Spring copper plated

Maintenance and Control of Acid Copper Plating Bath (Maintenance and Control)

Composition: Copper sulfate is the source of copper ions in the solution. Since the current efficiency of the cathode and anode is normally close to 100%, the copper ions supplemented by the anode copper is quite stable. Sulfuric acid improves the conductivity of the solution and reduces the polarization of the anode and cathode, prevents salt precipitation and improves throwing power. The ratio of copper to sulfuric acid in the high uniformity plating bath should be maintained at 1:10. When the sulfuric acid content exceeds 11 vol%, the current efficiency decreases. Chloride ions can reduce polarization and eliminate striated deposits with high current density in the high uniformity and gloss plating bath. Phosphor bronze spring

# Temperature: Too part of the plating bath is operated at room temperature. If the temperature is too low, the current efficiency and plating range will be reduced. If gloss is not required, the bath temperature can be increased to 50°C to increase the electroplating range, which can be used in electroforming, printed circuits or printed boards.

# Stirring: It can be stirred by air, mechanical, solution jet or moving plating. The better the stirring, the greater the allowable current density.

# Impurities: Organic impurities are the most common in acid plating baths, and their sources are the decomposition products of brighteners. The tank lining and anode bag are not filtered to the substances, electroplating stopoffs, rust prevention substances and Impurities of acid and salt. The green of the plating bath indicates a considerable amount of organic pollution. Activated carbon must be used to remove organic impurities. Sometimes hydrogen peroxide and potassium permanganate can help activated carbon to remove organic impurities, but cellulose filters cannot used.

Metal impurities and their effects are as follows:

Antimony (antimony): 10-80 g/l, rough and embrittled coating, adding glue (gelatin) or monocitrate (tannin) can inhibit antimony co-precipitation (codeposition).

Arsenic 20-100 ppm: same as antimony.

Bismuth: Same as antimony.

Cadmium>500ppm: It will cause immersion deposit and anodic polarization, which can be controlled by chlorine.

Nickel>1000 ppm: same as iron.

Iron>1000 ppm: reduce uniformity and conductivity.

Tin 500-1500ppm: same as cadmium.

Zinc>500ppm: same as cadmium.

4.3.4 Failures and causes of acid copper plating bath

1. Burn in high current density area:

Too little copper, organic pollution

The temperature is too low and there are too few chloride ions

Not enough stirring

2. Loss of luster:

Too little gloss agent, too high temperature

Organic pollution, too little copper

Low chloride ion concentration

3. Rough coating:

Solid particle pollution Poor quality of anode copper

Broken anode bag, insufficient chloride ion content

4. Pinhole:

Organic matter pollution Too little chloride ion

Anode bag rot

5. The current is too low:

Organic pollution too much chlorine

The sulfuric acid content is not enough, the current density is too small

Insufficient additive temperature too high

6. Anode polarization:

Tin and gold pollution, too much chlorine

Temperature is too low too much sulfuric acid

Anode copper quality is not good enough copper sulfate content is insufficient

4.3.5 Additives for acid copper plating bath

There are many additives such as glue, dextrin, sulfur, interface active agent, dye, urea, etc. The main purposes are:

Smooth coating, reduce dendrites

Increase current density and gloss

Hardness change prevents pinholes

4.4 Copper Cyanide Baths

Cyanide copper plating brings human health hazards and waste disposal problems. The use of thick plating has been reduced, but it is still widely used in primer plating. Cyanide copper plating The most important chemical composition of the plating bath is the free cyanide and total cyanide content. The calculation equation is as follows:

K2Cu(CN)3 total potassium cyanide amount = cuprous cyanide required amount × 1.45 + free potassium cyanide required amount

K2Cu(CN)3 Total sodium cyanide amount = cuprous cyanide required amount × 1.1 + free sodium cyanide required amount

Example: The plating bath requires 2.0g/l copper cyanide and 0.5g/l free potassium cyanide. How much potassium cyanide is required?

The amount of potassium cyanide needed for solution=2.0×1.45+0.5=3.4g/l

The anode copper whisker is pure copper without oxides. It can be packed in a steel basket with copper plates or copper blocks and wrapped in anode bags. The steel anode plate is used to adjust the copper content. The area ratio of cathode to anode should be 1:1 and 1:2.

