CN111101164B

CN111101164B - Preparation method of high-bonding-force coating with anodized aluminum as base material

Info

Publication number: CN111101164B
Application number: CN202010193557.7A
Authority: CN
Inventors: 王永芝
Original assignee: Individual
Current assignee: Li Yulong
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-01-01
Anticipated expiration: 2040-03-18
Also published as: CN111101164A

Abstract

The invention provides a preparation method of a high-bonding-force coating taking anodic aluminum oxide as a base material.

Description

Preparation method of high-bonding-force coating with anodized aluminum as base material

Technical Field

The invention relates to a preparation method of a high-binding-force coating with anodized aluminum as a base material, belongs to the field of preparing an anodic oxide film aluminum material without a shielding layer by an electrochemical method, and is particularly suitable for improving the binding force of the aluminum material and electroplated metal.

Technical Field

With the rapid development of science and technology and industry, people have more and more strict requirements on metal performance, light high-hardness metal alloy materials are widely applied in related fields, and the light metal aluminum alloy materials are concerned because the global yield of aluminum is second to that of iron. Aluminum and aluminum alloy materials are low in hardness, poor in wear resistance and prone to intergranular corrosion, a thin oxide film is prone to form on the surface of aluminum under natural conditions, the oxide film is prone to damage, particularly, the aluminum and aluminum alloy materials are rapidly dissolved under acid (alkali) conditions, corrosion resistance of the aluminum and aluminum alloy materials is greatly reduced, application of aluminum and aluminum alloy substrates is greatly limited, a strong corrosion-resistant film needs to cover the surface of the aluminum and aluminum alloy substrates, the purpose of protection is achieved, and the aluminum and aluminum alloy materials can be protected through oxidation treatment, additional coating, electroplating and the like. The standard potential of nickel is-0.25V, which has strong corrosion resistance and is the metal with the largest consumption, therefore, nickel is concerned by people as the protective and decorative coating of the aluminum alloy material and becomes a good metal protective coating.

In the prior art, there are many methods for electroplating on the surface of aluminum material, such as CN 1793436A, which is a method for directly electroplating on the surface of aluminum or aluminum alloy, and the method comprises the following steps:

1) pretreatment: mechanical pretreatment and chemical polishing are included;

2) electroplating nickel: directly electroplating the aluminum alloy in a plating solution by adopting a direct current or pulse current method; and adding a complexing film removing agent into the electroplating solution, wherein the concentration of the complexing film removing agent is controlled to be 20-40 g/L.

Although the method for electroplating Ni on the surface of the aluminum material is simple, the method has the obvious technical problem that the peeling strength of a plating layer and the aluminum material is not high, and the industrial requirement is difficult to meet.

Further, Honda technical research industries, Inc. US577589A (same family CN 1144852A) discloses a silicon anodizing method comprising subjecting the silicon-containing aluminum alloy to an anodizing treatment, plating nickel on the anodized film to form a nickel-plated film; and plating chromium on the nickel-plated surface, wherein the bonding force between the base material and the plating layer can be effectively improved by anodizing the intermediate layer on the surface of the aluminum material, but the problem of poor conductivity of the anodic oxide film is seriously ignored in the prior art, and the adverse effect of the anodic oxide film on the bonding force between the plating layer and the base material is further ignored.

Further, shenzhen futai macro precision industries limited company US2013164555A (congener CN 103173834A) discloses a method for surface treatment of aluminum or aluminum alloy and a product thereof, wherein the anodic oxide film comprises a barrier layer and a porous layer which are sequentially formed on the surface of an aluminum or aluminum alloy substrate, the anodic oxide film further comprises a plurality of second oxide holes which penetrate through the barrier layer and the porous layer, the product further comprises a plating layer formed on the anodic oxide film, the prior art clearly states that "the formation of the second oxide holes 40 causes a snap effect to occur between the plating layer 15 and the aluminum or aluminum alloy substrate 11, and the bonding force between the plating layer 15 and the aluminum or aluminum alloy substrate 11 is enhanced. Although it is explicitly mentioned that the barrier layer in the anodized film should be removed in the anodized film plating process, the principle and method of removing the barrier layer are clearly contrary to the electrochemical principle, and specifically, as described in the specification, "in the anodization process," first, the anodized film 13 is formed on the surface of the aluminum or aluminum alloy substrate 11, the anodized film 13 includes the barrier layer 131 and the porous layer 133 formed on the surface of the aluminum or aluminum alloy substrate 11 in this order, and the porous layer 133 is formed with the plurality of first pores 20. Because of the moderate acidity of the electrolyte, the complex formed by complexing EDTA and aluminum ions is easy to dissociate, and the formation of the complex does not obstruct the growth of the barrier layer 131; with the increase of the reaction time, the oxygen evolution reaction of the area at the bottom end of the first oxidation hole 20 close to the barrier layer 131 is intensified, the produced hydrogen ions are increased, the electrolyte in the area is strongly acidic, and the stability of the complex of EDTA and aluminum ions is stronger in the strongly acidic environment, so that the growth of the barrier layer 131 can be hindered; and the barrier layer 131 is also dissolved while growing due to the balance of electrochemical reaction during the anodic oxidation process, so that, when the growth of the barrier layer 131 is hindered, finally, the barrier layer 131 at the bottom of the first oxide hole 20 is gradually dissolved to form the second oxide hole 40. The second oxide hole 40 penetrates the barrier layer 131 and the porous layer 133. ", i.e. the prior art can avoid the formation of the shielding layer at the bottom of the anodic oxide film pore path directly by controlling the parameters in the anodic oxidation process, which is seriously contrary to the principle of anodic oxide film formation.

Specifically, the method comprises the following steps: the anodic oxidation of aluminum or an aluminum alloy refers to a process in which aluminum or an aluminum alloy is immersed in a suitable electrolyte as an anode and subjected to an electrical treatment to form an oxide film (Al2O layer) on the surface of the aluminum or the aluminum alloy. The existence of the oxide film can improve the corrosion resistance of the aluminum alloy, and meanwhile, by means of the special structure of the oxide film and the post treatment process, for example, the anodic oxide film can be matched with surface painting and other further treatments, so that the base body can achieve a better protection effect in a harsher environment, or aluminum and aluminum alloy workpieces are decorated by dyeing, and the film layer has decoration and other protective properties. Common anodizing processes include sulfuric acid anodizing, chromic acid anodizing, and the like.

