CN110791797B - High-corrosion-resistance conductive protection method for magnesium-lithium alloy and corresponding part - Google Patents
High-corrosion-resistance conductive protection method for magnesium-lithium alloy and corresponding part Download PDFInfo
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Abstract
The invention relates to a high-corrosion-resistance conductive protection method for a magnesium-lithium alloy. The colloid palladium one-step method sensitization-activation treatment and reduction treatment adopted in the method break through the key bottleneck that a magnesium-lithium alloy (brand LZ91) micro-arc oxidation film is easy to dissolve and difficult to plate, and successfully obtains a metal coating with good binding force on the magnesium-lithium alloy (brand LZ91) micro-arc oxidation film. The surface of the magnesium-lithium alloy (the trademark LZ91) composite protective layer consisting of the micro-arc oxidation film (inner layer) and the metal coating (outer layer) is conductive and firmly combined with the matrix, and no phenomena such as foaming or layering and the like occur between the protective layer and the matrix after a thermal shock test at 200 ℃; the composite protective layer has excellent corrosion resistance, and the protective grade Rp of the composite protective layer reaches 9 grades after a 192-hour acid salt spray test. The invention can be used for the conductive and high-corrosion-resistance composite protection treatment of the magnesium-lithium alloy (with the trade name of LZ91) workpiece in severe environment. The method provided by the invention is suitable for automatic mass production and high in production efficiency.
Description
Technical Field
The invention relates to the field of materials, in particular to a high-corrosion-resistance conductive protection method for a magnesium-lithium alloy.
Background
The magnesium-lithium alloy is used as the lightest metal structure material, has the density which is 1/4-1/3 lighter than that of the common magnesium alloy and 1/3-1/2 lighter than that of the aluminum alloy, has excellent mechanical properties of high specific rigidity and high specific strength, high damping performance of shock absorption and noise elimination, and radiation and electromagnetic interference resistance, is called as the most environment-friendly revolutionary material in the future, and is one of ideal structure materials in the fields of aerospace, weapons industry, nuclear industry, automobiles, 3C industry, medical appliances and the like.
Due to the limited carrying capacity of the electronic equipment of the military aircraft, the demand for miniaturization and light weight of the airborne electronic equipment is more and more urgent, and magnesium-lithium alloy is used as the lightest metal structure material available at present and is gradually applied as a light metal material for replacing aluminum alloy. The lightweight design of reasonably selecting the magnesium-lithium alloy in the airborne electronic equipment effectively ensures the weight reduction effect and improves the maneuvering performance of the airplane.
As is known to all, magnesium and lithium are elements with strong activity, so that the magnesium-lithium alloy has strong activity, is very easy to corrode in a humid atmosphere or corrosive environment, has poor corrosion resistance, and can be used only by being subjected to complex surface protection treatment.
At present, the common surface treatment methods of the magnesium-lithium alloy comprise chemical plating, micro-arc oxidation, painting and the like, and the corrosion resistance of the magnesium-lithium alloy subjected to the surface treatment can be improved to a certain extent. According to different application conditions, the magnesium-lithium alloy part can be generally divided into two types, namely a surface needing electric conduction and a surface not needing electric conduction; the more mature surface treatment method of the conductive part is chemical nickel plating and can be checked through a neutral salt spray test for 48-96 h, the more extensive surface treatment method of the part without the conductive requirement is micro-arc oxidation/paint coating and can be checked through a neutral salt spray test for 120-200 h, and the application requirement of aerospace products is met.
For magnesium-lithium alloy products under the application working condition that the surface needs to be conductive and has high corrosion resistance requirements, the current single conductive plating layer or non-conductive covering layer can not meet the use requirements; therefore, the high corrosion resistance conductive protection method of the magnesium-lithium alloy has become a bottleneck limiting the application of the magnesium-lithium alloy in certain specific fields.
Disclosure of Invention
In some special circumstances, magnesium-lithium alloys are used for modular construction in order to meet weight constraints. Based on severe service environment conditions, the environmental adaptability of the electronic equipment required by a user is very strict, the requirement is that the electronic equipment passes an acid salt spray test of 192h, and meanwhile, due to the electromagnetic shielding requirement, the inner surface and the outer surface of the module are required to be conductive, and the conventional surface protection technology cannot meet the use requirement easily. At present, no manufacturers capable of producing the material are reported.