Spring copper plated

Spring copper plated
4.1 Properties of copper

4.2 Types of copper plating solution formula

4.3 Copper Sulfate Baths

4.4 Copper Cyanide Baths

4.5 Copper Pyrophosphate Plating Bath

4.6 Copper Fluoborate Bath

4.7 Stainless steel copper plating process

4.8 Stripping of copper plating

4.9 Copper Plating Patent Literature (US Patent)

4.10 Journal papers related to copper plating

4.1 Properties of copper

Color: rose red Atomic weight: 63.54

Atomic number: 29 Specific gravity: 8.94 Melting point: 1083°C

Boiling point: 2582℃ Brinell hardness 43-103

Resistance: 1.673 l W -cm, 20 ℃ Tensile strength: 220~420MPa

Standard potential: Cu++e- →Cu is +0.52V; Cu++ +2e-→Cu is +0.34V.

Soft and tough, good ductility, easy plastic processing, excellent electrical and thermal conductivity

Good polishing and optical rotation, easy to oxidize, especially when heated, it cannot be used as protective coating

It will react with sulfur in the air to form brown copper sulfide. It will react with carbon dioxide in the air to form a copper record.

Will form copper chloride powder with chlorine in the air

The copper plating layer has good uniformity, compactness, adhesion and polishing rotation, so it can be used as the bottom plating layer of other electroplating metals.

The plating layer can be used to prevent carburizing and copper nitride. The only practical application for the electroplating of zinc castings.

The source of copper is sufficient. Copper is easily electroplated and easy to control

The amount of copper plating is second only to nickel

4.2 Types of copper plating solution formula

Can be divided into two categories:

1. Acid copper electroplating solution:

The advantages are:

Simple ingredients, low toxicity, easy to dispose of waste liquid

Stable plating bath without heating, high current efficiency

Low price, low equipment cost, high current density, high production rate

The disadvantages are:

Coating crystals are coarse and cannot be directly plated on steel

Poor uniformity

2. Formula of copper cyanide electroplating solution:

The advantages are:

Fine coating, good uniformity

Can be plated directly on steel

The disadvantages are:

Strong toxicity, troublesome waste disposal, low current efficiency

High price, high equipment cost, low current density, low production efficiency

The plating solution is unstable and needs to be heated

With the advantages of the above two formulas, P.S generally uses cyanide copper plating solution for primer, and then uses acid copper plating solution for copper plating, especially for plating parts with thicker plating thickness.

4.3 Copper Sulfate Baths

The preparation, operation and waste treatment of copper sulfate plating bath are very economical, and can be applied to printed circuits, electronics, photogravure, electroforming, and decoration (decorative) and plastic plating (plating on plastics). Its chemical composition is simple, containing copper sulfate and sulfuric acid. The plating solution has good conductivity and poor uniformity, but there are special formulas and additives that can be improved. Steel plated parts must be primed with a copper cyanide bath or strike with nickel to avoid the formation of replacement diposits and low adhesion. Copper-plated spring

Zinc castings and other acid-sensitive metals must be fully primed to prevent corrosion by sulfuric acid. The plating bath is operated at room temperature. The anode must be high-purity rolled copper, free of oxides and phosphating (0.02 to 0.08wt%P), and copper anode nuggets can be used in titanium baskets. The anode must be added with an anode bag, the area ratio of the anode to the cathode should be 2:1, the current efficiency of the anode and the cathode can reach 100%, and the anode copper should be taken out when it is not electroplated.

4.3.1 Standard acid copper plating

(1) General formulation:

Copper sulfate 195-248 g/l

Sulfuric acid 30-75 g/l

Chloride 50-120 ppm

Current density 20-100 ASF

(2) Semibright plating: Clifton-Phillips formula

Copper Sulfate 248 g/l

Sulfuric acid 11 g/l

Chloride 50-120 ppm

Thiourea 0.00075 g/l

Wetting agent 0.2 g/l

(3) Bright plating: beaver formula

Copper sulfate 210 g/l

Sulfuric 60 g/l

Chloride 50-120 ppm

Thiourea 0.1 g/l

Dextrin 0.01 g/l

(4) Bright plating: Clifton-Phillips formula

Copper sulfate 199 g/l

Sulfuric acid 30 g/l

Chloride 50-120 ppm

Thiourea 0.375 g/l

Wolasses 0.75 g/l

4.3.2 High uniformity acid copper plating bath formula (High Throw Bath)

Used for printed circuits, drum plating and other plating applications that require high uniformity.

