A high pitting resistance aluminum alloy internal threaded pipe and surface treatment method thereof

Abstract

The present application provides a highly pitting-resistant aluminum alloy internally threaded pipe and a surface treatment method thereof, comprising the following steps: performing zinc spraying treatment on the surface of the aluminum alloy internally threaded pipe to form a zinc layer; heating the aluminum alloy internally threaded pipe with the zinc layer formed on the surface to a first temperature at a first rate for a first time, heating the aluminum alloy internally threaded pipe at a second rate for a second time to a second temperature, and heating the aluminum alloy internally threaded pipe at a third rate for a third time to a third temperature under the protection of an inert gas, and then performing a heat preservation treatment; the first rate is greater than the second rate, and the second rate is greater than the third rate. The present application first sprays zinc on the surface of the aluminum alloy internally threaded pipe, and then performs a zinc infiltration treatment on the aluminum alloy internally threaded pipe with the zinc layer formed on the surface by heating the pipe at a gradually decreasing three-stage heating rate, which can significantly increase the zinc infiltration depth and improve the corrosion resistance of the aluminum alloy internally threaded pipe.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy materials, and in particular to a high pitting corrosion resistant aluminum alloy internally threaded pipe and a surface treatment method thereof. Background Art

[0002] Copper is widely used in key parts such as evaporators, condensers and indoor and outdoor unit connection pipes of heat exchangers in the air-conditioning industry due to its excellent electrical and thermal conductivity and long service life. With the scarcity of copper resources and the continuous rise in copper prices, the costs of air-conditioning companies have increased dramatically. In order to reduce the cost of air-conditioning and effectively utilize natural resources and break the dependence on copper resources, the home appliance air-conditioning industry has adopted aluminum tubes instead of copper tubes in heat exchangers, evaporators, radiators, etc.

[0003] Among the aluminum alloy series, 3 series aluminum alloys have good corrosion resistance, electrical and thermal conductivity, as well as weldability and machinability, and are favored by the air conditioning field. At present, 3003, 3103 and other 3 series aluminum alloy tubes widely used in air conditioning heat exchangers are easily corroded in harsh working environments. As the corrosion depth increases, aluminum tubes are prone to perforation corrosion, that is, corrosion that extends from the surface of the aluminum tube to the inside. This type of corrosion is called pitting corrosion, which will cause refrigerant leakage and heat exchanger scrapping. Therefore, improving the pitting corrosion resistance of aluminum alloys has become an inevitable requirement to increase the scope of use of aluminum alloys in the air conditioning field. Summary of the invention

[0004] In view of this, the present invention provides a highly pitting-resistant aluminum alloy internally threaded pipe and a surface treatment method thereof. The surface treatment method provided in the present application can increase the zinc infiltration depth of the surface of the aluminum alloy internally threaded pipe and improve its pitting resistance.

[0005] The present application provides a surface treatment method for a high pitting corrosion resistant aluminum alloy internally threaded pipe, comprising the following steps:

[0006] The surface of the aluminum alloy internally threaded pipe is subjected to zinc spraying treatment to form a zinc layer;

[0007] The aluminum alloy internally threaded pipe with a zinc layer formed on the surface is heated at a first rate for a first time to a first temperature, at a second rate for a second time to a second temperature, and at a third rate for a third time to a third temperature under the protection of an inert gas, and then subjected to a heat preservation treatment;

[0008] The first rate is greater than the second rate, and the second rate is greater than the third rate.

[0009] In some specific implementations, the first rate is 3°C / min to 8°C / min greater than the second rate, and the second rate is 3°C / min to 8°C / min greater than the third rate.

[0010] In some specific implementations, the second time is shorter than the first time.

[0011] In some specific implementations, the first rate is 15°C / min to 25°C / min, the second rate is 10°C / min to 20°C / min, and the third rate is 5°C / min to 15°C / min;

[0012] The third temperature is 450°C to 650°C;

[0013] The first time is 15 minutes to 25 minutes, and the second time is 5 minutes to 15 minutes.

