Corrosion solution and corrosion treatment methods; zinc coating quality testing methods for zinc-sprayed aluminum pipes

Abstract

This invention discloses an etching solution and etching treatment method, as well as a method for detecting the zinc layer quality of zinc-sprayed aluminum pipes, relating to the field of coating inspection technology. The technical solution of this invention designs an etching solution with a specific formula, and based on this etching solution, designs an etching treatment method and a method for detecting the zinc layer quality of zinc-sprayed aluminum pipes. Compared with existing technologies, the technical solution of this invention can reveal the distribution morphology of the zinc layer, thereby measuring the zinc penetration depth, obtaining the proportion of zinc-free areas, the optimal zinc penetration depth proportion, and the maximum zinc penetration depth, thus better controlling the quality of zinc-sprayed aluminum pipes. Furthermore, the detection method of this invention has a shorter detection cycle and significantly lower costs compared to existing technologies, possessing high market application value.

Description

Technical Field

[0001] This invention relates to the field of coating inspection technology, and in particular to a corrosion solution and corrosion treatment method, and a method for inspecting the zinc coating quality of zinc-sprayed aluminum pipes. Background Technology

[0002] After aluminum tubes undergo arc spraying and heat treatment zinc diffusion processes, the corrosion resistance and reliability of the resulting zinc-sprayed aluminum tubes are significantly improved, laying the technical foundation for the application of aluminum tubes in heat exchangers. However, there is no good characterization method for the quality requirements of aluminum tubes used in heat exchangers. Related technologies mainly rely on zinc content and maximum zinc diffusion depth for quality control. Zinc content is primarily detected by ICP, while zinc diffusion depth is detected by EPMA line scanning. However, this method cannot reveal the full distribution of the zinc layer, making it prone to errors. Furthermore, EPMA testing is time-consuming and expensive. Summary of the Invention

[0003] The main objective of this invention is to develop a method for detecting the zinc layer quality of zinc-sprayed aluminum tubes used in heat exchangers. This method has a shorter testing cycle, lower cost, and can reveal the distribution pattern of the zinc layer, thereby enabling better control of the quality of zinc-sprayed aluminum tubes.

[0004] To achieve the above objectives, the present invention provides a corrosive liquid comprising an alkali, an oxidant, a corrosion inhibitor, and a color developer; the corrosion inhibitor comprises a water-soluble silicate; and the color developer is selected from either an iron salt or a copper salt.

[0005] In one embodiment, the water-soluble silicate in the corrosion inhibitor includes at least one of sodium silicate and potassium silicate; in another embodiment, the color developer is selected from at least one of ferric chloride and copper chloride.

[0006] In one embodiment, the oxidant is selected from at least one of nitrate, nitrite, chlorate, hypochlorite and hydrogen peroxide.

[0007] In one specific embodiment, the corrosive liquid comprises an alkali with a mass fraction of 1 wt% to 10 wt%.

[0008] In a preferred embodiment, the corrosive liquid comprises 5 wt% to 10 wt% alkali.

[0009] In one specific embodiment, and / or, the etching solution includes an oxidant with a mass fraction of 1wt% to 2wt%; and / or, the etching solution includes a corrosion inhibitor with a mass fraction of 0.1wt% to 0.3wt%; and / or, the etching solution includes a color developer with a mass fraction of 0.05wt% to 0.15wt%.

[0010] The present invention also proposes a corrosion treatment method, wherein the corrosion treatment method applies the corrosion solution.

[0011] In one embodiment, the corrosion treatment method includes the following steps:

[0012] The cross-section of the metal substrate is ground and polished, and then immersed in the heated etching solution to complete the etching process.

[0013] In one specific embodiment, the temperature of the corrosive liquid during the immersion process is 50°C to 70°C.

[0014] The present invention also proposes a method for detecting the zinc layer quality of a zinc-sprayed aluminum pipe, wherein the zinc layer quality detection method of the zinc-sprayed aluminum pipe applies the corrosion solution; or, the zinc layer quality detection method of the zinc-sprayed aluminum pipe applies the corrosion treatment method.