Copper sulfate 60-90 g/l

Sulfuric acid 172-217 g/l

Chloride 50-100 ppm

Proprietary additive   as indicated

Heat treatment of steel-soft nitriding

In order to shorten the nitriding cycle and make the nitriding process not restricted by the steel type, two new nitriding processes have been developed on the basis of the original nitriding process in the past one to twenty years.
Soft nitriding is essentially a low-temperature carbonitriding based on nitriding. At the same time as the nitrogen atomization of steel, there is also a small amount of carbon atom infiltration. Compared with the aforementioned general gas nitrogen, the hardness of the nitrided layer is higher. It is low and brittle, so it is called soft nitriding.

1. Soft nitriding method, soft nitriding method is divided into gas soft nitriding and liquid soft nitriding. At present, the most widely used in domestic production is gas nitrocarburizing. <,br>Gas nitrocarburizing is a low-temperature carbon and nitrocarburizing in an atmosphere containing activated carbon and nitrogen atoms. Commonly used co-permeating media are urea, formamide and triethanolamine, which generate heat at the nitrocarburizing temperature. The decomposition reaction produces activated carbon and nitrogen atoms.

The activated carbon and nitrogen atoms are absorbed by the surface of the workpiece and penetrate into the surface of the workpiece through diffusion, thereby obtaining a nitrogen-based carbonitriding layer.

The gas nitrocarburizing temperature is usually 560-570℃, because the hardness of the nitrided layer is the highest at this temperature. The nitriding time is usually 2-3 hours, because more than 2.5 hours, the depth of the nitriding layer increases slowly with time.

2. The structure and characteristics of nitrocarburizing layer: After the steel is nitrocarburized, the outermost layer of the surface can obtain a white layer of several microns to tens of microns, which is composed of ε phase, γ`phase and nitrogen-containing Carbon body is composed of Fe3 (C, N), and the sublayer is a 0.3-0. 4 mm diffusion layer, which is mainly composed of γ`phase and ε phase.

Soft nitriding has the following characteristics:

(1) The processing temperature is low, the time is short, and the deformation of the workpiece is small.

(2) Not limited by steel type, carbon steel, low alloy steel, tool and die steel, stainless steel, cast iron and iron-based powder metallurgical materials can all be soft-nitrided. The surface hardness of the workpiece after nitrocarburizing is related to the nitriding process and material.

3. It can significantly improve the fatigue limit, wear resistance and corrosion resistance of the workpiece. It also has anti-abrasion and anti-seize properties under dry friction conditions.

4. Since there is no brittle ξ phase in the soft nitrided layer, the nitrided layer is hard and has certain toughness and is not easy to peel off.

Therefore, nitrocarburizing has been widely used in the treatment of wear-resistant workpieces such as molds, measuring tools, high-speed steel tools, crankshafts, gears, and cylinder liners.

It should be noted that the current problem of gas nitrocarburizing is that the thickness of the iron-nitrogen compound layer in the surface layer is relatively thin (0.01-0.02mm), and the hardness gradient of the nitride layer is steep, so it is not suitable to work under heavy load conditions. In addition, during the nitriding process, toxic gases such as HCN will be generated in the furnace. Therefore, attention must be paid to the sealing of the equipment during production to prevent the furnace gas from leaking out and polluting the environment.

Heat treatment basis: annealing-quenching-tempering

1. Types of annealing
1. Complete annealing and isothermal annealing

Complete annealing is also called recrystallization annealing, generally referred to as annealing. This annealing is mainly used for castings, forgings and hot-rolled sections of various carbon and alloy steels with hypoeutectoid compositions, and sometimes also used for welded structures. Generally used as the final heat treatment of some non-heavy workpieces, or as the pre-heat treatment of some workpieces.

2. Spheroidizing annealing

Spheroidizing annealing is mainly used for hypereutectoid carbon steels and alloy tool steels (such as steel grades used in manufacturing cutting tools, measuring tools, and molds). Its main purpose is to reduce hardness, improve machinability, and prepare for subsequent quenching.

3. Stress relief annealing

Stress relief annealing is also called low temperature annealing (or high temperature tempering). This annealing is mainly used to eliminate residual stress in castings, forgings, welded parts, hot rolled parts, cold drawn parts, etc. If these stresses are not eliminated, the steel parts will be deformed or cracked after a certain period of time or in the subsequent cutting process.

