Method suitable for electroplating Zn and Al composite coating on magnesium alloy

Abstract

The invention belongs to the technical field of magnesium alloy surface treatment, and discloses a Zn and Al composite coating electroplating method suitable for a magnesium alloy, which comprises the following steps: step 1, zinc electro-deposition of the magnesium alloy; step 2, preparing electroplating aluminum ion liquid; 3, the magnesium alloy subjected to zinc electroplating is directly subjected to aluminum electroplating; step 4, cleaning; and 5, detecting the binding force. The technology of direct aluminum plating after magnesium alloy electrogalvanizing is adopted, the technology is simplified, the stability and controllability are high, the cost is low, the plating layer binding force is excellent, and bubbling, falling and even peeling are avoided after 200 DEG C-2h room temperature water quenching and a cross-grid test can be resisted. And meanwhile, successful deposition can be performed on the two magnesium alloys AZ31B and AZ91D, so that the process is less affected by a base material, and the process has a very good commercial application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface treatment of magnesium alloys, and particularly relates to a method for electroplating Zn and Al composite coatings suitable for magnesium alloys. Background Art

[0002] Magnesium alloys have the lowest density among structural metals and their alloy materials, about 1.74 g / cm3, which is 2 / 3 of aluminum and 1 / 4 of iron. In addition, magnesium alloys also have a series of advantages, such as: (1) low elastic modulus. (2) A structural metal that is easy to process. (3) Strong thermal and electrical conductivity. (4) Good electromagnetic shielding property, etc. However, magnesium is highly active, with a standard hydrogen electrode potential of -2.37 V and a large thermodynamic corrosion tendency, so it is extremely corrosion-resistant. The poor corrosion resistance of magnesium alloys severely restricts their applications. Therefore, without sacrificing the mechanical properties of magnesium alloys themselves, through surface engineering technology, the purpose of anti-corrosion can be achieved and it can have a certain degree of aesthetics.

[0003] The surface treatment of magnesium alloys mainly involves conversion and plating: Although chemical conversion has a strong bond with the substrate, the film layer is thin and soft, and is usually only used as a coating substrate. Although anodic oxidation and micro-arc oxidation have a good bond with the substrate, and have good insulation, decoration and wear resistance, the process is complex and unstable, the equipment investment is large, the efficiency is low, and the cost is high. Among the plating methods, the bonding force between the coating and the substrate is the main difficulty. So far, only zinc and nickel can deposit coatings with excellent bonding force on the surface of magnesium alloys. Considering the influence of galvanic corrosion between the coating and the substrate, zinc coatings are usually selected. There are two methods for depositing zinc coatings: zinc immersion and electroplating. Zinc immersion treatment is to obtain a thin zinc layer on the surface of magnesium alloys through a displacement reaction, while electroplating is to obtain a zinc layer with a required thickness on the surface of magnesium alloys through electro-deposition according to the electro-deposition time. The bonding force between the electro-deposited zinc coating and the substrate is jointly affected by the stability of the plating solution, the type of substrate material and process parameters. It is the biggest difficulty to obtain a coating with excellent bonding force and certain stability. In addition, on the premise of having a zinc coating with a certain bonding force, it is further difficult to obtain a zinc layer with a certain density and flatness.

[0004] Metallic aluminum (Al) has a low density, high ductility, and a certain luster. In particular, Al can form a uniform and dense passivation film on its surface in a natural environment, with a certain corrosion resistance, and the post-treatment of aluminized coatings, such as anodic oxidation process, can further improve corrosion resistance and wear resistance. There are many methods for preparing aluminum coatings, such as physical / chemical vapor deposition, hot dipping, inorganic molten salt electroplating, etc. However, the first two methods both have problems such as poor bonding force, low density, and high shape requirements. Inorganic molten salt electroplating has a high temperature, serious equipment corrosion, and a certain damage to the mechanical properties of magnesium alloy substrates at high temperatures.