The invention aims to provide a high-corrosion-resistance conductive protection method for a magnesium-lithium alloy, wherein after corresponding treatment is carried out according to the technical method, the surface of a magnesium-lithium alloy product is conductive and can pass an acid salt spray test for 192 hours (the protection grade Rp after the test is not lower than 9).
Specifically, the invention provides a high-corrosion-resistance conductive protection method for a magnesium-lithium alloy, which is characterized by comprising the following steps of:
step (1), carrying out micro-arc oxidation on a target magnesium-lithium alloy material to form an oxide film layer;
step (2), carrying out surface sensitization-activation on the target magnesium-lithium alloy material after the oxide film layer is formed;
step (3), carrying out reduction treatment on the sensitized and activated target magnesium-lithium alloy material;
step (4), carrying out chemical copper plating on the reduced target magnesium-lithium alloy material;
step (5), carrying out electro-coppering on the target magnesium-lithium alloy material subjected to electroless copper plating;
step (6), electroplating zinc-nickel alloy on the surface of the target magnesium-lithium alloy material;
step (7), passivating the target magnesium-lithium alloy material by using SL-10 hexavalent chromium;
and (8) drying the target magnesium-lithium alloy material.
In a preferred implementation mode, the solution adopted by the micro-arc oxidation in the step (1) comprises 15g/L to 20g/L of sodium silicate, 8g/L to 10g/L of sodium fluoride and 3g/L to 5g/L of sodium hydroxide, wherein the solution temperature is as follows: 20 ℃ to 40 ℃, oxidation current density: 5A/dm2～10A/dm2And the oxidation time is as follows: 30 min-40 min, and the thickness of the oxide film is controlled to be 20 mu m-25 mu m.
In another preferred implementation, the process of sensitization-activation in the step (2) includes: adopting a colloidal palladium one-step method to treat the target magnesium-lithium alloy material, wherein the adopted solution is as follows: PdCl21g/L～1.2g/L、SnCl2·H235-40 g/L, NaCl 80-100 g/L of O, 1.19g/mL of HCl and 30-40 mL/L of HCl; the solution temperature was: 38-42 ℃, treatment time: 3min to 5 min.
In another preferred implementation manner, the formula of the solution used in the reduction treatment in step (3) is as follows: HCl1.19g/mL, 60 mL/L-80 mL/L, solution temperature: 20-25 ℃, treatment time: 3min to 5 min.
In another preferred implementation manner, the formula of the plating solution for electroless copper plating in the step (4) is as follows: 10g/L, EDTA g of copper sulfate, 20g/L of disodium, 3g/L of sodium hydroxide, 37 percent of formaldehyde, 6mL/L of thiourea and 20mg/L of additive, wherein the temperature of the plating solution is as follows: the thickness of the copper plating layer is 1-2 mu m at the temperature of 28-35 ℃.
In another preferred implementation, the thickness of the electroplated copper in the step (5) is 10 μm to 15 μm.
In another preferred implementation manner, the step of electroplating the zinc-nickel alloy in the step (6) comprises electroplating by adopting a ZNICKEL980 alkaline cyanide-free zinc-nickel alloy process, wherein the nickel content is 13%, and the thickness of the plated layer is controlled to be 10-15 μm.
In another aspect, the invention provides an equipment part comprising a magnesium lithium alloy protective layer, wherein the magnesium lithium alloy protective layer is covered on the surface of the equipment part by the method.
The invention adopts self-grinding micro-arc oxidation, sensitization-activation, film coating and other formulas and processes to successfully realize the preparation of the high-quality magnesium-lithium alloy corrosion-resistant material.
The invention has obvious beneficial effects, and mainly comprises the following points:
1) the protection method successfully realizes the dual functional requirements of surface conductivity and high corrosion resistance (the protection level Rp reaches 9 levels after 192h acid salt spray test) of the magnesium-lithium alloy (the brand LZ91), ensures that the magnesium-lithium alloy product is successfully delivered and used, and meets the weight reduction requirement.
2) The magnesium-lithium alloy finished product produced by the method has good quality consistency and high qualification rate: the appearance of the finished product is rainbow color, the surface protective layer is continuous, uniform and complete, and the defects of pulverization, looseness, scratch and the like are avoided; the surface protective layer has excellent binding force with the matrix, and no foaming or layering and other phenomena occur between the protective layer and the matrix after a thermal shock test at 200 ℃; the qualified rate of the product is more than 98 percent.