[0014] In some specific implementations, the heat preservation treatment time is 3h to 9h.

[0015] In some specific implementations, the amount of zinc layer attached to the surface of the aluminum alloy internally threaded pipe is 1 g / m 2 ~5g / m 2 .

[0016] In some specific implementations, the zinc spraying treatment on the surface of the aluminum alloy internally threaded pipe specifically includes:

[0017] Arc zinc spraying is used, the diameter of the zinc material is 1mm~2mm, and the zinc content is 99.5%~99.7%; the vertical distance from the spray gun nozzle to the aluminum alloy internal threaded pipe is 100mm~120mm, and the angle between the center line of the nozzle and the vertical working surface is 70°~90°; the wire feeding speed is 120mm / s~150mm / s, and the spray gun moving speed is 0.3m / min~0.35m / min; the zinc spraying temperature is greater than 500℃.

[0018] In some specific implementations, the material of the aluminum alloy internally threaded tube includes:

[0019] 1.00 wt% to 1.20 wt% of Mn;

[0020] 0 to 0.10 wt% of Si (not equal to 0);

[0021] 0 to 0.20 wt% of Fe but not equal to 0;

[0022] 0 to 0.01 wt% Cu not equal to 0;

[0023] 0 to 0.01 wt% of Mg (not equal to 0);

[0024] 0 to 0.02 wt% of Ti (not equal to 0);

[0025] 0 to 0.01 wt% of Ni but not equal to 0;

[0026] The balance is Al.

[0027] The present application also provides an aluminum alloy internally threaded pipe, comprising an aluminum alloy body and a sherardizing layer formed on the surface of the aluminum alloy body, wherein the thickness of the sherardizing layer is greater than 300 μm.

[0028] In some specific implementations, the thickness of the zinc-diffusion layer is 320 μm to 400 μm.

[0029] The surface treatment method of the high pitting corrosion resistant aluminum alloy internal threaded pipe provided by the present application comprises the following steps: spraying zinc on the surface of the aluminum alloy internal threaded pipe to form a zinc layer; heating the aluminum alloy internal threaded pipe with the zinc layer formed on the surface to the first temperature at the first rate for the first time, heating the second temperature at the second rate for the second time, and heating the third temperature at the third rate for the third time under the protection of inert gas, and then performing heat preservation treatment; the first rate is greater than the second rate, and the second rate is greater than the third rate. The present application first sprays zinc on the surface of the aluminum alloy internal threaded pipe, and then heats the aluminum alloy internal threaded pipe with the zinc layer formed on the surface at a gradually decreasing three-stage heating rate to perform zinc infiltration treatment, which can significantly increase the zinc infiltration depth and improve the corrosion resistance of the aluminum alloy internal threaded pipe. Experimental results show that the surface treatment method provided by the present application can form a zinc infiltration layer with a thickness of more than 300μm, can increase the salt spray corrosion resistance time of the aluminum alloy internal threaded pipe to more than 4000h, and reduce the depth of the corrosion pit to less than 90μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram of the zinc penetration depth of the aluminum tube surface prepared in Example 1 of the present application;

[0031] Figure 2 This is a diagram of the zinc penetration depth of the aluminum tube surface prepared in Example 2 of the present application;

[0032] Figure 3 This is a diagram of the zinc penetration depth of the aluminum tube surface prepared in Example 3 of the present application;

[0033] Figure 4 The depth of zinc infiltration on the aluminum tube surface prepared in comparative example 1 of this application

[0034] Figure 5 This is a corrosion pit depth diagram of the aluminum alloy prepared in Example 1;

[0035] Figure 6 This is a corrosion pit depth diagram of the aluminum alloy prepared in Example 2;

[0036] Figure 7 This is a corrosion pit depth diagram of the aluminum alloy prepared in Example 3;

[0037] Figure 8 This is the corrosion pit depth diagram of the aluminum alloy prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] It should be understood that the expression "one or more of..." includes each of the items recited after the expression individually and in various different combinations of two or more of the recited items, unless otherwise understood from the context and usage. The expression "and / or" in combination with three or more recited items should be understood to have the same meaning, unless otherwise understood from the context.

