A surface passivation process for alloy castings

Abstract

The present invention discloses a surface passivation process for alloy castings, and relates to the technical field of alloy passivation. The surface passivation process for alloy castings includes an activation step and a passivation step, wherein the activation step includes a degreasing step and at least two pickling steps, wherein the degreasing step and the two pickling steps are used to remove the release agent on the surface of the alloy casting, and the at least two pickling steps are also used to remove the oxide layer on the surface of the alloy casting; the passivation step includes at least one film forming step, and a surface conditioning step located before the film forming step, wherein the surface conditioning step is used to expose the main material of the alloy casting, and the film forming step is used to form a passivation layer on the surface of the alloy casting after the surface conditioning step. The process of the present invention can more thoroughly remove the release agent and the oxide layer on the surface of the alloy casting, and more quickly prepare a passivation layer with high corrosion resistance on the main material of the casting, so as to improve the problem of poor corrosion resistance and dust falling of the alloy passivation layer.

Description

Technical Field

[0001] The invention relates to the technical field of metal alloys, and in particular to a surface passivation process for alloy castings. Background Art

[0002] An alloy is a substance composed of two or more metallic elements, or a metal and nonmetallic elements. These components are combined together (usually in a liquid state and then cooled to solidify) to form a new material that has different properties than its individual constituent elements. The purpose of alloying is to improve or adjust the properties of the original metals, such as strength, hardness, corrosion resistance, conductivity, magnetism, etc., to meet specific application requirements.

[0003] Alloys are usually divided into light metal alloys and heavy metal alloys. Light metal alloys such as magnesium alloys have high density and good electromagnetic shielding performance. They can absorb electromagnetic interference better and are better than electroplated shielding films. They are the best choice for 3C products and structural parts such as mobile phone middle frames, laptop computer shells, and game console middle frames.

[0004] Usually, alloys such as magnesium alloys can be formed in one piece by casting to save the subsequent processing steps. Castings usually have poor surface corrosion resistance, so they need to be optimized by combining chemical conversion with organic coating. However, the corrosion resistance of the passivation layer obtained by chemical conversion is relatively unstable, and there will be dusting on the surface, which will affect subsequent processes such as gluing. Summary of the invention

[0005] The main purpose of the present invention is to provide a surface passivation process for alloy castings, aiming to solve the problems of poor corrosion resistance of the passivation layer of alloy castings and dust falling on the surface in the prior art.

[0006] To achieve the above object, the present invention provides a surface passivation process for an alloy casting, which is used to remove a release agent on the surface of the alloy casting and form a passivation layer on the surface of the alloy casting. The surface passivation process for the alloy casting comprises:

[0007] an activation step, comprising a degreasing step and at least two pickling steps, wherein the degreasing step and the two pickling steps are used to remove a release agent on the surface of the alloy casting, and the at least two pickling steps are also used to remove an oxide layer on the surface of the alloy casting; and

[0008] The passivation step includes at least one film forming step and a surface conditioning step before the film forming step, wherein the surface conditioning step is used to expose the main material of the alloy casting, and the film forming step is used to form a passivation layer on the surface of the alloy casting after the surface conditioning step.

[0009] In one embodiment, the activating step comprises:

[0010] A first pickling step, using a first acidic solution to clean the surface of the alloy casting to remove an oxide layer and a portion of a release agent on the surface of the alloy casting;

[0011] a degreasing step, using a first alkaline solution to clean the surface of the alloy casting after the first pickling step, so as to remove part of the grease release agent on the surface of the alloy casting and the residues of the first pickling step; and

[0012] The second pickling step uses a second acidic solution to clean the surface of the alloy casting after the degreasing step to remove the mold release agent, oxide layer and residues of the degreasing step remaining deep on the surface of the alloy casting.

[0013] In one embodiment, in the first pickling step:

[0014] The acidic substance in the first acidic solution at least includes hydrofluoric acid; and / or,

[0015] The mass concentration of the acidic substance in the first acidic solution is 20 to 180 g / L; and / or,

[0016] The cleaning temperature is 10-60°C; and / or,

[0017] The cleaning time is 30 to 360 seconds.

[0018] In one embodiment, in the degreasing step:

[0019] The alkaline substance in the first alkaline solution includes a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance; and / or,

[0020] The mass concentration of the alkaline substance in the first alkaline solution is 20 to 500 g / L; and / or,

[0021] The cleaning temperature is 30 to 95° C.; and / or,

[0022] The cleaning time is 30 to 600 seconds.

[0023] In one embodiment, in the degreasing step: the alkaline substance in the first alkaline solution includes a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance;

[0024] The first alkaline substance includes at least one of sodium hydroxide, potassium hydroxide and potassium carbonate, and the second alkaline substance includes at least one of sodium carbonate, sodium bicarbonate, sodium pyrophosphate, sodium dodecylbenzene sulfonate and sodium gluconate.

[0025] In one embodiment, in the second pickling step:

[0026] The acidic substance in the second acidic solution includes a first acidic substance and / or a second acidic substance, and the first acidic substance contains fluorine; and / or,

[0027] The mass concentration of the acidic substance in the second acidic solution is 20 to 180 g / L; and / or,

[0028] The cleaning temperature is 10-60°C; and / or,

[0029] The cleaning time is 5 to 240 seconds.

[0030] In one embodiment, in the second pickling step: the acidic substance in the second acidic solution includes a first acidic substance and / or a second acidic substance, and the first acidic substance contains fluorine element;

[0031] Wherein, the first acidic substance includes hydrofluoric acid, and the second acidic substance includes at least one of citric acid, oxalic acid, sulfuric acid and acetic acid.

