A magnesium alloy and a surface treatment process thereof

Abstract

The application discloses a magnesium alloy and a surface treatment process thereof, and comprises the following steps: (1) surface pretreatment: sequentially performing oil removal, dirt removal and activation on the magnesium alloy; (2) one-step zinc deposition and zinc plating: immersing the pretreated magnesium alloy into a reaction solution to perform one-step zinc deposition, and then directly performing zinc electroplating in the reaction container and the reaction solution of the one-step zinc deposition; and (3) pre-plating copper: performing copper electroplating on the surface of the magnesium alloy after the zinc electroplating. The one-step zinc deposition and zinc plating of the application replaces the secondary zinc deposition method in the traditional process, can avoid frequent tank replacement in the zinc deposition and zinc plating process, simplifies the process of the traditional magnesium alloy electroplating process, is beneficial to saving time cost and labor cost, improving economic benefits, and the obtained plating layer has excellent adhesion, and the magnesium alloy obtained after the surface treatment has excellent corrosion resistance.

Description

Technical Field

[0001] This invention relates to a surface treatment process, specifically to a magnesium alloy and its surface treatment process. Background Technology

[0002] Magnesium alloys are the lightest of the metallic structural materials, with a density of only 1.74 g / cm³. 3 Magnesium alloys have a tensile strength approximately 2 / 3 that of aluminum and 1 / 4 that of iron. Their tensile strength is about 200–350 MPa, similar to aluminum alloys, but their specific strength is higher than aluminum alloys and some high-strength steels. Using magnesium alloys can reduce the weight of metal structural components. Magnesium alloys have a low modulus of elasticity, approximately 45,000 MPa, resulting in good vibration damping properties and the ability to withstand large impact loads, making them suitable for components subjected to severe vibrations. They are widely used in the automotive, aerospace, and electronics industries. Magnesium is abundant, ranking eighth in natural resources, but as a structural material, magnesium alloys have poor corrosion resistance, limiting their wider application.

[0003] Therefore, effective decorative and corrosion-resistant treatment of magnesium alloy surfaces is particularly important. Commonly used treatment techniques include electroplating, electroless plating, conversion coating, anodizing, organic coatings, and vapor deposition. The simplest and most effective method is electroplating, which involves depositing a metal or alloy with the desired properties onto the magnesium or magnesium alloy substrate using electrochemical methods. The purpose of electroplating is both protection and aesthetics. However, electroplating magnesium alloy materials is currently a major challenge for the international electroplating industry, mainly due to the following reasons:

[0004] (1) An inert oxide film is easily formed on the surface of magnesium alloys, which affects the bonding force between the coating metal and the base metal;

[0005] (2) Magnesium has a very low electrode potential (-2.36V) and high chemical reactivity. After it is removed from the metal ions in the plating solution, it will produce a violent displacement reaction, forming a loose contact plating solution, which seriously affects the bonding force between the coating and the substrate metal.

[0006] (3) Different types of magnesium alloys have different constituent elements and surface states, and contain a large number of intermetallic compounds, which makes the potential distribution on the substrate surface uneven, increasing the difficulty of electroplating and electroless plating.

[0007] Therefore, before conventional electroplating, pretreatment of the magnesium and magnesium alloy surfaces is usually required to achieve the purpose of surface protection and decoration. In recent years, domestic magnesium alloy electroplating still mostly adopts traditional processes, which are complex. In addition, the complex pre-plating treatment and pre-plating process requires multiple tank changes, increasing labor and time costs. At the same time, magnesium alloy parts need to be transferred between various different process environments, increasing process instability, affecting the performance of finished products, increasing the scrap rate and production costs. Summary of the Invention

[0008] The problem to be solved by the present invention is to provide a magnesium alloy and a surface treatment method thereof, which simplifies the process of traditional magnesium alloy electroplating, and the resulting coating has excellent adhesion. The magnesium alloy obtained after surface treatment has excellent corrosion resistance.

