Alkaline polishing solution and alkaline polishing method

Abstract

The invention provides an alkaline polishing solution and an alkaline polishing method. The alkaline polishing solution comprises the following components: 250 to 400 g / L of sodium hydroxide, 250 to 500 g / L of sodium nitrate, 130 to 220 g / L of boric acid and 25 to 70 g / L of thiourea; according to the alkaline polishing solution, a metal part is placed in the alkaline polishing solution to be polished. The alkaline chemical polishing method is environmentally friendly, the polished aluminum alloy surface is good in brightness and flatness, the polished product can stay in air for a long time and then is cleaned, and the surface polishing state is not affected.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to an alkaline polishing liquid and an alkaline polishing method. Background Technology

[0002] The main methods for polishing the surface of metal parts (including alloy parts) include mechanical, electrochemical, and chemical methods. Mechanical and electrochemical polishing are limited in their application due to certain requirements on the shape and size of the parts. Chemical polishing, on the other hand, is not limited by the shape or size of the parts and can process a large number of parts at once; therefore, it is currently the most commonly used polishing method.

[0003] Current chemical polishing methods primarily utilize acidic chemical polishing solutions (containing phosphoric acid, sulfuric acid, and nitric acid, commonly known as tri-acid polishing solutions), with a few alkaline polishing solutions used secondarily. The advantages of acidic chemical polishing solutions are: better polishing effect, resulting in a bright and smooth surface on the polished parts; the disadvantage is: the polishing process generates a large amount of NO. x Gases cause serious environmental pollution. The advantages of alkaline polishing slurry are: good polishing effect, bright and smooth surface of polished parts; no harmful gases are produced, making it environmentally friendly; the disadvantages are: after being polished with alkaline polishing slurry, the parts must be quickly immersed in the cleaning solution and cannot remain in the air for 5 seconds or more, otherwise cloud-like or fog-like marks are easily formed on the surface, affecting the appearance of the product in subsequent processing.

[0004] Therefore, it is necessary to provide an alkaline polishing liquid and an alkaline polishing method to alleviate or solve the above problems. Summary of the Invention

[0005] To address the technical problem in commonly used technologies that alkaline polished parts develop cloud-like or fog-like marks on their surface when left in the air for 5 seconds or more before entering the cleaning solution, this invention provides an alkaline polishing solution comprising: sodium hydroxide 250-400 g / L, sodium nitrate 250-500 g / L, boric acid 130-220 g / L, and thiourea 25-70 g / L.

[0006] Furthermore, its composition includes: sodium hydroxide 280-380 g / L, sodium nitrate 300-450 g / L, boric acid 150-200 g / L, and thiourea 30-60 g / L.

[0007] This invention provides an alkaline polishing method, comprising:

[0008] The metal parts are polished by placing them in any of the alkaline polishing solutions described above to obtain alkaline polished parts.

[0009] The alkaline polishing parts are neutralized and then washed to obtain the polished product.

[0010] The alkaline polished part is allowed to remain in the air for more than 5 seconds before the neutralization treatment is performed.

[0011] Furthermore, the metal parts include aluminum and / or aluminum alloy parts.

[0012] Furthermore, before polishing the aluminum and / or aluminum alloy, the aluminum and / or aluminum alloy are pretreated, the pretreatment including: the aluminum and / or aluminum alloy being cleaned in sequence with a degreasing cleaning solution and deionized water.

[0013] Furthermore, the polishing temperature is 90–110°C, and the polishing duration is 10–20 seconds.

[0014] Furthermore, the neutralization treatment includes placing the alkaline polished part in an acid solution for a duration of 2 to 10 minutes.

[0015] Furthermore, the acid solution includes a nitric acid solution with a concentration of 20% to 50%.

[0016] Furthermore, the alkaline polished part is allowed to remain in the air for a period of 10 to 30 seconds before the neutralization treatment is performed.

[0017] Furthermore, the metal parts include one or more of the following: medium-complexity alloy parts, high-complexity alloy parts, medium-weight alloy parts, and high-weight alloy parts.