[0032] In one embodiment, the passivation step comprises:

[0033] A first surface conditioning step, using a second alkaline solution to clean the surface of the alloy casting after the activation step, so as to remove the residues of the activation step on the surface of the alloy casting and expose the main body material of the alloy casting;

[0034] a first film-forming step, using a first passivating agent to passivate the surface of the alloy casting after the first surface conditioning step, so as to form a first passivation layer on the surface of the alloy casting;

[0035] A second surface conditioning step, using a third alkaline solution to clean the surface of the alloy casting after the first film forming step, so as to remove the residue of the first film forming step on the surface of the alloy casting and the ash-like substance formed by the residual release agent in the first film forming step, and expose the main material of the alloy casting;

[0036] In the second film forming step, a second passivating agent is used to passivate the surface of the alloy casting after the second surface conditioning step, so as to form a second passivation layer on the surface of the alloy casting.

[0037] In one embodiment, in the first table adjustment step and / or the second table adjustment step:

[0038] The alkaline substance in the second alkaline solution and / or the third alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate; and / or,

[0039] The mass concentration of the alkaline substance in the second alkaline solution and / or the third alkaline solution is 20 to 500 g / L; and / or,

[0040] The cleaning temperature is 30 to 95° C.; and / or,

[0041] The cleaning time is 30 to 600 seconds.

[0042] In one embodiment, in the first film forming step and / or the second film forming step:

[0043] The first passivating agent and / or the second passivating agent comprises a phosphate aqueous solution, a chromate aqueous solution, a molybdate aqueous solution, a stannate aqueous solution or a permanganate aqueous solution; and / or,

[0044] The passivation temperature is 10 to 60° C.; and / or,

[0045] The passivation time is 5 to 240 seconds.

[0046] In one embodiment, in the first film-forming step and / or the second film-forming step, the first passivating agent and / or the second passivating agent comprises a phosphate aqueous solution:

[0047] The solutes in the phosphate aqueous solution include phosphoric acid, manganese dihydrogen phosphate, calcium dihydrogen phosphate and metavanadate; and / or,

[0048] The concentration of phosphate ions in the phosphate aqueous solution is 6.5 to 60 g / L; and / or,

[0049] The mass concentration of the solute in the phosphate aqueous solution is 20 to 180 g / L.

[0050] In one embodiment, the solute in the phosphate aqueous solution further includes at least one of citric acid, oxalic acid, nitric acid, calcium nitrate, and calcium citrate.

[0051] In one embodiment, the surface passivation process of the alloy casting is used to remove the release agent on the surface of the aluminum alloy casting and form a passivation layer on the surface of the aluminum alloy casting.

[0052] In the technical solution of the present invention, the surface of the alloy casting is first activated by an activation step to remove impurities to increase the activation energy of the surface of the alloy casting. The activation step specifically includes a degreasing step and at least two pickling steps. Among them, the degreasing step is used to remove grease in the release agent on the surface of the alloy casting, and the pickling step is used to remove metal oxides on the surface of the alloy casting and organic silicon polymers in the release agent to obtain the alloy casting after the activation step. The above-mentioned activation step can more thoroughly remove the release agent and impurities such as the oxide layer on the surface of the alloy casting. Subsequently, the alloy casting after the activation step is subjected to a passivation step, and the passivation step specifically includes at least two surface adjustment steps and at least two film forming steps, and the surface adjustment step is before the film forming step. Among them, the surface adjustment step is used to expose the alloy main material of the alloy casting, so as to facilitate the preparation of a passivation layer on the alloy main material. The above-mentioned passivation step can quickly prepare a passivation layer on the main material of the alloy casting, and the corrosion resistance of the obtained passivation layer is high, and the ash falling phenomenon is reduced or even eliminated, so as to improve the problem of poor corrosion resistance and ash falling of the alloy passivation layer. DETAILED DESCRIPTION

[0053] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0054] An alloy is a substance composed of two or more metallic elements, or a metal and nonmetallic elements. These components are combined together (usually in a liquid state and then cooled to solidify) to form a new material that has different properties than its individual constituent elements. The purpose of alloying is to improve or adjust the properties of the original metals, such as strength, hardness, corrosion resistance, conductivity, magnetism, etc., to meet specific application requirements.

[0055] Alloys are usually divided into light metal alloys and heavy metal alloys. Light metal alloys such as magnesium alloys have high density and good electromagnetic shielding performance. They can absorb electromagnetic interference better and are better than electroplated shielding films. They are the best choice for 3C products and structural parts such as mobile phone middle frames, laptop computer shells, and game console middle frames.

[0056] Usually, alloys such as magnesium alloys can be formed in one piece by casting to save the subsequent processing steps. Castings usually have poor surface corrosion resistance, so they need to be optimized by combining chemical conversion with organic coating. However, the corrosion resistance of the passivation layer obtained by chemical conversion is relatively unstable, and there will be dusting on the surface, which will affect subsequent processes such as gluing.

[0057] In view of this, the present invention provides a surface passivation process for an alloy casting, which is used to remove a release agent on the surface of the alloy casting and form a passivation layer on the surface of the alloy casting. The surface passivation process for the alloy casting comprises: an activation step, including a degreasing step and at least two pickling steps, wherein the degreasing step and the two pickling steps are used to remove the release agent on the surface of the alloy casting, and the at least two pickling steps are also used to remove an oxide layer on the surface of the alloy casting; and a passivation step, including at least one film forming step and a surface conditioning step located before the film forming step, wherein the surface conditioning step is used to expose the main material of the alloy casting, and the film forming step is used to form a passivation layer on the surface of the alloy casting after the surface conditioning step.