From the thermodynamic conditions of chemical reactions, aluminum can generate a stable oxide film layer over a considerable pH range (pH = 4.45-8.38). However, from the mechanism of electrochemical reaction, the formation of the anodic oxide film is actually a result of the combined action of the two processes of film growth and film dissolution.

(1) And (3) growing the film:

cathode, hydrogen evolution reaction 2H⁺+2e→H₂

Anodic oxidation reaction of H₂O-2e→O+2H⁺

Oxygen generated in the anode reaction can form oxygen molecules to be separated out in a gaseous state, and an aluminum oxide film layer can be formed on the surface of the anode:

2Al+3O→Al₂O₃+Q。

the reaction is exothermic, Q =1669J/mol, the anodic oxidation process is fast, a thin, non-porous, compact, strong-adhesion and high-insulation oxide film can be generated by electrifying for a few seconds, the film grows continuously, the thickness increases continuously, the resistance increases, and the reaction speed of the generated film is reduced continuously until the reaction stops.

(2) And (4) dissolving the film. It is the dissolution of the film that allows the film to grow continuously. During the reaction, both the aluminum and the resulting alumina film layer may dissolve in the acidic electrolyte solution.

2Al+6H⁺→2Al³⁺+3H₂

Al₂O₃+6H⁺→2Al³⁺+3H₂O

The dissolution reaction causes a large number of small pores to be formed on the surface of the aluminum. The dissolving process of the membrane is carried out synchronously with the generating process of the membrane, because the nascent membrane layer is not uniform, the thin part of the membrane layer is easy to dissolve to generate small holes, electrolyte solution can pass through the small holes to enter the membrane, an oxidation membrane is continuously generated on an aluminum substrate and is continuously dissolved at the same time, the small holes (pinholes) of the oxidation membrane are finally formed to form a conical structure from the outside to the inside, and the dissolving of the membrane is related to factors such as the property of the electrolyte, the structure of a reaction product, current, voltage, the temperature of the solution, the electrifying time and the like.

The porous honeycomb structure of the aluminum and aluminum alloy anode oxide film has the film layer with micropores perpendicular to the surface, and the size, the pore diameter, the wall thickness, the thickness of the barrier layer and other parameters of the structural unit are all controlled by electrolyte components and process parameters, namely the aluminum anode oxide film has two major types, namely a barrier type anode oxide film and a porous type anode oxide film. The barrier type anodic oxide film is a compact nonporous thin anodic oxide film, called barrier film for short, which is close to the metal surface, the thickness of the barrier type anodic oxide film is generally very thin depending on the applied anodic oxidation voltage, and the barrier type anodic oxide film is mainly used for manufacturing electrolytic capacitors, and the thickness of the barrier type anodic oxide film is not more than 0.1 mu m. The barrier type anodic oxide film is also called a barrier layer anodic oxide film, and in a simple aspect, the porous anodic oxide film comprises a barrier layer and a porous layer which are significantly different in specific structure and composition, wherein the barrier layer is a dense non-porous amorphous oxide, usually gamma-Al 2O3, and the porous layer is composed of amorphous alumina, the main component of which is alpha-AlOOH alumina.

In general, the above-mentioned shielding layer at the bottom of the anodic oxide film pore channel contributes positively to the corrosion resistance and hardness of the anodic oxide film, such as higher hardness, which can resist external erosion, i.e. the shielding layer of the aluminum anodic oxide film is usually not needed to be concerned and not needed to be treated, but in a specific field, the shielding layer of the anodic oxide film must be removed, otherwise the subsequent product production is adversely affected, such as plating a metal layer on the surface of the anodic oxide film, to improve or completely change the physicochemical properties of the surface of the anodic oxide film aluminum material, specifically:

CN201710570978, applicant's Friedel-crafts discloses a preparation method of an aluminum matrix composite, which comprises the following steps:

A. preparing a base body made of aluminum;

B. forming an AAO template, at least comprising forming the AAO template on the surface of the substrate by an anodic oxidation method;

C. generating a high-molecular nanowire, namely polymerizing an AAO template to obtain the nanowire, and removing part of the AAO template to reduce the thickness of the template so that the high-molecular nanowire is at least partially exposed out of the AAO template;

D. and forming an outer coating layer, wherein the outer coating layer is coated on the polymer nanowires, and the polymer nanowires exposed out of the AAO template are coated in the outer coating layer.

And B, corroding the bottom aluminum oxide layer of part of the nano holes of the AAO template to form cavities.

I.e. for improving gold in said prior artThe method for removing the shielding layer in the prior art records paste, has large technical difficulty and high requirement on equipment by using a microneedle carbon tube, and in addition, when the number of pore passages of the anodic oxide film is usually less, 4-8/mum is provided, and the requirement on equipment is high, and when the number of pore passages of the anodic oxide film is usually less, 4-8/mum is provided²Many, many thousands, and no ability to etch the shielding layer individually.

(II) CN201110174169, applicant Fuzhou university discloses a method for preparing a field emission cathode array material by using an anodized aluminum template, which mainly comprises the following steps:

(1) preparing a pre-made anodic alumina template with an aluminum substrate;

(2) removing the non-oxidized aluminum substrate;

(3) removing the bottom of the oxidation layer and reaming;

(4) pouring solution into the alumina cavity;

(5) removing the surface sol and gelatinizing;

(6) carbonizing at high temperature;

(7) plating a metal conducting layer;

(8) fixing the sample on the substrate

(9) And corroding the aluminum oxide to expose the carbon nanowire array.

In order to remove the barrier layer at the bottom of the anodic oxide film and directly and reversely remove the bottom aluminum substrate, the barrier layer is removed together, although the method is convenient for subsequent electroplating treatment, the obtained anodic oxide film is not supported by the aluminum substrate, the obtained aluminum oxide film is extremely soft in placement and easy to disperse, the subsequent electroplating process is extremely difficult to operate in practice, and the capability is not provided, so that all anode oxide film pore channels are vertically upward, the capillary pressure cannot be effectively overcome, and the full electroplating in each pore channel is realized.

