CN116334441A

CN116334441A - Free-cutting high-conductivity oxygen-free lead copper alloy and preparation method thereof

Info

Publication number: CN116334441A
Application number: CN202310258019.5A
Authority: CN
Inventors: 李周遥; 郑恩奇; 段超男; 刘喆
Original assignee: Ningbo Jintian Copper Group Co Ltd
Current assignee: Ningbo Jintian Copper Group Co Ltd
Priority date: 2023-03-17
Filing date: 2023-03-17
Publication date: 2023-06-27

Abstract

The free-cutting high-conductivity oxygen-free lead-copper alloy comprises the following components in percentage by mass: 0.003% -0.012%, pb:0.8 to 1.2 percent, O:1 to 10ppm, the balance of Cu and unavoidable impurities, and controlling the content of impurity elements Fe and Si to be less than or equal to 0.005 percent, al, sb, mn, ni to be less than or equal to 0.02 percent and the total content of the impurity elements to be less than or equal to 0.05 percent. The preparation adopts a bottom blowing refining technology, charcoal coverage, annealing times reduction, cold working pass deformation increase and other methods, and the process comprises the following steps: smelting, casting, extruding, pickling, cold drawing processing, annealing, straightening and sawing. The invention has simple and reasonable process, the oxygen content of the prepared oxygen-free lead-copper alloy is lower than 10ppm, the lead particles are tiny and dispersed, the grain size is moderate, the machinability is good and can reach more than 85%, and the oxygen-free lead-copper alloy can be used for precision machining, and has better conductivity (more than 90% IACS) and hydrogen embrittlement resistance (grade 1-3) compared with the traditional lead-copper alloy.

Description

Free-cutting high-conductivity oxygen-free lead copper alloy and preparation method thereof

Technical Field

The invention belongs to the technical field of copper alloy, and relates to a free-cutting high-conductivity oxygen-free lead copper alloy and a preparation method thereof.

Background

The high-conductivity copper alloy is widely applied to the fields of optoelectronic devices, microwave technology, aerospace, national defense and military industry, electronic industry, connectors in household appliance industry and the like. Most high-conductivity copper alloy materials have poor cutting performance, and the machining precision of the materials is directly influenced by the cutting performance.

The lead element is the most commonly used alloy element for improving the cutting performance, the cutting performance of the material can be obviously improved, the cutting performance improving effect of the alloy is obviously superior to that of other free-cutting elements such as sulfur, selenium, tellurium and the like, and the exemption clause of the European Union RoHS lead element exempts the lead with low content (lower than 4 wt.%) in the copper alloy.

However, lead-copper alloy has no standard requirement on oxygen content, and oxygen-containing lead-copper alloy is easy to induce hydrogen embrittlement in a high-temperature reducing atmosphere to cause cracks, so that high-temperature application of the high-conductivity lead-copper alloy is limited; too high an oxygen content will also produce more oxidation products and thus lower thermal and electrical conductivity. In addition, the aggregation growth of lead particles in the heat processing and heat treatment process of the lead-copper alloy can cause the reduction of cutting performance.

Aiming at the defects of the cutting performance of the current high-conductivity copper alloy material and the hydrogen embrittlement resistance of the lead copper alloy, the original lead copper alloy needs to be improved, and the oxygen-free lead copper alloy which is low in cost, easy to realize industrialization and easy to cut and has high conductivity is developed.

Disclosure of Invention

The first technical problem to be solved by the invention is to provide the free-cutting high-conductivity oxygen-free lead-copper alloy which has better cutting performance and hydrogen embrittlement resistance.

The second technical problem to be solved by the invention is to provide a preparation method of the free-cutting high-conductivity oxygen-free lead copper alloy, which has simple process and lower cost and can realize industrial production.

The technical scheme adopted by the invention for solving the first technical problem is as follows: a free-cutting high-conductivity oxygen-free lead copper alloy is characterized in that: the lead-copper alloy comprises the following components in percentage by mass:

P 0.003％～0.012％；

Pb 0.8％～1.2％；

O 1～10ppm；

unavoidable impurities are less than or equal to 0.05 percent, and the content of impurity elements Fe and Si is controlled to be less than or equal to 0.005 percent, and Al, sb, mn, ni is controlled to be less than or equal to 0.02 percent;

the balance being Cu.

Further, the oxygen content of the lead-copper alloy is lower than 10ppm, the grain size is 25-50 mu m, and the lead particle number per square millimeter is 10000-20000.

Further, the lead copper alloy has a hydrogen embrittlement rating of 1 to 3.