[0058] The release agent components on the surface of alloy castings include base oil, wax, silicone polymer, etc. Common base oils include mineral oil, vegetable oil, synthetic oil, etc. In the casting process, the release agent is usually applied to the mold surface before injecting the molten metal to ensure that the release agent can form an effective isolation layer between the mold and the alloy casting, thereby achieving a smooth demoulding process and protecting the mold surface from damage. Therefore, the surface of the alloy casting has a layer of release agent.

[0059] In the technical scheme of the present invention, the surface of the alloy casting is first activated by an activation step to remove impurities to increase the activation energy of the surface of the alloy casting. The activation step specifically includes a degreasing step and at least two pickling steps. Among them, the degreasing step is used to remove grease in the release agent on the surface of the alloy casting, and the pickling step is used to remove metal oxides on the surface of the alloy casting and organic silicon polymers in the release agent to obtain the alloy casting after the activation step. The above-mentioned activation step can more thoroughly remove impurities such as the release agent and the oxide layer on the surface of the alloy casting. Subsequently, the alloy casting after the activation step is subjected to a passivation step, and the passivation step specifically includes at least two surface adjustment steps and at least two film forming steps, and the surface adjustment step is before the film forming step. Among them, the surface adjustment step is used to expose the alloy main material of the alloy casting, so as to facilitate the preparation of a passivation layer on the alloy main material. The above-mentioned passivation step can quickly prepare a passivation layer on the main material of the alloy casting, and the corrosion resistance of the obtained passivation layer is high, and the ash falling phenomenon is reduced or even eliminated, so as to improve the poor corrosion resistance and ash falling problems of the alloy passivation layer.

[0060] In some embodiments of the present invention, the activation step includes: a first pickling step, using a first acidic solution to clean the surface of the alloy casting to remove the oxide layer and part of the mold release agent on the surface of the alloy casting; a degreasing step, using a first alkaline solution to clean the surface of the alloy casting after the first pickling step to remove part of the grease mold release agent and the residues of the first pickling step on the surface of the alloy casting; and a second pickling step, using a second acidic solution to clean the surface of the alloy casting after the degreasing step to remove the mold release agent, oxide layer and residues of the degreasing step remaining deep on the surface of the alloy casting.

[0061] In the technical scheme of the present invention, the activation step includes sequentially performing a first pickling step, a degreasing step and a second pickling step on the surface of the alloy casting. Among them, the first pickling step preliminarily removes the metal oxide layer on the surface of the alloy casting and the silicide component in the surface release agent to reduce the oxide and the residual amount of the release agent; the degreasing step mainly removes the grease component in the release agent on the surface of the alloy casting after the first pickling step, and the residue of the first pickling step, further reducing the residual amount of the release agent, and the residue of the first pickling step specifically includes the pickling residual reagent and the reaction product of the pickling reagent with the oxide and the silicide (in the form of black ash); the second pickling step mainly removes the release agent and oxide remaining in the deeper layer of the surface of the alloy casting after the degreasing step, so that most of the release agent layer and the oxide layer on the surface of the main material of the alloy casting are removed, the surface activity of the alloy casting is improved, and it is convenient to carry out the subsequent passivation step. It should be noted that the degreasing step is preferably: using a first alkaline solution to ultrasonically clean the surface of the alloy casting after the first pickling step to improve the degreasing efficiency.

[0062] In some embodiments of the present invention, in the first pickling step: the acidic substance in the first acidic solution includes at least hydrofluoric acid. When the acidic substance in the first acidic solution includes hydrofluoric acid, that is, it has hydrogen ions and fluorine ions, the hydrogen ions in the first acidic solution can acidify the metal oxides of the surface oxide layer, and in the process of the surface oxide layer slowly acidifying to generate metal ions and water and entering the first acidic solution, the silicon-based mold release agent between the oxide layer and the main material of the alloy casting is gradually exposed, and the silicon-oxygen bonds (Si-O-Si) in the exposed silicon-based mold release agent react with the fluorine ions in the first acidic solution to generate soluble fluorosilicates, so that the silicon-based mold release agent dissolves from the surface of the casting into the first acidic solution, thereby preliminarily removing the mold release agent and oxides remaining on the surface of the casting.

[0063] In some embodiments of the present invention, in the first pickling step: the mass concentration of the acidic substance in the first acidic solution is 20 to 180 g / L. The mass concentration of the acidic substance in the first acidic solution within the above range can ensure that the surface oxide on the surface of the alloy casting and the silicon-based substances in the release agent are removed sufficiently quickly.

[0064] In some embodiments of the present invention, in the first pickling step: the cleaning temperature is 10-60° C. The cleaning temperature within the above range can ensure that the surface oxide and the release agent on the surface of the alloy casting can react with the first acidic solution quickly.

[0065] In some embodiments of the present invention, in the first pickling step: the cleaning time is 30 to 360 seconds. The cleaning time within the above range can ensure that the surface oxide and the release agent on the surface of the alloy casting can fully react with the first acidic solution.