[0005] The existing process of magnesium alloy zinc plating, aluminum-manganese plating and aluminum plating is complex, but the process is not highly controllable and is affected by the size and shape of the parts, and the bonding strength cannot be fully guaranteed. In the CN101781785 patent, pinholes will appear in the zinc plating layer during magnesium alloy electrodeposition due to material problems. At this time, secondary zinc plating is required, which has a complex process and unstable quality. Summary of the invention

[0006] The object of the present invention is to provide a method for electroplating Zn and Al composite coatings on magnesium alloys to solve the above technical problems.

[0007] In order to solve the above technical problems, the specific technical solution of a method for electroplating Zn and Al composite coatings on magnesium alloys of the present invention is as follows: A method for electroplating a Zn and Al composite coating on a magnesium alloy comprises the following steps: Step 1, electroplating zinc on the magnesium alloy; Step 2, preparing electroplating aluminum ion liquid; Step 3, the magnesium alloy after electroplating zinc is directly electroplated with aluminum; Step 4: Cleaning; Step 5: Binding strength test.

[0008] Furthermore, the step 1 comprises the following steps: Step 1.1, substrate preparation: use AZ31B or AZ91D magnesium alloy, sandpaper polished to 800# for later use; Step 1.2, electroplating zinc: pretreating the magnesium alloy substrate, and then electroplating zinc on it to construct an electroplated zinc layer on the surface of the magnesium alloy.

[0009] Furthermore, the step 2 comprises the following steps: Step 2.1, preparation of additive-free ionic liquid: Step 2.2: Add additives with brightening and smoothing effects.

[0010] Furthermore, the step 2.1 includes the following steps: Take anhydrous AlCl3 and EMIC as raw materials, and prepare the liquid in a glove box. The water and oxygen content in the glove box is ≤0.01ppm, so that the molar ratio of AlCl3 and EMIC is 1.5~2:1, and the temperature is controlled to be ≤60°C during liquid preparation.

[0011] Furthermore, the step 2.2 includes the following steps: Add additives to the ionic liquid prepared in step 2.1. The additives are 3-pyridinecarboxamide, 4-cyanopyridine, nicotinamide, and o-phenanthroline. The concentration is 0.01-2 g / L", the preparation temperature is room temperature, and the mixture is stirred until the complexation is complete.

[0012] Further, step 3 includes the following steps: For electroplating aluminum, a high-purity aluminum plate is used as the anode and a galvanized magnesium alloy is used as the cathode for electrodeposition under an inert atmosphere condition, ensuring that the water and oxygen content is ≤ 0.01 ppm. An additive with a bright and smooth effect of 0.01 - 2 g / L is added to the ionic liquid with a molar ratio of AlCl3 to EMIC of 1.5 - 2:1, and the electrodeposition current density is 5 - 20 mA / cm 2 , and the electrodeposition temperature is from room temperature to 60 °C.

[0013] Further, step 4 includes the following steps: Step 4, cleaning: After the aluminum coating obtained by electrodeposition is taken out from the glove box, it is immediately put into anhydrous ethanol for cleaning. The cleaning time is 1 - 2 min, the cleaning temperature is room temperature, and the number of cleaning times is 2 times. At the same time, it is cleaned with deionized water. The cleaning temperature is room temperature, the cleaning time is 1 - 2 min, and the number of cleaning times is 2 times.

[0014] Further, step 5 uses thermal shock and combines with the cross-cut test to test the bonding performance of the Zn, Al composite coating.

[0015] A method for electroplating Zn, Al composite coatings suitable for magnesium alloys of the present invention has the following advantages: The present invention adopts the technology of directly electroplating aluminum after electroplating zinc on magnesium alloys: the process is simplified, with high stability and controllability, low cost, and excellent coating adhesion, that is, it can withstand water quenching at room temperature after 200 °C for 2 h + cross-cut test without bubbling, peeling or even flaking. At the same time, it can be successfully deposited on two kinds of magnesium alloys, AZ31B and AZ91D, so it is less affected by the substrate and is a process with very promising commercial application prospects. Brief Description of the Drawings

[0016] Figure 1 is the surface microscopic morphology diagram of the Al coating on the magnesium alloy; Figure 2 is the SEM diagram of the Al coating on the AZ31B magnesium alloy after 200 °C thermal shock + cross-cut test; Figure 3 is the SEM diagram of the Al coating on the AZ91D magnesium alloy after 200 °C thermal shock + cross-cut test; Figure 4 is the cross-sectional SEM diagram of the magnesium alloy electroplated with Zn / Al composite coating after thermal shock + cross-cut test; Figure 5 is the appearance diagram of the electroplated aluminum layer on the 10 cm × 10 cm × 0.06 cm size AZ31B magnesium alloy. Detailed Description of the Embodiment

[0017] In order to better understand the purpose, structure and function of the present invention, the following further describes in detail a method for electroplating Zn, Al composite coatings suitable for magnesium alloys of the present invention with reference to the drawings.