Further, the cutting performance of the lead-copper alloy reaches more than 85 percent (taking HPb63-3 as a standard), and the conductivity reaches more than 90 percent IACS.

Finally, the tensile strength of the hard lead-copper alloy is 270-320 MPa, the yield strength is 210-260 MPa, the elongation is 8-12%, and the Vickers hardness is 100-130 HV.

The invention solves the second technical problem by adopting the technical proposal that: the preparation method of the free-cutting high-conductivity oxygen-free lead copper alloy is characterized by comprising the following steps of:

1) Casting

Proportioning according to the mass percentage, wherein the P element is added by using a phosphorus-copper intermediate alloy; heating high-purity cathode copper and lead to above 100 ℃ by using a preheating furnace, drying water, putting the preheated cathode copper and lead into a power frequency induction furnace for melting, blowing inert gas into the bottom of the induction furnace through a ventilation device, heating up for melting under the covering protection of a covering agent, keeping the temperature and standing for not less than 30min after the melting temperature reaches 1200-1300 ℃; transferring molten copper into a heat preservation furnace, adding phosphorus-copper intermediate alloy into the heat preservation furnace during transferring copper, arranging a ventilation device at the bottom of the heat preservation furnace, blowing inert gas into the furnace through the ventilation device to ensure that the oxygen content of copper in the furnace is less than 10ppm and the hydrogen content is less than 5ppm, controlling the temperature of the heat preservation furnace to be 1100-1200 ℃, pouring purified copper into a crystallizer, cooling and forming into a casting blank, wherein the casting speed is 20-60 mm/min, and the temperature of the casting blank out of the crystallizer is 600-950 ℃;

2) Extrusion

Placing the casting blank obtained in the step 1) into an induction furnace, heating to 600-900 ℃, preserving heat for 5-30 min, and then performing extrusion processing, wherein the extrusion ratio is 30-200, and the extrusion speed is 0.5-5 mm/s;

3) Acid washing

Pickling the rod blank extruded in the step 2) to remove surface oxides;

4) Cold drawing and annealing

Cold drawing the pickled bar blank, stretching the bar blank for multiple times, carrying out intermediate annealing and pickling after 2 times of stretching, wherein the annealing temperature is 300-500 ℃ and the time is 2-5 hours, and then stretching the bar blank for the subsequent times;

5) Straightening sawing

Sawing the cold-processed material to a specified length, straightening the material on a straightening machine, and packaging and warehousing after appearance inspection and physical property inspection are qualified.

Preferably, the covering agent in the step 1) is charcoal, and the covering thickness of the charcoal is not less than 20cm.

Preferably, the phosphorus-copper intermediate alloy in the step 1) is CuP14, inert gas blown into the smelting furnace and the heat-preserving furnace bottom is any one of argon and nitrogen, the gas flow is 50-200L/min, the oxygen content in the inert gas is not more than 0.03vol.%, and the water content is not more than 3.0g/L.

Further, an acid pickling corrosion inhibitor capable of reducing the precipitation of hydrogen is required to be added in the acid pickling process of the step 3).

Finally, the number of drawing passes of the cold drawing in the step 4) is 3 to 4, the drawing processing rate of each pass is controlled to be 10 to 30 percent, and the total drawing processing rate is 50 to 90 percent.

Compared with the prior art, the invention has the advantages that: based on copper-lead alloy, adding phosphorus element as deoxidizer, and regulating and controlling oxygen content by combining bottom blowing refining technology, charcoal covering and other methods to make oxygen content lower than 10ppm to reach oxygen-free copper standard; the addition of trace phosphorus in the copper alloy can improve the fluidity of the melt, improve the welding performance and corrosion resistance of the copper alloy and improve the softening resistance; the lead element has the function of improving the machinability of the alloy; the annealing times are reduced, the pass deformation of cold working is increased, lead particles are dispersed finely, the grain size is controlled, the cutting performance, the conductivity and the cold heading performance of the alloy are improved, the temperature and the strain rate of hot working are adjusted, and the oxygen-free lead copper alloy which is low in cost, easy to cut and high in conductivity and is industrialized is obtained. The process is simple and reasonable, and the oxygen content of the prepared oxygen-free lead copper alloy is lower than 10ppm, so that the oxygen-free copper TU2 level is achieved; and lead particles in the oxygen-free lead copper alloy are fine and dispersed, the grain size is moderate, the machinability is good, more than 85 percent (taking HPb63-3 as a standard) can be achieved, the oxygen-free lead copper alloy can be used for precision machining, and compared with the traditional lead copper alloy, the oxygen-free lead copper alloy has better conductivity (more than 90 percent IACS) and hydrogen embrittlement resistance (grade 1-3).

