Anti-ablation micro-arc oxidation method for die-casting aluminum alloy

Abstract

This invention relates to the field of surface treatment technology for die-cast aluminum alloys, and discloses a micro-arc oxidation method for die-cast aluminum alloys to resist ablation. By optimizing the pretreatment process and electrolyte formulation, the overall performance of the coating is improved. In the pretreatment process, a high-concentration hot alkaline solution reacts and dissolves most of the aluminum-silicon phase exposed on the surface of the die-cast aluminum alloy, followed by a high-concentration nitric acid solution to passivate the material surface, which can prevent ablation during micro-arc oxidation. In the first micro-arc oxidation process, an electrolyte system containing sodium fluoride and stannate is used, which helps to form a uniform substrate layer and reduce discharge concentration. In the second micro-arc oxidation process, metavanadate is used as a colorant, which can obtain a uniform black coating.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for die-cast aluminum alloys, and in particular to a method for resisting ablation micro-arc oxidation of die-cast aluminum alloys. Background Technology

[0002] Die-cast aluminum alloys such as A380 and ADC12 are widely used in lightweight structural and aesthetic components due to their excellent casting properties and high specific strength. To ensure casting fluidity, these alloys typically contain high levels of silicon, leading to the formation of numerous aluminum-silicon hard precipitates in the microstructure. These second phases exhibit significant physical property differences from the aluminum matrix: the aluminum matrix is ​​a good conductor, while the aluminum-silicon phase is an intermetallic compound with poor conductivity. Under the high-voltage electric field of the micro-arc oxidation process, the current preferentially concentrates at the interface between the aluminum-silicon phase and the aluminum matrix, resulting in severe electric field distortion and triggering intense and localized micro-arc discharge. This phenomenon manifests macroscopically as "ablation" of the workpiece surface, forming white bright spots, molten pits, and rough protrusions. This severely damages the continuity, aesthetics, and overall protective properties of the coating, including corrosion resistance and wear resistance, leading to low product yield and becoming a key technical bottleneck restricting its application in demanding scenarios.

[0003] To improve the performance of micro-arc oxidation coatings on aluminum alloys, existing technologies have proposed various solutions. For example, some technologies employ an EDTA salt-phosphate-silicate-metavanadate-tungstate composite electrolyte system to prepare a black film layer in a single process, aiming to balance coloring and bonding strength. Other technologies propose a stepwise micro-arc oxidation method, introducing tungstate into the primary electrolyte to construct a base layer, and then using molybdate and metavanadate for coloring in the secondary electrolyte, aiming to obtain a corrosion-resistant black coating. Furthermore, research has explored the introduction of nanoparticles combined with specific salts to enhance the hardness and wear resistance of the black film layer.

[0004] However, while the aforementioned existing technologies have achieved improvements in aspects such as coloring, adhesion, or hardness, their design concepts are mostly focused on "performance optimization" after coating formation. They do not offer a direct and effective strategy to suppress the root cause of "ablation" in die-cast aluminum alloys due to their inherent microstructure. Specifically, the energy buffering capacity of existing solutions is still insufficient when facing concentrated discharges caused by high-silicon aluminum precipitates, and they cannot fundamentally intervene in and homogenize the initial discharge behavior. Therefore, the purpose of this invention is to provide a novel method that can fundamentally suppress micro-arc oxidation ablation defects in high-silicon die-cast aluminum alloys. Summary of the Invention

[0005] The purpose of this invention is to provide an anti-ablation micro-arc oxidation method for die-cast aluminum alloys, which solves the problem of severe ablation caused by the presence of aluminum-silicon second phases in the material when the existing micro-arc oxidation method is used to process high-silicon die-cast aluminum alloys.

[0006] To achieve the above objectives, the present invention provides a method for resisting ablation micro-arc oxidation of die-cast aluminum alloys, comprising the following steps: The die-cast aluminum alloy samples were subjected to alkaline washing, water washing, acid washing, re-water washing and drying to remove surface contaminants and passivate the surface. A substrate layer was prepared by micro-arc oxidation of a pretreated sample using a primary electrolyte containing silicates, phosphates, sodium fluoride, stannates, fluorozirconates, and hydroxides in a constant current mode. Using a secondary electrolyte containing silicates, phosphates, metavanadates, borates and EDTA salts, a sample with a substrate layer was subjected to micro-arc oxidation treatment in constant current mode to obtain an ablation-resistant black coating on aluminum alloy. The sample after secondary electrolyte treatment was cleaned and dried.

