CN115418523B - A kind of corrosion-resistant brass and preparation method thereof - Google Patents

Abstract

The invention discloses corrosion-resistant brass, which is characterized by comprising the following components in percentage by mass: 63-65 wt%, sn:0.05 to 0.2 percent of Al:0.01 to 0.05 percent, B: 0.002-0.006%, RE:0.015 to 0.04 weight percent, less than or equal to 0.01 weight percent of Fe, less than or equal to 0.01 weight percent of Pb and the balance of zinc. The brass does not contain arsenic elements polluting the environment and affecting the health of human bodies, the dezincification corrosion of the brass is inhibited by adding trace tin, aluminum, boron and rare earth, a single alpha-phase structure is obtained, the corrosion resistance of the low-copper and arsenic-free brass is improved from a microstructure, the maximum dezincification layer depth of the brass is less than 300 mu m, and the brass can pass the 8-hour neutral salt spray test.

Description

A kind of corrosion-resistant brass and preparation method thereof

Technical Field

The invention relates to the technical field of copper alloys, and in particular to corrosion-resistant brass and a preparation method thereof.

Background Art

Brass is a copper-zinc binary alloy with excellent comprehensive properties and is widely used. Corrosion resistance is one of the important performance properties of brass. There are two main forms of brass corrosion: dezincification corrosion and stress corrosion. The corrosion of brass in the present invention refers to dezincification corrosion. In the natural environment, the degree of dezincification corrosion of brass is slow. In order to detect the dezincification corrosion resistance of brass, a salt spray test is usually carried out before the product leaves the factory. The salt spray test is an artificially created corrosive environment to accelerate the corrosion of brass to detect the corrosion resistance of brass.

At present, the corrosion resistance of brass is improved by adding 0.02-0.06% arsenic, because arsenic has a strong inhibitory effect on the dezincification process, making arsenic-containing brass have good corrosion resistance. Although brass will not be toxic when arsenic is added, arsenic oxide As ₂ O ₃ (commonly known as arsenic) is toxic. Arsenic-containing brass pollutes the environment during smelting and is harmful to the human body. People are afraid of arsenic, so under the psychological suggestion, arsenic-containing brass products are rejected in the market, so it is necessary to develop arsenic-free and corrosion-resistant brass.

When brass is exposed to corrosive media, since Zn is more active than Cu, the Zn on the alloy surface preferentially dissolves from the brass to produce vacancies, and then the Zn inside the alloy continues to dissolve through vacancy diffusion, and the copper with a more positive potential is left behind to form a loose copper layer. Therefore, improving the corrosion resistance of brass is mainly achieved by inhibiting the dezincification corrosion of zinc.

The method of preventing brass dezincification corrosion can be started from the metallurgical aspect or from the environmental improvement aspect. To improve the corrosion environment, cathodic protection, adding corrosion inhibitors, reducing the corrosiveness of the medium, etc. can be used. Due to the limitations of working conditions, these external measures cannot completely inhibit the dezincification of brass. The best way to prevent brass dezincification corrosion is to improve the brass' own anti-dezincification ability through metallurgical methods.

The dezincification corrosion of brass is mainly related to the copper content, and secondly to the phase structure, grain size, surface treatment, etc. of brass. In addition, adding some special trace elements during alloy smelting can also improve the corrosion resistance of brass. However, increasing the copper content will increase the cost of raw materials, and the market is not very receptive to brass with high copper content, which limits its application.

Therefore, in order to solve the above problems, it is necessary to improve the existing arsenic-containing corrosion-resistant brass and enhance the corrosion resistance of brass with lower copper content.

Summary of the invention

The first technical problem to be solved by the present invention is to provide a low-copper, arsenic-free, corrosion-resistant brass.

The second technical problem to be solved by the present invention is to provide a method for preparing corrosion-resistant brass.

The technical solution adopted by the present invention to solve the first technical problem is: a corrosion-resistant brass, characterized in that the mass percentage composition of the brass is Cu: 63-65wt%, Sn: 0.05-0.2%, Al: 0.01-0.05%, B: 0.002-0.006%, RE: 0.015-0.04wt%, Fe≤0.01wt%, Pb≤0.01wt%, and the balance is zinc.