[0018] In commonly used techniques, the reasons why alkaline polished parts develop blemishes after prolonged exposure to air include:

[0019] Chemical reaction between residual alkali and alloys: After alkali polishing, alkaline components remain on the surface of the polished part. If the exposure time exceeds 5 seconds, the residual alkali continues to react with the surface of the polished part, generating a large amount of gas that pushes away the liquid on the surface and causes a large amount of moisture to evaporate. This results in uneven distribution of the alkali on the aluminum alloy surface, causing different areas to react for different durations. Areas with alkali continue to react, forming uneven depressions, which appear as cloud-like, fog-like, or other shaped marks. For example, when polishing aluminum and / or aluminum alloys with an alkaline polishing solution, if the polished part remains in the air for 5 seconds or more, the residual alkali on the aluminum surface will quickly form an uneven distribution. If not cleaned in time, the alkali will continue to react until it is completely consumed, thus forming marks.

[0020] To address the aforementioned problems, this invention provides an alkaline polishing solution comprising: 250–400 g / L sodium hydroxide, 250–500 g / L sodium nitrate, 130–220 g / L boric acid, and 25–70 g / L thiourea. By using boric acid and thiourea in combination, both the gloss and smoothness of the aluminum alloy surface can be improved, resolving defects such as "small bubbles" and "skin-like" defects on the surface, as well as hazy marks caused by prolonged air exposure after polishing. Furthermore, this alkaline chemical polishing solution is environmentally friendly.

[0021] Thiourea chemically adsorbs sulfur and nitrogen atoms onto the surface of alkaline polished parts, forming a dense organic protective film. This film exhibits selective coverage and dynamic repair capabilities, preferentially adsorbing onto active sites on the alkaline polished surface (such as grain boundaries and dislocations), inhibiting preferential oxidation in these areas while preventing localized damage to the film due to mechanical friction or environmental factors—thiourea molecules can quickly migrate to the damaged area and re-adsorb, maintaining the integrity of the film. Furthermore, the film surface exhibits hydrophobic properties, reducing the adsorption of moisture from the air on the aluminum surface, thereby lowering the oxidation reaction rate.

[0022] Sodium nitrate can form a dense passivation film on the surface of alkaline polished parts. At the same time, by controlling the concentration of sodium nitrate (250-500 g / L), the formation and dissolution rate of the passivation film can reach a dynamic balance. This balance ensures that the film layer is neither too thick, which would cause surface roughening, nor too thin, which would cause local corrosion. For example, when aluminum and / or aluminum alloys are polished in an alkaline polishing solution, sodium nitrate oxidizes the aluminum surface into a dense Al2O3 passivation film in an alkaline environment.

[0023] The aforementioned organic protective film and passivation film work synergistically to prevent the formation of surface defects such as blemishes. Based on this, alkaline polished parts can remain in air for more than 5 seconds, resulting in a breakthrough in process compatibility.

[0024] Mechanization and automation adaptation: After polishing, the aluminum parts can remain in the air for more than 5 seconds, providing a sufficient time window for the robotic arm to grasp and transfer them to the cleaning station, avoiding the chemical waste caused by the short dripping time in traditional processes.

[0025] Continuous processing of multiple workpieces: On automated production lines, extending the dwell time allows multiple workpieces to be polished sequentially and then cleaned in a concentrated manner, reducing the start-up and shutdown frequency of cleaning equipment and improving production efficiency. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0028] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0029] The present invention provides an alkaline polishing solution, the composition of which includes: sodium hydroxide 250-400 g / L, sodium nitrate 250-500 g / L, boric acid 130-220 g / L, and thiourea 25-70 g / L.

[0030] In some embodiments, the composition of the alkaline polishing solution may include: sodium hydroxide 280-380 g / L, sodium nitrate 300-450 g / L, boric acid 150-200 g / L, and thiourea 30-60 g / L.

[0031] In some embodiments, the composition of the alkaline polishing solution may include: sodium hydroxide 310-350 g / L, sodium nitrate 330-420 g / L, boric acid 160-190 g / L, and thiourea 40-50 g / L.

[0032] In some embodiments, the alkaline polishing solution may also include a solvent, which may include water.

[0033] This invention provides an alkaline polishing method, comprising:

[0034] S1. Polish the metal part in the alkaline polishing solution described in any of the above methods to obtain an alkaline polished part.

[0035] In some embodiments of the present invention, the metal part includes an alloy part.

[0036] S2. The alkaline polishing parts are neutralized and then washed to obtain the polished product.

[0037] In this invention, the alkaline polished part is allowed to remain in the air for more than 5 seconds before the neutralization treatment is performed.