[0039] The use of the terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, for example not excluding other unrecited elements or steps, unless otherwise specifically stated or otherwise understood from the context.

[0040] It should be understood that the order of steps or the order in which certain actions are performed is not important as long as the present invention remains operable. In addition, two or more steps or actions may be performed simultaneously.

[0041] The use of any and all examples or exemplary language, such as "for example" or "including", herein is intended only to better illustrate the invention and does not limit the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating that any non-claimed element is essential to the practice of the invention.

[0042] In addition, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise expressly stated, it should be understood that all ranges, quantities, values ​​and percentages used in this disclosure are modified by "about". Here, "about" generally means that the actual value is within plus or minus 10%, 5%, 1% or 0.5% of a specific value or range.

[0043] The present application provides a surface treatment method for a high pitting corrosion resistant aluminum alloy internally threaded pipe, comprising the following steps:

[0044] The surface of the aluminum alloy internally threaded pipe is subjected to zinc spraying treatment to form a zinc layer;

[0045] The aluminum alloy internally threaded pipe with a zinc layer formed on the surface is heated at a first rate for a first time to a first temperature, at a second rate for a second time to a second temperature, and at a third rate for a third time to a third temperature under the protection of an inert gas, and then subjected to a heat preservation treatment;

[0046] The first rate is greater than the second rate, and the second rate is greater than the third rate.

[0047] The present application first sprays zinc on the surface of the aluminum alloy internally threaded pipe, and then heats the aluminum alloy internally threaded pipe with a zinc layer formed on the surface at a gradually decreasing three-stage heating rate to perform a zinc infiltration treatment, which can significantly increase the zinc infiltration depth, and utilize the principle of thermal diffusion of metal atoms to dissolve Zn in the surface zinc infiltration layer area into the aluminum matrix, further increasing the electrode potential of the aluminum alloy matrix, so that the zinc infiltration layer acts as a sacrificial anode to preferentially and uniformly corrode, inhibiting the corrosion from developing into the interior of the metal, effectively alleviating the corrosion of the core layer matrix, and greatly improving the corrosion resistance of the aluminum alloy internally threaded pipe.

[0048] The present application uses an aluminum alloy internally threaded tube as a raw material and performs surface treatment on the tube. The present application has no special restrictions on the aluminum alloy internally threaded tube, and the tube can be prepared according to the following method:

[0049] The aluminum alloy rod is subjected to hot extrusion and thread forming to obtain an aluminum alloy internally threaded tube.

[0050] In some specific implementations, the material of the aluminum alloy internally threaded tube includes:

[0051] 1.00 wt% to 1.20 wt% of Mn;

[0052] 0 to 0.10 wt% of Si (not equal to 0);

[0053] 0 to 0.20 wt% of Fe but not equal to 0;

[0054] 0 to 0.01 wt% Cu not equal to 0;

[0055] 0 to 0.01 wt% of Mg (not equal to 0);

[0056] 0 to 0.02 wt% of Ti (not equal to 0);

[0057] 0 to 0.01 wt % (not equal to 0) of Ni; and the balance of Al.

[0058] The present application first performs zinc spraying treatment on the surface of the aluminum alloy internally threaded tube to form a zinc layer. Specifically, the present application first performs pretreatment on the aluminum alloy internally threaded tube, including but not limited to cleaning, degreasing, rust removal, etc., to facilitate uniform adhesion of the zinc layer. After pretreatment, the aluminum alloy internally threaded tube is sandblasted, and zinc spraying treatment is performed within 2 to 3 hours after the sandblasting treatment is completed. At this time, the activation degree of the substrate surface reaches the maximum, the electrode potential value is the lowest, and the coating bonding strength is the highest.