[0018] A method for electroplating Zn and Al composite coatings suitable for magnesium alloys according to the present invention comprises the following steps: Step 1, electro-deposit zinc on the magnesium alloy; Step 1.1, substrate preparation: Use two kinds of magnesium alloys, AZ31B or AZ91D, and polish them with sandpaper to 800# for standby; Step 1.2, electro-deposit zinc: The AZ31B or AZ91D substrate is pretreated with the same process parameters and then electro-galvanized. An electro-galvanized layer is constructed on the surface of the magnesium alloy. The electro-deposition zinc process is an existing process and will not be described in detail here.

[0019] Step 2, configure electroplating aluminum ionic liquid; Step 2.1, preparation of additive-free ionic liquid: Take a certain amount of anhydrous AlCl3 and EMIC as raw materials, and carry out liquid preparation in a glove box (water and oxygen content ≤ 0.01 ppm) so that the molar ratio of AlCl3 to EMIC is 1.5 - 2:1. The temperature should be controlled ≤ 60 °C during liquid preparation.

[0020] Step 2.2, add additives with bright and smooth effects: Add additives to the ionic liquid prepared in Step 2.1. The additives are 3-pyridinecarboxamide, 4-cyanopyridine, nicotinamide, and o-phenanthroline, and the concentration is 0.01 - 2 g / L. The configuration temperature is room temperature, and stir well until completely complexed.

[0021] Step 3, directly carry out electroplating aluminum experiment on the electro-galvanized magnesium alloy: Electroplating aluminum process parameters: Electroplating aluminum is carried out under an inert atmosphere condition, that is, it is necessary to ensure that the water and oxygen content ≤ 0.01 ppm. An ionic liquid with a molar ratio of AlCl3 to EMIC of 1.5 - 2:1, add 0.01 - 2 g / L of additives with bright and smooth effects, the electro-deposition current density is 5 - 20 mA / cm 2 , the electro-deposition thickness (depending on the actual required thickness), and the electro-deposition temperature is room temperature - 60 °C. In the experiment, a high-purity aluminum plate is used as the anode and the electro-galvanized magnesium alloy is used as the cathode for electro-deposition experiments.

[0022] Step 4, cleaning: The electroplated aluminum coating obtained by electro-deposition needs to be taken out from the inert atmosphere. Its surface contains residual ionic liquid. After taking out of the glove box, it needs to be immediately put into absolute ethanol for cleaning. The cleaning time is 1 - 2 min, the cleaning temperature is room temperature, and the cleaning times are 2 times. At the same time, it is necessary to clean with deionized water. The cleaning temperature is room temperature, the cleaning time is 1 - 2 min, and the cleaning times are 2 times.

[0023] Step 5, adhesion detection; Adopt thermal shock and combine with cross-cut test to test the adhesion performance of the Zn and Al composite coatings.

[0024] Due to the fact that the ionic liquid of the present invention is in a liquid state at room temperature, electroplating experiments can be carried out at room temperature and slightly above room temperature. The plating solution is non-volatile and can be recycled, so its cost is low and it is more environmentally friendly.

[0025] Example 1: Step 1, Mechanical polishing: The substrate types are two types of magnesium alloys, AZ31B and AZ91D, and the substrate size is 2 cm × 3 cm × 0.06 cm. The substrate is polished successively with 600-mesh and 800-mesh sandpapers.

[0026] Step 2, Degreasing: Degreasing treatment is carried out by ultrasonic treatment with absolute ethanol at room temperature for 15 min.

[0027] Step 3, Electroplating zinc.

