Method for recovering size of rod type aluminum alloy workpiece through micro-arc oxidation technology

Abstract

The invention discloses a method for recovering the size of a rod type aluminum alloy workpiece through a micro-arc oxidation technology, and belongs to the technical field of aluminum alloy friction piece surface pairs. The method comprises the following steps that (1) surface cleaning is conducted, specifically, a common anodic oxidation film on the surface of the rod type aluminum alloy friction piece is cleaned, and the treated rod type aluminum alloy friction piece is obtained; (2) preparing a working solution: preparing the working solution from at least one of potassium hydroxide, sodium hydroxide, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate and glycerol; and (3) micro-arc oxidation treatment is conducted, specifically, the working solution is placed in an electrolytic bath, the treated rod type aluminum alloy friction piece serves as an anode to be immersed in the working solution, a stainless steel plate serves as a cathode counter electrode, then a bipolar pulse power source is applied to the two sides of the cathode and the anode, and a micro-arc oxidation ceramic film layer can be obtained on the surface of the rod type aluminum alloy friction piece. According to the method, the removal of the base material is avoided, the loss of the base material is avoided, and the process steps can be simplified.

Description

Technical Field

[0001] The invention relates to the technical field of surface auxiliary technology of aluminum alloy friction parts, and more particularly to a method for restoring the dimensions of a rod-type aluminum alloy workpiece by utilizing a micro-arc oxidation technology. Background Art

[0002] The primary purpose of hard anodizing on the surfaces of aluminum alloy rod-type friction parts is to improve their wear resistance. During hard anodizing, the high current and resulting heat are significant. This can easily lead to current concentration at sharp edges, creating a tip effect and resulting in a defective film. Furthermore, the oxide film itself is brittle, so when it encounters other objects or rubs against each other, it can easily break off.

[0003] Friction pairs are generally divided into parts that are susceptible to wear and parts that are difficult to wear. Hard anodized parts are often used as wear-resistant parts. However, friction between hard and soft parts will cause wear, but the hard part will wear less, while the soft part will wear more. Low surface roughness can reduce wear on the workpiece. The outer layer of the hard anodized film has a loose structure and a relatively rough surface. Scratching and friction will cause hard particles to fall off, causing wear and failure of the part.

[0004] Hard anodizing is a thick-film anodizing method that can produce an oxide film of approximately 25-150μm on aluminum alloy surfaces. Most hard anodized films are 50-80μm thick. Hard anodized films with a thickness of less than 25μm are used for components in applications such as shaft-hole friction pairs, gear keys, and screw threads. Hard anodized films for wear resistance are approximately 50μm thick. Under certain special process conditions, hard anodized films with a thickness of 125μm or greater are required. However, it must be noted that the thicker the anodized film, the lower the microhardness of the outer layer and the increased surface roughness. The surface microhardness is generally 350-550HV, and can withstand salt spray tests for more than 150 hours.

[0005] The micro-arc oxidation film growth process is a sequential process of electrochemical discharge and plasma discharge. The former is the foundation of the latter, and the latter is organically integrated with the former through microporous gas breakdown discharge, ultimately completing the micro-arc oxidation process. Under the action of an applied electric field, the interelectrode voltage increases from 0, first satisfying the electrochemical passivation reaction conditions, forming a thin barrier layer and tiny bubbles on the anode surface. The barrier layer and bubbles increase the interelectrode resistance, hindering the increase in current, thereby continuously increasing the interelectrode voltage. Gradually, the electrochemical anodic oxidation conditions are met, and the anodic oxidation reaction rapidly thickens the barrier layer, forming micropores within the barrier layer. The substrate and working fluid maintain contact at the bottom of the micropores, allowing the anodic oxidation to continue. Simultaneously, a large number of bubbles are generated and escaped, forming gas capacitance, causing the interelectrode voltage to rise rapidly, reaching over 400V in a very short time. After breaking through the Faraday discharge region, a plasma reaction occurs on the anode surface, generating discharge sparks. At the moment of plasma discharge, the temperature is extremely high, and heat is locally concentrated within the micropores, prolonging the transformation time from the less hard γ-Al2O3 phase to the harder α-Al2O3 phase. Externally, the working fluid's rapid cooling effect causes the molten oxide to form a loose layer structure dominated by γ-Al2O3, while internally, a dense layer structure dominated by α-Al2O3 forms. At the boundary between the micromolten pool and the substrate, the high-temperature active particles chemically react with the substrate, forming a thin barrier layer that separates the substrate from the micromolten pool. This completes the micro-arc oxidation discharge and film formation process. When the electric field is re-established, the micro-arc oxidation process repeats. Micro-arc oxidation films can reach thicknesses of 30-80μm, surface microhardnesses of 1300-1600Hv, and salt spray test durations of 240-300h.

