cm2, a bath temperature of 20°C, an electroplating time of 100 min, and gas stirring. The magnesium alloy coated with the Al-Mn / Al composite coating was anodized in a sulfuric acid solution.

[0030] After the surface treatment in Example 1, the zinc-immersed magnesium alloy ionic liquid electroplated Al-Mn / Al composite coating and anodized can withstand at least 600 hours of neutral salt spray test without corrosion. Figure 2 ), the Al-Mn coating is smooth, dense and composed of nanocrystals ( Figure 3 ), the Al coating is composed of micron-crystals and presents a polyhedral morphology ( Figure 4 The interface between the Al-Mn / Al composite coating and the zinc-magnesium substrate is well bonded, and no interface defects such as gaps and holes are found ( Figure 5a , Figure 5b ), proving the feasibility of the pre-treatment scheme and the key role of the Al-Mn transition layer. Example

[0031] AZ31B magnesium substrate, 5000 grit sandpaper polishing, citric acid (10 g / L) pickling at room temperature for 30s, ammonium bifluoride (100 g / L) and phosphoric acid (100 mL / L) activation at room temperature for 3 min, zinc immersion at 60℃ for 5min (zinc immersion solution consists of ZnSO4.7H2O (30g / L), K4P2O7 (130g / L), Na2CO3 (5g / L) and KF (6g / L)), dezincification in activation solution for 2min, secondary zinc immersion for 5min. Al-Mn electroplating solution is prepared from anhydrous manganese chloride (0.2 mol / L) and ionic liquid, and the ionic liquid is prepared from anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 1.5:1. The current density of Al-Mn electroplating is 10 mA / cm2, the plating temperature is 40℃, the electroplating time is 100 min, and the gas is stirred. The Al electroplating bath was prepared by anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 2:1, with a current density of 15 mA / cm2, a bath temperature of 20°C, an electroplating time of 90 min, and gas stirring. The magnesium alloy coated with the Al-Mn / Al composite coating was anodized in a sulfuric acid solution. Example

[0032] AZ91D magnesium substrate, 1000 grit sandpaper polishing, citric acid (5 g / L) pickling at room temperature for 10s, ammonium bifluoride (120 g / L) and phosphoric acid (100 mL / L) activation at room temperature for 2 min, zinc immersion at 40℃ for 1min (zinc immersion solution consists of ZnSO4.7H2O (36g / L), K4P2O7 (140g / L), Na2CO3 (5g / L) and KF (5g / L)), dezincification in activation solution for 2min, secondary zinc immersion for 5min. Al-Mn electroplating solution is prepared from anhydrous manganese chloride (0.05 mol / L) and ionic liquid, and the ionic liquid is prepared from anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 2:1. The current density of Al-Mn electroplating is 5 mA / cm2, the plating temperature is 20℃, the electroplating time is 5 min, and the gas is stirred. The Al electroplating bath was prepared by anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 1:1, with a current density of 100 mA / cm2, a bath temperature of 60°C, an electroplating time of 5 min, and gas stirring. The magnesium alloy coated with the Al-Mn / Al composite coating was anodized in a sulfuric acid solution. Example

[0033] ZM5 magnesium substrate, 3000 grit sandpaper polishing, citric acid (200 g / L) pickling at room temperature for 10 min, ammonium bifluoride (5 g / L) and phosphoric acid (200 mL / L) activation at room temperature for 5 min, zinc immersion at 80℃ for 10 min (zinc immersion solution consists of ZnSO4.7H2O (40 g / L), K4P2O7 (130 g / L), Na2CO3 (6 g / L) and KF (6 g / L)), dezincification in activation solution for 2 min, secondary zinc immersion for 5 min. Al-Mn electroplating solution is prepared from anhydrous manganese chloride (0.075 mol / L) and ionic liquid, the ionic liquid is prepared from anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 1.5:1, the current density of Al-Mn electroplating is 100 mA / cm2, the plating temperature is 80℃, the electroplating time is 240 min, and gas stirring is used. The Al electroplating bath was prepared by anhydrous aluminum chloride and 1-ethyl-3-methylimidazole chloride in a molar ratio of 1:1, with a current density of 5 mA / cm2, a bath temperature of 20°C, an electroplating time of 240 min, and gas stirring. The magnesium alloy coated with the Al-Mn / Al composite coating was anodized in a sulfuric acid solution.