(iii) US201113310135A, applicant company limited responsibility for general automotive globalization technology operations, discloses a method of bonding a metal to a substrate, the method comprising:

forming a nano-brush on the substrate surface, the nano-brush comprising a plurality of nanowires extending over the substrate surface;

introducing the metal in a molten state onto the substrate surface, the metal surrounding the plurality of nanowires; and

solidifying the metal surrounding the plurality of nanowires by cooling, wherein during the solidification at least a mechanical interlock is formed between the metal and the substrate;

wherein the formation of the nano-brush comprises:

forming a plurality of nanopores in a surface of the substrate;

depositing a material into the plurality of nanopores;

growing a nanowire from the deposited material in each of the plurality of nanopores; and

a portion of the substrate surface is removed to expose the nanowires grown therein.

Referring specifically to fig. 1 and the associated text, it is stated that "in some cases, the oxide structure 18 may be etched to remove its portion (including the barrier layer) at the bottom of the nanopore 16, thereby exposing the underlying aluminum substrate 12", i.e., the prior art either directly abandons the treatment of the barrier layer 19 or directly etches it away ambiguously, and no specific etching method is disclosed at all.

In addition, methods for removing the barrier layer are also described in the prior art, including the use of oxalic acid or phosphoric acid, or other mixtures, but all have the following significant technical problems: (1) the porous oxide layer and the shielding layer can not be distinguished limitedly by using acid liquor corrosion, namely the anodic oxide film is corroded by the acid liquor nondifferentially, so that the array structure of the anode oxide film pore canal is seriously influenced, the collapse or the non-uniform corrosion of the array structure of the anodic oxide film is caused, the subsequent electroplating process is not facilitated, and the electroplating uniformity of the coating and the stability of the binding force are seriously reduced; (2) in the corrosion process, after the shielding layer is penetrated, the corrosion liquid can obviously corrode the aluminum material, so that the base material is damaged.

Disclosure of Invention

Based on the problems of the prior art, the invention provides a preparation method of a high-bonding-force coating taking anodic aluminum oxide as a base material,

the method comprises the following steps: (1) pre-treating; (2) anodizing; (3) positioning and marking the protective film, wherein the solution used in the step is a mixed solution of gamma-chloropropyltrimethylsilane and anhydrous toluene; (4) removing the anode oxide film shielding layer, wherein the solution used in the step is a mixed solution of NaOH, NaF and ethanol; (5) electroplating a single metal layer, wherein the peel strength of the metal layer and the aluminum substrate is 7-8N/cm.

Further, the electroplating single metal layer is made of Ni metal, and the electroplating parameters are as follows: the electroplating solution is prepared from 200-230 g/L of nickel sulfate, 30-40 g/L of nickel chloride, 20-30g/L of boric acid, 45-50g/L of magnesium sulfate, 1-2g/L of sodium dodecyl sulfate and 3-6 of pH, and the electroplating process adopts pulse electroplating: the pulse frequency is 10-20Hz, the pulse duty ratio is 50-65%, and the temperature is 20-40%^oC, current density of 0.7-0.9A/dm²The electroplating time is 1-2 h, and no ultrasonic assistance is needed.

Further, the vacuum pumping treatment is assisted in the step (3), the vacuum degree is 90-100Pa, the nitrogen protection treatment is assisted in the step (4), and the vacuum freeze drying treatment is carried out between the steps (4) and (5).

Further, after vacuum freeze drying, ultrasonic-assisted pre-soaking treatment is carried out before single metal electroplating, electrolyte used in the pre-soaking process is consistent with electroplating solution used for electroplating a single metal layer, and the soaking temperature is 20-40 DEG C^oAnd C, soaking for 30s-60 min.

Further, the pretreatment process sequentially comprises mechanical polishing, oil removal, hot water washing, alkali washing, hot water washing, cold water washing, acid washing and water washing, wherein the mechanical polishing comprises one or more of sand blasting, brushing and tumbling, the oil removal is alkaline oil removal, and the oil removal is performedThe solution is a mixed aqueous solution of 20-25 g/L sodium carbonate and 2-3g/L sodium phosphate at the temperature of 65-70 DEG C^oC, soaking for 5-6 min; the alkaline washing solution is 20-30g/L of LNaOH and 3-5g/L of sodium citrate aqueous solution, and the temperature is 10-20^oC, soaking for 15-20min, wherein the acid washing ash removal liquid is HNO (HNO) with the concentration of 50-70g/L₃And 4-8g/LNaF mixed aqueous solution at normal temperature for 2-3 min.

Further, the solution used for anodic oxidation is a mixed solution of oxalic acid, phosphoric acid and sulfosalicylic acid, wherein the concentration of the oxalic acid is 0.25-0.3M, the concentration of the phosphoric acid is 0.2-0.4M, and the concentration of the sulfosalicylic acid is 0.05-0.15M.

Further, the voltage of the anodic oxidation process is 20-30V, and the temperature is 30V^oC, current density 2-3A/dm²The time is 20-30min, the average pore diameter of the anodic oxidation pore passage obtained by anodic oxidation is 150-200nm, and the pore number is 80-150/mum²The thickness of the anodic oxide film is 0.5-1 μm, and the thickness of the shielding layer is 5-15 nm.

Further, the concentration of the gamma-chloropropyltrimethylsilane is 10-20 wt%, and the dosage of the gamma-chloropropyltrimethylsilane is 3-5% of the weight of the anodized aluminum material.

Further, the NaOH: NaF: the mass ratio of the ethanol is (2-5) to (1-2) to 7.

Further, the coefficient of variation of the peel strength between the metal layer and the aluminum substrate was 0.041.

The following detailed explanation is made with respect to the reagents, concentrations, and principles used in the above-described preparation method:

(1) in principle, as shown in FIG. 5, the anodic oxide film generally comprises a shielding layer and a nano-array porous layer at the bottom of the anodic oxide film pore, wherein the main component of the shielding layer is γ -Al2O3, i.e. anhydrous, with few hydroxyl groups, and the porous layer is generally α -AlOOH alumina, rich in crystalline water and hydroxyl groups, and based on the above-mentioned difference between the shielding layer and the porous layer, γ -chloropropyltrimethylsilane is introduced by vacuum pumping inside the anodic oxide film, and at 75^oAnd C, reacting the gamma-chloropropyltrimethylsilane with hydroxyl to form a tripodal silicon-oxygen bond with strong binding force, wherein the reaction formula is as follows:

and the surface of the anode oxide film porous layer is effectively coated, because the bottom of the shielding layer has no or only few hydroxyl groups, the gamma-chloropropyltrimethylsilane is not pasted and adsorbed on the surface of the shielding layer, so that the gamma-chloropropyltrimethylsilane is accurately coated, in addition, a vacuumizing means is assisted in the process of positioning and marking the protective film, so that the gamma-chloropropyltrimethylsilane effectively overcomes the capillary effect of the anode oxide film nanotube, in addition, the nanopore of the anode oxide film is open at one end, the aluminum base at one end is sealed, and the gamma-chloropropyltrimethylsilane can enter the nanopore more conveniently by vacuumizing, which is an indispensable auxiliary means in the invention.