[0006] For occasions with more severe friction, although the film thickness of parts after hard anodizing can reach more than 50μm, the hardness of the inner layer of the film is greater than that of the outer layer due to the tip effect. The outer layer is a loose layer with micropores. The hard particles that fall off after mutual friction will cause great wear on the friction pair, thereby causing the parts to fail. The micro-arc oxidation film is dense and uniform, and its hardness, wear resistance, corrosion resistance and other properties are all higher than those of the hard anodizing film. In addition, the surface of the micro-arc oxidation film is smooth and the surface roughness is low. Micro-arc oxidation treatment of aluminum alloy parts can significantly improve the service life of rod-type aluminum alloy parts and friction parts. However, the traditional treatment of hard anodized parts requires that the hard anodized film layer on the surface of the friction parts of rod-type aluminum alloy parts be completely removed by mechanical means (including turning, milling, planing, grinding, etc.). This will not only reduce the size of the aluminum alloy substrate, but also make the process cumbersome and increase the cost.

[0007] Therefore, how to develop a method for restoring the size of rod-type aluminum alloy workpieces using micro-arc oxidation technology is an urgent problem that technicians in this field need to solve. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology, so as to address the deficiencies in the prior art.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology specifically comprises the following steps:

[0011] (1) Surface cleaning

[0012] Cleaning the common anodic oxide film on the surface of the rod-type aluminum alloy friction part to obtain a treated rod-type aluminum alloy friction part;

[0013] (2) Preparation of working fluid

[0014] A working fluid is prepared using at least one of potassium hydroxide, sodium hydroxide, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate and glycerol;

[0015] (3) Micro-arc oxidation treatment

[0016] The working fluid is placed in the electrolytic cell, the treated rod-type aluminum alloy friction parts are immersed in the working fluid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and anode. The bidirectional working mode is adopted, with a forward voltage of 350-600V, a reverse voltage of 80-120V, and a current density of 100-150A / dm 2 The positive and negative pulse frequency is 500-2500Hz, the duty cycle is 10%-40%, the working fluid temperature is 20-50℃, and the treatment time is 30-60min. Then, a micro-arc oxidation ceramic film layer can be obtained on the surface of the rod-type aluminum alloy friction parts.

[0017] Furthermore, in the above step (1), the common anodized film includes a sulfate film and an oxalate film, and the film thickness is 30-80 μm.

[0018] Furthermore, in the above step (1), the surface cleaning reagent is deionized water.

[0019] Furthermore, in the above step (2), the content of potassium hydroxide in the working solution is 1-10 g / L.

[0020] Furthermore, in the above step (2), the content of sodium hydroxide in the working solution is 1-20 g / L.

[0021] Furthermore, in the above step (2), the content of sodium silicate in the working solution is 5-30 g / L.

[0022] Furthermore, in the above step (2), the content of sodium tungstate in the working solution is 5-20 g / L.

[0023] Furthermore, in the above step (2), the content of sodium tetraborate in the working solution is 1-50 g / L.

[0024] Furthermore, in the above step (2), the content of sodium hexametaphosphate in the working solution is 15-100 g / L.

[0025] Furthermore, in the above step (2), the content of glycerol in the working solution is 15-25 mL / L.