3) The method provided by the invention is suitable for automatic mass production and high in production efficiency.
Drawings
FIG. 1 is a detailed processing flow chart of the high corrosion resistance conductive protection method of the magnesium-lithium alloy adopted by the invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Taking a magnesium-lithium alloy (model LZ91) module shell of an airborne electronic device as an example, the detailed process of the high corrosion resistance conductive protection treatment is as follows, and the shell and a test piece (the material model and the surface state are the same as the shell) are treated together with a groove in the whole process.
(1) And (4) acceptance: visual appearance inspection is carried out on the shell, and the surface of the shell is free from mechanical damage such as heavy oil contamination, scratches and collisions;
(2) mounting and hanging: selecting a proper hanging tool and a proper hanging position, hanging a target shell to be treated, and enabling the hanging tool (made of aluminum alloy or copper alloy materials), the target shell and a plating bath pole bar (made of red copper materials) to be in close contact with each other and to be mutually conductive, so that good conductivity is ensured;
(3) oil removal: carrying out chemical oil removal on the hung target shell by using a neutral oil removal agent until oil stains are removed completely so as to ensure that the preparation of a subsequent protective layer is not influenced by the oil stains;
(4) hot water washing: rinsing the target shell in hot water at 60-70 ℃ for 10-15 s;
(5) secondary countercurrent cold water washing: performing secondary counter-current cold water rinsing on the target shell for 15-20 s;
(6) micro-arc oxidation: micro-arc oxidation is carried out on the target shell in an electroplating bath, and the bath solution formula comprises sodium silicate (15 g/L-20 g/L), sodium fluoride (8 g/L-10 g/L), sodium hydroxide (3 g/L-5 g/L) and additiveAgent A (5 mL/L-10 mL/L); temperature of the solution: 20 ℃ to 40 ℃, oxidation current density: 5A/dm2～10A/dm2And the oxidation time is as follows: the thickness of the oxide film is controlled to be 20-25 mu m within 30-40 min, and the film layer is not subjected to sealing treatment; preferably, the additive a is an organic amine, preferably triethanolamine.
(7) Secondary countercurrent cold water washing: secondary countercurrent cold water rinsing is carried out on the target shell for 15-20 s again;
(8) sensitization-activation: sensitizing and activating a target shell, wherein the formula of the solution is as follows: PdCl2(1g/L～1.2g/L)、SnCl2·H2O (35 g/L-40 g/L), NaCl (80 g/L-100 g/L), HCl (1.19g/mL, 30 mL/L-40 mL/L), additive B (0.02 g/L-0.05 g/L); temperature of the solution: 38-42 ℃, treatment time: 3 min-5 min; preferably, the additive B is a surfactant (wetting agent), preferably sodium stearyl sulfate.
(9) Secondary countercurrent cold water washing: secondary countercurrent cold water rinsing is carried out on the target shell for 15-20 s again;
(10) reduction: the target shell is subjected to reduction treatment by adopting the following solution formula: HCl (1.19g/mL, 60 mL/L-80 mL/L), solution temperature: 20-25 ℃, treatment time: 3 min-5 min;
(11) secondary countercurrent cold water washing: secondary countercurrent cold water rinsing is carried out on the target shell for 15-20 s again;
(12) chemical copper plating: carrying out chemical copper plating on the target shell, wherein the formula of plating solution is as follows: copper sulfate (10g/L), disodium EDTA (20g/L), sodium hydroxide (3g/L), formaldehyde (37%, 6mL/L), thiourea (2mg/L), plating solution temperature: controlling the thickness of the copper plating layer to be 1-2 mu m at 28-35 ℃; preferably, an additive C (20mg/L) may also be added, the additive being succinonitrile.
(13) Secondary countercurrent cold water washing: performing secondary counter-current cold water rinsing on the target shell for 15-20 s;
(14) copper electroplating: performing electro-coppering on the target shell, adopting a conventional acid copper sulfate plating solution system, and controlling the thickness of a copper plating layer to be 10-15 mu m;
(15) secondary countercurrent cold water washing: performing secondary counter-current cold water rinsing on the target shell for 15-20 s;
(16) electroplating zinc-nickel alloy: electroplating zinc-nickel alloy on the target shell subjected to the copper electroplating treatment, wherein the zinc-nickel alloy plating layer with the nickel content of about 13% is obtained by adopting a ZNICKEL980 alkaline cyanide-free zinc-nickel alloy process, and the thickness of the plating layer is controlled to be 10-15 mu m; the nickel content in the zinc-nickel alloy plating layer obtained by the zinc-nickel alloy electroplating process reaches about 13 percent, which is obviously higher than that of the conventional zinc-nickel alloy electroplating process, and the plating layer has better corrosion resistance under the same thickness.