[0015] In one specific embodiment, the method for detecting the zinc layer quality of the zinc-sprayed aluminum pipe includes the following steps:

[0016] S1. Fix the zinc-sprayed aluminum pipe in the mold, and then grind and polish the cross-section of the zinc-sprayed aluminum pipe in sequence.

[0017] S2. Prepare the etching solution, and then immerse the cross-section of the zinc-sprayed aluminum pipe after the polishing treatment into the heated etching solution for soaking, thereby completing the etching treatment of the zinc-sprayed aluminum pipe.

[0018] S3. Using a microscope, photographs are taken at different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe, and the images are stitched together to obtain the overall zinc layer distribution of the zinc-sprayed aluminum pipe, and the quality technical indicators of the zinc layer are measured.

[0019] In one embodiment, during step S1, the cross-section of the zinc-coated aluminum tube is polished at least four times using metallographic sandpaper with grits decreasing from large to small; and when polishing with the next grit sandpaper, the cross-section of the zinc-coated aluminum tube is rotated 90 degrees.

[0020] In one embodiment, during step S1, the abrasive particle size is 0.5μm-1μm, and / or the material-to-liquid ratio is 1:3-6.

[0021] In one embodiment, during the immersion process in step S2, the temperature of the corrosive solution is 50°C to 70°C; and / or, during the immersion process in step S2, the immersion time is increased by 1 min to 2 min for every 10 μm increase in the thickness of the zinc layer in the zinc-sprayed aluminum pipe.

[0022] In one embodiment, in step S3, a metallographic microscope with magnification of 50x to 100x is used to photograph different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe after corrosion treatment in step S2. The metallographic photographs of the different points are stitched together to form a complete metallographic image of the cross-section of the zinc-sprayed aluminum pipe. On the complete metallographic image, radii are reselected at intervals of 7.2 degrees to 14.4 degrees, and the zinc layer depth on the radius is measured to obtain several zinc layer depth data. The average zinc penetration depth, maximum zinc penetration depth, and optimal zinc penetration depth ratio of the cross-section are calculated. And / or, on the complete metallographic image, radii are reselected at intervals of 7.2 degrees to 14.4 degrees, and the boundary points of the zinc-free area on different radii are observed and measured to calculate the zinc-free area ratio of the cross-section.

[0023] The technical solution of this invention designs a corrosion solution with a specific formula, and based on this corrosion solution, designs a corrosion treatment method and a zinc layer quality detection method for zinc-sprayed aluminum pipes. Compared with existing technologies, the technical solution of this invention can reveal the distribution morphology of the zinc layer, thereby measuring the zinc penetration depth, obtaining the proportion of zinc-free areas, the optimal zinc penetration depth proportion, and the maximum zinc penetration depth, thus better controlling the quality of zinc-sprayed aluminum pipes. Furthermore, the detection method of this invention has a shorter detection cycle and significantly lower costs compared to existing technologies, making it highly valuable for market application. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a photograph of the cross-section of the zinc-coated aluminum pipe in Embodiment 1 of the present invention after corrosion treatment.

[0026] Figure 2 This is a photograph of the cross-section of the zinc-aluminum sprayed pipe in Embodiment 2 of the present invention after corrosion treatment.

[0027] Figure 3 This is a graph showing the energy value of zinc content at a single point on the cross-section of the zinc-sprayed aluminum tube in Comparative Example 1 of the present invention versus the scanning depth curve.

[0028] Figure 4 This is a schematic diagram of the zinc layer distribution in the cross-section of the zinc-sprayed aluminum tube in Comparative Example 1 of the present invention, obtained by EPMA testing.

[0029] Figure 5This is a line graph showing the zinc penetration depth at different locations on the cross-section of the zinc-sprayed aluminum pipe in Embodiment 1 and Comparative Example 1 of the present invention.