[0009] The present invention includes a magnesium alloy surface treatment process, comprising the following steps:

[0010] (1) Surface pretreatment: The magnesium alloy is sequentially degreased, descaled and activated;

[0011] (2) One-step zinc plating: The pretreated magnesium alloy is immersed in the reaction solution for one zinc immersion, and then electroplating is carried out directly in the reaction container and reaction solution of the one zinc immersion.

[0012] (3) Pre-plating copper: Copper is pre-plated on the magnesium alloy surface after zinc plating.

[0013] Furthermore, the temperature for zinc immersion is 75–85°C, and the immersion time is 1–5 minutes.

[0014] Furthermore, the current density for electroplating zinc is 1–3 A / dm². 2 The electroplating time is 15 minutes.

[0015] Furthermore, the reaction solution composition is as follows: 50 g / L zinc sulfate or zinc acetate, 5 g / L potassium fluoride, 5 g / L sodium carbonate, 150 g / L complexing agent, 10 ml / L ammonia water or 15 g / L ammonium bifluoride buffer, with the remainder being water.

[0016] Furthermore, the complexing agent is at least one of potassium pyrophosphate or sodium pyrophosphate, and the buffer is at least one of ammonia and ammonium bifluoride.

[0017] Furthermore, the surface pretreatment also includes heat treatment, which involves ultrasonically dewaxing the magnesium alloy, then immersing it in an isopropanol solution for 15 minutes, and then heating it to 220°C for 2 hours.

[0018] Degreasing involves immersing the heat-treated magnesium alloy in a solution containing 60 g / L sodium hydroxide, 10 g / L trisodium phosphate, and 0.5 g / L surfactant at 60°C for 5 minutes.

[0019] Descaling involves immersing the degreased magnesium alloy in a solution containing 190 g / L of chromic anhydride at a temperature of 80–85°C for 5 minutes.

[0020] Activation involves immersing the descaled magnesium alloy in a solution containing 420 ml / L hydrofluoric acid for 10 minutes.

[0021] Furthermore, the pre-plating of copper includes immersing the magnesium alloy after one-step zinc plating in a pre-plating copper cyanide solution at a solution temperature of 50°C and a current density of 1.5 A / dm³. 2 The electroplating time is 10 minutes.

[0022] Furthermore, it also includes:

[0023] (4) The magnesium alloy after copper plating is pre-plated with neutral nickel, basic chemical nickel and acidic chemical nickel in sequence.

[0024] Furthermore, the pre-plating of neutral nickel includes immersing the magnesium alloy in a pre-plating neutral nickel solution at a solution temperature of 45°C and a current density of 1 A / dm³. 2 The electroplating time is 25 minutes;

[0025] Alkaline electroless nickel plating involves immersing a magnesium alloy in an alkaline electroless nickel plating solution at a temperature of 80°C for 60 minutes.

[0026] Acidic electroless nickel plating involves immersing a magnesium alloy in an acidic electroless nickel plating solution at a temperature of 80°C for 90 minutes.

[0027] A magnesium alloy obtained by any of the above-mentioned magnesium alloy surface treatment processes.

[0028] The beneficial effects of this invention are:

[0029] This invention employs a one-step zinc plating method to replace the traditional two-step zinc plating process. Traditional magnesium alloy electroplating typically involves two zinc plating steps to optimize oxide film removal, specifically a first zinc plating, stripping, and second zinc plating. After the second zinc plating, the magnesium alloy is usually cleaned and then transferred to a specialized zinc plating solution for galvanizing. In this process, the magnesium alloy undergoes five steps: first zinc plating, stripping, second zinc plating, cleaning, and electroplating. This invention, however, involves direct zinc plating after a single zinc plating step, simplifying the process, saving time and cost, and reducing production costs. Traditional processes require two entries and exits from the zinc plating tank, one entry and exit from the cleaning tank, and finally entry into the zinc plating tank. In this invention, zinc plating and electroplating are carried out in the same reaction solution. After zinc plating, electroplating is performed directly in the zinc plating reaction vessel using the zinc plating solution, eliminating concerns about the zinc plating solution affecting different zinc plating solutions. Therefore, the intermediate cleaning step is eliminated, and frequent tank switching is unnecessary. This avoids excessive operational steps that reduce process stability, decrease scrap rates, and improve economic efficiency.