[0007] The step of “treating the die-cast aluminum alloy sample with alkaline washing, water washing, acid washing, re-water washing and drying to remove surface contaminants and passivate the surface” includes the following steps: The die-cast aluminum alloy sample was placed in a sodium hydroxide solution with a concentration of 40-70 g / L and treated at 50-70℃ for 30-150 seconds. Thoroughly clean the sample surface with flowing deionized water for at least 2 minutes. Place the sample in a nitric acid solution with a concentration of 200-600 mL / L and treat it at room temperature for 30-90 seconds; The sample surface should be thoroughly rinsed again with flowing deionized water for at least 2 minutes. Dry the sample in a forced-air drying oven at 60-80℃.

[0008] The step of "preparing a substrate layer by performing micro-arc oxidation treatment on a pretreated sample using a primary electrolyte containing silicates, phosphates, sodium fluoride, stannates, fluorozirconates, and hydroxides in a constant current mode" includes the following steps: A primary electrolyte containing 10-20 g / L silicate, 8-15 g / L phosphate, 1-3 g / L sodium fluoride, 2-5 g / L stannate, 0.5-2 g / L potassium fluorozirconate, and 0.5-1.5 g / L hydroxide was used. Micro-arc oxidation is performed using a constant current mode, with a processing time of 10-25 minutes.

[0009] The section on "using a secondary electrolyte containing silicates, phosphates, metavanadates, borates, and EDTA salts to perform micro-arc oxidation treatment on a sample with a substrate layer in a constant current mode to obtain an ablation-resistant black coating on aluminum alloy" includes the following steps: A secondary electrolyte containing 8-15 g / L silicate, 15-25 g / L phosphate, 6-10 g / L metavanadate, 4-8 g / L borate, and 3-5 g / L EDTA salt was used. A black coating resistant to ablation was obtained by micro-arc oxidation treatment in constant current mode.

[0010] The step of "cleaning and drying the sample after secondary electrolyte treatment" includes the following steps: Remove the sample from the electrolyte and rinse it thoroughly with deionized water; After drying the surface moisture of the sample with compressed air, place the sample in a 65℃ oven for 30 minutes.

[0011] This invention discloses an anti-ablation micro-arc oxidation method for die-cast aluminum alloys, which improves the overall performance of the coating by optimizing the pretreatment process and electrolyte formulation. In the pretreatment process, a high-concentration hot alkaline solution reacts and dissolves most of the exposed aluminum-silicon phase on the die-cast aluminum alloy surface. Subsequently, a high-concentration nitric acid solution passivates the material surface, preventing ablation during micro-arc oxidation. In the primary micro-arc oxidation process, an electrolyte system containing sodium fluoride and stannate is used, which helps to form a uniform substrate layer and reduces discharge concentration. In the secondary micro-arc oxidation process, metavanadate is used as a colorant, resulting in a uniformly colored black coating.

[0012] Compared with existing technologies, this method can effectively suppress the ablation defects unique to high-silicon aluminum alloys, resulting in a smooth coating surface without ablation marks. Furthermore, the coating also exhibits good adhesion and impact resistance, while maintaining the inherent high hardness and wear resistance of micro-arc oxidation coatings. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0014] Figure 1 This is a process flow diagram of an anti-ablation micro-arc oxidation method for die-cast aluminum alloys provided by the present invention.