Copper: As is known to all, the corrosion resistance of brass increases with the increase of copper content. This is because zinc is more active than copper and is corroded first. Therefore, the higher the copper content, the better the corrosion resistance of brass. However, increasing the copper content will increase the cost of raw materials. Brass with low copper content and corrosion resistance is more easily accepted by the market. On the contrary, when the copper content is further reduced to below 65%, β phase will appear in the normal temperature organization. As the copper content gradually decreases, the β phase gradually increases. The zinc content of the β phase is about 8% higher than that of the α phase. The β phase is less corrosion-resistant than the α phase. Therefore, the corrosion resistance of brass decreases with the increase of the β phase. To improve the corrosion resistance of brass with a copper content below 65%, it is necessary to control the appearance of the β phase in the organization. When the copper content is lower than 63%, the increased β phase in the organization is difficult to eliminate through a process method. Therefore, the copper content of the corrosion-resistant brass of the present invention is controlled in the range of 63-65wt%.

Tin: Adding a small amount of tin to brass can prevent dezincification and improve the corrosion resistance of brass. Since the zinc equivalent coefficient of tin is +4, when the tin content exceeds 0.2%, the β phase in the structure will increase, which will reduce the dezincification corrosion resistance of brass. Therefore, the addition amount of tin in the brass of the present invention is controlled at 0.05-0.2%.

Aluminum: After aluminum is dissolved in copper, _{an Al2O3} protective film is formed on the surface of copper to prevent the diffusion and loss of zinc and improve the oxidation resistance of copper. A trace amount of aluminum has no obvious effect on the mechanical properties and process properties of copper. Since the zinc equivalent coefficient of aluminum is +6, when the aluminum content exceeds 0.05%, more β appears in the structure, which reduces the dezincification corrosion resistance of brass. Therefore, the addition amount of aluminum in the brass of the present invention is controlled at 0.01-0.05%.

Boron: Boron atoms can fill in the grain boundaries and divacancy, strengthen the bonding force in these places, and hinder the migration of zinc atoms through divacancy and grain boundaries. In addition, the addition of boron changes the defect structure of the surface cuprous oxide, making the cuprous oxide film more uniform and dense, and less susceptible to corrosion. The optimal content range of boron is 0.002-0.006%. Below the lower limit, the effect is weak. Since boron atoms gather at the grain boundaries, the grain boundary strength decreases with the increase of boron content. Therefore, the upper limit of boron content should not exceed 0.006%.

Iron: At 1050°C, the solubility of iron in copper is 3.5%, which drops to 0.015% at 635°C. The solubility of iron in copper is extremely low at room temperature, so a trace amount of iron exists in the form of particles in the tin-phosphor bronze, which plays a role in refining the grains. However, since the corrosion resistance of iron particles is very poor, they are prone to rust first. Therefore, the iron content of the corrosion-resistant brass of the present invention must be strictly controlled below 0.01%.

Lead: The brass alloy of the present invention has a Pb content of ≤0.01wt%, which is lead-free brass.

RE: Rare earth forms a protective film on the interface of the base metal, preventing the diffusion of zinc atoms and inhibiting the dissolution of copper and zinc, making the alloy structure more compact, hindering the precipitation of zinc atoms in the lattice, and improving the dezincification corrosion resistance of brass. However, if excessive rare earth is added, a large amount of rare earth compounds will be formed, and the alloy structure will deteriorate.

Preferably, the added amounts of Sn and Al satisfy: 350≤W _Cu /W _(Sn+Al) ≤1100, wherein W _Cu is the mass percentage composition of Cu, and W _(Sn+Al) is the sum of the mass percentage compositions of Sn and Al.

Although both Sn and Al elements can inhibit the dezincification of brass, the zinc equivalent coefficients of Sn and Al are +4 and +6 respectively. Sn and Al will increase the amount of β phase in the brass structure. The increase of β phase will reduce the dezincification corrosion resistance of brass. To increase the content of Sn and Al elements, it is necessary to increase the Cu content accordingly. To reduce the content of Sn and Al elements, the Cu content can be reduced accordingly. In this way, the side effects of adding Sn and Al elements can be avoided. Therefore, the addition amount of Sn and Al satisfies: 350≤W _Cu /W _(Sn+Al) ≤1100.