Drawings

FIG. 1 is a photograph of a metallographic structure of example 1 provided by the present invention;

FIG. 2 is a photograph of a metallographic structure of example 2 provided by the present invention;

FIG. 3 is a metallographic photograph of the lead particle distribution of example 1 provided by the present invention;

fig. 4 is a metallographic photograph of the lead particle distribution of example 2 provided by the present invention.

Detailed Description

The invention is described in further detail below with reference to the embodiments of the drawings.

In the following examples and comparative examples, the raw materials were added in weight fractions. The specific components are shown in Table 1.

Table 1 the ingredients of examples, comparative examples

The preparation method of the free-cutting high-conductivity oxygen-free lead copper alloy comprises the following steps:

(1) Casting

Proportioning according to the mass percentage, wherein the P element is added by using a phosphorus-copper intermediate alloy; and heating the high-purity cathode copper and the lead block to above 100 ℃ by using a preheating furnace, drying the water, putting the preheated cathode copper and lead block into a power frequency induction furnace for melting, blowing inert gas into the bottom of the induction furnace through a ventilation device, heating and melting under the protection of charcoal covering, wherein the charcoal covering thickness is not less than 20cm. And (3) keeping the temperature and standing after the melting temperature reaches 1200-1300 ℃, wherein the standing time is not less than 30min. Transferring molten copper into a heat preservation furnace, adding phosphorus-copper intermediate alloy into the heat preservation furnace during transferring copper, arranging a ventilation device at the bottom of the heat preservation furnace, blowing high-purity argon gas into the heat preservation furnace through the ventilation device, further purifying the copper to remove impurities, so that the oxygen content of the copper in the furnace is less than 10ppm, the hydrogen content is less than 5ppm, controlling the temperature of the heat preservation furnace to 1100-1200 ℃, pouring the purified copper into a crystallizer, cooling and molding to obtain a casting blank, wherein the casting speed is 20-60 mm/min, and the temperature of the casting blank out of the crystallizer is 600-950 ℃.

(2) Extrusion

And after the components and the surface quality of the rod blank are detected to be qualified, placing the rod blank into an induction furnace, heating to 600-900 ℃, preserving the heat for 5-30 min, and then performing extrusion processing, wherein the extrusion ratio is 30-200, and the extrusion speed is 0.5-5 mm/s.

The specific process parameters of casting and extrusion are shown in tables 2 and 3.

TABLE 2 control of casting process parameters for examples and comparative examples of the present invention

TABLE 3 extrusion process parameter control for examples, comparative examples

(3) Acid washing

And (3) pickling the extruded rod blank to remove surface oxides. During the pickling process, a pickling corrosion inhibitor is added, so that the precipitation of hydrogen is reduced, the hydrogen absorption of the alloy is inhibited, and the hydrogen embrittlement resistance of the material is improved.

(4) Cold drawing and annealing

Carrying out cold drawing processing on the pickled bar blank, wherein the drawing is carried out in a plurality of times, the number of times of drawing is 3-4 times, the drawing processing rate of each time is controlled to be 10-30%, and the total drawing processing rate is 50-90%; and after 2 passes of stretching processing, carrying out intermediate annealing and acid washing, wherein the annealing temperature is 300-500 ℃, the time is 2-5 hours, the grain size of the annealed alloy is 25-50 mu m, and then carrying out subsequent passes of stretching.

The specific process parameters of the cold drawing process and the annealing are shown in table 4.

Table 4 control of cold drawing and annealing process parameters for examples and comparative examples

(5) Straightening sawing

Sawing the material to a specified length after cold drawing, straightening the material on a straightener, and packaging and warehousing after appearance inspection and physical property inspection are qualified.

Comparative example 1 is a commercial lead copper alloy C18700.

Comparative example 2 is different from example 1 in that the impurity element content is excessively high.

Comparative example 3 is different from example 1 in that the annealing temperature is too low.

Comparative example 4 differs from example 1 in that the annealing temperature is too high.

Comparative example 5 is different from example 1 in that bottom-blowing refining was not performed.

Comparative example 6 is different from example 1 in that the gas flow rate of bottom-blowing refining is too low.

Comparative example 7 differs from example 1 in that the gas flow rate of bottom-blowing refining was too high.

Comparative example 8 differs from example 1 in that the draw casting speed was too low.