Then, the shielding layer is corroded by using a corrosive liquid, wherein the corrosive liquid is an alkaline corrosive liquid but not an acidic corrosive liquid, protons used in the acidic corrosive liquid are easy to dissociate silicon-oxygen bonds adsorbed on the surface of the porous layer, so that the gamma-chloropropyltrimethylsilane is desorbed from the surface of the porous layer and finally loses the function of the protective layer, the alkaline sodium hydroxide does not influence the gamma-chloropropyltrimethylsilane, and meanwhile, the alkaline sodium hydroxide can be effectively contacted with the shielding layer to generate NaOH + Al contact, so that NaOH + Al contact is generated, and the shielding layer is protected against corrosion₂O₃→NaAlO₂+H₂O, and further, a reaction for effectively removing alumina is realized, and in addition, the above-mentioned corrosion reaction can occur at normal temperature without heating.

In addition, the corrosive liquid of the invention consists of NaOH, NaF and ethanol, does not contain any water, and is mainly because Al + NaOH + H is very easy to occur under the condition of water existence₂O—NaAlO2+3H₂Cause the loss of substrate, when there is not moisture in the corrosion process (the water that produces in the corrosion shielding layer process is less, can be ignored), it is difficult only to take place the reaction of Al and NaOH, in addition, in this corrosion process, the supplementary nitrogen protection that has, the corruption of alkali and substrate can not or hardly take place more, simple easy location is corroded, and the damage of substrate does not take place, in addition, NaF is the penetrant, be favorable to the corruption of sodium hydroxide and compact sclausura shielding layerAnd (4) reacting.

(2) With regard to the process for preparing gamma-chloropropyltrimethylsilane, reference is made to the relevant prior art, in particular to the following: preparing gamma-chloropropyltrichlorosilane: the equipment comprises a thermometer, a constant-pressure dropping funnel and a reflux condenser pipe, wherein the upper end of the condenser pipe is provided with a cold trap, a calcium chloride drying pipe and a paraffin oil bubble counter, and a 1000mL three-neck flask, 4.5M trichlorosilane and 3-chloropropene 3M are mixed and placed in the constant-pressure dropping funnel, about 25mL of feed liquid is firstly placed into a reaction bottle, 0.15mL of 0.1mol/L chloroplatinic acid-isopropanol solution, 0.15mL of cocatalyst and 0.25g of hydroquinone are added, the reaction is rapidly initiated at room temperature, the temperature is increased to 75 ℃, the feed liquid is started to be dripped, the dripping speed is adjusted, the temperature is controlled to be 80 ℃, the dripping is finished within about 2 hours, the reflux is carried out for 3 hours, and the reaction is finished when the reaction temperature is finally increased to 90 ℃. And (3) fractionating the reaction mixture at normal pressure, and collecting the fraction at 182 ℃, namely 3-chloropropyltrichlorosilane with the yield of 85%.

(3) Regarding the pretreatment:

no matter what kind of surface treatment process, to obtain good effect, the surface pretreatment is the primary condition, mainly because the surface of the aluminum material has various defects such as grinding marks, pits, burrs, scratches, etc., and has lubricating oil traces or covers abrasive materials and some dirt to different degrees, if not cleaned, the surface of the aluminum material will be exposed after the anodic oxidation treatment, and the pore structure and the performance of the surface of the anodic oxide film are affected, and the pretreatment is simple as follows: (1) the adhesion between the oxide film and the surface of the substrate is ensured, and as the subsequent treatment needs to plate other metals on the surface of the anodic oxide film, the oxide film exists as an intermediate layer, and the adhesion bonding force is the basic requirement; (2) ensuring the uniformity of the bonding force between the substrate and the subsequent plating layer.

(a) Mechanical polishing: the method comprises one or more of sand blasting, brushing and tumbling, wherein the sand blasting is a finishing method for spraying abrasive on the surface of a workpiece by using compressed air, removing oxide skin, corrosion and other defects on the surface of the workpiece by using the kinetic energy of high-speed abrasive, and forming a uniform matt surface, and the sand blasting effect is related to factors such as spraying distance, spraying angle, pressure, nozzle size and shape, abrasive size, abrasive and water mixing ratio and the like. In simple terms, such as fine grit, a soft matte smooth surface can be produced; the coarse particle size of the abrasive can generate a rough and dark surface, and is used for eliminating surface defects with large areas and deep scars. The small steel shot particles can make the surface of the aluminum generate light gray, and the large steel shot particles do not change the natural color of the surface of the aluminum. The aluminum surface was given a light gray color with silicon carbide particles and a blue color with powdered silica.

Brushing: brushing is a process of processing a metal surface by using a brush made of metal wires, animal hair and other natural or artificial fibers, and can be a dry brush or a wet brush. The brushing effect depends on the shape and the characteristics of the brush wheel and the material and the thickness of the metal wire.

And (3) rolling finish: the tumbling is to put the workpiece and the abrasive material in a roller for low-speed rotation, and the polishing treatment is carried out by the relative friction of the workpiece and the abrasive material.

(b) Degreasing: the invention adopts alkaline solution for degreasing, which can saponify the vegetable oil and the animal oil on the surface of the substrate to generate soap dissolved in water, and then the soap is removed, and the reaction is as follows:

(C17H35COO)₃C₃H₅+3NaOH→3C₁₇H₃₅COONa+C₃H₅(OH)₃

the deoiling liquid is a mixed aqueous solution of 20-25 g/L sodium carbonate and 2-3g/L sodium phosphate, the temperature is 65-70 ℃, the soaking time is 5-6min, the alkali of sodium carbonate is weaker than that of sodium hydroxide, the deoiling liquid has certain saponification capacity, the pH value of the solution is buffered, the corrosivity to metal and the irritation to skin are lower than those of sodium hydroxide, the price is low, the deoiling liquid is often used as main salt in aluminum alloy degreasing liquid, the sodium phosphate is alkalescent, has certain saponification capacity and the buffering effect on the pH value, can complex metal ions in water, enables the water quality to be soft, and is an emulsifier, high in solubility and good in washability. The alkaline degreasing comprises primary washing and secondary washing, for example, the primary washing can be washed by hot water at 60-70 ℃, so that pollutants remained on the surface of the workpiece after degreasing can be effectively removed.