Preferably, the phase structure of the brass is a single-phase α phase, wherein the average grain size of the α phase is 10 to 20 μm. The single α phase structure improves the corrosion resistance of low-copper and arsenic-free brass. The corrosion resistance of brass is related to the surface finish, and the finish is related to the grain size of the brass in addition to the mold. The smaller the grain size, the smoother the surface of the brass after cold working. However, if the grain size is too small, it is easy for customers to crack when the degree of cold deformation is large when processing products. Therefore, the average grain size of the finished brass product of the present invention (i.e., the average grain size of the α phase) is controlled at 10 to 20 μm.

The technical solution adopted by the present invention to solve the second technical problem is: a method for preparing corrosion-resistant brass, characterized in that it includes the following preparation steps:

1) Melting: Prepare the required raw materials and melt them in a melting furnace at a temperature of 980-1030°C. Adjust the alloy composition after melting. When the composition meets the requirements, transfer the molten copper from the melting furnace to a holding furnace at a temperature of 1020-1050°C.

2) Horizontal continuous casting: casting temperature: 1020-1050°C, casting speed 5-30 mm/s;

3) Extrusion: Ingot heating temperature is 670-760°C, extrusion force is 7-28MN;

4) Intermediate stretching and intermediate annealing: The extruded billet is stretched to a certain specification through multiple passes, and intermediate annealing is set between passes. The processing rate between adjacent intermediate annealing is controlled at 20-50%, and the processing rate of the last stretching is not less than 40%; annealing temperature: 450-580℃, heating time: 30-60min, starting temperature is room temperature, holding time: 90-240min, and naturally cool after leaving the furnace;

5) Bottom annealing: annealing temperature 480-510℃, heating time: 30-60min, starting temperature is room temperature, holding time: 120-240min, water quenching after the billet is taken out of the furnace, the time interval from the billet being taken out of the furnace to entering the water must be controlled within 50s, and the water temperature shall not exceed 50℃;

7) Finished product drawing: obtain rods and wires.

The processing rate between adjacent intermediate annealing should be controlled at 20-50%. When the processing rate is lower than 20%, the difference in work hardening between the outer and inner layers of the billet is large, and the recrystallization structure of the inner and outer layers after annealing is uneven. If the processing rate is too high, the wire is easily broken during stretching, and the production is unstable. Considering that the processing rate of the last stretching determines the uniformity of the recrystallization structure of the bottom annealing, the larger the processing rate, the more uniform the recrystallized grain size. Therefore, the processing rate of the last stretching in this process shall not be lower than 40%.

The annealing temperature is 480-510℃. Bottom specification annealing is carried out in this temperature range to avoid the transformation of β phase into α phase. The time interval from the billet being taken out of the furnace to the billet being put into the water must be controlled within 50s, and the water temperature must not exceed 50℃ to ensure that no β phase appears in the internal structure of the billet after bottom annealing.

In order to resist air and water erosion and further improve corrosion resistance, preferably, in step 6), lubricating oil is used during the stretching process, and the mass percentage composition of the lubricating oil is dimethyl silicone oil: 20-40wt%, sodium petroleum sulfonate: 4-7wt%, ethanolamine: 3-5wt%, fatty acid soap: 2-5wt%, benzotriazole: 0.1-0.2wt%, and the remainder is cycloalkane oil.

Dimethyl silicone oil: As one of the main components of lubricating oil, it can be completely mixed with cycloalkyl oil to further improve lubricity. It can also form a waterproof and mildew-proof film on the surface of copper wire to prevent the product from absorbing moisture and changing color in humid air. If the content of dimethyl silicone oil is low, the film formed will be thinner. If the content is high, the viscosity of the oil will be increased, and the copper powder that falls off during the wire billet stretching process is not easy to separate from the oil. In the present invention, the appropriate content range is: 20-40wt%.

Sodium petroleum sulfonate: As a supplement to dimethyl silicone oil, it is a surfactant that can be adsorbed on the metal surface to form a protective film, which has moisture resistance and salt spray corrosion resistance and can prevent metal corrosion. If its content is low, the effect is poor. If the content exceeds 7%, more foam will be formed, which will affect heat dissipation and accelerate the oxidation and deterioration of lubricating oil.