[0038] In some embodiments of the present invention, the alkaline polished part is allowed to remain in the air for more than 10 seconds before the neutralization treatment is performed; in other embodiments of the present invention, the alkaline polished part is allowed to remain in the air for more than 15 seconds before the neutralization treatment is performed; exemplary alkaline polished parts obtained by the present invention can remain in the air for more than 20 seconds or even more than 30 seconds.

[0039] In some embodiments of the present invention, the alkaline polished part is allowed to remain in the air for a period of 0 to 30 seconds before the neutralization treatment is performed; for example, the alkaline polished part is allowed to remain in the air for a period of 5 to 30 seconds, 10 to 30 seconds, 15 to 30 seconds, or 20 to 30 seconds before the neutralization treatment is performed.

[0040] In fact, the alkaline polished parts prepared by this invention will not produce cloud-like or fog-like marks when left in the air.

[0041] It should be noted that in commonly used techniques, after the alkaline polishing parts are removed from the polishing solution, they must be quickly immersed in the cleaning solution and cannot remain in the air for 5 seconds or more. Otherwise, cloud-like or fog-like marks are easily generated on the surface, affecting the appearance of the product in subsequent processing.

[0042] For example, when the material of the alkaline polished part is aluminum and / or aluminum alloy, the allowable dwell time in the air after applying the alkaline polishing liquid in commonly used techniques is generally no more than 5 seconds.

[0043] In this invention, the metal parts include aluminum and / or aluminum alloy parts; in some embodiments, the aluminum alloy parts may be 2A12-T4 aluminum alloy.

[0044] In this invention, before polishing the aluminum and / or aluminum alloy, the aluminum and / or aluminum alloy are pretreated. The pretreatment includes: subjecting the aluminum and / or aluminum alloy to a double cleaning process using an oil-removing cleaning solution and deionized water.

[0045] In some embodiments of the present invention, the degreasing cleaning solution can be an alkaline degreasing solution. For example, the metal parts can be immersed in the degreasing cleaning solution for 5 minutes to remove oil, and then rinsed with deionized water.

[0046] In this invention, the polishing temperature is 90-110°C and the polishing time is 10-20 seconds.

[0047] In this invention, the neutralization process may include: placing the alkaline polished part in an acid solution for a duration of 2 to 10 minutes.

[0048] In some embodiments, the acid solution may include a nitric acid solution, the concentration of which may be 20% to 50%.

[0049] In this invention, the metal part includes one or more of medium-complexity alloy parts, high-complexity alloy parts, medium-weight alloy parts, and / or high-weight alloy parts.

[0050] In some embodiments, low-complexity alloy parts are alloy parts with no internal structure or only simple through holes, such as flat plates and profiles; medium-complexity alloy parts are alloy parts with holes or shallow grooves with a depth ≤ 5 times the diameter, such as heat sink fins and motor housings; high-complexity alloy parts are alloy parts with blind holes, cross holes or threaded structures with a depth > 5 times the diameter, such as photovoltaic aluminum frames and new energy vehicle battery trays.

[0051] In some embodiments, low-weight alloy parts weigh ≤10kg, such as mobile phone frames; medium-weight alloy parts weigh 10kg < ≤50kg, such as automobile wheel hubs; and high-weight alloy parts weigh >50kg, such as new energy vehicle battery trays and photovoltaic brackets.

[0052] It should be noted that medium-complexity alloy parts, high-complexity alloy parts, medium-weight alloy parts, and / or high-weight alloy parts are more prone to developing cloud-like or hazy marks during the air exposure process after polishing and before neutralization. Therefore, the need to avoid the formation of cloud-like or hazy marks is particularly urgent.

[0053] Causes of blemishes on complex alloy parts and highly complex alloy parts:

[0054] Residual liquid retention in deep holes and grooves: Alkali solutions tend to remain in deep holes and threads of complex products (such as photovoltaic aluminum frames and new energy vehicle battery trays). Due to gravity, the residual liquid is difficult to drip off naturally in these areas, leading to prolonged localized corrosion time.

[0055] Non-uniform corrosion caused by microstructure: Microstructures such as microtextures and irregular contours can change the flow path of alkaline solution, forming local high concentration areas.