2. When quenching, the most commonly used cooling media are brine, water and oil. Salt water quenched workpieces are easy to obtain high hardness and smooth surface, and it is not easy to produce soft spots that are not hardened, but it is easy to cause serious deformation of the workpiece and even cracks. The use of oil as the quenching medium is only suitable for the quenching of some alloy steels or small-sized carbon steel workpieces with relatively large stability of undercooled austenite.

3. The purpose of steel tempering

1. Reduce brittleness and eliminate or reduce internal stress. There is a large internal stress and brittleness of steel parts after quenching. If not tempered in time, the steel parts will often deform or even crack.

2. Obtain the required mechanical properties of the workpiece. After quenching, the workpiece has high hardness and high brittleness. In order to meet the different performance requirements of various workpieces, the hardness can be adjusted by appropriate tempering to reduce the brittleness and obtain the required Toughness, plasticity.

3. Stable workpiece size

4. For some alloy steels that are difficult to soften by annealing, high temperature tempering is often used after quenching (or normalizing), so that the carbides in the steel are properly aggregated and the hardness is reduced to facilitate cutting.

Super hardening treatment technology for metal mold surface

Super hardening treatment technology for metal mold surface
1. Introduction of diffusion method metal carbide coating technology

1. Technical introduction    diffusion method metal carbide coating technology is to place the workpiece in a special medium, and form a metal carbide layer of several microns to tens of microns on the surface of the work piece by diffusion. The carbide layer has extremely high hardness, and the HV can reach 1600″3000 (determined by the type of carbide). In addition, the carbide layer is metallurgically combined with the substrate, which does not affect the surface finish of the workpiece, and has extremely high wear resistance and resistance. Occlusion (bonding), corrosion resistance, etc., can greatly increase the service life of molds and mechanical parts.

2. Compared with related technologies, the method of forming a superhard compound film on the surface of the workpiece can greatly improve its wear resistance, seizure resistance (anti-bonding), corrosion resistance and other properties, thereby greatly improving its service life. And the economical method. At present, the surface super-hardening treatment methods of workpieces mainly include physical vapor deposition (PVD), chemical vapor deposition (CVD), physical chemical vapor deposition (PCVD), and diffusion metal carbide layer technology. Among them, the PVD method has a low deposition temperature. The advantages of small deformation of the workpiece, but due to the poor bonding force between the film layer and the substrate, and the poor process winding and plating, it is often difficult to give play to the performance advantages of the superhard compound film layer.

The CVD method has outstanding advantages such as good film-base bonding and good process winding and plating properties. However, for a large number of steel materials, the subsequent hardening of the matrix is ​​more troublesome. If you are not careful, the film layer is easily damaged. Therefore, its application is mainly concentrated on materials such as cemented carbide. The PCVD method has a low deposition temperature, and the film base bonding force and process winding property are greatly improved compared with the PVD method. However, compared with the diffusion method, the film base bonding force still has a large gap.

In addition, the PCVD method is still plasma film formation Although the winding performance is improved compared with PVD method, it cannot be eliminated. The metal carbide coating formed by the diffusion method metal carbide coating technology forms a metallurgical bond with the substrate, and has a film-base bonding force that PVD and PCVD can’t match. Therefore, this technology can really give play to the performance advantages of the super hard film layer. , This technology does not have the problem of winding and plating, the subsequent hardening of the substrate is convenient, and the treatment can be repeated many times, which makes the applicability of this technology more extensive.

3. Technical advantages    diffusion method metal carbide coating technology is widely used in Japan, European countries, Australia, South Korea and other countries. According to investigations, many matching molds on imported equipment use this technology in large quantities. When these molds are made domestically, due to the lack of corresponding mature technology, the mold life is often low, and some of them cannot even be made domestically.

This technology has been studied in the 1970s in China, but due to various conditions, the process and equipment are often difficult to pass the test of batch and long-term production, so that some actual problems in the technology are not easy to expose or solve, and they are often abandoned halfway. . In the process of more than ten years of research and application, we have conducted in-depth research on the actual problems of the technology and equipment, and made effective improvements. The improved process and complete equipment have been able to meet the long-term The requirements of stable production, the life level of the molds handled have reached the life level of imported similar molds, and the rich production experience in practical application of various molds has been obtained, which has laid a solid technical foundation for the large-scale promotion and application of this technology.