Ethanolamine: It is a metal corrosion inhibitor that can absorb acidic gases. If the content is low, the effect is poor. Ethanolamine has an ammonia smell. If the content is high, the lubricating oil will have an unpleasant smell. The appropriate addition amount is 3-5wt%.

Fatty acid soap: It is an anionic surfactant that can remove black spots on the surface of the wire. If the content is low, the effect is poor. If the content is high, the viscosity of the lubricating oil will increase, which will affect the heat dissipation and the surface of the wire will be prone to silk flow after stretching.

Benzotriazole: It is a copper alloy corrosion inhibitor that can prevent wire from oxidative discoloration. The added amount is 0.1-0.2wt%. If the content is too low, the effect is poor. If the content exceeds 0.2%, the slow-release effect cannot be improved.

Cycloalkane oil: It has a natural saturated ring-shaped stable structure. As one of the main components of lubricating oil, it has good chemical stability, stable lubrication performance, and the surface of the wire is smooth after stretching.

Preferably, an oil film with a thickness of 2 to 5 μm is attached to the surface of the rod or wire.

Compared with the prior art, the advantages of the present invention are: the brass of the present invention does not contain arsenic elements that pollute the environment and affect human health, and the dezincification corrosion of the brass is inhibited by adding trace amounts of tin, aluminum, boron and rare earth, thereby obtaining a single α-phase structure, thereby improving the corrosion resistance of low-copper, arsenic-free brass from the microscopic structure, the maximum dezincification layer depth of the brass is less than 300 μm, and the brass can pass an 8-hour neutral salt spray test.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a metallographic structure photograph of Example 1 of the present invention (magnified 100 times).

FIG. 2 is a metallographic structure photograph of a comparative example of the present invention (magnified 100 times).

FIG3 is a photograph of Example 1 of the present invention after salt spraying.

FIG. 4 is a photograph of a comparative example of the present invention after salt spraying.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to the accompanying drawings.

The present invention provides 3 embodiments and 2 comparative examples, and the specific components are shown in Table 1.

Embodiment 1:

Corrosion-resistant brass rods, 6.6 mm in diameter, are prepared as follows:

1) Melting: Prepare the required raw materials and melt them in a melting furnace at a temperature of 1000-1030°C. Adjust the alloy composition after melting. When the composition meets the requirements, transfer the molten copper from the melting furnace to a holding furnace at a temperature of 1020-1050°C.

2) Horizontal continuous casting: casting temperature: 1030-1050°C, casting speed 14 mm/s, ingot diameter 245 mm, sawing length 600 mm.

3) Extrusion: The heating temperature of the ingot is 730°C, and the heated ingot is subjected to double-hole extrusion on a 3150T extruder. The specification of the extruded blank is φ13mm and the extrusion force is 21MN.

4) Intermediate stretching and intermediate annealing: the extruded billet is stretched and peeled to φ11.2mm, and then stretched and peeled to φ9.6mm after intermediate annealing and pickling, and then stretched to φ7.3mm. Intermediate annealing temperature: 540℃, heating time: 40min, starting temperature is room temperature, holding time: 150min, and after the time is up, it is taken out of the furnace and cooled naturally.

5) Bottom annealing: annealing in a pit furnace, annealing temperature 500℃, heating time: 40min, starting temperature is room temperature, holding time: 180min, water quenching after the wire billet is taken out of the furnace, the time interval from the wire billet being taken out of the furnace to entering the water must be controlled within 40s, and the water temperature shall not exceed 50℃;

7) Finished product stretching: Before the finished product is stretched, it is necessary to peel the skin, the peeling amount is 0.018mm, and the blank after peeling is stretched to a φ6.6mm rod. The stretching die is a polycrystalline die, and lubricating oil is used during the stretching process.

8) Inspection and packaging: Finished products will be packaged after passing the inspection.

Embodiment 2:

Corrosion-resistant brass rods with a diameter of 5.8 mm are prepared as follows:

1) Melting: Prepare the required raw materials and melt them in a melting furnace at a temperature of 990-1020°C. Adjust the alloy composition after melting. When the composition meets the requirements, transfer the molten copper from the melting furnace to a holding furnace at a temperature of 1020-1050°C.