[0056] Causes of blemishes on medium-weight and high-weight alloy parts:

[0057] Synergistic effect of thermal stress and alkaline corrosion: During the polishing process of heavy products (such as wind turbine blade molds and large aerospace aluminum forgings), the surface temperature is uneven due to the large heat capacity and slow cooling. When the dwell time is too long, the alkaline corrosion rate in high-temperature areas (such as the curved surface of the mold) is 3 to 5 times faster than that in low-temperature areas, resulting in differences in surface gloss and blemishes.

[0058] Uncontrollable dwell time due to transportation difficulties: Heavy products require specialized equipment (such as overhead cranes and vacuum suction cups) for transportation, resulting in long operation times. Alkaline corrosion continues during transportation, causing the blemish area to expand.

[0059] To address the aforementioned issues, this invention provides an alkaline polishing solution and an alkaline polishing method. By utilizing the synergistic effect of the organic protective film generated by thiourea and the passivation film formed by boric acid, the generation of surface defects such as blemishes is avoided. This alleviates the technical problem that cloud-like or hazy blemishes are easily generated in medium-complexity alloy parts, high-complexity alloy parts, medium-weight alloy parts, and / or high-weight alloy parts due to their structural complexity or heavy weight, thus affecting surface quality.

[0060] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0061] Example 1

[0062] This embodiment describes alkaline chemical polishing of a medium-complexity 2A12-T4 aluminum alloy surface, and includes the following steps:

[0063] Immerse the 2A12-T4 aluminum alloy in a degreasing cleaning solution for 5 minutes to remove oil, and then rinse with deionized water.

[0064] The cleaned 2A12-T4 aluminum alloy was placed in an alkaline polishing solution and subjected to alkaline chemical polishing at 100°C for 15 seconds to obtain an alkaline polished part. The alkaline chemical polishing solution is an aqueous solution composed of the following components at the following concentrations: sodium hydroxide 250g / L, sodium nitrate 250g / L, boric acid 130g / L, and thiourea 25g / L.

[0065] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0066] The alkaline polished parts were neutralized in a 1:1 nitric acid solution for 5 minutes, then ultrasonically cleaned in deionized water for 5 minutes, and finally removed and dried.

[0067] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process in this embodiment.

[0068] Example 2

[0069] The conditions remain the same in this embodiment, except that the composition of the alkaline polishing solution is adjusted to: sodium hydroxide 320g / L, sodium nitrate 360g / L, boric acid 160g / L, and thiourea 45g / L.

[0070] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0071] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process in this embodiment.

[0072] Example 3

[0073] The conditions remain the same in this embodiment, except that the composition of the alkaline polishing solution is adjusted to: sodium hydroxide 250g / L, sodium nitrate 500g / L, boric acid 130g / L, and thiourea 70g / L.

[0074] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0075] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process of this embodiment.

[0076] Example 4

[0077] The conditions remain the same in this embodiment, except that the composition of the alkaline polishing solution is adjusted to: sodium hydroxide 400g / L; sodium nitrate 250g / L; boric acid 200g / L; thiourea 25g / L.

[0078] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0079] The 2A12-T4 aluminum alloy surface after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process of this embodiment.

[0080] Example 5

[0081] The conditions remain the same in this embodiment, except that the composition of the alkaline polishing solution is adjusted to: sodium hydroxide 400g / L, sodium nitrate 500g / L, boric acid 200g / L, and thiourea 70g / L.

[0082] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0083] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process of this embodiment.

[0084] Example 6

[0085] Compared to Example 1, all other conditions remain the same in this example, except that the medium-complexity 2A12-T4 aluminum alloy is replaced with a high-complexity 2A12-T4 alloy part.

[0086] After being exposed to air for 30 seconds, no cloud-like or fog-like marks were observed on the surface of the alkaline polished part, meaning that the alkaline polished part in this embodiment will not exhibit cloud-like or fog-like marks.

[0087] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this embodiment has a semi-mirror gloss and good flatness, and no harmful gases are generated throughout the entire process of this embodiment.

[0088] Analysis example 1

[0089] The longest residence time of the alkaline polished parts in air after polishing and before neutralization in each embodiment was examined:

[0090] Example 1: When alkaline polished parts, after polishing and before neutralization, are placed in air, no cloud-like or fog-like marks are observed.

[0091] Example 2: After polishing and before neutralization, the alkaline polished parts were placed in air, and no cloud-like or fog-like marks were observed.