[0030] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0033] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0034] The technical problem addressed in this application is that by subjecting aluminum tubes used in air conditioning heat exchangers to arc spraying and heat treatment zinc diffusion processes, zinc-sprayed aluminum tubes are obtained, significantly improving the corrosion resistance and reliability of the aluminum tube material and laying a technical foundation for the use of aluminum tubes in air conditioning heat exchangers. However, there is no good characterization method for the quality requirements of zinc-sprayed aluminum tubes; related technologies mainly control quality through zinc content and maximum zinc diffusion depth, with zinc content primarily determined by ICP testing.

[0035] It should be noted that the quality of the zinc layer in zinc-sprayed aluminum pipes is mainly controlled through three technical indicators to ensure the corrosion resistance reliability of the aluminum pipes: the proportion of zinc-free areas, the proportion of optimal zinc penetration depth, and the average and maximum zinc penetration depth. EPMA line scanning inspection can only obtain local information about the zinc layer and cannot show the overall distribution of the zinc layer, which leads to the distortion of the above three technical indicators and causes the test results to deviate from the actual situation. In addition, EPMA testing has a long cycle and is expensive.

[0036] To address the aforementioned technical problems, this invention proposes a corrosion solution comprising an alkali, an oxidant, a corrosion inhibitor, and a color developer; the corrosion inhibitor comprises a water-soluble silicate; and the color developer is selected from either an iron salt or a copper salt.

[0037] The purpose of the etchant is to quickly, cost-effectively, and macroscopically characterize the zinc layer distribution in the cross-section of the zinc-sprayed aluminum pipe.

[0038] Specifically, the alkali is used to dissolve the alumina passivation film at the cross-section of the zinc-sprayed aluminum tube, and reacts with the aluminum and zinc. The color developer undergoes a displacement or complexation reaction with the dissolved zinc ions, forming an attached colored metal hydroxide precipitate on the zinc layer surface of the aluminum tube cross-section under alkaline conditions, thus visualizing the zinc distribution; areas with higher zinc content and stronger activity show a darker color. The corrosion inhibitor forms a dense silica gel protective film on the aluminum substrate surface, significantly inhibiting excessive corrosion of the aluminum substrate in areas without zinc or with a thin zinc layer by the alkali and oxidant. The oxidant promotes the dissolution of zinc in the alkaline solution and also promotes the passivation reaction on the aluminum substrate surface.

[0039] By employing the above technical solution, due to the synergistic effect of the oxidant and corrosion inhibitor, after the natural oxide film on the aluminum tube cross-section is dissolved by the alkali, water-soluble silicates can preferentially adsorb onto the alkali-activated aluminum surface and form a protective gel layer, greatly slowing down the reaction rate between aluminum and alkali. Simultaneously, under the action of the oxidant, a more stable passivation film rapidly forms on the exposed aluminum surface, thereby inhibiting aluminum dissolution. Meanwhile, the zinc layer on the aluminum tube cross-section undergoes a rapid displacement reaction under the synergistic effect of the oxidant and colorant, generating a colored metal hydroxide precipitate layer on the zinc layer surface, forming a striking contrast with the aluminum substrate.

[0040] In one embodiment, the water-soluble silicate in the corrosion inhibitor includes at least one of sodium silicate and potassium silicate.

[0041] It should be noted that it is precisely because water-soluble silicates preferentially form an effective protective film on the aluminum surface rather than the zinc surface that the corrosion solution can quickly, cost-effectively, and macroscopically characterize the zinc layer distribution in the cross-section of the zinc-sprayed aluminum pipe. Furthermore, dissolved aluminum ions react with silicate ions to form aluminum silicate or a denser aluminum-silica composite gel, which possesses dense and strong adhesion properties. While zinc ions, although forming zinc silicate with silicate ions, also exhibit stability, it presents as a loose, flocculent substance and cannot form a continuous, dense protective film. Moreover, under the action of oxidants, the zinc layer surface not only fails to form a dense oxide protective film but also accelerates its reaction and dissolution with the alkaline solution, resulting in a large amount of zinc dissolving in the solution surrounding the zinc layer in a short period.