[0015] Figure 2 This is the morphology of the black oxide film coating on the surface of the die-cast aluminum alloy in Embodiment 1 of the present invention. Detailed Implementation

[0016] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0017] Please see Figures 1 to 2 This invention provides a method for resisting ablation micro-arc oxidation of die-cast aluminum alloys, comprising the following steps: S1 involves alkali washing, water washing, acid washing, re-water washing, and drying of the die-cast aluminum alloy sample to remove surface contaminants and passivate the surface. S11 Place the die-cast aluminum alloy sample in a sodium hydroxide solution with a concentration of 40-70 g / L and treat it at 50-70℃ for 30-150 seconds; S12. Thoroughly clean the sample surface with flowing deionized water for at least 2 minutes. S13 Place the sample in a nitric acid solution with a concentration of 200-600 mL / L and treat it at room temperature for 30-90 seconds; S14 The sample surface is thoroughly cleaned again with flowing deionized water for at least 2 minutes. S15 The sample was dried in a forced-air drying oven at 60-80℃.

[0018] Specifically, place the die-cast aluminum alloy sample in a sodium hydroxide solution with a concentration of 40-70 g / L and treat it at 50-70℃ for 30-150 seconds; thoroughly clean the sample surface with flowing deionized water for at least 2 minutes; place the sample in a nitric acid solution with a concentration of 200-600 mL / L and treat it at room temperature for 30-90 seconds; thoroughly clean the sample surface with flowing deionized water for at least 2 minutes; and dry the sample in a forced-air drying oven at 60-80℃. S2 utilizes a primary electrolyte containing silicates, phosphates, sodium fluoride, stannate, fluorozirconate, and hydroxides to perform micro-arc oxidation on the pretreated sample in a constant current mode to prepare the substrate layer. S21 utilizes a primary electrolyte containing 10-20 g / L silicate, 8-15 g / L phosphate, 1-3 g / L sodium fluoride, 2-5 g / L stannate, 0.5-2 g / L potassium fluorozirconate, and 0.5-1.5 g / L hydroxide. S22 undergoes micro-arc oxidation treatment in constant current mode for 10-25 minutes.

[0019] Specifically, the primary electrolyte comprises: 10-20 g / L silicate, 8-15 g / L phosphate, 1-3 g / L sodium fluoride, 2-5 g / L stannate, 0.5-2 g / L potassium fluorozirconate, and 0.5-1.5 g / L hydroxide; the secondary electrolyte comprises: 8-15 g / L silicate, 15-25 g / L phosphate, 6-10 g / L metavanadate, 4-8 g / L borate, and 3-5 g / L EDTA salt.

[0020] The silicate is sodium silicate pentahydrate, the phosphate is trisodium phosphate dodecahydrate or sodium hexapolyphosphate, the stannate is sodium stannate, the fluorozirconate is potassium fluorozirconate, the borate is sodium borate, the EDTA salt is EDTA-2Na, the hydroxide is sodium hydroxide or potassium hydroxide, and the metavanadate is sodium metavanadate dihydrate.

[0021] The primary electrolyte micro-arc oxidation is performed in constant current mode for 10-25 min to prepare the substrate layer. The current parameters are: frequency 400-800 Hz, pulse width 40-100 μs, termination voltage 400-450 V, and termination current density 1-3 A / dm². The electrolyte temperature is controlled at 20-35℃, and mechanical stirring is used to maintain uniform mixing of the electrolyte. Both the primary electrolyte micro-arc oxidation and the secondary electrolyte micro-arc oxidation employ a segmented current control strategy: a lower current density is used when the voltage is below 300V, a medium current density is used when the voltage reaches 300-450V, and a higher current density is used when the voltage exceeds 450V.

[0022] The primary electrolyte focuses on "constructing a homogeneous substrate and homogenizing discharge": sodium fluoride is not used as a conventional activator; its core role is to selectively activate the aluminum-silicon phase in situ. F- ions preferentially react with the native alumina on the aluminum substrate surface to form soluble [AlF6]. 3- The complex, along with slight etching of the highly insulating aluminum-silicon phase surface, reduces its interfacial impedance, thereby effectively homogenizing the electric field distribution between the aluminum / silicon phases. This suppresses current concentration at the interface from the source, preventing ablation caused by violent discharge. Stannate acts as an energy buffer; its Sn(IV) content can be instantaneously reduced within the high-temperature, high-pressure micro-region of micro-arc discharge. This valence change process effectively absorbs and dissipates some of the instantaneous discharge energy, acting as a "current spike discharger," thus softening the discharge process. The introduction of potassium fluorozirconate, with its Zr... 4+ It can participate in film formation, forming more stable Zr-O-Si bonds, and improving the thermal stability and density of the substrate.