[0034] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. An Al-Mn / Al composite coating suitable for magnesium alloys, characterized in that: include: A magnesium alloy substrate (1), a transition Al-Mn coating (2) and a metal Al coating (3), wherein the magnesium alloy substrate 1 has a transition Al-Mn coating (2) on the outside, and the transition Al-Mn coating (2) has a metal Al coating (3) on the outside.

2. The Al-Mn / Al composite coating suitable for magnesium alloy according to claim 1, characterized in that: The magnesium alloy matrix (1) comprises AZ31B magnesium alloy, AZ91D magnesium alloy, AZ41 magnesium alloy, AM60 magnesium alloy, ZK61M magnesium alloy, ZM5 magnesium alloy or LZ91 magnesium-lithium alloy.

3. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 1, characterized in that: The pretreatment steps of the magnesium alloy substrate (1) include: polishing, pickling, activation, zinc immersion, zinc stripping, secondary zinc immersion, and electroplating.

4. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: The pickling solution components of the pickling process include chromic acid, phosphoric acid, oxalic acid, hydrochloric acid, acetic acid, hydrofluoric acid, nitric acid, citric acid, and ammonium bifluoride, either alone or in combination; the concentration of the acid solution is 5 g / L to 200 g / L, the pickling time is 10s to 10 min, and the temperature is room temperature 20 to 25°C.

5. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: The activation solution components of the activation process include hydrofluoric acid, phosphoric acid, nitric acid, ammonium bifluoride, potassium fluoride, potassium pyrophosphate, sodium fluoride, sodium pyrophosphate, sodium carbonate or a combination thereof, the concentration of each component in the activation solution is 5 g / L~200 g / L, the activation treatment time is 1 min~5 min, and the temperature is room temperature 20~25°C.

6. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: The zinc immersion solution comprises ZnSO4.7H2O, K4P2O7, Na2CO3 and KF, the zinc immersion temperature is 40°C to 80°C, and the zinc immersion time is 1 min to 10 min.

7. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: There are two ways to strip zinc. One is to use activation solution to strip zinc at room temperature for 2 minutes. The other is to use one or more combinations of hydrofluoric acid, ammonium bifluoride and nitric acid to strip zinc at room temperature for 2 minutes, where the concentration of a single reagent is 5 g / L ~200 g / L.

8. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: The electroplating solution in the electroplating process of the transition Al-Mn coating (2) is an Al-Mn electroplating solution, which is prepared from anhydrous manganese chloride and a room temperature ionic liquid, wherein the ionic liquid is prepared from anhydrous aluminum chloride and an imidazole ionic liquid, the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1, the concentration of anhydrous manganese chloride is 0.01 mol / L to 0.2 mol / L, the plating solution temperature is 20°C to 80°C, and the current density is 5 mA / cm 2 ~100 mA / cm 2 The electrodeposition time is 5 min~240 min.

9. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: The Al plating solution in the electroplating process of the metal Al plating layer (3) is a room temperature ionic liquid, which is prepared from anhydrous aluminum chloride and an imidazole ionic liquid, the molar ratio of aluminum chloride to imidazole ionic liquid is between 2:1 and 1:1, the plating solution temperature is 20°C to 80°C, the current density is 5 mA / cm2 to 100 mA / cm2, and the electrodeposition time is 5 min to 240 min.

10. The method for preparing an Al-Mn / Al composite coating suitable for magnesium alloy according to claim 3, characterized in that: Rinse thoroughly with water for at least 10 seconds between each process.

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