[0042] In one embodiment, the color developer includes at least one of ferric chloride and copper chloride.

[0043] Specifically, in the presence of strong alkalinity and oxidizing agents, iron or copper ions in the color developer preferentially nucleate and deposit on the zinc layer surface, forming a non-ferrous metal hydroxide precipitate layer. On the aluminum substrate surface, however, the sodium silicate has formed a dense aluminum silicate gel protective film. This film physically prevents the vigorous dissolution of aluminum, preventing the formation of conditions similar to the intense ion disturbance and supersaturated precipitation at the aluminum substrate-solution interface. Consequently, a non-ferrous metal hydroxide precipitate layer cannot form on the aluminum substrate surface, resulting in a striking color contrast between the zinc layer and the aluminum substrate surface.

[0044] In a preferred embodiment, the color developer includes ferric chloride and copper chloride; it should be noted that the co-precipitation of mixed metal hydroxides is more stable than that of a single hydroxide, and the color may also be more vivid due to the synergistic effect of the metal ions.

[0045] In one embodiment, the oxidant is selected from at least one of nitrate, nitrite, chlorate, hypochlorite, and hydrogen peroxide.

[0046] In a preferred embodiment, the oxidant is selected from nitrates. It is understood that nitrate ions are good oxidants under alkaline conditions and can effectively inhibit hydrogen evolution corrosion of aluminum, helping to stabilize the passivation state of the aluminum surface; and the reduction products of nitrate ions do not generate corrosive anions, thus not damaging the passivation film.

[0047] In one embodiment, the etching solution comprises an alkali with a mass fraction of 1 wt% to 10 wt%. It is understood that the mass fraction of alkali in the etching solution can be 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, or 10 wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0048] Specifically, the alkali is not limited to highly soluble potassium hydroxide or sodium hydroxide, but can also be calcium hydroxide, barium hydroxide, etc., as long as the hydroxide concentration in the solution is approximately equal to the hydroxide concentration corresponding to a mass fraction of 1wt% to 10wt% of sodium hydroxide or potassium hydroxide.

[0049] In a preferred embodiment, the etching solution comprises 5 wt% to 10 wt% alkali. Under this alkaline environment, the precipitation of metal ions in the colorimetric agent can be promoted more effectively, the colorimetric time can be shortened, and the adsorption of the precipitate on the zinc layer surface can be facilitated.

[0050] In one embodiment, the etching solution includes an oxidant with a mass fraction of 1 wt% to 2 wt%. It is understood that the mass fraction of the oxidant in the etching solution can be 1 wt%, 1.1 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, or 2 wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0051] In one embodiment, the corrosive liquid includes a corrosion inhibitor with a mass fraction of 0.1 wt% to 0.3 wt%. It is understood that the mass fraction of the corrosion inhibitor in the corrosive liquid can be 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, or 0.3 wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0052] In one embodiment, the etching solution includes a colorimetric agent with a mass fraction of 0.05 wt% to 0.15 wt%. It is understood that the mass fraction of the colorimetric agent in the etching solution can be 0.05 wt%, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.11 wt%, or 0.15 wt%, but is not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0053] In a preferred embodiment, the corrosive liquid comprises: 5wt% to 10wt% alkali, 1wt% to 2wt% oxidant, 0.1wt% to 0.3wt% corrosion inhibitor, and 0.05wt% to 0.15wt% color developer.

[0054] In another preferred embodiment, the corrosive liquid comprises sodium hydroxide with a mass fraction of 5wt% to 10wt%, sodium nitrate with a mass concentration of 10g / L to 20g / L, sodium silicate with a mass concentration of 1g / L to 3g / L, and ferric chloride with a mass concentration of 0.5g / L to 1.5g / L.