[0059] The present application has no special restrictions on the zinc spraying treatment, and preferably specifically includes:

[0060] Use arc zinc spraying, the diameter of the zinc material is 1mm~2mm, and the zinc content is 99.5%~99.7%; the vertical distance from the spray gun nozzle to the aluminum alloy internal threaded pipe is 100mm~120mm, and the angle between the center line of the nozzle and the vertical working surface is 70°~90°; the wire feeding speed is 120mm / s~150mm / s, the order weight of the zinc spraying is about 2kg / h~3kg / h, the spray gun moving speed is 0.3m / min~0.35m / min, and the spraying directions between the two layers should be perpendicular to each other; the zinc spraying temperature is greater than 500℃.

[0061] After the zinc spraying treatment, the adhesion amount of the formed zinc layer on the surface of the aluminum alloy internal threaded pipe is 1g / m 2 ~5g / m 2 , preferably 3g / m 2 After the zinc layer is formed, the core layer is sealed to enhance the protective performance of the coating. The present application has no special restrictions on the sealing method, and those skilled in the art can select it according to their needs.

[0062] After zinc spraying is completed, the coating surface is visually inspected for debris, bubbles, voids, uneven particles and cracks. If it meets the quality standards, it can be subjected to zinc infiltration treatment, that is, heat treatment at high temperature to diffuse zinc atoms into the aluminum matrix.

[0063] Specifically, the present application can perform a zincizing treatment on the aluminum alloy internally threaded pipe in an inert gas atmosphere in a tubular heating furnace. In some specific implementations, the inert gas atmosphere is preferably nitrogen. In some specific implementations, in order to promote the depth of zincizing, the present application performs a zincizing treatment on the aluminum alloy internally threaded pipe with a zinc layer formed on the surface by heating at a gradually decreasing three-stage heating rate, that is:

[0064] The temperature is increased at a first rate for a first time to a first temperature, increased at a second rate for a second time to a second temperature, and increased at a third rate for a third time to a third temperature, and then heat preservation treatment is performed, wherein the first rate is greater than the second rate, and the second rate is greater than the third rate.

[0065] It can be understood by those skilled in the art that, in the above heat treatment process, the first temperature and the second temperature are both intermediate temperatures, the third temperature is the final temperature, the third temperature is higher than the second temperature, and the second temperature is higher than the first temperature. In some specific implementations, the third temperature is 450°C to 650°C, preferably 500 to 600°C. This application has no special restrictions on the first temperature and the second temperature, which can be determined according to the first rate, the first time, the second rate and the second time.

[0066] In some specific implementations, the first rate is 3°C / min to 8°C / min greater than the second rate, preferably 5°C / min greater; the second rate is 3°C / min to 8°C / min greater than the third rate, preferably 5°C / min greater. In some specific implementations, the first rate is 15°C / min to 25°C / min, preferably 20°C / min; the second rate is 10°C / min to 20°C / min, preferably 15°C / min; the third rate is 5°C / min to 15°C / min, preferably 10°C / min.

[0067] In some specific implementations, the second time is shorter than the first time, and the third time is: t3 = [(T3-T0)-v1*t1-v2*t2] / v3. Wherein, t3 is the third time, t2 is the second time, t1 is the first time; T3 is the third temperature, T0 is the room temperature; v1 is the first rate, v2 is the second rate, and v3 is the third rate. In some specific implementations, the first time is 15min to 25min, preferably 20min, and the second time is 5min to 15min, preferably 10min.

[0068] After the temperature is raised, a heat preservation treatment is performed. In some specific implementations, the heat preservation treatment time is 3h to 9h, preferably 4h to 8h, and more preferably 6h. After the heat treatment is completed, the temperature is lowered to obtain an aluminum alloy internally threaded pipe with a zinc-diffused layer.

[0069] The present application also provides an aluminum alloy internally threaded pipe, comprising an aluminum alloy body and a sherardizing layer formed on the surface of the aluminum alloy body, wherein the thickness of the sherardizing layer is greater than 300 μm.

[0070] In some specific implementations, the thickness of the zinc-diffusion layer is 320 μm to 400 μm.