[0026] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The film layer generated by hard anodizing is a porous film layer with a double-layer structure. The thin and dense barrier layer is close to the aluminum substrate, and the thick and loose porous layer is above the barrier layer. The micropores in the porous layer are nearly circular, closely arranged, and evenly distributed in almost the same size. The micropores have a surface that directly reaches the junction between the film layer and the aluminum alloy, which allows the working fluid to penetrate the micropores and reach the barrier layer directly. The micro-arc oxidation discharge process is a sequential process of electrochemical discharge and plasma discharge. The former is the basis of the latter. The latter and the former are organically combined through microporous gas breakdown discharge, ultimately completing the micro-arc oxidation process and generating a micro-arc oxidation ceramic film layer in situ. The prerequisite for micro-arc oxidation to discharge is the barrier layer produced in the anodizing stage, which happens to be present in hard anodized workpieces. Therefore, this favorable condition can be utilized. When the working fluid meets the discharge conditions, micro-arc oxidation discharge can continue to discharge using the barrier layer at the bottom of the anodized film layer, forming a new micro-arc oxidation film layer with better mechanical properties. This provides the possibility of leveraging strengths and overcoming weaknesses, and developing a method for restoring the size of rod-type aluminum alloy workpieces using micro-arc oxidation technology.

[0028] 2. Although the micro-arc oxidation ceramic film layer generated by the method of the present invention is directly generated by reaction on the anodized sample, the anodized sample substrate and the working fluid remain in contact at the bottom of the micropores. The conditions for the micro-arc oxidation discharge reaction are all met. The discharge breaks through the anodized film layer, and the film layer grows directly on the surface of the aluminum alloy substrate. Compared with the original ordinary anodized film layer, it has better bonding strength with the substrate and has the advantages of high surface hardness, high wear resistance, low friction coefficient, and high corrosion resistance.

[0029] 3. The thickness of the micro-arc oxidation ceramic film layer generated by the method of the present invention is about 30-80 μm, and the surface quality is good, without ablation spots and powdery loose layers.

[0030] 4. The method of the present invention generates a micro-arc oxidation film layer on the surface of the rod-type aluminum alloy friction part in situ through direct micro-arc oxidation discharge without removing the original ordinary anodic oxidation film layer of the rod-type aluminum alloy friction part, thereby avoiding the removal of the substrate, without the loss of the substrate, and simplifying the process steps.

[0031] 5. The initial voltage applied to the treated rod-type aluminum alloy friction parts of the present invention is 350V. The time taken to increase from 0V to 350V is only 5-10s, and the total treatment time is 30-60min. There is no time for mechanically removing the anodized film layer. Compared with ordinary anodizing treatment, it can reduce processing time and save costs. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] Example 1

[0034] The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology specifically includes the following steps:

[0035] (1) Surface cleaning

[0036] Cleaning the common anodic oxide film on the surface of the rod-type aluminum alloy friction part with deionized water to obtain a treated rod-type aluminum alloy friction part;

[0037] Among them, the material of the rod-type aluminum alloy friction part is aluminum alloy 2024, and the sample size is a cylindrical inner wall with a bottom inner diameter of 45mm and a width of 4mm;

[0038] The common anodic oxide film is an oxalate film with a thickness of 50 μm.

[0039] (2) Preparation of working fluid

[0040] Prepare the working solution using 3 g / L potassium hydroxide, 5 g / L sodium tungstate, 1.5 g / L sodium tetraborate and 3 mL / L glycerol;

[0041] (3) Micro-arc oxidation treatment

[0042] The working fluid is placed in the electrolytic cell, the treated rod-type aluminum alloy friction parts are immersed in the working fluid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and anode. The bidirectional working mode is adopted, with a forward voltage of 550V, a reverse voltage of 110V, and a current density of 135A / dm 2The positive and negative pulse frequency is 1700 Hz, the duty cycle is 25%, the working fluid temperature is 40 ° C, and the treatment is 60 minutes to obtain a micro-arc oxidation ceramic film layer on the surface of the rod-type aluminum alloy friction parts.