[0055] The present invention also proposes a corrosion treatment method, which uses the above-mentioned corrosion solution to corrode zinc-sprayed aluminum pipes, galvanized aluminum pipes, or other materials.

[0056] It should be noted that the corrosion solution and corrosion treatment method in this application are not only applicable to the corrosion treatment of zinc-sprayed aluminum pipes or galvanized aluminum pipes, but also applicable to the corrosion treatment of electro-galvanized materials, hot-dip galvanized steel, anodized, micro-arc-oxidized metal parts, etc., and can be further used for the detection of material defects and quality.

[0057] In one specific embodiment, the corrosion treatment method includes the following steps:

[0058] The cross-section of the metal substrate is ground and polished, and then immersed in the heated etching solution to complete the etching process.

[0059] In a more specific embodiment, the temperature of the corrosive solution is controlled at 50°C to 70°C during the immersion process.

[0060] Understandably, by further limiting the temperature of the corrosion treatment, the reaction rate and corrosion effect are further optimized, thereby obtaining a clear boundary and high contrast color development cross section in a shorter time. Too low a reaction temperature will result in a slow reaction and pale color development; too high a reaction temperature will result in an overly vigorous reaction, blurred color development boundaries, and instability of the aluminum substrate protective film, among other problems.

[0061] The present invention also proposes a method for detecting the zinc layer quality of zinc-sprayed aluminum pipes, by applying the above-mentioned corrosive liquid and / or the above-mentioned corrosion treatment method.

[0062] In one embodiment, the method for detecting the zinc layer quality of the zinc-sprayed aluminum pipe includes the following steps:

[0063] S1. Fix the zinc-sprayed aluminum pipe in the mold, and then grind and polish the cross-section of the zinc-sprayed aluminum pipe in sequence.

[0064] S2. Prepare the etching solution, and then immerse the cross-section of the zinc-sprayed aluminum pipe after the polishing treatment into the heated etching solution for soaking, thereby completing the etching treatment of the zinc-sprayed aluminum pipe.

[0065] S3. Using a microscope, photographs are taken at different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe, and the images are stitched together to obtain the overall zinc layer distribution of the zinc-sprayed aluminum pipe, and the quality technical indicators of the zinc layer are measured.

[0066] In a specific embodiment, in step S1, during the polishing process, the cross-section of the zinc-sprayed aluminum tube is polished at least four times using metallographic sandpaper with grits decreasing from large to small; and when polishing with the next grit sandpaper, the cross-section of the zinc-sprayed aluminum tube is rotated by 90°.

[0067] In a preferred embodiment, in step S1, during the grinding process, 240#, 800#, 1200#, and 2000# metallographic sandpaper are used sequentially to mechanically grind the cross-section of the sample.

[0068] In a specific embodiment, in step S1, during the polishing process, the particle size of the abrasive is 0.5μm-1μm, and / or the material-to-liquid ratio is 1:3~6; and polishing continues until there are no obvious wear marks on the cross-section of the zinc-aluminum spraying tube.

[0069] In one specific embodiment, during the immersion process in step S2, the temperature of the corrosive liquid is 50℃~70℃; in another specific embodiment, the immersion time is increased by 1min~2min for every 10μm increase in the thickness of the zinc layer in the zinc-sprayed aluminum pipe.

[0070] Understandably, the immersion time depends on the zinc layer thickness; when the zinc layer thickness is less than 10μm, the immersion time is 1min~2min; when the zinc layer thickness is 10μm~20μm, the immersion time is 2min~4min; when the zinc layer thickness is 20μm~30μm, the immersion time is 3min~6min; when the zinc layer thickness is 30μm~40μm, the immersion time is 4min~8min; and so on.