[0071] The aluminum alloy internally threaded pipe provided in the present application has excellent corrosion resistance, and its salt spray corrosion resistance can reach more than 4000h, and the depth of the corrosion pit is less than 90μm.

[0072] The surface treatment method of the high pitting corrosion resistant aluminum alloy internal threaded pipe provided by the present application comprises the following steps: spraying zinc on the surface of the aluminum alloy internal threaded pipe to form a zinc layer; heating the aluminum alloy internal threaded pipe with the zinc layer formed on the surface to the first temperature at the first rate for the first time, heating the second temperature at the second rate for the second time, and heating the third temperature at the third rate for the third time under the protection of inert gas, and then performing heat preservation treatment; the first rate is greater than the second rate, and the second rate is greater than the third rate. The present application first sprays zinc on the surface of the aluminum alloy internal threaded pipe, and then heats the aluminum alloy internal threaded pipe with the zinc layer formed on the surface at a gradually decreasing three-stage heating rate to perform zinc infiltration treatment, which can significantly increase the zinc infiltration depth and improve the corrosion resistance of the aluminum alloy internal threaded pipe. Experimental results show that the surface treatment method provided by the present application can form a zinc infiltration layer with a thickness of more than 300μm, can increase the salt spray corrosion resistance time of the aluminum alloy internal threaded pipe to more than 4000h, and reduce the depth of the corrosion pit to less than 90μm.

[0073] The following is a further description of a highly pitting-resistant aluminum alloy internally threaded pipe and a surface treatment method thereof provided by the present application in conjunction with embodiments.

[0074] Example 1

[0075] The aluminum rod obtained by molten casting is subjected to hot extrusion and thread forming to obtain an internally threaded aluminum tube, wherein the alloy composition comprises: 0.98wt% Si, 0.12wt% Fe, 0.011wt% Cu, 0.012wt% Mg, 0.016wt% Ti, 0.01wt% Ni; the rest is Al and unavoidable impurities;

[0076] The aluminum tube surface is cleaned, degreased, and rusted to ensure that the zinc coating can adhere evenly; then sandblasting is performed, and zinc spraying is performed within 2 to 3 hours after sandblasting is completed. The zinc spraying process parameters are: arc zinc spraying, zinc material diameter is 1.2mm, zinc content is 99.5%, and high-quality zinc wire without oil stains; the vertical distance from the spray gun nozzle to the structure is 110mm, and the angle between the nozzle center line and the vertical working surface is 80°; the wire feeding speed is controlled at 150mm / s, and the order weight of zinc spraying is about 2.65Kg / h; the movement speed of the spray gun is generally about 0.32m / minute, and the spraying directions between the two layers should be perpendicular to each other; when the zinc spraying temperature is greater than 500℃, the zinc layer is sprayed on the surface of the aluminum tube through the zinc spraying system, and the average zinc adhesion on the surface of the aluminum tube is controlled to be 3g / m 2 .

[0077] After zinc spraying is completed, sealing treatment is carried out to enhance the protective performance of the coating. After the appearance inspection of the coating surface for debris, bubbles, voids, uneven particles and cracks, zinc infiltration treatment is carried out. Specifically:

[0078] The aluminum tube treated with zinc spraying was placed in a tubular heating furnace. The zinc infiltration parameters were set as follows: room temperature was 20°C, the heating rate of the three-stage tubular heating furnace was set, and N 2 Atmosphere protection, set the heating temperature to 500℃, heat and keep warm for 15min at a heating rate of 20℃ / min in the first stage; heat and keep warm for 10min at a heating rate of 15℃ / min in the second stage; heat and keep warm for 3min at a heating rate of 10℃ / min in the third stage, and keep warm for 6 hours.

[0079] The depth of zinc penetration on the surface of the aluminum tube prepared in Example 1 was analyzed, and the results are shown in Figure 1 and Table 1, Figure 1 1 is a diagram of the zinc penetration depth on the surface of the aluminum tube prepared in Example 1 of the present application, and Table 1 is the statistical data of the zinc content on the surface of the aluminum tube prepared in Example 1 of the present application.