[0023] S3 utilizes a secondary electrolyte containing silicates, phosphates, metavanadates, borates, and EDTA salts to perform micro-arc oxidation treatment on a sample with a substrate layer in a constant current mode, thereby obtaining an ablation-resistant black coating on aluminum alloy. S31 utilizes a secondary electrolyte containing 8-15 g / L silicate, 15-25 g / L phosphate, 6-10 g / L metavanadate, 4-8 g / L borate, and 3-5 g / L EDTA salt. S32 undergoes micro-arc oxidation treatment in constant current mode to obtain an ablation-resistant black coating on aluminum alloy.

[0024] Specifically, a micro-arc oxidation treatment is performed on die-cast aluminum alloy samples with a dense substrate layer using a secondary electrolyte. The treatment time is 20-30 minutes, for example, 20 minutes, 25 minutes, or 30 minutes, to obtain an ablation-resistant black coating on the aluminum alloy. The micro-arc oxidation power supply adopts a constant current mode, and the set current parameters are: frequency 500-800Hz, for example, 500Hz, 550Hz, 600Hz, 700Hz, or 800Hz; pulse width 40-100μs, for example, 40μs, 50μs, 60μs, 70μs, or 80μs; ​​termination voltage 450-500V, for example, 450V, 460V, 470V, 480V, or 490V; termination current density 3-5A / dm², for example, 3A / dm², 4A / dm², or 5A / dm².

[0025] The secondary electrolyte micro-arc oxidation is performed in constant current mode for 20-30 minutes to obtain an ablation-resistant black coating on the aluminum alloy. The current parameters are: frequency 400-800Hz, pulse width 40-100μs, termination voltage 450-500V, and termination current density 3-5A / dm². The electrolyte temperature is controlled at 20-35℃, and air stirring is used to maintain uniform mixing of the electrolyte. The secondary electrolyte focuses on "growing a strong and tough coloring layer on a high-quality substrate": metavanadate is used as the colorant, and its V 5+ It is reduced to V in the discharge region. 4+ / V 3+ A black coloring is achieved by embedding a coating. The addition of borate promotes the glassy phase [BO3] at the discharge interface. -3 The formation of [a specific substance] effectively fills the micropores in the coating, reduces the surface roughness of the coloring layer, and decreases stress concentration points, thereby significantly improving the density and impact resistance of the coating. EDTA salt, as an effective metal complexing agent, reacts with V [a specific substance] in the solution. 5+ A l3+ Plasma forms stable complexes, which not only prevents metavanadate precipitation and maintains electrolyte stability, but also allows for the smooth regulation of film formation rate by controlling the concentration of free metal ions, promoting uniform and dense growth of the colored layer.

[0026] S4 involves cleaning and drying the sample after secondary electrolyte treatment.

[0027] S41 Remove the sample from the electrolyte and rinse it with deionized water; After drying the surface moisture of the sample with compressed air, S42 places the sample in a 65℃ oven for 30 minutes to dry.

[0028] Specifically, the sample is removed from the electrolyte, rinsed with deionized water, dried with compressed air, and finally dried in an oven at 65°C for 30 minutes.

[0029] Both the primary electrolyte micro-arc oxidation and the secondary electrolyte micro-arc oxidation employ a segmented current control strategy: a lower current density is used when the voltage is below 300V, a medium current density is used when the voltage reaches 300-450V, and a higher current density is used when the voltage exceeds 450V.

[0030] The sample transfer time between the primary electrolyte micro-arc oxidation and the secondary electrolyte micro-arc oxidation should be controlled within 5 minutes to prevent contamination or oxidation of the substrate surface.