[0071] In a specific embodiment, in step S3, a metallographic microscope with magnification of 50x to 100x is used to photograph different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe after corrosion treatment in step S2. The metallographic photographs of the different points are stitched together to form a complete metallographic image of the cross-section of the zinc-sprayed aluminum pipe. On the complete metallographic image, a radius is selected again according to the central angle interval of 7.2 degrees to 14.4 degrees, and the zinc layer depth on the radius is measured to obtain several zinc layer depth data. The average zinc penetration depth, maximum zinc penetration depth, and optimal zinc penetration depth ratio of the cross-section are calculated.

[0072] It should be noted that the complete metallographic image of the cross-section of the spliced ​​zinc-aluminum pipe presents as a regular circular image; sampling at equal central angles of 7.2 degrees to 14.4 degrees helps ensure the comprehensiveness and accuracy of the samples. By statistically analyzing the zinc layer depth of multiple samples, the average zinc penetration depth and the maximum zinc penetration depth can be calculated; by counting the number of samples that achieve the optimal zinc penetration depth and dividing by the total number of samples, the percentage of samples with the optimal zinc penetration depth can be calculated.

[0073] In another specific embodiment, in step S3, a metallographic microscope with magnification of 50x to 100x is used to photograph different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe after corrosion treatment in step S2. The metallographic photographs of the different points are stitched together to form a complete metallographic image of the cross-section of the zinc-sprayed aluminum pipe. On the complete metallographic image, radii are reselected at intervals of 7.2 degrees to 14.4 degrees, and the boundary points of the zinc-free area on different radii are observed and measured to calculate the proportion of the zinc-free area of ​​the cross-section.

[0074] It should be noted that sampling with equal central angles of 7.2 degrees to 14.4 degrees helps ensure the comprehensiveness and accuracy of the samples. By statistically analyzing the zinc layer depth of multiple samples and presenting it in the form of a radar chart, the perimeter of the zinc-free area was measured and divided by the circumference of the entire cross-section to calculate the proportion of the zinc-free area.

[0075] The present invention will be further illustrated below through specific embodiments:

[0076] All raw materials used in the embodiments of this invention are commercially available, and this invention does not impose any restrictions on the source of raw materials.

[0077] Example 1

[0078] The zinc coating quality testing method for the zinc-sprayed aluminum pipe in Example 1 includes the following steps:

[0079] S1. In a cold-mounted mold, epoxy resin and curing agent are used. After curing, a 7mm outer diameter double-gun zinc-aluminum spraying tube is placed horizontally in the mold. Epoxy resin and curing agent are added until the sample is completely covered. After curing, the sample is removed from the mold. The cross-section of the sample is polished sequentially using 240#, 800#, 1200#, and 2000# metallographic sandpaper. When using the next grit sandpaper for mechanical polishing, the sample must be rotated 90 degrees to continuously reduce the polishing marks. Then, the cross-section is polished with a polishing agent of 0.5μm alumina powder and pure water at a material-to-liquid ratio of 1:4 until there are no obvious polishing marks on the cross-section.

[0080] S2. Prepare an etching solution by adding sodium hydroxide (5wt%~10wt%), sodium nitrate (10g / L~20g / L), sodium silicate (1g / L~3g / L), ferric chloride (0.5g / L~1.5g / L), and the remainder pure water. Heat the solution in a water bath to 60°C and keep it warm. Immerse the cross-section of the polished zinc-sprayed aluminum pipe in the etching solution for 6 minutes, then remove it, rinse it, and dry it.

[0081] S3. Under a metallographic microscope, photographs were taken at multiple points on the cross-section of the zinc-aluminum sprayed tube using a 50° field of view. The photographs were then stitched together to obtain a metallographic image of the entire cross-section, revealing the overall zinc layer distribution of the sample. Figure 1As shown. Sampling with equal central angles of 7.2° to 14.4° helps ensure the comprehensiveness and accuracy of the samples. By statistically analyzing the zinc layer depth of multiple samples, the average zinc penetration depth and the maximum zinc penetration depth can be calculated. By counting the number of samples that achieve the optimal zinc penetration depth and dividing it by the total number of samples, the percentage of the optimal zinc penetration depth can be calculated. Sampling with equal central angles of 7.2° to 14.4° helps ensure the comprehensiveness and accuracy of the samples. By statistically analyzing the zinc layer depth of multiple samples and presenting it in the form of a radar chart, and then measuring the perimeter of the zinc-free area and dividing it by the circumference of the entire cross-section, the percentage of the zinc-free area can be calculated.