[0080] Table 1 Statistical data of zinc content on the surface of the aluminum tube prepared in Example 1 of the present application

[0081] area Depth(μm) Zn (wt%) 1 0～81.75 0.85 2 81.76～163.52 0.47 3 163.53～245.24 0.10 4 245.25～327 0.00

[0082] Depend on Figure 1 It can be seen that the method provided in Example 1 can achieve a sherardizing depth of 327 μm.

[0083] Example 2

[0084] The difference from Example 1 is that the sherardizing parameters are different. The sherardizing parameters are shown in Table 2, which shows the sherardizing parameters provided by the examples and comparative examples of the present application.

[0085] Table 2 Sherardizing parameters provided in the examples and comparative examples of the present application

[0086]

[0087] The depth of zinc penetration on the surface of the aluminum tube prepared in Example 2 was analyzed, and the results are shown in Figure 2 and Table 3, Figure 2 3 is a diagram of the zinc penetration depth on the surface of the aluminum tube prepared in Example 2 of the present application. Table 3 is the statistical data of the zinc content on the surface of the aluminum tube prepared in Example 2 of the present application.

[0088] Table 3 Statistical data of zinc content on the surface of aluminum tube prepared in Example 2 of the present application

[0089] area Depth(μm) Zn (wt%) 1 0～88.74 1.04 2 88.75～177.49 0.82 3 177.50～266.24 0.30 4 266.25～355.00 0.00

[0090] Depend on Figure 1 It can be seen that the method provided in Example 2 can achieve a sherardizing depth of 355 μm.

[0091] Example 3

[0092] The difference from Example 1 is that the sherardizing parameters are different. The sherardizing parameters are shown in Table 2, which shows the sherardizing parameters provided by the examples and comparative examples of the present application.

[0093] The surface sherardizing depth of the aluminum tube prepared in Example 3 was analyzed, and the results are shown in Figure 3 and Table 4, Figure 3 4 is a diagram of the zinc penetration depth on the surface of the aluminum tube prepared in Example 3 of the present application. Table 4 is the statistical data of the zinc content on the surface of the aluminum tube prepared in Example 3 of the present application.

[0094] Table 4 Statistical data of zinc content on the surface of aluminum tube prepared in Example 3 of the present application

[0095] area Depth(μm) Zn (wt%) 1 0～103.49 1.13 2 103.50～206.99 0.32 3 207.00～310.49 0.14 4 310.50～414.00 0.00

[0096] Depend on Figure 1 It can be seen that the method provided in Example 2 can achieve a sherardizing depth of 294 μm.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that the sherardizing parameters are different. The sherardizing parameters are shown in Table 2, which shows the sherardizing parameters provided by the examples and comparative examples of the present application.

[0099] The surface zinc penetration depth of the aluminum tube prepared in Comparative Example 1 was analyzed, and the results are shown in Figure 4 and Table 5, Figure 4 1 is a diagram of the zinc penetration depth on the surface of the aluminum tube prepared in comparative example 1 of the present application, and Table 5 is the statistical data of the zinc content on the surface of the aluminum tube prepared in comparative example 1 of the present application.

[0100] Table 5 Statistical data of zinc content on the surface of aluminum tube prepared in comparative example 1 of this application

[0101] area Depth(μm) Zn (wt%) 1 0.00～42.99 2.10 2 43.00～85.99 1.10 3 86.00～128.99 0.50 4 129.00～172.00 0.00

[0102] Depend on Figure 4 It can be seen that the zinc penetration depth of the method provided in Comparative Example 1 can reach 172 μm.

[0103] Depend on Figure 1 to Figure 4 It can be seen that the method provided in the present application significantly promotes the depth of sherardizing.

[0104] The aluminum alloys prepared in Examples 1 to 3 and Comparative Example 1 were subjected to a SWAAT test in accordance with ASTM G85 A3 to test the leakage time of the alloys. The results are shown in Table 6, which is a comparison of the corrosion resistance of the aluminum alloys prepared in the Examples and Comparative Examples of the present application.