[0031] Example 1

[0032] (1) Prepare primary and secondary electrolytes in two electrolytic cells respectively. The primary electrolyte consists of: sodium silicate pentahydrate 15 g / L, trisodium phosphate dodecahydrate 12 g / L, sodium fluoride 2 g / L, sodium stannate 3 g / L, potassium fluorozirconate 0.5 g / L, and potassium hydroxide 0.8 g / L; the secondary electrolyte consists of: sodium silicate pentahydrate 10 g / L, trisodium phosphate dodecahydrate 20 g / L, sodium metavanadate 8 g / L, sodium borate 6 g / L, and EDTA-2Na 4 g / L.

[0033] (2) For example Figure 1 As shown, the die-cast aluminum alloy sample was subjected to the following treatments in sequence: first, it was alkaline washed in a 50 g / L sodium hydroxide solution at 60°C for 60 seconds, and then rinsed with deionized water for 2 minutes; then, it was brightened in a 400 mL / L nitric acid solution at room temperature for 45 seconds, and then rinsed with deionized water for 2 minutes; finally, it was dried in a forced-air drying oven at 65°C for 25 minutes.

[0034] (3) Connect the sample piece after step (2) to the anode output terminal of the micro-arc oxidation power supply, immerse it in the primary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode terminal of the power supply.

[0035] (4) Turn on the micro-arc oxidation power supply, set the working mode to constant current mode, adopt a bidirectional pulse power supply and set a segmented current control strategy. Initially, the positive current density is given as 0.5 A / dm² and the negative current density as 0.2 A / dm². When the positive voltage increases to 250V and 380V, the positive current density is adjusted to 1.2 A / dm² and 2 A / dm², respectively; at the same time, when the negative voltage increases to 30V and 100V, the negative current density is adjusted to 0.3 A / dm² and 0.8 A / dm², respectively.

[0036] (5) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 15 min, with the electrolyte temperature controlled at 25±5℃; then clean the sample along with the hanger with deionized water.

[0037] (6) Connect the sample piece treated in step (5) to the anode output end of the micro-arc oxidation power supply, immerse it in the secondary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode end of the power supply.

[0038] (7) Turn on the micro-arc oxidation power supply, set the working mode to constant current mode, use a bidirectional pulse power supply and set a segmented current control strategy. Initially, the positive current density is given as 0.5 A / dm² and the negative current density as 0.2 A / dm². When the positive voltage increases to 300V and 400V respectively, the positive current density is adjusted to 2 A / dm² and 3 A / dm² respectively; at the same time, when the negative voltage increases to 40V and 120V respectively, the negative current density is adjusted to 0.3 A / dm² and 0.8 A / dm² respectively. The electrolyte temperature is controlled at 25±5℃ and air stirring is used to maintain uniformity.

[0039] (8) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 25 min, with the electrolyte temperature controlled at 25±5℃; after treatment, remove and rinse with deionized water, blow dry with compressed air, and dry in a 65℃ oven for 30 min to obtain a die-cast aluminum alloy sample with a black micro-arc oxidation coating. Figure 2 As shown.

[0040] Example 2

[0041] (1) Prepare primary and secondary electrolytes in two electrolytic cells respectively. The primary electrolyte consists of: sodium silicate pentahydrate 18 g / L, trisodium phosphate dodecahydrate 10 g / L, sodium fluoride 1.5 g / L, sodium stannate 2 g / L, potassium fluorozirconate 1 g / L, and potassium hydroxide 1 g / L; the secondary electrolyte consists of: sodium silicate pentahydrate 12 g / L, trisodium phosphate dodecahydrate 18 g / L, sodium metavanadate 7 g / L, sodium borate 5 g / L, and EDTA-2Na 3.5 g / L.

[0042] (2) The die-cast aluminum alloy sample was subjected to the following treatments in sequence: first, it was alkali washed in 55 g / L sodium hydroxide solution at 55°C for 70 seconds and then rinsed with deionized water for 2 minutes; then it was brightened in 350 mL / L nitric acid solution at room temperature for 50 seconds and rinsed with deionized water for 2 minutes; finally, it was dried in a forced-air drying oven at 65°C for 30 minutes.

[0043] (3) Connect the sample piece after step (2) to the anode output terminal of the micro-arc oxidation power supply, immerse it in the primary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode terminal of the power supply.