[0028] Step 4, Cleaning with deionized water: Cleaning is carried out with deionized water in two passes, and each is rinsed at room temperature for 15 s to remove the residual zinc solution.

[0029] Step 5, Cleaning with absolute ethanol: Rinsing with absolute ethanol at room temperature for 15 s and drying for standby.

[0030] Step 6, Electroplating aluminum coating: The molar ratio of AlCl3 to EMIC is 2:1, 0.1 g / L of an additive with a bright and smooth effect is added, and the current density is 10 mA / cm 2 , the electroplating time is 120 min, and the electroplating temperature is 35 °C. In the experiment, a high-purity aluminum plate is used as the anode, and the zinc-plated magnesium alloy is used as the cathode for electroplating experiments.

[0031] Step 7, Cleaning: Ultrasonic treatment with absolute ethanol for 2 min, the cleaning temperature is room temperature, and the number of cleaning times is 2 times. Ultrasonic cleaning with deionized water, the cleaning temperature is room temperature, the cleaning time is 2 min, and the number of cleaning times is 2 times.

[0032] Step 8, Adhesion detection: 200 °C - 2 h - quenching in room temperature water + cross-cut test. After testing, there are no bubbling, peeling or even flaking phenomena on the surface of the coating.

[0033] Example 2: Step 1, Mechanical polishing: The substrate types are two types of magnesium alloys, AZ31B and AZ91D, and the substrate size is 2 cm × 3 cm × 0.06 cm. The substrate is polished successively with 600-mesh and 800-mesh sandpapers.

[0034] Step 2, Degreasing: Degreasing treatment is carried out by ultrasonic treatment with absolute ethanol at room temperature for 15 min.

[0035] Step 3, Electroplating zinc.

[0036] Step 4, Cleaning with deionized water: Cleaning is carried out with deionized water in two passes, and each is rinsed at room temperature for 15 s to remove the residual zinc solution.

[0037] Step 5, Cleaning with absolute ethanol: Rinse with absolute ethanol at room temperature for 20 s, and dry for standby.

[0038] Step 6, Electroplating aluminum coating: The molar ratio of AlCl3 to EMIC is 1.5:1, the additive is 0.5 g / L, the current density is 20 mA / cm2, the electro-deposition time is 100 min, and the electro-deposition temperature is 40 °C. In the experiment, a high-purity aluminum plate is used as the anode, and the zinc-plated magnesium alloy is used as the cathode for electro-deposition experiments.

[0039] Step 7, Cleaning: Ultrasonic clean with absolute ethanol for 2 min, the cleaning temperature is room temperature, and the number of cleaning times is 2 times. Ultrasonic clean with deionized water, the cleaning temperature is room temperature, the cleaning time is 2 min, and the number of cleaning times is 2 times.

[0040] Step 8, Adhesion test: 200 °C - 2 h - water quenching at room temperature + cross-cut test. After testing, there are no blisters, peeling or even flaking phenomena on the coating surface.

[0041] Example 3: Step 1, Mechanical grinding: The substrate type is AZ31B magnesium alloy, the substrate size is 10 cm × 10 cm × 0.06 cm, and the substrate is ground with 600-mesh and 800-mesh sandpapers in sequence.

[0042] Step 2, Degreasing: Carry out degreasing treatment by ultrasonic cleaning with absolute ethanol at room temperature for 15 min.

[0043] Step 3, Electro-deposit zinc.

[0044] Step 4, Cleaning with deionized water: Carry out two-pass cleaning with deionized water, and rinse at room temperature for 15 s each time to remove the residual zinc solution.

[0045] Step 5, Cleaning with absolute ethanol: Rinse with absolute ethanol at room temperature for 15 s, and dry for standby.

[0046] Step 6, Electroplating aluminum coating: The molar ratio of AlCl3 to EMIC is 2:1, the additive is 1.2 g / L, the current density is 5 mA / cm2, the electro-deposition time is 80 min, and the electro-deposition temperature is 25 °C. In the experiment, a high-purity aluminum plate is used as the anode, and the zinc-plated magnesium alloy is used as the cathode for electro-deposition experiments.