[0030] In conventional electroplating, one step is conventionally used to complete one operation. The one-step immersion zinc plating of this invention breaks this fixed mindset, realizing the completion of two operations in one step, and achieving satisfactory results.

[0031] This invention requires only one zinc plating process, which eliminates the need for a second zinc plating process compared to traditional magnesium alloy electroplating processes. This reduces energy consumption. By immediately performing zinc electroplating in the original reaction solution after the first zinc plating, a dense and well-bonded zinc metal layer is deposited on the surface of the magnesium alloy substrate, which acts as an intermediate protection and ensures excellent adhesion between the substrate and the coating. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Furthermore, the technical solutions of the various embodiments of this invention can be combined with each other, but only on the basis of being achievable by one of ordinary skill in the art. When a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0034] This invention provides a magnesium alloy surface treatment process, including the following steps:

[0035] (1) Surface pretreatment: The magnesium alloy is sequentially degreased, descaled and activated;

[0036] (2) One-step zinc plating: The pretreated magnesium alloy is immersed in the reaction solution for one zinc immersion, and then electroplating is performed directly in the reaction container and reaction solution of the one zinc immersion.

[0037] (3) Pre-plating copper: Copper is pre-plated on the magnesium alloy surface after zinc plating.

[0038] This invention employs a one-step zinc plating method to replace the traditional two-step zinc plating process. Traditional magnesium alloy electroplating typically involves two zinc plating steps to optimize oxide film removal, specifically a first zinc plating, stripping, and second zinc plating. After the second zinc plating, the magnesium alloy is usually cleaned and then transferred to a specialized zinc plating solution for galvanizing. In this process, the magnesium alloy undergoes five steps: first zinc plating, stripping, second zinc plating, cleaning, and electroplating. This invention, however, involves direct zinc plating after a single zinc plating step, simplifying the process, saving time and cost, and reducing production costs. Traditional processes require two entries and exits from the zinc plating tank, one entry and exit from the cleaning tank, and finally entry into the zinc plating tank. In this invention, zinc plating and electroplating are carried out in the same reaction solution. After zinc plating, electroplating is performed directly in the zinc plating reaction vessel using the zinc plating solution, eliminating concerns about the zinc plating solution affecting different zinc plating solutions. Therefore, the intermediate cleaning step is eliminated, and frequent tank switching is unnecessary. This avoids excessive operational steps that reduce process stability, decrease scrap rates, and improve economic efficiency.

[0039] In a preferred embodiment, the temperature for zinc immersion is 75–85°C, and the immersion time is 1–5 minutes.

[0040] In a preferred embodiment, the current density for electroplating zinc is 1–3 A / dm². 2 The electroplating time is 15 minutes.

[0041] Traditional magnesium alloy electroplating processes employ a two-stage zinc plating method, with each zinc plating session typically taking 15-20 minutes. Including the time for zinc stripping between the two zinc plating sessions, the total time is around 40 minutes. In contrast, the embodiment of this invention uses a one-stage zinc plating process, which takes only 16-20 minutes, greatly saving process time and improving production efficiency and economic benefits.

[0042] In a preferred embodiment, the reaction solution comprises: 30-50 g / L zinc sulfate or zinc acetate, 3-7 g / L potassium fluoride, 3-7 g / L sodium carbonate, 100-200 g / L complexing agent, 5-15 ml / L buffer, and the remainder being water.