4. Scope of application    diffusion metal carbide coating technology can be widely used in all kinds of molds or mechanical parts that fail due to wear and seizure. Among them, failures caused by wear (such as punching, cold heading, powder molding and other molds) can increase the service life by several to tens of times; product or mold strain problems caused by seizure (such as drawing die, flanging) Modulus, etc.) can be fundamentally solved.

Applicable materials: die steel, structural steel with carbon content greater than 0.3%, cast iron, cemented carbide.

2. Ultra-hardening treatment technology of stainless steel welded pipe mold surface

Stainless steel welded pipe is formed by rolling a stainless steel plate through several molds on a welded pipe forming machine and then welded. Due to the high strength of stainless steel and its structure is a face-centered cubic lattice, it is easy to form work hardening, so that when the welded pipe is formed: on the one hand, the mold has to withstand greater friction, making the mold easy to wear; on the other hand, stainless steel sheet It is easy to form adhesion (occlusion) with the mold surface, causing strain on the welded pipe and mold surface. Therefore, a good stainless steel forming mold must have extremely high wear resistance and anti-bonding (seizure) performance. Our analysis of imported welded pipe molds shows that the surface treatment of this type of mold is treated with superhard metal carbide or nitride coating.

Stainless steel welded pipe forming die material is generally made of Cr12MoV (or SRD11, D2, DC53) with high carbon and high chromium. At present, the following process flow is generally used to make molds in China: blanking%26rarr; rough machining%26rarr; heat treatment (high temperature quenching and high temperature tempering)%26rarr; finishing%26rarr; nitriding%26rarr; finished product (Note: To save costs, Generally, manufacturers now omit the two time-consuming and expensive processes of forging and spheroidizing annealing).

Because Cr12MoV materials belong to high-carbon and high-chromium alloy steels, there is a large segregation of components in the original structure (this segregation cannot be eliminated even by general forging). In this way, the internal structure of the mold after heat treatment (high quenching and high recovery) is extremely uneven, and the macroscopic appearance is extremely uneven (HRC about 40 to 60). After nitriding treatment, the uneven surface of the mold cannot be eliminated. The hardness is even further reduced. In actual use, the surface of the mold and the welded pipe is easy to strain, and the mold life is low.

The ultra-hardening treatment technology of the mold surface that has been researched by a company from Hu has been successfully applied to the forming mold of stainless steel welded pipe. The mold treated by this technology forms a metal carbide layer with a hardness of about HV3000 on its surface. The carbide layer is dense and closely combined with the substrate. It does not affect the surface finish of the workpiece.

It has extremely high wear resistance and seizure resistance. Fundamentally solve the problem of picking of welded pipes, reduce the workload of the subsequent polishing process of pipe making and improve product quality, greatly increase the service life of the mold, and reduce the workload of after-sales service. Practice shows that this technology has extremely high use value. The following is a comparison between the process mold and the nitriding mold.

1. Performance:    nitriding mold The surface hardness of the mold treated by this process: HV700″ about 1000 HV3000    matrix hardness: extremely uneven HRC58″62   HRC40″60

2. Process flow:    nitriding mold: blanking %26rarr; rough machining %26rarr; heat treatment (high quenching and high recovery) %26rarr; finishing %26rarr; nitriding %26rarr; finished product, this process mold: blanking %26rarr; All processed in place (no heat treatment required)% 26rarr; this process treatment (matrix hardening and surface treatment are completed at one time). %26rarr; Grinding inner hole %26rarr; The finished product can be seen from the process flow. This process can shorten the mold processing cycle.

3. Use effect:   The mold processed by this process can fundamentally solve the fuzz of the welded pipe compared with the nitriding mold, thereby reducing the workload of the subsequent polishing process of the welded pipe and improving the product quality (the pipe wall is reduced due to a large amount of polishing). Improve the service life of the mold and reduce the workload of after-sales service.

The mold surface super-hardening treatment technology developed by a Hunan company has been widely used in actual production. The life of the mold treated by this process is greatly improved compared with the traditional process such as nitriding, and it exceeds the performance of some molds. Foreign level, and the price is only 1/4″1/10 of the foreign equivalent.

The molds processed by this process include rolls, punches, color tube series cold work molds, standard parts molds, pyrophyllite molds, copper-aluminum profile extrusion molds, etc., which have produced high benefits for customers and made the mold cost-effective. Quality improvement.