[0066] In some embodiments of the present invention, in the degreasing step: the alkaline substances in the first alkaline solution include a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance. The second alkaline substance plays a surface activation role, emulsifies the grease in the release agent on the surface of the alloy casting after the first pickling step and disperses it into tiny oil droplets that are dissolved in the first alkaline solution. These tiny oil droplets are surrounded by the water phase to form a stable emulsion, thereby preventing the grease from re-depositing on the surface of the casting; at the same time, the first alkaline substance and the fatty acids in the emulsified grease react with acid-base neutralization to generate fatty acid salts and glycerol that are easily soluble in water. The first alkaline solution also dissolves and removes the pickling residues on the surface of the alloy casting that has also undergone the first pickling step.

[0067] In some embodiments of the present invention, in the degreasing step: the mass concentration of the alkaline substance in the first alkaline solution is 20 to 500 g / L. The mass concentration of the alkaline substance in the first alkaline solution within the above range can ensure that the grease on the surface of the alloy casting and the acid residue of the first pickling step are fully removed.

[0068] In some embodiments of the present invention, in the degreasing step: the cleaning temperature is 30-95° C. The cleaning time within the above range can ensure that the grease on the surface of the alloy casting and the acid residue of the first pickling step can react with the first alkaline solution quickly and be removed.

[0069] In some embodiments of the present invention, in the degreasing step: the cleaning time is 30 to 600 seconds. The cleaning time within the above range can ensure that the grease on the surface of the alloy casting and the acid residue in the first pickling step can fully react with the first alkaline solution.

[0070] In some embodiments of the present invention, in the degreasing step: the alkaline substance in the first alkaline solution includes a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance; wherein the first alkaline substance includes at least one of sodium hydroxide, potassium hydroxide and potassium carbonate, and the second alkaline substance includes at least one of sodium carbonate, sodium bicarbonate, sodium pyrophosphate, sodium dodecylbenzene sulfonate and sodium gluconate. The first alkaline substance can be any one of sodium hydroxide, potassium hydroxide and potassium carbonate, or the first alkaline substance can be two or three of sodium hydroxide, potassium hydroxide and potassium carbonate, all within the protection scope of the present invention. The above-mentioned first alkaline substance can react with oil and fat to neutralize the oil and fat quickly, so that the oil and fat are dissolved in the first alkaline solution. Similarly, the second alkaline substance can be any one of sodium carbonate, sodium bicarbonate, sodium pyrophosphate, sodium dodecylbenzene sulfonate and sodium gluconate, and the second alkaline substance can also be two or more of sodium carbonate, sodium bicarbonate, sodium pyrophosphate, sodium dodecylbenzene sulfonate and sodium gluconate. The second alkaline substance can quickly emulsify the grease on the surface of the alloy casting and disperse it into small oil droplets to prevent it from re-aggregating on the surface of the casting, and also facilitate the first alkaline substance to neutralize the grease.

[0071] In some embodiments of the present invention, in the second pickling step: the acidic substance in the second acidic solution includes the first acidic substance and / or the second acidic substance, and the first acidic substance contains the fluorine element. That is, the second acidic solution may contain the first acidic substance containing the fluorine element, or the first acidic substance containing the fluorine element and the second acidic substance (the second acidic substance does not contain the fluorine element), or the second acidic substance, and the acidic substance in the second acidic solution is selected based on whether the surface of the alloy casting after the degreasing step still contains a silicon-based release agent. The hydrogen ions (and / or fluorine ions) in the second acidic solution can react well with the release agent and the oxide layer remaining deep on the surface of the alloy casting to generate a water-soluble substance.

[0072] In some embodiments of the present invention, in the second pickling step: the mass concentration of the acidic substance in the second acidic solution is 20 to 180 g / L. The mass concentration of the acidic substance in the second acidic solution within the above range can ensure that it can fully react with the stripping agent and the oxide layer remaining deep on the surface of the alloy casting after degreasing treatment.

[0073] In some embodiments of the present invention, in the second pickling step, the cleaning temperature is 10-60° C. The cleaning time within the above range can ensure that the stripping agent and the oxide layer remaining deep on the surface of the degreased alloy casting can react with the second acidic solution quickly and be removed.

[0074] In some embodiments of the present invention, in the second pickling step: the cleaning time is 5 to 240 seconds. The cleaning time within the above range can ensure that the stripping agent and the oxide layer remaining deep on the surface of the alloy casting after degreasing can react with the second acidic solution to be removed.

[0075] In some embodiments of the present invention, in the second pickling step: the acidic substance in the second acidic solution includes a first acidic substance and / or a second acidic substance, and the first acidic substance contains fluorine element; wherein the first acidic substance includes hydrofluoric acid, and the second acidic substance includes at least one of citric acid, oxalic acid, sulfuric acid and acetic acid. Preferably, the second acidic solution contains the first acidic substance and at least one second acidic substance, or the second acidic solution contains at least two second acidic substances. This preferred method can ensure the removal of deep oxide layers, release agents and other contaminants while minimizing corrosion to the casting matrix and improving processing efficiency.

[0076] In some embodiments of the present invention, the passivation step comprises:

[0077] A first surface conditioning step, using a second alkaline solution to clean the surface of the alloy casting after the activation step, so as to remove the residues of the activation step on the surface of the alloy casting and expose the main body material of the alloy casting;

[0078] a first film-forming step, using a first passivating agent to passivate the surface of the alloy casting after the first surface conditioning step, so as to form a first passivation layer on the surface of the alloy casting;

[0079] The second surface conditioning step: using a third alkaline solution to clean the surface of the alloy casting after the first film forming step, so as to remove the residue of the first film forming step and the ash-like substance formed by the residual release agent in the first film forming step on the surface of the alloy casting, and expose the main material of the alloy casting;

[0080] Second film-forming step: using a second passivating agent to passivate the surface of the alloy casting after the second surface conditioning step, so as to form a second passivation layer on the surface of the alloy casting.