[0043] In a preferred embodiment, the reaction solution consists of: 50 g / L zinc sulfate or zinc acetate, 5 g / L potassium fluoride, 5 g / L sodium carbonate, 150 g / L complexing agent, 10 ml / L buffer, and the remainder is water.

[0044] In a preferred embodiment, the complexing agent is at least one of potassium pyrophosphate or sodium pyrophosphate, and the buffer is at least one of ammonia or ammonium bifluoride.

[0045] In a preferred embodiment, the surface pretreatment further includes heat treatment, specifically comprising the following steps:

[0046] 1.1 Heat treatment: The magnesium alloy surface to be treated is dewaxed by ultrasonication, then immersed in isopropanol solution for 15 minutes, and then placed in a heating device and heated to 220°C for 2 hours to remove the magnesium alloy.

[0047] 1.2 Degreasing: The magnesium alloy is degreased by alkali. The heat-treated magnesium alloy is immersed in a solution containing 60 g / L sodium hydroxide, 10 g / L trisodium phosphate and 0.5 g / L surfactant. The solution temperature is 60℃ and the degreasing time is 5 min.

[0048] 1.3 Descaling: Descaling treatment is performed on the magnesium alloy by immersing the degreased magnesium alloy in a solution containing 190 g / L of chromic anhydride at a temperature of 80–85°C for 5 min.

[0049] 1.4 Activation: The magnesium alloy is activated by immersing it in a solution containing 420 ml / l of hydrofluoric acid for 10 min after descaling.

[0050] In a preferred embodiment, the pre-plating of copper specifically involves immersing the magnesium alloy after one-step zinc plating in a pre-plating copper cyanide solution at a solution temperature of 50°C and a current density of 1.5 A / dm³. 2 The electroplating time is 10 minutes.

[0051] In a preferred embodiment, the magnesium alloy surface treatment process further includes nickel plating on the magnesium alloy surface:

[0052] (4) The magnesium alloy after copper plating is pre-plated with neutral nickel, basic chemical nickel and acidic chemical nickel in sequence.

[0053] In a preferred embodiment, nickel plating specifically includes the following steps:

[0054] 4.1 Pre-plating with neutral nickel: The magnesium alloy pre-plated with copper is immersed in a pre-plating neutral nickel solution at a temperature of 45℃ and a current density of 1A / dm³. 2 The electroplating time is 25 minutes;

[0055] 4.2 Alkaline electroless nickel plating: The magnesium alloy pre-plated with neutral nickel is immersed in an alkaline electroless nickel plating solution at a temperature of 80°C for 60 minutes.

[0056] 4.3 Acidic electroless nickel plating: The magnesium alloy after alkaline electroless nickel plating is immersed in an acidic electroless nickel plating solution at a temperature of 80°C for 90 minutes.

[0057] This invention provides a magnesium alloy obtained through any of the above-described magnesium alloy surface treatment processes. The magnesium alloy substrate has a dense and well-bonded zinc metal layer deposited on its surface, serving as an intermediate protective layer and ensuring excellent adhesion between the substrate and the coating.

[0058] Example 1

[0059] This embodiment provides a magnesium alloy surface treatment process, including the following steps:

[0060] (1) Surface pretreatment, including:

[0061] 1.1 Heat treatment: The magnesium alloy surface to be treated is dewaxed by ultrasonication, then immersed in isopropanol solution for 15 minutes, and then placed in a heating device and heated to 220°C for 2 hours to remove the magnesium alloy.

[0062] 1.2 Degreasing: The magnesium alloy is degreased by alkali. The heat-treated magnesium alloy is immersed in a solution containing 60 g / L sodium hydroxide, 10 g / L trisodium phosphate and 0.5 g / L surfactant. The solution temperature is 60℃ and the degreasing time is 5 min.

[0063] 1.3 Descaling: Descaling treatment is performed on the magnesium alloy by immersing the degreased magnesium alloy in a solution containing 190 g / L of chromic anhydride at a temperature of 80–85°C for 5 min.