2) Horizontal continuous casting: casting temperature: 1030-1050°C, casting speed 18 mm/s, ingot diameter 195 mm, sawing length 650 mm.

3) Extrusion: The heating temperature of the ingot is 720°C, and the heated ingot is subjected to double-hole extrusion on a 2200T extruder. The specification of the extruded blank is φ12.5mm, and the extrusion force is 16MN.

4) Intermediate stretching and intermediate annealing: the extruded billet is stretched and peeled to φ10.4mm, and then stretched and peeled to φ8.5mm after intermediate annealing and pickling, and then stretched to φ6.5mm. Intermediate annealing temperature: 520℃, heating time: 40min, starting temperature is room temperature, holding time: 180min, and after the time is up, it is taken out of the furnace and cooled naturally.

5) Bottom annealing: annealing in a pit furnace, annealing temperature 490 ° C, heating time: 40 minutes, starting temperature is room temperature, holding time: 180 minutes, water quenching after the wire billet is taken out of the furnace, the time interval from the wire billet being taken out of the furnace to entering the water must be controlled within 45 seconds, and the water temperature shall not exceed 50 ° C;

7) Finished product stretching: Before the finished product is stretched, it is necessary to peel the skin, the peeling amount is 0.016mm, and the blank after peeling is stretched to a φ5.8mm rod. The stretching die is a polycrystalline die, and lubricating oil is used during the stretching process.

8) Inspection and packaging: Finished products will be packaged after passing the inspection.

Embodiment 3:

Corrosion-resistant brass rods, 4 mm in diameter, are prepared as follows:

1) Melting: Prepare the required raw materials and melt them in a melting furnace at a melting temperature of 1010-1040°C. Adjust the alloy composition after melting. When the composition meets the requirements, transfer the molten copper from the melting furnace to a holding furnace at a temperature of 1020-1050°C.

2) Horizontal continuous casting: casting temperature: 1030-1050°C, casting speed 22 mm/s, ingot diameter 145 mm, sawing length 500 mm.

3) Extrusion: The heating temperature of the ingot is 710°C, and the heated ingot is subjected to double-hole extrusion on a 1250T extruder. The specification of the extruded blank is φ8.5mm and the extrusion force is 9MN.

4) Intermediate stretching and intermediate annealing: the extruded billet is stretched and peeled to φ7mm, and then stretched and peeled to φ6mm after intermediate annealing and pickling, and then stretched to φ4.5mm. Intermediate annealing temperature: 540℃, heating time: 40min, starting temperature is room temperature, holding time: 150min, and after the time is up, it is taken out of the furnace and cooled naturally.

5) Bottom annealing: annealing in a pit furnace, annealing temperature 480℃, heating time: 40min, starting temperature is room temperature, holding time: 180min, water quenching after the wire billet is taken out of the furnace, the time interval from the wire billet being taken out of the furnace to entering the water must be controlled within 40s, and the water temperature shall not exceed 50℃;

7) Finished product stretching: Before the finished product is stretched, it is necessary to peel the skin, the peeling amount is 0.016mm, and the blank after peeling is stretched to a φ5.8mm rod. The stretching die is a polycrystalline die, and lubricating oil is used during the stretching process.

8) Inspection and packaging: Finished products will be packaged after passing the inspection.

Comparative Example 1: Commercially available H65 brass rod, with a diameter of 6.6 mm.

Comparative Example 2: Commercially available arsenic-containing C46500 brass rod with a diameter of 6.6 mm.

The following microstructure and corrosion resistance tests were performed on the obtained embodiments and comparative examples. Specific data are shown in Tables 3 and 4.

Grain size measurement: Three examples and two comparative examples of metallographic specimens were prepared according to GB/T 13298. The grain size was measured according to the comparison method specified in GB/T 6394-2017 (Method for determination of average grain size of metals), that is, the grain size was evaluated by comparing with the standard rating chart.

β phase area ratio: automatic quantitative analysis is performed using metallographic analysis software.