[0081] In the technical solution of the present invention, the first surface conditioning step is mainly used to treat the residues produced on the surface of the alloy casting in the activation step. When the last step of the activation step is the second pickling step, that is, the second acidic residual reagents and the reactants of the reagents and oxides (in black and gray), after the first surface conditioning step is completed, the main material of the alloy casting is exposed.

[0082] The main function of the passivator is to prevent the metal from contacting with corrosive media in the environment (such as oxygen, water, chloride ions, etc.) by forming a dense protective film (which can be an oxide or hydroxide) on the metal surface, thereby delaying or preventing further corrosion of the metal. The first passivation layer is formed on the exposed surface of the main material by the passivator, and then it is determined whether there is ash-like substance in the first passivation layer. This is because the activation step mainly removes the film-like release agent and the oxide layer. When the release agent contains tiny solid particles for auxiliary effect or the release agent forms solid particles at high temperature, the solid particles are strongly and deeply bonded to the surface of the alloy casting, and are difficult to be removed in the aforementioned activation step. In the first film-forming step, the passivator reacts with the surface main material of the alloy casting, so that the surface layer of the main material is reacted, the thickness gradually decreases, and the solid particles that are deeply bonded to the main body of the alloy casting are exposed. The solid particles are converted into ash-like substances during the passivation process and exist between the first passivation layer and the main body of the alloy. Its presence will affect the tightness of the further gluing process of the alloy casting. When the first passivation layer is wiped by hand and there is dust falling off, a second surface conditioning step is required to remove the solid particles of the release agent between the inlay and the main body and the first passivation layer through the third alkali solution. Then the alloy casting that has undergone the second surface conditioning step is subjected to a second film forming treatment to form a second passivation layer on the surface of the first passivation layer after the third alkaline solution treatment, and the passivation rate of the second film forming step is faster, and a passivation layer with better corrosion resistance can be formed in a shorter time.

[0083] In some embodiments of the present invention, in the first surface conditioning step: the alkaline substance in the second alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate. The alkaline substance in the second alkaline solution can be any one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate, or two or three of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate, all within the protection scope of the present invention. The above alkaline substances can better remove the residues of the activation step.

[0084] In some embodiments of the present invention, in the first surface conditioning step: the mass concentration of the alkaline substance in the second alkaline solution is 20-500 g / L. The mass concentration of the alkaline substance in the second alkaline solution within the above range can ensure that the residues on the surface of the alloy casting in the activation step are well removed.

[0085] In some embodiments of the present invention, in the first surface conditioning step: the cleaning temperature is 30-95° C. The cleaning temperature within the above range can ensure that the residues generated on the surface of the alloy casting in the activation step react with the second alkaline solution quickly and are removed.

[0086] In some embodiments of the present invention, in the first surface conditioning step: the cleaning time is 30 to 600 seconds. The cleaning time within the above range can ensure that the residues generated on the surface of the alloy casting in the activation step react fully with the second alkaline solution and are removed.

[0087] In some embodiments of the present invention, in the first film-forming step: the first passivating agent includes a phosphate aqueous solution, a chromate aqueous solution, a molybdate aqueous solution, a stannate aqueous solution or a permanganate aqueous solution. When the first passivating agent is a phosphate aqueous solution, the phosphate ions in the phosphate aqueous solution react with the alloy main body material to form a water-insoluble phosphate film, i.e., the first passivation layer. Similarly, when the first passivating agent is a chromate aqueous solution, a molybdate aqueous solution, a stannate aqueous solution or a permanganate aqueous solution, the materials of the formed first passivation layer are chromate, molybdate, stannate, and permanganate, which are insoluble in water, respectively. The above-mentioned first passivating agent can ensure that a denser first passivation film is formed on the surface of the alloy main body more quickly.

[0088] In some embodiments of the present invention, in the first film forming step: the passivation temperature is 10-60° C. The passivation temperature within the above range can ensure that the first passivator forms a denser first passivation film on the surface of the alloy body faster and that the solid particles are converted into ash-like substances faster.

[0089] In some embodiments of the present invention, in the first film forming step: the passivation time is 5 to 240 seconds. The passivation time within the above range can ensure that the first passivator forms a denser first passivation film on the surface of the alloy body and that the solid particles are fully converted into ash-like substances.

[0090] In some embodiments of the present invention, in the first film-forming step, the first passivator includes a phosphate aqueous solution: the solute in the phosphate aqueous solution includes phosphoric acid, manganese dihydrogen phosphate, calcium dihydrogen phosphate and metavanadate. The phosphate ions in the phosphate solution can react with the main material of the alloy casting to form a water-insoluble phosphate salt film. Among them, phosphoric acid can provide an acidic environment for passivation to ensure that the passivation reaction is carried out under acidic conditions; calcium dihydrogen phosphate can adjust the thickness of the phosphate film to make it more uniform and avoid local excessive thickness or thinness; manganese dihydrogen phosphate can refine the grains of the phosphate film and make the film layer more dense, thereby improving its protective performance; metavanadate includes metavanadic acid and / or metavanadate amine, and metavanadate can react with metal ions on the surface of the alloy to generate vanadium-containing compounds, which can fill the micropores of the phosphate film, making the film layer more dense and uniform, thereby improving its corrosion resistance. At the same time, the vanadium-containing compound can regenerate a protective layer when the film layer is slightly damaged, prolonging the protective effect and improving the stability of the passivation layer.