Characteristics of heat treatment of explosive composite materials

There are many similarities between the heat treatment of metal explosive composite materials and the heat treatment of single metal materials. For example, the materials are heated to a predetermined high temperature at a certain heating rate, maintained at this temperature for a certain period of time, and then cooled at a certain rate. The whole process is carried out in air, in vacuum or in other media (water, oil). Take annealing as an example, divided into high temperature, medium temperature and low temperature annealing. The purpose is also to recrystallize or relieve stress. According to different material, organization, state and performance requirements, heat treatment under different processes.

The heat treatment of explosive composite materials also has its special features, that is, the two or more components that make up the composite materials must first be considered, their respective melting points and recrystallization temperatures, strength and plasticity, corrosion resistance and wear resistance, and ratios. Physical and chemical properties such as thermal and thermal expansion coefficients, especially their interaction characteristics at high temperatures. So as to correctly design the process parameters of heat treatment and predict the influence of heat treatment on their bonding zone structure, bonding strength and respective matrix structure and performance.

The heat treatment of explosive composite materials and the formulation of process parameters must correctly handle the above-mentioned many contradictions, and achieve the unity of process, organization and performance in the vastly different metal combinations, so as to provide reliable organization and performance for the normal use of explosive composite materials. Guarantee.

4.2 Annealing of explosive composite materials

Annealing is an important process that is frequently used in the subsequent processing of explosive composite materials. Annealing of this type of material has three purposes:

First, eliminate the residual stresses of different directions and magnitudes formed on the surface, interface, bottom surface and interior of the composite material during the explosive welding process, including the residual stress in the welds of the equipment and components made of explosive composite materials. This annealing temperature is the lowest.

Second, eliminate explosive hardening and explosive strengthening, creating conditions for subsequent mechanical processing of composite materials. For metal materials with higher original hardness and strength, their explosive hardening and explosive strengthening tendencies are stronger. At this time, this annealing is particularly important. Their annealing temperature is higher.

Third, recrystallization annealing. This kind of annealing can maximize the recrystallization of the deformed structure of the bonding zone, the composite layer and the base layer without severely losing the bonding strength of the composite material, thereby creating conditions for their subsequent pressure processing, mechanical processing and use. In the press working process, intermediate annealing is sometimes performed. The final product sometimes has to undergo finish annealing (soft state). This annealing temperature is the highest.

The annealing process of explosive composite materials is formulated according to the above-mentioned different purposes. A lot of practical experience points out that the principle of formulating the annealing process for this type of material is to first consider the melting point of the lowest melting point in the metal combination, and then consider whether the phase diagram based on the main element in the combined metal is a solid solution or contains intermetallic compounds, or Both. Especially important when annealing at high temperature.

Heat treatment of metal explosive composite materials

Table 1 Annealing process of several explosive composite panels

Composite material

Annealing temperature/℃

Holding time/h

Titanium-steel stainless steel-steel nickel-titanium nickel-stainless steel zirconium-steel copper-aluminum copper-LY12 copper-LY2M

500 500 500 500 500 300 300 300

600 600 600 600 600 350 350 350

700 700 700 700 700 400 400 400

800 800 800 800 800 450 450 450

850 900 900 900 900 500 500 500

900 1000 1000 1000 1000 550 550 550

1000 1100

1 1 1 1 1 0.5 0.5 0.5

Since the sample is air-cooled after annealing, the structure of the metal at high temperature is basically retained. This method of treatment is quite beneficial to the study of similar subjects.

Figure 2 shows the bonding zone morphology of other explosive composite panels after high temperature heat treatment. Figures 2a-e show an intermediate layer similar to Figure 1h. These intermediate layers are formed by the violent diffusion and combination of the atoms of the base metal at high temperatures, and they contain all the intermetallic compounds that they can form at high temperatures [2, 3]. As for the situation shown in Figure 2f (there are also bimetals such as stainless steel-steel and nickel-steel), although the annealing temperature is very high, the above-mentioned intermediate layer does not appear at their bonding interface. After high-temperature annealing, except for the recrystallization and grain growth of the base metal, the bonding interface (including the waveform) did not change significantly.