[0064] 1.4 Activation: The magnesium alloy is activated by immersing it in a solution containing 420 ml / l of hydrofluoric acid for 10 min after descaling.

[0065] (2) One-step zinc plating: Remove the surface-treated magnesium alloy and immerse it in a reaction solution containing 50 g / L zinc sulfate or zinc acetate, 5 g / L potassium fluoride, 5 g / L sodium carbonate, 150 g / L potassium pyrophosphate (a complexing agent), and 10 ml / L ammonia (a buffer). The solution temperature is 75°C, and the zinc plating time is 2 min. The magnesium alloy does not need to be removed from the zinc plating reaction container; it can be directly electroplated in the one-step zinc plating reaction solution with a current density of 2 A / dm³. 2 The electroplating time is 15 minutes;

[0066] (3) Pre-plating with copper cyanide: The magnesium alloy after one-step zinc plating is immersed in a pre-plating copper cyanide solution at a solution temperature of 50℃ and a current density of 1.5A / dm³. 2 The electroplating time is 10 minutes;

[0067] (4) Nickel plating, including:

[0068] 4.1 Pre-plating with neutral nickel: The magnesium alloy pre-plated with copper is immersed in a pre-plating neutral nickel solution at a temperature of 45℃ and a current density of 1A / dm³. 2 The electroplating time is 25 minutes;

[0069] 4.2 Alkaline electroless nickel plating: The magnesium alloy pre-plated with neutral nickel is immersed in an alkaline electroless nickel plating solution at a temperature of 80°C for 60 minutes.

[0070] 4.3 Acidic electroless nickel plating: The magnesium alloy after alkaline electroless nickel plating is immersed in an acidic electroless nickel plating solution at a temperature of 80°C for 90 minutes.

[0071] Example 2,

[0072] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1, except that the zinc immersion complexing agent is replaced with sodium pyrophosphate 150g / l.

[0073] Example 3

[0074] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1, except that the zinc buffer is replaced with ammonium bifluoride 15g / l.

[0075] Example 4

[0076] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1, except that the zinc immersion time is changed to 4 minutes.

[0077] Example 5

[0078] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1, except that the zinc immersion time is changed to 5 minutes.

[0079] Example 6

[0080] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1. The only difference is that in the one-step zinc plating, the current density is changed to 1 A / dm³. 2 .

[0081] Example 7

[0082] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1. The only difference is that in the one-step zinc plating, the current density is changed to 3A / dm³. 2 .

[0083] Example 8

[0084] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1. The only difference is that in the one-step zinc immersion plating, the solution temperature is changed to 80°C.

[0085] Example 9

[0086] This embodiment provides a magnesium alloy surface treatment process. The process steps and parameter settings are the same as in Embodiment 1. The only difference is that in the one-step zinc immersion plating, the solution temperature is changed to 85°C.

[0087] The performance of the nickel-plated magnesium alloy samples from Examples 1-9 was evaluated using the following method.

[0088] Evaluation of coating adhesion: The scratch test and thermal shock test recommended by GB / T5270-2005 were used for evaluation. In the scratch test, a steel knife with a ground 30° acute angle was used to scratch 5 rows of square grids with a length and width of 1 mm on the sample. The coating between the scratches was observed to see if it peeled or fell off. The coating in the grid was then pulled vertically with strong adhesive tape, and the peeling of the coating after pulling was observed to compare the strength of the adhesion. In the thermal shock test, the coated part was heated to 250°C, kept at that temperature for 1 hour, and then quickly immersed in cold water. This was repeated 20 times, and the coating was observed to see if it peeled or fell off.