Comparative example 9 is different from example 1 in that the drawing-casting speed is excessively high.

Comparative example 10 is different from example 1 in that the extrusion speed is excessively high.

The lead-copper alloy prepared in the examples and the comparative examples are subjected to mechanical property and/or microstructure detection, and specific detection indexes and detection standards are as follows:

1) Hardness HV5: GB/T4340.1-2009 Vickers hardness test section 1: test methods.

2) Tensile strength, yield strength, elongation: GB/T228.1-2010 Metal tensile test part 1: room temperature tensile test method.

3) Metallographic microscopic test: YS/T449-2002 copper and copper alloy casting and processing product microstructure inspection method.

4) Cutting index: the cutting performance was evaluated according to the method for measuring cutting performance in appendix B of YS-T647-2007 copper zinc bismuth tellurium alloy rod, and the cutting index of C36000 (HPb 63-3) was set to 100%.

5) Conductivity of: GB/T351-2019 metal material resistivity measurement method.

6) Oxygen content/hydrogen embrittlement rating: YS/T335-2009 oxygen-free copper oxygen content metallographic examination method, GB/T5121.8-2008 copper and copper alloy chemical analysis method part 8: measurement of oxygen content.

TABLE 5 Properties of examples and comparative examples of the invention

The innovation point and the determination of the process data of the invention are further described below:

the invention is based on copper-lead alloy, and phosphorus element is added as deoxidizer, and oxygen content is controlled by combining bottom blowing refining and charcoal covering. In addition, the addition of trace phosphorus in the copper alloy can improve the fluidity of the melt, improve the welding performance and corrosion resistance of the copper alloy and improve the softening resistance. The effect of the lead element in the invention is to improve the cutting processability of the alloy, but the lead element can obviously reduce the high-temperature processability of the copper alloy, and the addition amount is too low to achieve better cutting performance, so that the addition amount of the lead is controlled within the range of 0.8-1.2%.

Among the possible impurity elements existing in the raw materials and introduced in the processing process, the Fe and Si elements have larger influence on the conductivity of the alloy, and the content of the Fe and Si elements is controlled to be less than or equal to 0.005 percent; the Al, sb, mn, ni element has a general influence on the conductivity of the alloy, the content is controlled to be less than or equal to 0.02 percent, and the total content of impurity elements is controlled to be less than or equal to 0.05 percent.

In the casting process, the temperature of a smelting furnace is 1200-1300 ℃, the temperature of a holding furnace is 1100-1200 ℃, and if the temperature is too high, energy sources are wasted, hydrogen is absorbed, crystal grains are coarse and phosphorus element is burnt; if the temperature is too low, the melting of alloy elements and the discharge of gas and impurities are not facilitated, the tendency of segregation, cold barrier and undercasting is increased, and the casting cannot be reasonably fed due to insufficient heat of a riser.

In the casting process, the casting speed is 20-50 mm/min, if the casting speed is too low, the production period of the product is increased, the production efficiency is reduced, and the defects of cold insulation, inclusion and the like of the cast ingot are easily caused due to shallower alloy liquid pits; if the pulling speed is too high, the defects of cracking, air holes and the like of the cast ingot are caused, and even copper liquid is not cooled for a sufficient time, so that copper leakage is caused.

In the casting process, the charcoal covering thickness is not less than 20cm, otherwise, the isolation effect of copper liquid and air is reduced, and air suction is caused.

In the bottom blowing refining process, inert gas is blown into the smelting furnace and the heat preservation furnace bottom through a ventilation device, wherein the inert gas is any one of argon and nitrogen, and the gas flow is 50-200L/min. The oxygen content in the inert gas must not exceed 0.03vol.%, and the moisture must not exceed 3.0g/L, otherwise the refining effect is significantly reduced. If the gas flow is too small, the number of bubbles is too small, and a good degassing and refining effect cannot be achieved; if the gas flow is too large, the volume of bubbles is increased, the number of bubbles is reduced, the degassing refining effect is reduced, even through flow is formed, and the copper liquid is splashed or slag covered on the surface is involved in the copper liquid to cause pollution.