[0044] (4) Turn on the micro-arc oxidation power supply, set the working mode to constant current mode, adopt a bidirectional pulse power supply and set a segmented current control strategy. The initial given positive current density is 0.8 A / dm² and negative current density is 0.25 A / dm². When the positive voltage increases to 260V and 390V, the positive current density is adjusted to 2.0 A / dm² and 3.0 A / dm², respectively; at the same time, when the negative voltage increases to 35V and 110V, the negative current density is adjusted to 0.4 A / dm² and 0.9 A / dm², respectively.

[0045] (5) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 20 min, with the electrolyte temperature controlled at 28±5℃; then clean the sample piece and the hanger with deionized water.

[0046] (6) Connect the sample piece treated in step (5) to the anode output end of the micro-arc oxidation power supply, immerse it in the secondary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode end of the power supply.

[0047] (7) Turn on the micro-arc oxidation power supply, set the working mode to constant current mode, adopt a bidirectional pulse power supply and set a segmented current control strategy. The initial given positive current density is 0.8 A / dm², and the negative current density is 0.25 A / dm². When the positive voltage increases to 360V and 460V respectively, the positive current density is adjusted to 2A / dm² and 4 A / dm² respectively; at the same time, when the negative voltage increases to 45V and 130V, the negative current density is adjusted to 0.4 A / dm² and 0.9 A / dm² respectively.

[0048] (8) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 20 min. The electrolyte temperature is controlled at 28±5℃. After the treatment is completed, take it out and rinse it with deionized water, blow it dry with compressed air, and dry it in an oven at 65℃ for 30 minutes to obtain a die-cast aluminum alloy sample with a black micro-arc oxidation coating.

[0049] Example 3

[0050] (1) Prepare primary and secondary electrolytes in two electrolytic cells respectively. The primary electrolyte consists of: sodium silicate pentahydrate 12 g / L, trisodium phosphate dodecahydrate 14 g / L, sodium fluoride 2.5 g / L, sodium stannate 2.5 g / L, potassium fluorozirconate 1.5 g / L, and potassium hydroxide 1.2 g / L; the secondary electrolyte consists of: sodium silicate pentahydrate 8 g / L, trisodium phosphate dodecahydrate 22 g / L, sodium metavanadate 9 g / L, sodium borate 7 g / L, and EDTA-2Na 4.5 g / L.

[0051] (2) The die-cast aluminum alloy sample was subjected to the following treatments in sequence: First, it was alkali washed in 45 g / L sodium hydroxide solution at 65°C for 50 seconds and then rinsed with deionized water for 2 minutes; then it was brightened in 450 mL / L nitric acid solution at room temperature for 40 seconds and rinsed with deionized water for 2 minutes; finally, it was dried in a forced-air drying oven at 65°C for 20 minutes.

[0052] (3) Connect the sample piece after step (2) to the anode output terminal of the micro-arc oxidation power supply, immerse it in the primary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode terminal of the power supply.

[0053] (4) Turn on the micro-arc oxidation power supply, set the working mode to constant current mode, use a bidirectional pulse power supply and set a segmented current control strategy. Initially, the positive current density is given as 1.0 A / dm² and the negative current density as 0.3 A / dm². When the positive voltage increases to 280V and 420V, the positive current density is adjusted to 2.5 A / dm² and 4.0 A / dm², respectively; at the same time, when the negative voltage increases to 40V and 120V, the negative current density is adjusted to 0.5 A / dm² and 1.0 A / dm², respectively.

[0054] (5) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 15 min, with the electrolyte temperature controlled at 22±5℃; then clean the sample piece and the hanger with deionized water.

[0055] (6) Connect the sample piece treated in step (5) to the anode output end of the micro-arc oxidation power supply, immerse it in the secondary electrolyte, and connect the stainless steel plate inside the electrolytic cell to the cathode end of the power supply.