(17) Secondary countercurrent cold water washing: performing secondary counter-current cold water rinsing on the target shell for 15-20 s;
(18) passivation: passivating the target shell treated by the electroplated zinc-nickel alloy, wherein an SL-10 hexavalent chromium passivation process is adopted, and the passivation temperature is as follows: 35-40 ℃, passivation time: 30 s-50 s;
(19) secondary countercurrent cold water washing: performing secondary counter-current cold water rinsing on the target shell for 15-20 s;
(20) and (3) drying: temperature: 60-65 ℃, time: 20min to 30 min.
And (4) checking: the module shell is in bright rainbow color along with the appearance of the test piece, and the surface protective layer is continuous, uniform and complete and has no defects of pulverization, looseness, scratch and the like; after the test piece is subjected to a thermal shock test at 200 ℃, no phenomena such as foaming or layering occur between the protective layer and the matrix; after 192h of acid salt spray test, the protective grade Rp of the test piece along with the groove is 9.
And (4) checking and concluding: the quality is qualified.
Plating a layer of metal on the micro-arc oxidation film by a wet chemical plating/electroplating method, which is a difficult problem in the field of surface engineering; this is especially a problem for very active magnesium-lithium alloys. The micro-arc oxidation film obtained on the surface of the magnesium-lithium alloy mainly comprises silica compounds of Mg, Al and Li, and the compounds can be chemically dissolved in an acidic medium or an alkaline medium. The self-grinding colloidal palladium one-step method sensitization-activation treatment solution is adopted, and the problem that the micro-arc oxidation film is easy to dissolve is perfectly solved through the precise compounding synergistic effect of the palladium salt and the stannous salt, which is the key point of successful plating.
Comparative example
One of the key steps of the present invention is the one-step surface sensitization-activation formulation and process.
The applicant has carried out a large number of experiments with respect to surface sensitization-activation. Three stannous salt sensitizing solutions with acidity, alkalinity and neutrality and two activating solutions (silver ions and palladium ions) with different proportions are tested, micro-arc oxidation films are dissolved to different degrees in a large number of test processes, the most serious matrix is also dissolved, the subsequent chemical copper plating process cannot be carried out, and the failure is reported.
For example, the applicant tests six two-step sensitization-activation methods of different combinations of three stannous chloride sensitizing solutions (acidic/neutral/alkaline) and two activation solutions (palladium salt/silver salt), the micro-arc oxidation film is dissolved in the process, the most serious matrix is also dissolved, so that subsequent procedures such as chemical copper plating and electro-coppering cannot be performed, and a high-corrosion-resistance conductive protection layer meeting the requirements cannot be obtained; when the one-step sensitization-activation treatment is carried out, the micro-arc oxidation film is not dissolved, and the subsequent working procedures of chemical copper plating, electro-coppering, electro-zinc-nickel alloy plating and the like can be smoothly carried out, so that the high-corrosion-resistance conductive protective layer meeting the requirements is successfully obtained.
For example, in the case of the other steps being unchanged, the applicant experimented that in the step (2), the acidic sensitizing solution SnCl is adopted210g/L + HCl 20mL/L, treating at room temperature for 3min, and then performing PdCl treatment on palladium ion activating solution21g/L + HCl 20mL/L, treating for 8min at room temperature, and obviously dissolving the micro-arc oxidation film after the two-step treatment.
Multiple experiments prove that the colloid palladium one-step sensitization-activation treatment and reduction treatment adopted in the method break through the key bottleneck that a magnesium-lithium alloy (the brand LZ91) micro-arc oxidation film is easy to dissolve and difficult to plate, and successfully obtains a metal coating with good binding force on the magnesium-lithium alloy (the brand LZ91) micro-arc oxidation film. The surface of the magnesium-lithium alloy (the trademark LZ91) composite protective layer consisting of the micro-arc oxidation film (inner layer) and the metal coating (outer layer) is conductive and firmly combined with the matrix, and no phenomena such as foaming or layering and the like occur between the protective layer and the matrix after a thermal shock test at 200 ℃; the composite protective layer has excellent corrosion resistance, and the protective grade Rp of the composite protective layer reaches 9 grades after a 192-hour acid salt spray test. The invention can be used for the conductive and high-corrosion-resistance composite protection treatment of the magnesium-lithium alloy (with the trade name of LZ91) workpiece in severe environment. The magnesium-lithium alloy (the brand LZ91) finished product produced by the method has good quality consistency and the qualification rate is more than 98 percent.