[0092] Example 3: After polishing and before neutralization, the alkaline polished parts were placed in air, and no cloud-like or fog-like marks were observed from the beginning.

[0093] Example 4: After polishing and before neutralization, the alkaline polished parts were placed in air, and no cloud-like or fog-like marks were observed.

[0094] Example 5: After polishing and before neutralization, the alkaline polished parts were placed in air, and no cloud-like or fog-like marks were observed from the beginning.

[0095] Example 6: After polishing and before neutralization, the alkaline polished parts were placed in air, and no cloud-like or fog-like marks were observed from the beginning.

[0096] Comparative Example 1

[0097] Compared to Example 1, this comparative example retains all other conditions except that the alkaline polishing solution is replaced with the alkaline chemical polishing solution mentioned in patent document CN102925900A. This alkaline chemical polishing solution consists of 280 g / L sodium hydroxide, 150 g / L sodium nitrite, 1.2 g / L sodium fluoride, 20 g / L sodium phosphate, and the balance being water. The steps include:

[0098] Immerse the 2A12-T4 aluminum alloy in a degreasing cleaning solution for 5 minutes to remove oil, and then rinse with deionized water.

[0099] The cleaned 2A12-T4 aluminum alloy was placed in the above-mentioned alkaline chemical polishing solution and subjected to alkaline chemical polishing at 100°C for 15 seconds to obtain an alkaline polished part.

[0100] After being left in the air for 5 seconds, cloud-like and hazy marks were observed on the surface of the alkaline polished parts.

[0101] The alkaline polished parts were neutralized in a 1:1 nitric acid solution for 5 minutes, then ultrasonically cleaned in deionized water for 5 minutes, and finally removed and dried.

[0102] The surface of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this comparative example has a mirror-like gloss and good flatness.

[0103] Comparative Example 2

[0104] This comparative example is the same as Example 1 in all other conditions, except that the boric acid in the alkaline polishing solution is replaced with acetic acid of the same concentration.

[0105] When alkaline polished parts, after polishing and before neutralization, were placed in air, no cloud-like or hazy marks were observed.

[0106] The surface gloss of the 2A12-T4 aluminum alloy after alkaline chemical polishing in this comparative example is relatively dark and does not reach a semi-mirror finish, but the flatness is relatively good.

[0107] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. An alkaline polishing liquid, characterized in that, Its composition includes: sodium hydroxide 250-400 g / L, sodium nitrate 250-500 g / L, boric acid 130-220 g / L, and thiourea 25-70 g / L.

2. The alkaline polishing liquid according to claim 1, characterized in that, Its composition includes: sodium hydroxide 280-380 g / L, sodium nitrate 300-450 g / L, boric acid 150-200 g / L, and thiourea 30-60 g / L.

3. An alkaline polishing method, characterized in that, include: The metal part is polished in the alkaline polishing solution described in any one of claims 1 to 2 to obtain an alkaline polished part; The alkaline polishing parts are neutralized and then washed to obtain the polished product. The alkaline polished part is allowed to remain in the air for more than 5 seconds before the neutralization treatment is performed.

4. The alkaline polishing method according to claim 3, characterized in that, The metal parts include aluminum and / or aluminum alloy parts.

5. The alkaline polishing method according to claim 4, characterized in that, Before polishing the aluminum and / or aluminum alloy, the aluminum and / or aluminum alloy are pretreated, the pretreatment including: the aluminum and / or aluminum alloy being cleaned in sequence with a degreasing cleaning solution and deionized water.

6. The alkaline polishing method according to claim 3, characterized in that, The polishing temperature is 90–110°C, and the polishing time is 10–20 seconds.

7. The alkaline polishing method according to claim 3, characterized in that, The neutralization process includes placing the alkaline polished part in an acid solution for 2 to 10 minutes.

8. The alkaline polishing method according to claim 7, characterized in that, The acid solution includes a nitric acid solution with a concentration of 20% to 50%.

9. The alkaline polishing method according to any one of claims 3 to 8, characterized in that, The alkaline polished part is allowed to remain in the air for 10 to 30 seconds before the neutralization treatment is performed.

10. The alkaline polishing method according to any one of claims 3 to 8, characterized in that, The metal parts include one or more of the following: medium-complexity alloy parts, high-complexity alloy parts, medium-weight alloy parts, and high-weight alloy parts.