In the extrusion process, the heating temperature is 600-900 ℃, and if the heating temperature is lower than 600 ℃, the metal deformation resistance is larger, the extrusion force is relatively increased, and the extrusion is difficult; if the temperature is too high, the hot cracking tendency of the copper alloy is increased, even overheating and overburning occur, so that the crystal grains of the metal are excessively grown, the crystal grains of the extruded product are coarse, and the metal strength is low. If the extrusion ratio is 30-200, the extrusion deformation is insufficient, so that the mechanical properties of the extruded product are reduced; if too high, the required pressing force becomes too high, which makes extrusion difficult and makes cracking easy. The extrusion speed is 1-10 mm/s, the extrusion time is increased due to the fact that the extrusion speed is too low, the temperature loss of an ingot is accompanied in the extrusion process, the extrusion force is greatly increased when the ingot is extruded to the tail stage, and extrusion efficiency and quality are affected; too high extrusion speeds can result in the accumulation of extrusion deformation heat, thereby causing an increase in temperature and increasing the thermal cracking tendency of the material.

In the pickling process, a pickling corrosion inhibitor is required to be added, so that the precipitation of hydrogen is reduced, the hydrogen absorption of the alloy is inhibited, and the hydrogen embrittlement resistance of the material is improved.

In the cold drawing process, the processing rate of each pass is 10-30%, if the processing rate of a single pass is too large, chuck breakage is easy to occur, and if the processing rate is too small, drawing passes are increased, and the production efficiency is reduced. The total processing rate is 50-90%, and the processing rate of the cold drawn product can be set according to the requirements, so that products in different states such as 1/4 hard state, semi-hard state or hard state and the like can be obtained.

In the annealing step, the annealing temperature is 300-500, the annealing time is 2-5 h, and the annealing is performed once after the stretching. Too low annealing temperature and too short annealing time can not completely eliminate residual stress; if the temperature is too high and the time is too long, lead particles are aggregated and grown, crystal grains are grown, and the cutting performance and mechanical property are reduced; multiple anneals may also cause lead particles to aggregate and grow. The grain size is controlled within the range of 25-50 mu m, the undersize of the grain leads to the reduction of the conductivity of the material, the material is easy to crack during cold heading, and the undersize of the grain leads to the reduction of the mechanical property of the material.

The above examples are provided for further illustration of the present invention and are not to be construed as limiting the scope of the present invention, and some insubstantial modifications and adaptations of the invention based on the above disclosure may be made by one skilled in the art.

Claims

1. A free-cutting high-conductivity oxygen-free lead copper alloy is characterized in that: the lead-copper alloy comprises the following components in percentage by mass:

P 0.003％～0.012％；

Pb 0.8％～1.2％；

O 1～10ppm；

the balance being Cu.

2. The free-cutting, highly conductive, oxygen-free lead copper alloy of claim 1, wherein: the oxygen content of the lead-copper alloy is lower than 10ppm, the grain size is 25-50 mu m, and the lead particle number per square millimeter is 10000-20000.

3. The free-cutting, highly conductive, oxygen-free lead copper alloy of claim 1, wherein: the hydrogen embrittlement grade of the lead-copper alloy is 1-3.

4. The free-cutting, highly conductive, oxygen-free lead copper alloy of claim 1, wherein: the cutting performance of the lead-copper alloy reaches more than 85 percent (taking HPb63-3 as a standard), and the conductivity reaches more than 90 percent IACS.

5. The free-cutting, high-conductivity, oxygen-free lead copper alloy according to any one of claims 1 to 4, wherein: the hard lead-copper alloy has tensile strength of 270-320 MPa, yield strength of 210-260 MPa, elongation of 8-12% and Vickers hardness of 100-130 HV.

6. A method for preparing the free-cutting high-conductivity oxygen-free lead copper alloy according to any one of claims 1 to 5, which is characterized by comprising the following steps:

1) Casting

2) Extrusion

3) Acid washing

Pickling the rod blank extruded in the step 2) to remove surface oxides;

4) Cold drawing and annealing

5) Straightening sawing

7. The method of manufacturing according to claim 6, wherein: the covering agent in the step 1) is charcoal, and the covering thickness of the charcoal is not less than 20cm.

8. The method of manufacturing according to claim 6, wherein: the phosphorus-copper intermediate alloy in the step 1) is CuP14, inert gas blown into the smelting furnace and the heat preservation furnace bottom is any one of argon and nitrogen, the gas flow is 50-200L/min, the oxygen content in the inert gas is not more than 0.03vol.%, and the water content is not more than 3.0g/L.

9. The method of manufacturing according to claim 6, wherein: and 3) adding an acid pickling corrosion inhibitor capable of reducing the precipitation of hydrogen in the acid pickling process of the step 3).

10. The method of manufacturing according to claim 6, wherein: the number of drawing channels of the cold drawing in the step 4) is 3-4, the drawing processing rate of each channel is controlled to be 10-30%, and the total drawing processing rate is 50-90%.