[0056] (7) Turn on the micro-arc oxidation power supply, adopt a bidirectional pulse power supply and set a segmented current control strategy. Initially, the positive current density is given as 0.5 A / dm² and the negative current density as 0.2 A / dm². When the positive voltage increases to 300V, the positive current density is adjusted to 1.2 A / dm²; when the positive voltage increases to 480V, the positive current density is adjusted to 2 A / dm². At the same time, when the negative voltage increases to 40V, the negative current density is adjusted to 0.3 A / dm²; when the negative voltage increases to 120V, the negative current density is adjusted to 0.8 A / dm².

[0057] (8) Start the micro-arc oxidation power supply and perform micro-arc oxidation treatment for 25 min. The electrolyte temperature is controlled at 28±5℃. Rinse the sample with deionized water, blow it dry with compressed air, and finally dry it in a 65℃ oven for 30 minutes to obtain a black micro-arc oxidation coating of die-cast aluminum alloy with high hardness and high blackness.

[0058] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. An anti-ablation micro-arc oxidation method for die-cast aluminum alloys, characterized in that, Includes the following steps: The die-cast aluminum alloy samples were subjected to alkaline washing, water washing, acid washing, re-water washing and drying to remove surface contaminants and passivate the surface. A substrate layer was prepared by micro-arc oxidation of a pretreated sample using a primary electrolyte containing silicates, phosphates, sodium fluoride, stannates, fluorozirconates, and hydroxides in a constant current mode. Using a secondary electrolyte containing silicates, phosphates, metavanadates, borates and EDTA salts, a sample with a substrate layer was subjected to micro-arc oxidation treatment in constant current mode to obtain an ablation-resistant black coating on aluminum alloy. The sample after secondary electrolyte treatment was cleaned and dried.

2. The method for resisting ablation micro-arc oxidation of die-cast aluminum alloys as described in claim 1, characterized in that, The process of "treating die-cast aluminum alloy samples with alkaline washing, water washing, acid washing, re-water washing, and drying to remove surface contaminants and passivate the surface" includes the following steps: The die-cast aluminum alloy sample was placed in a sodium hydroxide solution with a concentration of 40-70 g / L and treated at 50-70℃ for 30-150 seconds. Thoroughly clean the sample surface with flowing deionized water for at least 2 minutes. Place the sample in a nitric acid solution with a concentration of 200-600 mL / L and treat it at room temperature for 30-90 seconds; The sample surface should be thoroughly rinsed again with flowing deionized water for at least 2 minutes. Dry the sample in a forced-air drying oven at 60-80℃.

3. The method for resisting ablation micro-arc oxidation of die-cast aluminum alloys as described in claim 2, characterized in that, The process of "preparing a substrate layer by micro-arc oxidation of a pretreated sample using a primary electrolyte containing silicates, phosphates, sodium fluoride, stannates, fluorozirconates, and hydroxides in a constant current mode" includes the following steps: A primary electrolyte containing 10-20 g / L silicate, 8-15 g / L phosphate, 1-3 g / L sodium fluoride, 2-5 g / L stannate, 0.5-2 g / L potassium fluorozirconate, and 0.5-1.5 g / L hydroxide was used. Micro-arc oxidation is performed using a constant current mode, with a processing time of 10-25 minutes.

4. The method for resisting ablation micro-arc oxidation of die-cast aluminum alloys as described in claim 3, characterized in that, The process of "using a secondary electrolyte containing silicates, phosphates, metavanadates, borates, and EDTA salts to perform micro-arc oxidation treatment on a sample with a substrate layer in constant current mode to obtain an ablation-resistant black coating on an aluminum alloy" includes the following steps: A secondary electrolyte containing 8-15 g / L silicate, 15-25 g / L phosphate, 6-10 g / L metavanadate, 4-8 g / L borate, and 3-5 g / L EDTA salt was used. A black coating resistant to ablation was obtained by micro-arc oxidation treatment in constant current mode.

5. The method for resisting ablation micro-arc oxidation of die-cast aluminum alloys as described in claim 4, characterized in that, The step of "cleaning and drying the sample after secondary electrolyte treatment" includes the following steps: Remove the sample from the electrolyte and rinse it thoroughly with deionized water; After drying the surface moisture of the sample with compressed air, place the sample in a 65℃ oven for 30 minutes.

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