[0091] In some embodiments of the present invention, in the first film forming step, the first passivating agent includes a phosphate aqueous solution: the concentration of phosphate ions in the phosphate aqueous solution is 6.5-60 g / L. The concentration of phosphate ions within the above range can ensure the formation of a water-insoluble phosphate film.

[0092] In some embodiments of the present invention, in the first film-forming step, the first passivating agent includes a phosphate aqueous solution: the mass concentration of the solute in the phosphate aqueous solution is 20 to 180 g / L. The mass concentration of the solute in the phosphate aqueous solution within the above range can ensure a water-insoluble phosphate film with a suitable thickness.

[0093] In some embodiments of the present invention, the solute in the phosphate aqueous solution further comprises at least one of citric acid, oxalic acid, nitric acid, calcium nitrate, and calcium citrate. Adding citric acid, oxalic acid, nitric acid, calcium nitrate, or calcium citrate to the phosphate aqueous solution can make the phosphate film more uniformly deposited on the metal surface, avoiding the problem of local excessive thickness or excessive thinness.

[0094] In some embodiments of the present invention, in the second surface conditioning step: the alkaline substance in the second alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate. The alkaline substance can effectively remove the solid particles of the release agent while reducing the corrosion effect on the first passivation layer.

[0095] In some embodiments of the present invention, in the second surface conditioning step: the mass concentration of the alkaline substance in the third alkaline solution is 20 to 500 g / L. The mass concentration of the alkaline substance in the third solution within the above range can ensure that the residual reagent on the surface of the alloy casting in the first film forming step and the ash-like substance formed by the solid particles of the release agent in the first film forming step are well removed.

[0096] In some embodiments of the present invention, in the second surface conditioning step: the cleaning temperature is 30-95° C. The cleaning temperature within the above range can ensure that the residual reagent on the surface of the alloy casting in the first film forming step and the ash-like substances formed by the solid particles of the release agent in the first film forming step react with the third alkaline solution quickly and are removed.

[0097] In some embodiments of the present invention, in the second surface conditioning step: the cleaning time is 30 to 600 seconds. The cleaning time within the above range can ensure that the residual reagent on the surface of the alloy casting in the first film forming step and the ash-like substance formed by the solid particles of the release agent in the first film forming step are fully reacted with the third alkaline solution and removed.

[0098] In some embodiments of the present invention, in the second film forming step, the second passivating agent includes a phosphate aqueous solution, a chromate aqueous solution, a molybdate aqueous solution, a stannate aqueous solution or a permanganate aqueous solution. The second passivating agent can ensure that a denser second passivation film is formed on the surface of the alloy body more quickly.

[0099] In some embodiments of the present invention, in the second film forming step: the passivation temperature is 10-60° C. The passivation temperature within the above range can ensure that the second passivator forms a denser second passivation film on the surface of the alloy body faster, thereby improving the corrosion resistance and stability of the passivation film.

[0100] In some embodiments of the present invention, in the second film-forming step: the passivation time is 5 to 240 seconds. The passivation time within the above range can ensure that the second passivator forms a denser second passivation film more fully on the surface of the alloy body, thereby improving the corrosion resistance and stability of the passivation film. In some embodiments of the present invention, in the second film-forming step, the second passivator includes a phosphate aqueous solution: the solute in the phosphate aqueous solution includes phosphoric acid, manganese dihydrogen phosphate, calcium dihydrogen phosphate and metavanadate. The phosphate ions in the phosphate solution can react with the main material of the alloy casting to form a phosphated salt film that is insoluble in water. Manganese dihydrogen phosphate, calcium dihydrogen phosphate and metavanadate can make the formed phosphated salt film have better uniformity, thickness and corrosion resistance.

[0101] In some embodiments of the present invention, in the second film forming step, the second passivating agent includes a phosphate aqueous solution: the concentration of phosphate ions in the phosphate aqueous solution is 6.5-60 g / L. The concentration of phosphate ions within the above range can ensure that the second layer of water-insoluble phosphate film is well formed.

[0102] In some embodiments of the present invention, in the second film-forming step, the second passivating agent includes a phosphate aqueous solution: the mass concentration of the solute in the phosphate aqueous solution is 20 to 180 g / L. The mass concentration of the solute in the phosphate aqueous solution within the above range can ensure a second layer of water-insoluble phosphate film with a suitable thickness, thereby improving the corrosion resistance and stability of the passivation layer.

[0103] In some embodiments of the present invention, the surface passivation process of the alloy casting further includes a drying step, which is after the passivation step and is used to remove moisture from the alloy casting after the passivation step. Preferably, the temperature of the drying step is 90 to 150° C., and the time of the drying step is 600 to 3600 seconds. The temperature and time of the drying step within the above range can ensure that the moisture in the alloy casting after the passivation step is fully removed.

[0104] In some embodiments of the present invention, the surface passivation process of the alloy casting further includes multiple water washing steps, the temperature of the water washing step is 10-40°C, and the time of the water washing treatment is 10-240s. Preferably, at least one water washing step is respectively set after the first pickling step, after the degreasing step, after the second pickling step, after the first surface conditioning step, after the first film forming step, after the second surface conditioning step, and after the second film forming step, which serves to clean the liquid medicine of the previous process remaining on the surface of the alloy casting to avoid over-reaction and contamination of the next process.