[0082] Example 2

[0083] The zinc layer quality testing method for the zinc-sprayed aluminum pipe in Example 2 is the same as that in Example 1, except that the sample in Example 2 uses a three-gun zinc-sprayed aluminum pipe with an outer diameter of 7mm.

[0084] A schematic diagram of the zinc layer color development of the cross-section of the zinc-sprayed aluminum pipe in Example 2 is shown below. Figure 2 .

[0085] Comparative Example 1

[0086] The zinc coating quality testing method for the zinc-sprayed aluminum pipe in Comparative Example 1 includes the following steps:

[0087] S1. In a cold-mounted mold, epoxy resin and curing agent are used. After curing, a 7mm outer diameter double-gun zinc-aluminum spraying tube is placed horizontally in the mold. Epoxy resin and curing agent are added until the sample is completely covered. After curing, the sample is removed from the mold. The cross-section of the sample is polished sequentially using 240#, 800#, 1200#, and 2000# metallographic sandpaper. When using the next grit sandpaper for mechanical polishing, the sample must be rotated 90 degrees to continuously reduce the polishing marks. Then, the cross-section is polished with a polishing agent of 0.5μm alumina powder and pure water at a material-to-liquid ratio of 1:4 until there are no obvious polishing marks on the cross-section.

[0088] S2. The cross-section of the zinc-aluminum sprayed tube is treated with gold spraying. EPMA is used to perform line scanning at any location on the sample, obtaining a curve of zinc content energy versus scanning depth. The inflection point of the zinc content energy value is then analyzed. Figure 3 Point A is shown in the diagram. The scanning depth value corresponding to point A is the zinc penetration depth. The zinc layer depth is measured at intervals of 14.4 degrees from the central angle, and the measured data are used to create a radar chart as shown. Figure 4 As shown, the average zinc penetration depth and the maximum zinc penetration depth are obtained; the number of optimal zinc penetration depths is divided by the total number of zinc penetration depths tested to obtain the percentage of optimal zinc penetration depths.

[0089] The zinc penetration depths of the 25 samples measured in Example 1 and Comparative Example 1 are shown in Table 1 and... Figure 5 .

[0090] Table 1

[0091]

[0092] Through the Figure 1-5 Analysis of Table 1 shows that the zinc layer quality detection method for zinc-sprayed aluminum pipes in Example 1 deviates from the existing EPMA test method by only 4.07%. This indicates that the zinc layer quality detection method for zinc-sprayed aluminum pipes in this invention, even without using an EPMA line scan device, yields results that are extremely close to those obtained by the EPMA line scan device. This demonstrates that the detection method in this invention has high accuracy and lower cost, making it suitable for widespread use in industrial production.

[0093] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An etching liquid characterized by comprising: The corrosive solution comprises an alkali, an oxidant with a mass fraction of 1 wt% to 2 wt%, a corrosion inhibitor with a mass fraction of 0.1 wt% to 0.3 wt%, and a color developer with a mass fraction of 0.05 wt% to 0.15 wt%. The corrosion inhibitor includes water-soluble silicates; The colorimetric reagent is selected from either iron salts or copper salts; The oxidant is selected from at least one of nitrate, nitrite, chlorate, hypochlorite and hydrogen peroxide; The hydroxide concentration in the corrosive solution is equal to the hydroxide concentration corresponding to a mass fraction of 1wt% to 10wt% of sodium hydroxide or potassium hydroxide.