(c) Alkali washing: after the degreasing process, the aluminum alloy workpiece cannot be subjected to conversion film treatment, the surface of the aluminum alloy workpiece generally has defects of a natural oxide film, processing stripes and the like, and the aluminum alloy workpiece needs to be subjected to corrosion treatment to remove the natural oxide film and activate the surface. The alkaline corrosion is the most common corrosion process, the main component is NaOH solution, the alkaline solution is 20-30g/LNaOH and 3-5g/L sodium citrate aqueous solution, the temperature is 10-20 ℃, the soaking time is 15-20min, wherein a natural alumina film and sodium hydroxide react to form sodium metaaluminate, the corrosion speed of the aluminum is in direct proportion to the total content of the sodium hydroxide in the solution, and the corrosion speed is increased along with the increase of the temperature. The sodium citrate is mainly used as a complexing agent, so that aluminum ions can be effectively masked, and the generation of hydrogen production aluminum oxide precipitates is avoided.

(d) Acid washing: the surface of an aluminum alloy workpiece subjected to alkaline degreasing and alkaline corrosion is generally provided with a layer of black ash. In order to obtain a bright metal surface, it is necessary to perform a brightening treatment with an acidic solution. Even pure aluminum workpieces and alkaline liquid on the surface are difficult to completely clean by water and need to be neutralized by acid solution, and the acid washing ash removing solution is mixed aqueous solution of 50-70g/L HNO3 and 4-8g/L NaF, and is at normal temperature for 2-3 min.

(e) Washing with water: any aluminum workpiece treated by the chemical solution should be immediately washed with water after being removed from the treatment solution, and the faster the aluminum workpiece is, the better the aluminum workpiece is. Since the workpiece is exposed to air away from the treatment liquid and the surface is in a non-uniform state, it is necessary to immediately wash away the chemical agent with water to terminate the chemical reaction. And simultaneously prevents the chemical agent from being brought into the next processing liquid to pollute the next chemical processing groove.

(4) Regarding anodic oxidation: the thickness of the barrier layer depends on the voltage of the anodic oxidation, the size of the pores and pore bodies of the porous layer is related to the composition, concentration and operating conditions of the electrolyte, the invention uses oxalic acid as main acid, and is compounded with phosphoric acid and sulfosalicylic acid, wherein the oxalic acid has smaller dissolving capacity to aluminum than sulfuric acid, so that a film layer which is more stable than the sulfuric acid anodic oxidation is easily obtained, such as the anodic oxidation film of the application with the thickness of 0.5-1 μm; when phosphoric acid is generally used for anodic oxidation, the porosity of the anodic oxide film can be effectively improved, the pore diameter is larger, for example, the pore number of the anodic oxide film is 80-150/mu m2, the addition of sulfosalicylic acid organic acid can effectively reduce the use amount of oxalic acid and phosphoric acid, and the reduction of the thickness of the shielding layer of the anodic oxide film is slightly promoted.

Voltage: during the oxidation of oxalic acid, the voltage should be increased slowly, for example, it should be increased too fast, which may cause current concentration at the non-uniform part where the oxide film is newly formed, resulting in severe electrical breakdown at that part, causing corrosion of aluminum metal, and the voltage is preferably 20-30V.

Current density: the current density is proportional to the alumina formation rate, and the higher the current density, the faster the alumina formation rate. However, the rate of formation of the oxide film is not completely proportional to the current density. The rate of formation of the oxide film is equal to the rate of formation of alumina minus the rate of dissolution of alumina in the electrolyte, which is a chemical process independent of the electrolytic current density and depends on the concentration of the electrolyte and the local temperature of the solution. The higher the concentration of the electrolyte, the higher the local temperature of the solution, and the faster the dissolution rate of alumina. Therefore, under the same electrolyte concentration and temperature conditions, the dissolution rate of alumina is not changed. The current density is increased, the generation speed of the oxide film is increased, and the porosity of the oxide film is reduced, so that the current density of the invention is 2-3A/dm²。

Temperature: the temperature is increased, the film layer is reduced, if the pH value of the electrolyte is increased at higher temperature, the thickness of the film can be increased, and the optimal temperature is 25-40 ℃, preferably 30 DEG C^oC。

(4) Regarding the plating: before electroplating single metal, soaking the anode oxidation aluminum alloy without the shielding layer by using a nickel electrolyte in advance, and accompanying with an ultrasonic process, aiming at enabling the electrolyte to be in full contact with the aluminum material at the bottom of the pore channel of the anode oxidation film, effectively removing redundant gas in the nanometer pore channel by ultrasonic, and realizing full contact of the plating solution and a base material.

The electroplating solution disclosed by the invention comprises 200-230 g/L of nickel sulfate, 30-40 g/L of nickel chloride, 20-30g/L of boric acid, 45-50g/L of magnesium sulfate and 1-2g/L of sodium dodecyl sulfate, wherein the pH value is 3-6, and the electroplating process adopts pulse electroplating: the pulse frequency is 10-20Hz, the pulse duty ratio is 50-65%, the temperature is 20-40 oC, the current density is 0.7-0.9A/dm2, the electroplating time is 1-2 h, and no ultrasonic assistance is provided.

Wherein, nickel sulfate is used as main salt, the concentration range is generally 200-230 g/L, and the nickel sulfate is used as main salt for generating nickel ions;

using nickel chloride as activator, wherein Ni⁺Can effectively reduce the usage amount of nickel sulfate, and Cl^-The conductivity and the cathode dispersing ability of the plating solution can be improved, and the activator can not introduce other additional metal ions into the plating solution;

magnesium sulfate is used as a conductive salt, and a reagent is not required to be added into the conductive salt, but the magnesium sulfate can improve the smoothness and the flexibility of a plating layer;

boric acid is used as a buffering agent, in order to prevent the acidity of the plating solution from changing rapidly in production, the boric acid is often added as the buffering agent, the pH = 3-6 is controlled, and the boric acid has a buffering effect and can improve the cathode polarization and the conductivity of the plating solution so as to improve the density of the scorching current;

sodium lauryl sulfate is used as a pinhole preventing agent which can reduce or eliminate the amount of hydrogen precipitated on the cathode, thereby eliminating pinholes and improving the plating effect.