Dezincification resistance test: The dezincification resistance of the material is evaluated by the maximum dezincification layer depth. The maximum dezincification layer depth of three examples and one comparative example sample is measured according to Articles 6 and 7 of GB/T 10119-2008 "Determination of dezincification corrosion resistance of brass".

Salt spray corrosion resistance test: The three examples and two comparative samples were subjected to salt spray comparative test according to the test method (neutral salt spray test method) of GB/T 10125-2012 (artificial atmosphere corrosion test salt spray test). The test conditions were: temperature: 35±2°C, pH value: 6.5-7.2, salt spray concentration: 5% NaCl solution, and the test time was 8h. After the test, the samples were taken out, washed and dried, and the corrosion degree and discoloration were visually observed to judge the corrosion resistance effect. The surface only had slight discoloration, and no pitting visible to the naked eye indicated that the salt spray corrosion resistance was good.

Table 1 Chemical compositions of the embodiments of the present invention and comparative examples

Table 2 Composition of lubricating oil in the embodiment of the present invention

Table 3 Metallographic structures of the embodiments of the present invention and the comparative examples

serial number Average grain size of α phase/μm β phase area ratio/% Example 1 15.5 0 Example 2 12.7 0 Example 3 18.0 0 Comparative Example 1 45.2 8.20 Comparative Example 2 33.7 26.8

Table 4 Dezincification resistance and salt spray corrosion resistance of the embodiments of the present invention and the comparative examples

Claims (5)

1. A kind of corrosion-resistant brass, it is characterized in that, the mass percentage of this brass is composed of Cu: 63~65wt%, Sn: 0.05~0.2%, Al: 0.01~0.05%, B: 0.002~0.006%, RE : 0.015~0.04wt%, Fe≤0.01wt%, Pb≤0.01wt%, the balance is zinc, the phase structure of the brass is a single-phase α phase, and the addition amount of Sn and Al satisfies: 350≤W _Cu / W _(Sn+Al) ≤1100, where W _Cu is the mass percent composition of Cu, and W _(Sn+Al) is the sum of the mass percent compositions of Sn and Al. 2. The corrosion-resistant brass according to claim 1, wherein the average grain size of the α phase is 10-20 μm. 3. A preparation method of the corrosion-resistant brass described in claim 1 or 2, characterized in that: comprising the following preparation steps: 1) Melting: Ingredients are prepared according to the required raw materials, and smelting is carried out in a smelting furnace. The smelting temperature is 980~1030°C. After melting, the composition of the alloy is adjusted. After the composition meets the requirements, the copper water in the smelting furnace is transferred to the holding furnace, and the temperature of the holding furnace is controlled. At 1020~1050°C; 2) Horizontal continuous casting: casting temperature: 1020~1050℃, casting speed 5~30mm/s; 3) Extrusion: the ingot heating temperature is 670~760℃, and the extrusion force is 7~28MN; 4) Intermediate stretching and intermediate annealing: the extruded billet is stretched to a billet of a certain specification after multiple passes, intermediate annealing is set between passes, the processing rate between adjacent intermediate annealing is controlled at 20~50%, and the last drawing The stretching processing rate is not less than 40%; annealing temperature: 450~580°C, heating time: 30~60min, the initial temperature is room temperature, holding time: 90~240min, and naturally cool after being out of the furnace; 5) Bottom annealing: annealing temperature 480~510°C, heating time: 30~60min, initial temperature at room temperature, holding time: 120~240min, water quenching after the billet is out of the furnace, the time interval between the billet out of the furnace and entering the water should be controlled at Within 50s, the water temperature does not exceed 50°C; 6) Stretching of finished products: get rods and wires. 4. The preparation method of corrosion-resistant brass according to claim 3, characterized in that: in the step 6), lubricating oil is used in the stretching process, and the mass percentage of the lubricating oil is composed of dimethyl silicone oil: 20~40wt%, sodium petroleum sulfonate: 4~7wt%, ethanolamine: 3~5wt%, fatty acid soap: 2~5wt%, benzotriazole: 0.1~0.2wt%, and the balance is naphthenic oil. 5 . The method for preparing corrosion-resistant brass according to claim 4 , wherein an oil film with a thickness of 2-5 μm is attached on the surface of the rod or wire.

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