[0105] The specific gravity of magnesium alloy is 2 / 3 of aluminum and 1 / 4 of iron; its specific strength is 500MPa higher than that of aluminum alloy and twice that of carbon steel, and its specific stiffness is equivalent to that of aluminum alloy and steel; it has good impact resistance. Under the same load, the shock absorption of magnesium alloy is 100 times that of aluminum and 300-500 times that of titanium alloy; it is soft and has low cutting resistance, which is 60% of aluminum alloy and 29% of cast iron. In some embodiments of the present invention, the surface passivation process of the aforementioned alloy casting is used to remove the release agent on the surface of the aluminum alloy casting and form a passivation layer on the surface of the aluminum alloy casting. The magnesium alloy casting with a passivation layer on the surface is suitable for making the shell of electronic products.

[0106] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0107] Example 1

[0108] A surface passivation process for a magnesium alloy casting, the size of the magnesium alloy casting is 300 mm × 170 mm × 2 mm, the magnesium alloy casting is a casting treated with a release agent, the specific components of the release agent are modified silicone wax, organic fatty alcohols, emulsifiers, polyethylene wax, and other synthetic esters, and the surface passivation process comprises the following steps:

[0109] The first pickling step: the mass concentration of hydrofluoric acid in the first acidic solution is 20 g / L, the mass concentration of sulfuric acid is 60 g / L, the pickling time is 120 s, and the acid temperature is 25°C;

[0110] Washing step: washing time is 60s, washing temperature is 25℃;

[0111] Degreasing step: the mass concentration of sodium hydroxide in the first alkaline solution is 40 g / L, the mass concentration of sodium carbonate is 60 g / L, the cleaning time is 210 s, and the cleaning temperature is 60° C.;

[0112] Washing step: washing time is 60s, washing temperature is 25℃;

[0113] Second pickling step: the mass concentration of hydrofluoric acid in the first acidic solution is 1 g / L, the mass concentration of sulfuric acid is 50 g / L, the pickling time is 25 s, and the acid temperature is 50°C;

[0114] Washing step: washing time is 60s, washing temperature is 25℃;

[0115] First surface conditioning step: the mass concentration of sodium hydroxide in the second alkaline solution is 60 g / L, the cleaning time is 210 s, and the cleaning temperature is 60° C.;

[0116] Washing step: washing time is 60s, washing temperature is 25℃;

[0117] The first film-forming step: the mass concentrations of phosphoric acid, calcium dihydrogen phosphate, manganese dihydrogen phosphate, and sodium metavanadate in the first passivator are 30 g / L, 45 g / L, 8 g / L, and 2 g / L, respectively, the passivation time is 15 s, and the passivation temperature is 30°C;

[0118] Washing step: washing time is 60s, washing temperature is 25℃;

[0119] Second surface adjustment step: the mass concentration of sodium hydroxide in the third alkaline solution is 60 g / L, the cleaning time is 210 s, and the cleaning temperature is 60° C.;

[0120] Second film-forming step: the second passivating agent comprises phosphoric acid, calcium dihydrogen phosphate, manganese dihydrogen phosphate, and sodium metavanadate, with mass concentrations of 30 g / L, 45 g / L, 8 g / L, and 2 g / L, respectively, the passivation time is 15 s, and the passivation temperature is 30°C;

[0121] Washing step: washing time is 60s, washing temperature is 25℃;

[0122] Drying step: drying time is 1500s, drying temperature is 100℃.

[0123] Comparative Example 1

[0124] Compared with Example 1, Comparative Example 1 is different in that:

[0125] The first pickling step, the water washing step, the second pickling step, the water washing step, and the degreasing step are performed in sequence, and the order and parameters of the remaining steps are the same as those in Example 1.

[0126] Comparative Example 2

[0127] Compared with Example 1, Comparative Example 2 is different in that:

[0128] The second surface conditioning step and the second film forming step are not performed.

[0129] Performance Testing

[0130] The corrosion resistance of the alloy castings with a passivation layer deposited on the surface in Example 1 and Comparative Examples 1-2 was tested by a 5% neutral salt spray test. The test results are shown in Table 1.

[0131] Table 1 Corrosion resistance of alloy castings with a passivation layer deposited on the surface in Example 1 and Comparative Examples 1-2

[0132] Corrosion resistance effect Example 1 Good corrosion resistance Comparative Example 1 Good corrosion resistance, but uneven appearance Comparative Example 2 Poor corrosion resistance, dust falling

[0133] It can be seen from Table 1 that (1) the first pickling must be followed by a degreasing step to remove the ash from the first pickling, otherwise the finished product will have an uneven appearance; (2) the film layer is thin and the surface uniformity is poor after the first film formation, and white ash exists on the surface of some products, which results in poor corrosion resistance of the product. Through secondary surface conditioning and secondary film formation, the surface of the film layer is cleaned and re-filmed to ensure good corrosion resistance and uniform appearance of the finished product.

[0134] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A surface passivation process for alloy castings, for removing a release agent on the surface of an alloy casting and forming a passivation layer on the surface of the alloy casting, characterized in that: The surface passivation process of the alloy casting comprises: an activation step, comprising a degreasing step and at least two pickling steps, wherein the degreasing step and the two pickling steps are used to remove a release agent on the surface of the alloy casting, and the at least two pickling steps are also used to remove an oxide layer on the surface of the alloy casting; and The passivation step includes at least one film forming step and a surface conditioning step before the film forming step, wherein the surface conditioning step is used to expose the main material of the alloy casting, and the film forming step is used to form a passivation layer on the surface of the alloy casting after the surface conditioning step.