[0105] The alloy after corrosion was analyzed and the results are shown in Figures 5 to 8 and Table 6, Figure 5 This is the corrosion pit depth diagram of the aluminum alloy prepared in Example 1. Figure 6This is the corrosion pit depth diagram of the aluminum alloy prepared in Example 2. Figure 7 This is the corrosion pit depth diagram of the aluminum alloy prepared in Example 3. Figure 8 This is the corrosion pit depth diagram of the aluminum alloy prepared in Comparative Example 1.

[0106] Table 6 Comparison of corrosion resistance of aluminum alloys prepared in the examples of the present application and the comparative examples

[0107] alloy Salt spray corrosion resistance / h Corrosion pit depth (μm) Example 1 4000 86.82 Example 2 4600 50.51 Example 3 5000 44.46 Comparative Example 1 3000 109.01

[0108] It can be seen from Table 6 that the aluminum alloy prepared by the method provided in this application has better corrosion resistance.

[0109] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A surface treatment method for a high pitting corrosion resistant aluminum alloy internally threaded pipe, characterized in that: The following steps are involved: The surface of the aluminum alloy internally threaded pipe is subjected to zinc spraying treatment to form a zinc layer; The aluminum alloy internally threaded pipe with a zinc layer formed on the surface is heated at a first rate for a first time to a first temperature, at a second rate for a second time to a second temperature, and at a third rate for a third time to a third temperature under the protection of an inert gas, and then subjected to a heat preservation treatment; The first rate is greater than the second rate, and the second rate is greater than the third rate.

2. The surface treatment method according to claim 1, characterized in that: The first rate is 3°C / min to 8°C / min greater than the second rate, and the second rate is 3°C / min to 8°C / min greater than the third rate.

3. The surface treatment method according to claim 3, characterized in that: The second time is shorter than the first time.

4. The surface treatment method according to any one of claims 1 to 3, characterized in that: The first rate is 15°C / min to 25°C / min, the second rate is 10°C / min to 20°C / min, and the third rate is 5°C / min to 15°C / min; The third temperature is 450°C to 650°C; The first time is 15 minutes to 25 minutes, and the second time is 5 minutes to 15 minutes.

5. The surface treatment method according to claim 4, characterized in that: The time of the heat preservation treatment is 3h to 9h.

6. The surface treatment method according to claim 5, characterized in that: The adhesion amount of the zinc layer on the surface of the aluminum alloy internal threaded pipe is 1g / m 2 ~5g / m 2 .

7. The surface treatment method according to claim 6, characterized in that: The zinc spraying treatment on the surface of aluminum alloy internal threaded pipe specifically includes: Arc zinc spraying is used, the diameter of the zinc material is 1mm~2mm, and the zinc content is 99.5%~99.7%; the vertical distance from the spray gun nozzle to the aluminum alloy internal threaded pipe is 100mm~120mm, and the angle between the center line of the nozzle and the vertical working surface is 70°~90°; the wire feeding speed is 120mm / s~150mm / s, and the spray gun moving speed is 0.3m / min~0.35m / min; the zinc spraying temperature is greater than 500℃.

8. The surface treatment method according to claim 7, characterized in that: The materials of the aluminum alloy internally threaded pipe include: 1.00 wt% to 1.20 wt% of Mn; 0 to 0.10 wt% of Si (not equal to 0); 0 to 0.20 wt% of Fe but not equal to 0; 0 to 0.01 wt% Cu not equal to 0; 0 to 0.01 wt% of Mg (not equal to 0); 0 to 0.02 wt% of Ti (not equal to 0); 0 to 0.01 wt% of Ni but not equal to 0; The balance is Al.

9. An aluminum alloy internally threaded pipe, comprising an aluminum alloy body and a sherardizing layer formed on the surface of the aluminum alloy body, wherein the thickness of the sherardizing layer is greater than 300 μm.

10. The aluminum alloy internally threaded pipe according to claim 9, characterized in that: The thickness of the zinc-diffusion layer is 320 μm to 400 μm.

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