2. The etching liquid according to claim 1, wherein In the corrosion inhibitor, the water-soluble silicate includes at least one of sodium silicate and potassium silicate; And / or, the colorimetric agent includes at least one of ferric chloride and copper chloride.

3. A method of etching treatment characterized by, The corrosion treatment method uses the corrosion solution described in any one of claims 1 to 2.

4. The etching treatment method according to claim 3, wherein The corrosion treatment method includes the following steps: The cross-section of the metal substrate is ground and polished, and then immersed in the heated etching solution to complete the etching process.

5. The etching treatment method according to claim 4, wherein During the immersion process, the temperature of the corrosive solution is 50℃~70℃.

6. A method for detecting the quality of a zinc layer of a zinc-aluminum coated pipe, characterized by, The zinc layer quality testing method for the zinc-sprayed aluminum pipe uses the corrosion solution according to any one of claims 1 to 2; or, the zinc layer quality testing method for the zinc-sprayed aluminum pipe uses the corrosion treatment method according to any one of claims 3 to 5.

7. The method of claim 6, wherein the zinc layer quality of the zinc-aluminum coated tube is detected by measuring the thickness of the zinc layer. The method for detecting the zinc coating quality of the zinc-sprayed aluminum pipe includes the following steps: S1. Fix the zinc-sprayed aluminum pipe in the mold, and then grind and polish the cross-section of the zinc-sprayed aluminum pipe in sequence. S2. Prepare the etching solution, and then immerse the cross-section of the zinc-sprayed aluminum pipe after the polishing treatment into the heated etching solution for soaking, thereby completing the etching treatment of the zinc-sprayed aluminum pipe. S3. Using a microscope, photographs are taken at different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe, and the images are stitched together to obtain the overall zinc layer distribution of the zinc-sprayed aluminum pipe, and the quality technical indicators of the zinc layer are measured.

8. The method of claim 7, wherein the zinc layer quality of the zinc-aluminum coated tube is detected by measuring the thickness of the zinc layer. In step S1, during the polishing process, the cross-section of the zinc-coated aluminum tube is polished at least four times using metallographic sandpaper with grits decreasing from large to small; and when polishing with the next grit sandpaper, the cross-section of the zinc-coated aluminum tube is rotated by 90°.

9. The method of claim 7, wherein the zinc layer quality of the zinc-aluminum coated tube is detected by measuring the thickness of the zinc layer. In step S1, during the polishing process, the particle size of the abrasive is 0.5μm-1μm, and the material-to-liquid ratio is 1:3~6.

10. The method of claim 7, wherein the zinc layer of the zinc-aluminum clad tube is sprayed by using a zinc-aluminum alloy wire having a diameter of 0.8 mm to 1.2 mm. During the immersion process in step S2, the temperature of the corrosive solution is 50℃~70℃; And / or, during the immersion process in step S2, the immersion time is increased by 1 min to 2 min for every 10 μm increase in the thickness of the zinc layer in the zinc-sprayed aluminum tube.

11. The method for detecting the zinc layer quality of a zinc-sprayed aluminum pipe as described in claim 7, characterized in that, In step S3, a metallographic microscope with magnification of 50x to 100x is used to take pictures of different points on the circumference of the cross-section of the zinc-sprayed aluminum pipe after corrosion treatment in step S2, and the metallographic pictures of the different points are stitched together to form a complete metallographic image of the cross-section of the zinc-sprayed aluminum pipe. On the complete metallographic image, a radius is reselected at intervals of 7.2 degrees to 14.4 degrees, and the zinc layer depth on this radius is measured to obtain several zinc layer depth data. The average zinc penetration depth, maximum zinc penetration depth, and optimal zinc penetration depth ratio of the cross section are calculated. And / or, on the complete metallographic image, a radius is reselected at intervals of 7.2 degrees to 14.4 degrees, and the boundary points of the zinc-free area on different radii are observed and measured to calculate the zinc-free area ratio of the cross section.

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