[0089] Evaluation of coating corrosion resistance: A neutral salt spray test was conducted according to the salt spray corrosion test standard of GB / T10125-97, with a test period of 24 hours. Then, the corrosion resistance level of the coating was evaluated according to the corrosion grade standard recommended in GB5944-86. The specific method is as follows: A transparent plastic film or plexiglass plate with 5mm × 5mm squares was covered over the test area of ​​the sample, dividing the test area into several squares with a side length of 5mm. The total number of squares was counted, denoted as N. Squares located at the edge of the sample that exceed half were counted as one square; those less than half were ignored. After the corrosion test, the number of corrosion points on the substrate and the number of squares corroded in the coating were counted, denoted as n. The corrosion rate was calculated using the formula: Corrosion rate (%) = 100 * n / N. The corrosion resistance of the coating was classified according to the coating corrosion rate, with grade 10 being the best and grade 0 the worst.

[0090] After scratch testing and thermal shock testing, the adhesion was divided into three levels according to the peeling condition of the coating, from worst to best: the coating peels during the scratching process, the coating does not peel during the scratching process but peels slightly after being peeled off with tape, and the coating is good and does not peel during the scratching process or after being peeled off with tape (represented by "〇" in Table 1).

[0091] As shown in Table 1, the composite coating formed by the electroless nickel plating method of the present invention, which constructs a magnesium alloy with a deposited active oxide film, has a bright appearance, with no peeling or flaking. The salt spray test corrosion level is greater than 9, which means the corrosion rate is less than 0.25%, indicating good adhesion and corrosion resistance.

[0092] Table 1. Test results of magnesium alloys in Examples 1-9

[0093]

[0094] The magnesium alloy parts obtained by one-step immersion zinc plating in this invention have excellent appearance and performance, and can fully meet the requirements of use.

[0095] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

[0097] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A surface treatment process for magnesium alloys, characterized in that, Includes the following steps: (1) Surface pretreatment, including: Heat treatment: The magnesium alloy surface to be treated is dewaxed by ultrasonication, then immersed in isopropanol solution for 15 minutes, and then placed in a heating device and heated to 220°C for 2 hours for heat treatment. Degreasing: The magnesium alloy is degreased by alkaline treatment. The heat-treated magnesium alloy is immersed in a solution containing 60 g / L sodium hydroxide, 10 g / L trisodium phosphate and 0.5 g / L surfactant. The solution temperature is 60℃ and the degreasing time is 5 min. Descaling: To descale the magnesium alloy, immerse the degreased magnesium alloy in a solution containing 190 g / L of chromic anhydride at a temperature of 80-85°C for 5 minutes. Activation: The magnesium alloy is activated by immersing the descaled magnesium alloy in a solution containing 420 mL / L hydrofluoric acid for 10 min. (2) One-step zinc plating: Take out the surface-treated magnesium alloy and immerse it in a reaction solution containing 50 g / L zinc sulfate or zinc acetate, 5 g / L potassium fluoride, 5 g / L sodium carbonate, 150 g / L potassium pyrophosphate as a complexing agent, and 10 mL / L ammonia or 15 g / L ammonium bifluoride as a buffer. The solution temperature is 75°C, and the zinc plating time is 2 min. There is no need to remove the magnesium alloy from the zinc plating reaction container. Electroplating is performed directly in the one-step zinc plating reaction solution with a current density of 2 A / dm. 2 The electroplating time is 15 minutes; (3) Pre-plating with copper cyanide: The magnesium alloy after one-step zinc plating is immersed in a pre-plating copper cyanide solution at a solution temperature of 50℃ and a current density of 1.5A / dm³. 2 The electroplating time is 10 minutes; (4) Nickel plating, including: Pre-plating neutral nickel: The magnesium alloy pre-plated with copper is immersed in a pre-plating neutral nickel solution at a temperature of 45°C and a current density of 1 A / dm³. 2 The electroplating time is 25 minutes; Alkaline electroless nickel plating: The magnesium alloy pre-plated with neutral nickel is immersed in an alkaline electroless nickel plating solution at a temperature of 80°C for 60 minutes. Acidic electroless nickel plating: The magnesium alloy after alkaline electroless nickel plating is immersed in an acidic electroless nickel plating solution at a temperature of 80°C for 90 minutes.

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