Acidity (pH value) is in a range of pH 3-6, when the pH value is low, a large amount of hydrogen is separated out from a cathode, the current efficiency is reduced, when the pH value is lower than 3, the hydrogen is violently discharged, even the current efficiency is 0, but when the pH value exceeds 6 or is close to neutral, nickel hydroxide precipitate is generated, the nickel hydroxide precipitate is mixed in a nickel layer to enable a plating layer to be peeled off, embrittled, difficult to deposit in deep holes and the like, when the pH value is high, the sulfuric acid solution is used for adjustment, and when the pH value is low, 3% of sodium hydroxide can be added for adjustment; when sodium hydroxide is added, precipitate is easy to generate, the sodium hydroxide is slowly added under continuous stirring, and the effect of replacing the sodium hydroxide by the nickel carbonate is better;

the temperature has great influence on the internal stress of the plating layer, when the temperature is increased from 10 ℃ to 35 ℃, the internal stress of the nickel layer is rapidly reduced, and the internal stress is slowly reduced when the temperature is increased from 35 ℃ to 60 ℃. When the temperature is further increased, the internal stress hardly changes. The heating can also increase the solubility of each component in the electroplating solution, and further, concentrated nickel plating solution can be adopted; meanwhile, the temperature is increased, the conductivity of the plating solution is increased, and the current efficiency is improved.

Compared with common electroplating, the pulse electroplating technology has the obvious advantages that the mass transfer process in the electroplating process can be controlled, and the peak current higher than the average current can be generated, so that the instantaneous current and the reaction speed in the electroplating process and the nucleation and growth of crystal grains in the electroplating process are influenced, and the current density is selected to be 0.7-0.9A/dm²The duty ratio is 50-65%, and the electroplating effect is best.

The scheme of the invention has the following beneficial effects:

(1) the shielding layer at the bottom of the anode oxide film pore channel can be effectively corroded through the selective adsorption reaction of gamma-chloropropyltrimethylsilane on the porous layer and the shielding layer and the subsequent alkaline corrosion reaction;

(2) the nano oxide film pore array can be obtained through pretreatment and anodic oxidation treatment, and the pore structure is complete and uniform.

(3) The removal of the gamma alumina shielding layer can effectively improve the conductivity of the anodic oxidation base material;

(4) the corrosion removal of the shielding layer can effectively improve the binding force between the subsequent plating layer and the aluminum base material, and the peel strength between the metal layer and the aluminum base material is 7-8N/cm;

(5) the fluctuation coefficient of the binding force between the plating layer and the base material is small, namely the stability of the plating layer is excellent.

Drawings

FIG. 1 is a top SEM image of an anodic oxide film pore array of the present invention.

FIG. 2 is an SEM image of a cross section of the pore channels of the anodic oxide film of the present invention.

FIG. 3 is a SEM image of the cross section of the pore array of the anodic oxide film of the present invention.

FIG. 4 is a SEM image of a cross section of an anodized pore array after selective etching.

FIG. 5 is a schematic diagram of the process of removing the shielding layer in the anodic aluminum oxide via according to the present invention.

Fig. 6 is a top SEM micrograph of nickel metal filled nanopores of the present invention.

Fig. 7 is a cross-sectional SEM image of a nickel metal filled nanopore of the present invention.

Fig. 8 is a top SEM micrograph of nickel metal filled nanopores of the present invention.

FIG. 9 is a SEM image of a cross section of an anodized aluminum alloy and a plating layer according to the present invention.

Detailed Description

Example 1

The pretreatment steps and solutions used in examples 1-3 were identical and all included mechanical polishing, degreasing, hot water washing, alkaline washing, hot water washing, cold water washing, acid washing, water washing:

the mechanical polishing is sand blasting,

the oil removal is alkaline oil removal, the oil removal liquid is a mixed aqueous solution of 23g/L sodium carbonate and 2.5g/L sodium phosphate, and the temperature is 67 DEG^oC, soaking for 5.5 min;

the alkaline solution is 25g/LNaOH and 4g/L sodium citrate aqueous solution, and the temperature is 15^oC, soaking for 17.5 min;

the acid washing ash removing liquid is 60g/L HNO₃And a mixed aqueous solution of 6g/LNaF at normal temperature for 2.5 min.

(2) Anodic oxidation: taking the aluminum material treated in the step (1) as an anode, taking graphite as a cathode, immersing the aluminum material into electrolyte, and respectively connecting the electrolyte with a power supply through leads, wherein the electrolyte is a mixed solution of oxalic acid, phosphoric acid and sulfosalicylic acid, the concentration of the oxalic acid is 0.2M, the concentration of the phosphoric acid is 0.2M, the concentration of the sulfosalicylic acid is 0.05M, the electrolysis parameters are as follows, the voltage is 20V, and the temperature is 30V^oC, Current Density 2A/dm²For 20 min; after anodic oxidation, ethanol is soaked and cleaned, vacuum drying is used, electrolyte in an oxide film is removed, and the whole process strictly avoids the contact of air or water with the anodized aluminum product and avoids hole sealing.

(3) A step of positioning and marking a protective film, which is to soak the aluminum material treated in the step (2) in a toluene solution of gamma-chloropropyltrimethylsilane, wherein the concentration of the aluminum material is 10 wt%, and the dosage of the aluminum material is 4% of the weight of the aluminum material after anodic oxidation; the vacuum pumping treatment is assisted in the soaking process, the vacuum degree is 100Pa, and after no bubble overflows from the pore channel, the soaking process is kept still for 7min, and the reaction is fully carried out.

(4) Removing the anode oxide film shielding layer: and (3) soaking the aluminum material treated in the step (3) in a mixed solution of NaOH, NaF and ethanol, and fully reacting for 5min under the protection of nitrogen, wherein the weight ratio of NaOH: NaF: the mass ratio of the ethanol is 2:1: 7.

(5) And (5) vacuum freeze drying.

(6) And (4) carrying out pre-foaming treatment.