While the principles of the invention have been described in detail in connection with the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing embodiments are merely illustrative of exemplary implementations of the invention and are not limiting of the scope of the invention. The details of the embodiments are not to be interpreted as limiting the scope of the invention, and any obvious changes, such as equivalent alterations, simple substitutions and the like, based on the technical solution of the invention, can be interpreted without departing from the spirit and scope of the invention.
Claims (6)
1. The high-corrosion-resistance conductive protection method for the magnesium-lithium alloy is characterized by comprising the following steps of:
step (1), carrying out micro-arc oxidation on a target magnesium-lithium alloy material to form an oxide film layer;
step (2), carrying out surface sensitization-activation on the target magnesium-lithium alloy material after the oxide film layer is formed;
step (3), carrying out reduction treatment on the sensitized and activated target magnesium-lithium alloy material;
step (4), carrying out chemical copper plating on the reduced target magnesium-lithium alloy material;
step (5), carrying out electro-coppering on the target magnesium-lithium alloy material after electroless copper plating;
step (6), electroplating zinc-nickel alloy on the surface of the target magnesium-lithium alloy material after copper plating;
step (7), passivating the target magnesium-lithium alloy material electroplated with the zinc-nickel alloy by using SL-10 hexavalent chromium;
step (8), drying the passivated target magnesium-lithium alloy material,
the process of sensitization-activation in the step (2) comprises the following steps: adopting a colloidal palladium one-step method to treat the target magnesium-lithium alloy material, wherein the adopted solution is as follows: PdCl2 1g/L～1.2g/L、SnCl2·H235 g/L-40 g/L, NaCl 80 g/L-100 g/L, HCl 1.19.19 g/mL of O, 30 mL/L-40 mL/L of O and 0.02 g/L-0.05 g/L of surfactant; the solution temperature was: 38-42 ℃, treatment time: 3 min-5 min;
the formula of the solution adopted in the reduction treatment in the step (3) is as follows: HCl1.19g/mL, 60 mL/L-80 mL/L, solution temperature: 20-25 ℃, treatment time: 3min to 5 min.
2. The method for conducting protection on the magnesium-lithium alloy with high corrosion resistance according to claim 1, wherein the solution adopted in the micro-arc oxidation in the step (1) comprises 15 g/L-20 g/L of sodium silicate, 8 g/L-10 g/L of sodium fluoride, 3 g/L-5 g/L of sodium hydroxide and 5 mL/L-10 mL/L of organic amine, wherein the temperature of the solution is as follows: 20 ℃ to 40 ℃, oxidation current density: 5A/dm2～10A/dm2And the oxidation time is as follows: 30 min-40 min, and the thickness of the oxide film is controlled to be 20 mu m-25 mu m.
3. The method for electrically conducting and protecting magnesium-lithium alloy with high corrosion resistance according to claim 1, wherein the formula of the electroless copper plating solution in the step (4) is as follows: 10g/L, EDTA g of copper sulfate, 20g/L of disodium, 3g/L of sodium hydroxide, 37% of formaldehyde, 6mL/L of thiourea and 20mg/L of succinonitrile, wherein the temperature of the plating solution is as follows: the thickness of the copper plating layer is 1-2 mu m at the temperature of 28-35 ℃.
4. The method for electrically conducting protection against corrosion of Mg-Li alloy as claimed in claim 1, wherein the thickness of electroplated copper in step (5) is 10-15 μm.
5. The method for electrically conducting and protecting magnesium-lithium alloy with high corrosion resistance according to claim 1, wherein the step of electroplating the zinc-nickel alloy in the step (6) comprises electroplating by using a ZNICKEL980 alkaline cyanide-free zinc-nickel alloy process, wherein the nickel content is 13%, and the thickness of the plated layer is controlled to be 10-15 μm.
6. An article of equipment comprising a protective layer of a magnesium lithium alloy, wherein the protective layer of a magnesium lithium alloy is applied to a surface of the article of equipment by the method of claim 1.
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