[0043] Performance Testing

[0044] The micro-arc oxidation ceramic film layer produced by the method of Example 1 was taken, and its film thickness, surface microhardness HV, surface roughness Ra and friction coefficient were measured respectively, and a salt spray test was performed.

[0045] The film thickness is measured by using a high-precision eddy current thickness gauge to perform multi-point measurements. When measuring, avoid sharp edges, select a representative plane position, and perform repeated measurements.

[0046] The method for determining the surface microhardness HV is: use a microhardness tester to measure, avoid the edge during measurement, and take repeated measurements on an area with uniform distribution of the film layer.

[0047] The surface roughness Ra is measured using a surface roughness meter (stylus Ra measuring instrument). Before measurement, ensure that the surface is clean and free of oil.

[0048] The friction coefficient is determined by using a friction coefficient tester (such as a reciprocating or rotary friction tester) under constant load (50 g, 100 g), speed and environmental conditions, recording the friction coefficient in the stable stage and taking the average value.

[0049] The salt spray test is carried out in accordance with the standard (such as ASTM B117 or GB / T 10125), and the sample is placed in the salt spray test chamber for a specified time, and the corrosion condition and film changes are observed and recorded.

[0050] The results are shown in Table 1.

[0051] Table 1 Performance test results of micro-arc oxidation ceramic film layer in Example 1

[0052]

[0053] It can be seen from Table 1 that the micro-arc oxidation ceramic film prepared in Example 1 performs well in various performance indicators. The film thickness is uniform, ranging from 58-70μm, indicating that the process is stable and good. The surface microhardness reaches 1568HV (100g), showing a high hardness, which helps to improve wear resistance. The surface roughness Ra is 0.099, indicating that the surface of the film is relatively smooth after polishing, which is beneficial to reducing friction resistance. The friction coefficient is 0.3, which is at a relatively low level, further verifying its good wear resistance. The salt spray test time exceeds 270h, and no obvious signs of corrosion are seen, indicating that the film has good corrosion resistance. Based on the above results, the micro-arc oxidation ceramic film of Example 1 has good comprehensive performance.

[0054] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology, characterized in that: The specific steps include: (1) Surface cleaning Cleaning the common anodic oxide film on the surface of the rod-type aluminum alloy friction part to obtain a treated rod-type aluminum alloy friction part; (2) Preparation of working fluid A working fluid is prepared using at least one of potassium hydroxide, sodium hydroxide, sodium silicate, sodium tungstate, sodium tetraborate, sodium hexametaphosphate and glycerol; (3) Micro-arc oxidation treatment The working fluid is placed in the electrolytic cell, the treated rod-type aluminum alloy friction parts are immersed in the working fluid as the anode, and the stainless steel plate is used as the cathode counter electrode. Then, a bipolar pulse power supply is applied on both sides of the cathode and anode. The bidirectional working mode is adopted, with a forward voltage of 350-600V, a reverse voltage of 80-120V, and a current density of 100-150A / dm 2 The positive and negative pulse frequency is 500-2500Hz, the duty cycle is 10%-40%, the working fluid temperature is 20-50℃, and the treatment time is 30-60min. Then, a micro-arc oxidation ceramic film layer can be obtained on the surface of the rod-type aluminum alloy friction parts.

2. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (1), the common anodized film includes a sulfate film and an oxalate film, and the film thickness is 30-80 μm.

3. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (1), the surface cleaning reagent is deionized water.

4. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of potassium hydroxide in the working solution is 1-10 g / L.

5. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium hydroxide in the working solution is 1-20 g / L.

6. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium silicate in the working solution is 5-30 g / L.

7. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium tungstate in the working solution is 5-20 g / L.

8. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium tetraborate in the working solution is 1-50 g / L.

9. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of sodium hexametaphosphate in the working solution is 15-100 g / L.

10. The method for restoring the dimensions of a rod-type aluminum alloy workpiece using micro-arc oxidation technology according to claim 1, characterized in that: In step (2), the content of glycerol in the working solution is 15-25 mL / L.

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