(7) Electroplating nickel: the electroplating solution is prepared from 200g/L of nickel sulfate, 30g/L of nickel chloride, 20g/L of boric acid, 45g/L of magnesium sulfate and 1g/L of sodium dodecyl sulfate, and the electroplating process adopts pulse electroplating: pulse frequency 10Hz, pulse duty cycle 50%, temperature 20^oC, current density 0.7A/dm²And the electroplating time is 1 h.

(8) After plating, the plate was washed and dried, and the obtained sample was named S-1.

Example 2

(2) Anodic oxidation: taking the aluminum material treated in the step (1) as an anode, taking graphite as a cathode, immersing the aluminum material into electrolyte, and respectively connecting the electrolyte with a power supply through leads, wherein the electrolyte is a mixed solution of oxalic acid, phosphoric acid and sulfosalicylic acid, the concentration of the oxalic acid is 0.275M, the concentration of the phosphoric acid is 0.3M, the concentration of the sulfosalicylic acid is 0.1M, the electrolysis parameters are as follows, the voltage is 25V, and the temperature is 30^oC, current density 2.5A/dm²For 25 min; after anodic oxidation, ethanol is soaked and cleaned, vacuum drying is used, electrolyte in an oxide film is removed, and the whole process strictly avoids the contact of air or water with the anodized aluminum product and avoids hole sealing.

(3) A step of positioning and marking a protective film, which is to soak the aluminum material treated in the step (2) in a toluene solution of gamma-chloropropyltrimethylsilane, wherein the concentration is 15 wt%, and the dosage of the protective film is 4% of the weight of the aluminum material after anodic oxidation; the vacuum pumping treatment is assisted in the soaking process, the vacuum degree is 100Pa, and after no bubble overflows from the pore channel, the soaking process is kept still for 7min, and the reaction is fully carried out.

(4) Removing the anode oxide film shielding layer: and (3) soaking the aluminum material treated in the step (3) in a mixed solution of NaOH, NaF and ethanol, and fully reacting for 5min under the protection of nitrogen, wherein the weight ratio of NaOH: NaF: the mass ratio of ethanol is 3.5:1.5: 7.

(5) And (5) vacuum freeze drying.

(6) And (4) carrying out pre-foaming treatment.

(7) Electroplating nickel: the electroplating solution is prepared from 225g/L nickel sulfate, 35g/L nickel chloride, 25g/L boric acid, 47.5g/L magnesium sulfate and 1.5g/L sodium dodecyl sulfate, and the electroplating process adopts pulse electroplating: pulse frequency 15Hz, pulse duty cycle 60%, temperature 30^oC, current density 0.8A/dm²And the electroplating time is 1.5 h.

(8) After plating, the plate was washed and dried, and the obtained sample was named S-2.

Example 3

(5) And (5) vacuum freeze drying.

(6) And (4) carrying out pre-foaming treatment.

(7) Electroplating nickel: the electroplating solution is prepared from 230g/L nickel sulfate, 40g/L nickel chloride, 30g/L boric acid, 50g/L magnesium sulfate and 2g/L sodium dodecyl sulfate by electroplatingThe process adopts pulse plating: pulse frequency 20Hz, pulse duty cycle 65%, temperature 40^oC, current density 0.9A/dm²And the electroplating time is 2 h.

(8) After plating, the plate was washed and dried, and the obtained sample was named S-3.

Comparative example 1

(2) Anodic oxidation: taking the aluminum material treated in the step (1) as an anode, taking graphite as a cathode, immersing the aluminum material into electrolyte, and respectively connecting the electrolyte with a power supply through leads, wherein the electrolyte is mixed solution of oxalic acid, phosphoric acid and sulfosalicylic acid, the concentration of the oxalic acid is 0.275M, the concentration of the phosphoric acid is 0.3M, the electrolysis parameters are as follows, the voltage is 25V, and the temperature is 30V^oC, current density 2.5A/dm²For 25 min; after anodic oxidation, ethanol is soaked and cleaned, vacuum drying is used, electrolyte in an oxide film is removed, and the whole process strictly avoids the contact of air or water with the anodized aluminum product and avoids hole sealing.

(3) And (3) corrosion: and (3) soaking the aluminum material treated in the step (2) in a mixed solution of NaOH, NaF and ethanol, and fully reacting for 5min under the protection of nitrogen, wherein the weight ratio of NaOH: NaF: the mass ratio of ethanol is 3.5:1.5: 7.

(4) And (4) carrying out pre-foaming treatment.

(5) Electroplating nickel: the electroplating solution is prepared from 225g/L nickel sulfate, 35g/L nickel chloride, 25g/L boric acid, 47.5g/L magnesium sulfate and 1.5g/L sodium dodecyl sulfate, and the electroplating process adopts pulse electroplating: pulse frequency 15Hz, pulse duty cycle 60%, temperature 30^oC, current density 0.8A/dm²And the electroplating time is 1.5 h.

(6) After plating, the plate was washed and dried, and the obtained sample was named D-1.

Comparative example 2

(2) And (5) activating and corroding.

(3) And (4) carrying out pre-foaming treatment.

(4) Electroplating nickel: the electroplating solution is prepared from 225g/L nickel sulfate, 35g/L nickel chloride, 25g/L boric acid, 47.5g/L magnesium sulfate and 1.5g/L sodium dodecyl sulfate, and the electroplating process adopts pulse electroplating: pulse frequency 15Hz, pulse duty cycle 60%, temperature 30^oC, current density 0.8A/dm²Time of plating1.5h。

(5) After plating, the plate was washed and dried, and the obtained sample was named D-2.

TABLE 1 comparative examples 1-2 and example 2 binding force data

As shown in the attached figure 1, by adopting the pretreatment and anodic oxidation means of the invention, a uniform and regular nano-oxide membrane pore array can be obtained, as shown in Table 1, the average pore diameter of the anodic oxide pore is 150-200nm, and by controlling the electrolysis parameters, the uniform and regular nano-oxide membrane pore array can be obtained

The number of pores is 80-150/mum²The thickness of the anodic oxide film is 0.5-1 μm, and the thickness of the shielding layer is 5-15 nm.

As shown in figure 2, after anodic oxidation, a remarkable shielding layer can be seen at the bottom of the pore canal, the thickness of the shielding layer is 5-15nm, as shown in figures 3 and 4, the shielding layer at the bottom of the anodic oxide membrane pore canal can be effectively corroded by subsequent alkaline corrosive liquid through the selective adsorption reaction of gamma-chloropropyltrichlorosilane.