2. The surface passivation process of the alloy casting according to claim 1, characterized in that: The activation step comprises: A first pickling step, using a first acidic solution to clean the surface of the alloy casting to remove an oxide layer and a portion of a release agent on the surface of the alloy casting; a degreasing step, using a first alkaline solution to clean the surface of the alloy casting after the first pickling step, so as to remove part of the grease release agent on the surface of the alloy casting and the residues of the first pickling step; and The second pickling step uses a second acidic solution to clean the surface of the alloy casting after the degreasing step to remove the mold release agent, oxide layer and residues of the degreasing step remaining deep on the surface of the alloy casting.

3. The surface passivation process of the alloy casting according to claim 2, characterized in that: In the first pickling step: The acidic substance in the first acidic solution at least includes hydrofluoric acid; and / or, The mass concentration of the acidic substance in the first acidic solution is 20 to 180 g / L; and / or, The cleaning temperature is 10-60°C; and / or, The cleaning time is 30 to 360 seconds.

4. The surface passivation process of the alloy casting according to claim 2, characterized in that: In the degreasing step: The alkaline substance in the first alkaline solution includes a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance; and / or, The mass concentration of the alkaline substance in the first alkaline solution is 20 to 500 g / L; and / or, The cleaning temperature is 30-95°C; and / or, The cleaning time is 30 to 600 seconds.

5. The surface passivation process of the alloy casting according to claim 2, characterized in that: In the degreasing step: the alkaline substance in the first alkaline solution includes a first alkaline substance and a second alkaline substance, and the alkalinity of the first alkaline substance is greater than that of the second alkaline substance; The first alkaline substance includes at least one of sodium hydroxide, potassium hydroxide and potassium carbonate, and the second alkaline substance includes at least one of sodium carbonate, sodium bicarbonate, sodium pyrophosphate, sodium dodecylbenzene sulfonate and sodium gluconate.

6. The surface passivation process of the alloy casting according to claim 2, characterized in that: In the second pickling step: The acidic substance in the second acidic solution includes a first acidic substance and / or a second acidic substance, and the first acidic substance contains fluorine; and / or, The mass concentration of the acidic substance in the second acidic solution is 20 to 180 g / L; and / or, The cleaning temperature is 10-60°C; and / or, The cleaning time is 5 to 240 seconds.

7. The surface passivation process of the alloy casting according to claim 2, characterized in that: In the second pickling step: the acidic substance in the second acidic solution includes the first acidic substance and / or the second acidic substance, and the first acidic substance contains fluorine element; Wherein, the first acidic substance includes hydrofluoric acid, and the second acidic substance includes at least one of citric acid, oxalic acid, sulfuric acid and acetic acid.

8. The surface passivation process of the alloy casting according to claim 1, characterized in that: The passivation step comprises: A first surface conditioning step, using a second alkaline solution to clean the surface of the alloy casting after the activation step, so as to remove the residues of the activation step on the surface of the alloy casting and expose the main body material of the alloy casting; a first film-forming step, using a first passivating agent to passivate the surface of the alloy casting after the first surface conditioning step, so as to form a first passivation layer on the surface of the alloy casting; A second surface conditioning step, using a third alkaline solution to clean the surface of the alloy casting after the first film forming step, so as to remove the residue of the first film forming step on the surface of the alloy casting and the ash-like substance formed by the residual release agent in the first film forming step, and expose the main material of the alloy casting; In the second film forming step, a second passivating agent is used to passivate the surface of the alloy casting after the second surface conditioning step, so as to form a second passivation layer on the surface of the alloy casting.

9. The surface passivation process of the alloy casting according to claim 8, characterized in that: In the first table adjustment step and / or the second table adjustment step: The alkaline substance in the second alkaline solution and / or the third alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate and sodium bicarbonate; and / or, The mass concentration of the alkaline substance in the second alkaline solution and / or the third alkaline solution is 20 to 500 g / L; and / or, The cleaning temperature is 30-95°C; and / or, The cleaning time is 30 to 600 seconds.

10. The surface passivation process of the alloy casting according to claim 8, characterized in that: In the first film forming step and / or the second film forming step: The first passivating agent and / or the second passivating agent comprises a phosphate aqueous solution, a chromate aqueous solution, a molybdate aqueous solution, a stannate aqueous solution or a permanganate aqueous solution; and / or, The passivation temperature is 10 to 60° C.; and / or, The passivation time is 5 to 240 seconds.

11. The surface passivation process of the alloy casting according to claim 8, characterized in that: In the first film-forming step and / or the second film-forming step, the first passivating agent and / or the second passivating agent comprises a phosphate aqueous solution: The solutes in the phosphate aqueous solution include phosphoric acid, manganese dihydrogen phosphate, calcium dihydrogen phosphate and metavanadate; and / or, The concentration of phosphate ions in the phosphate aqueous solution is 6.5 to 60 g / L; and / or, The mass concentration of the solute in the phosphate aqueous solution is 20 to 180 g / L.

12. The surface passivation process of the alloy casting according to any one of claims 1 to 11, characterized in that: The method is used for removing the demoulding agent on the surface of the aluminum alloy casting and forming a passivation layer on the surface of the aluminum alloy casting.