[0047] Step 7, Cleaning: Ultrasonic clean with absolute ethanol for 2 min, the cleaning temperature is room temperature, and the number of cleaning times is 2 times. Ultrasonic clean with deionized water, the cleaning temperature is room temperature, the cleaning time is 2 min, and the number of cleaning times is 2 times.

[0048] Step 8, Adhesion test: 200 °C - 2 h - water quenching at room temperature + cross-cut test. After testing, there are no blisters, peeling or even flaking phenomena on the coating surface.

[0049] Experimental results: Figure 1 It is the surface microtopography diagram of electroplated aluminum on magnesium alloy. The pure aluminum coating is flat and dense. Figure 2 Figure 3 It is the micrograph of crosshatch test of electroplated aluminum on AZ31B and AZ91D magnesium alloys after thermal shock test. Figure 4 It is the cross-sectional SEM diagram of the Zn / Al composite coating on magnesium alloy after thermal shock + crosshatch test. Figure 5 It is the appearance diagram of the electroplated aluminum layer of AZ31B magnesium alloy with the size of 10 cm × 10 cm × 0.06 cm. There are no bubbles or peeling on the coating, and there is no obvious peeling at the edge of the micro lattice, etc. The adhesion is excellent.

[0050] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. In addition, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations 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 belong to the scope protected by the present invention.

Claims

1. A method for electroplating Zn and Al composite coatings suitable for magnesium alloys, characterized in that, The method comprises the following steps: step 1, electro-depositing zinc on magnesium alloy; Step 2, preparing electroplating aluminum ion liquid; Step 3, the magnesium alloy after electroplating zinc is directly electroplated with aluminum; Step 4: Cleaning; Step 5: Binding strength test.

2. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 1, characterized in that The step 1 comprises the following steps: Step 1.1, substrate preparation: use AZ31B or AZ91D magnesium alloy, sandpaper polished to 800# for later use; Step 1.2, electroplating zinc: pretreating the magnesium alloy substrate, and then electroplating zinc on it to construct an electroplated zinc layer on the surface of the magnesium alloy.

3. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 1, wherein The step 2 comprises the following steps: Step 2.1, preparation of additive-free ionic liquid: Step 2.2: Add additives with brightening and smoothing effects.

4. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 3, characterized in that The step 2.1 comprises the following steps: Take anhydrous AlCl3 and EMIC as raw materials, and prepare the liquid in a glove box. The water and oxygen content in the glove box is ≤0.01ppm, so that the molar ratio of AlCl3 and EMIC is 1.5~2:1, and the temperature is controlled to be ≤60°C during liquid preparation.

5. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 3, characterized in that, The step 2.2 comprises the following steps: Add additives to the ionic liquid prepared in step 2.

1. The additives are 3-pyridinecarboxamide, 4-cyanopyridine, nicotinamide, and o-phenanthroline. The concentration is 0.01-2 g / L", the preparation temperature is room temperature, and the mixture is stirred until the complexation is complete.

6. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 3, characterized in that, The step 3 comprises the following steps: Electroplated aluminum is electrodeposited with a high-purity aluminum plate as the anode and a galvanized magnesium alloy as the cathode under an inert atmosphere condition, ensuring that the water and oxygen content is ≤ 0.01 ppm. An additive with a bright and smooth effect is added at 0.01 - 2 g / L in an ionic liquid with a molar ratio of AlCl3 to EMIC of 1.5 - 2:1, and the electrodeposition current density is 5 - 20 mA / cm 2 , and the electrodeposition temperature is from room temperature to 60 °C.

7. The method for electroplating Zn, Al composite coating applicable to magnesium alloy according to claim 1, characterized in that, The step 4 comprises the following steps: Step 4, cleaning: the aluminum coating obtained by electrodeposition is taken out from the glove box and immediately washed with anhydrous ethanol for 1 to 2 minutes at room temperature and twice. At the same time, deionized water is used for washing at room temperature for 1 to 2 minutes and twice.

8. The method for electroplating Zn and Al composite coating applicable to magnesium alloy according to claim 1, characterized in that, The step 5 adopts thermal shock and combines with hundred grid test to test the bonding performance of Zn and Al composite coating.

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