As shown in fig. 6, 7, 8, and 9, the nickel alloy can completely enter the pores of the anodic oxide film, the filling effect is good, and when the shielding layer inside the pores of the oxide film is removed, as shown in table 1, the peel strength of the metal layer and the aluminum substrate is 7-8N/cm, the average bonding strength is 7.48N/cm, the standard deviation is 0.30, and the fluctuation coefficient is 0.041, and it can be seen from the data that the bonding force of the plating layer and the substrate is high and stable.

And as shown by removing the shielding layer D-1 in the anodic oxide film, the bonding strength is 2.1-3.9N/cm, the average bonding strength is 3.04N/cm, the standard deviation is 0.61, the coefficient of variation is 0.20, the coefficient of variation is large, the main reason is that the conductivity coefficient of each pore channel in the anodic oxide film is different, and the metal can not be deposited uniformly, in contrast, the nickel layer D-2 is directly electroplated on the surface of the aluminum material, the average bonding strength is 2.24N/cm, the standard deviation is 0.56, the fluctuation coefficient is 0.25, because of no buckling effect between the aluminum material and the plating layer, the peeling strength is not as good as D-1, and in addition, since the D-2 treatment process includes corrosion of the substrate, the corrosion may cause roughness and fluctuation of the substrate surface, thus, D-2 has a higher coefficient of variation in peel strength than S-2 and D-1.

To sum up, the following steps: (1) the nano oxide film pore array can be obtained through pretreatment and anodic oxidation treatment, the pore structure is complete and uniform, in addition, the gamma-chloropropyltrimethylsilane can selectively adsorb the porous layer and the shielding layer and can effectively corrode the shielding layer at the bottom of the anodic oxide film pore by subsequent alkaline corrosion reaction, so that the conductivity of the anodic oxide substrate can be effectively improved, and the subsequent plating layer and the aluminum substrate can be effectively combined; (2) the shielding layer at the bottom of the anode oxide film pore canal is removed, and Ni single metal is electroplated on the shielding layer, so that the high-bonding-force plating material taking the anode oxide as the base material is obtained, the peel strength of the metal layer of the material and the aluminum base material is 7-8N/cm, the average bonding strength is 7.48N/cm, and the fluctuation coefficient is 0.041, namely, the bonding force and the stability are better.

Although the present invention has been described above by way of examples of preferred embodiments, the present invention is not limited to the specific embodiments, and can be modified as appropriate within the scope of the present invention.

Claims

1. A preparation method of a high-bonding-force coating taking anodic aluminum oxide as a base material is characterized by comprising the following steps: (1) pre-treating; (2) anodizing; (3) positioning and marking the protective film, wherein the solution used in the step is a mixed solution of gamma-chloropropyltrimethylsilane and anhydrous toluene; (4) removing the anode oxide film shielding layer, wherein the solution used in the step is a mixed solution of NaOH, NaF and ethanol; (5) electroplating a single metal layer, wherein the peel strength of the metal layer and an aluminum substrate is 7-8N/cm, the concentration of gamma-chloropropyltrimethylsilane is 10-20 wt%, the dosage of the gamma-chloropropyltrimethylsilane is 3-5% of the weight of the anodized aluminum material, vacuumizing is assisted in the step (3), and the vacuum degree is 90-100 Pa.

2. Such as rightThe method for preparing the high-bonding-force coating by using the anodized aluminum as the base material according to claim 1, wherein the electroplated single metal layer is Ni metal, and the electroplating parameters are as follows: the electroplating solution is prepared from 200-230 g/L of nickel sulfate, 30-40 g/L of nickel chloride, 20-30g/L of boric acid, 45-50g/L of magnesium sulfate, 1-2g/L of sodium dodecyl sulfate and 3-6 of pH, and the electroplating process adopts pulse electroplating: the pulse frequency is 10-20Hz, the pulse duty ratio is 50-65%, and the temperature is 20-40%^oC, current density of 0.7-0.9A/dm²The electroplating time is 1-2 h, and no ultrasonic assistance is needed.

3. The method for preparing a high-bonding-force coating on an anodized aluminum substrate according to claim 1, wherein a nitrogen protection treatment is added during the step (4), and a vacuum freeze drying treatment is carried out between the steps (4) and (5).

4. The method according to claim 3, wherein the pre-soaking treatment is performed by ultrasonic assistance before the single metal layer is electroplated after the vacuum freeze drying, the electrolyte used in the pre-soaking process is the same as the electroplating solution used for electroplating the single metal layer, and the soaking temperature is 20-40%^oAnd C, soaking for 30s-60 min.

5. The method according to claim 1, wherein the pretreatment comprises one or more of mechanical polishing, degreasing, hot water washing, alkaline washing, hot water washing, cold water washing, acid washing and water washing, wherein the degreasing is alkaline degreasing, and the degreasing liquid is a mixed aqueous solution of 20-25 g/L sodium carbonate and 2-3g/L sodium phosphate at a temperature of 65-70%^oC, soaking for 5-6 min; the alkaline washing solution is 20-30g/L of LNaOH and 3-5g/L of sodium citrate aqueous solution, and the temperature is 10-20^oC, soaking for 15-20min, wherein the acid washing ash removal liquid is HNO (HNO) with the concentration of 50-70g/L₃And 4-8g/LNaF mixed aqueous solution at normal temperature for 2-3 min.

6. The method according to claim 1, wherein the solution used in the anodic oxidation is a mixture of oxalic acid, phosphoric acid and sulfosalicylic acid, the concentration of oxalic acid is 0.25-0.3M, the concentration of phosphoric acid is 0.2-0.4M, and the concentration of sulfosalicylic acid is 0.05-0.15M.

7. The method according to claim 1, wherein the anodizing process is performed at a voltage of 20-30V and a temperature of 30V^oC, current density 2-3A/dm²The time is 20-30min, the average pore diameter of the anodic oxidation pore passage obtained by anodic oxidation is 150-200nm, and the pore number is 80-150/mum²The thickness of the anodic oxide film is 0.5-1 μm, and the thickness of the shielding layer is 5-15 nm.

8. The method of claim 1, wherein the NaOH: NaF: the mass ratio of the ethanol is (2-5) to (1-2) to 7.

9. The method of claim 1 wherein the coefficient of variation of peel strength between the metal layer and the aluminum substrate is 0.041.