Figure 2 The micro morphology of the bonding zone of several composite plates after high temperature annealing (all reduced by 1 times)

(a) Copper-LY2M 550℃ annealing×100 (b) Copper-LY12550℃ annealing×100 (c) Ni-Ti 1000℃ annealing×50(d) Zirconium-steel 1000℃ annealing×100(e) Copper-aluminum 550℃ Annealing×50(f) Nickel-stainless steel 1100℃ annealing×50

Heat treatment of metal explosive composite materials

Heat treatment is an important processing procedure for single metal materials to obtain a certain structure and performance, and it is also an important processing procedure for metal explosive composite materials to obtain a certain structure and performance. The heat treatment types of this kind of materials also include annealing, quenching, tempering, normalizing and aging. This article takes the annealing of several explosive composite panels as an example to discuss the related issues.
1 Test materials

The following explosive clad plates were used in this test: titanium-steel, stainless steel-steel, nickel-titanium, nickel-stainless steel, copper-aluminum, copper-LY12, copper-LY2M and zirconium-steel.

2 Test method

The blanks of the explosive composite board samples were annealed and heat treated according to the process shown in Table 1. Then carry out the following work:

(1) A part of the above-mentioned blank is made into metallographic samples by explosive welding metallographic technology, and the microstructure of the bonding zone of the composite plate under different annealing processes is observed under a metallographic microscope, and the corresponding metallographic photos are taken.

(2) Use the above-mentioned titanium-steel, stainless steel-steel, nickel-titanium and nickel-stainless steel composite plate blanks to make shear specimens, test their shear strength on a universal material testing machine, and plot these data in different annealing processes The change curve under.

(3) Using metallographic samples of titanium-steel, stainless steel-steel, nickel-titanium and nickel-stainless steel composite plates, measure the microhardness on the microhardness tester according to the predetermined procedures and methods, and draw the bonding area of ​​the corresponding materials Microhardness distribution curve.

3.1 The bonding zone organization of the composite board

It can be seen from Figure 1 that the microscopic morphology of the bonding zone of the titanium-steel composite plate has undergone significant changes after annealing. Figure 1a shows the structure of the explosion state before annealing. It can be seen from this figure that the bonding interface is a wave shape. This wave interface is unique to the transition zone of explosively welded composite materials. It can also be seen from the figure that two different forms of plastic deformation structures appear on both sides of the wave interface. On the steel side, this deformation is manifested by the elongated crystal grains, just like the deformed fibers in the conventional rolling process. Moreover, the degree of deformation is the most serious near the interface, and the degree of deformation decreases as the distance from the interface increases. The original structure of steel appears below the waveform, and some twin crystals can also be seen. Under high magnification, sub-grains and equiaxed grains similar to recrystallization can be observed on the interface. On the titanium side, the deformation of the metal appears in the form of “flying lines” flying from the interface into the titanium. This kind of flying line is adiabatic shear line, which is essentially a special form of plastic deformation line [1]. There are more twin crystals in titanium than steel. There is a vortex area in the wave front, where most of the molten metal formed during the explosive welding process is gathered, a small amount of which is distributed on the wave ridge, and its thickness is measured in μm. The bonding zone with such characteristics is the welding transition zone of explosive welding metal composite materials.

After annealing, many changes have taken place in the microstructure in the bonding zone: the flying lines on the titanium side disappeared at 500°C, the titanium began to recrystallize, and the deformed streamlines on the steel side remained (Figure 1b). The grains of annealed titanium at 600°C are growing; although there are still deformed streamlines in some places on the steel side, most of them also begin to recrystallize, and the amount of pearlite decreases (Figure 1c). When annealing at 700°C, the deformed structure in the steel disappears completely, the pearlite also disappears, and the grains are growing; the grains of titanium grow larger (Figure 1d). The crystal grains of titanium and steel are still growing after annealing at 800 and 850°C. At this time, an intermittent cluster of new phase regions appear at their interface (Figure 1e, f). At 900°C, the new phase zone has been connected into a band (Figure 1g). At this time, due to the diffusion of iron in the steel to the titanium side, the α→β phase transition temperature of titanium is increased, that is, the phase transition has not yet occurred at this temperature (the phase transition temperature is 882°C). When the temperature rises to 1000°C, the titanium side changes from α-Ti to β-Ti. In addition, due to the diffusion of iron, carbon and titanium through the interface, several distinct organizational morphologies appear on the interface and on both sides (Figure 1h), that is, an intermediate layer containing a large amount of intermetallic compounds.

Basic knowledge of metal heat treatment

Basic knowledge of metal heat treatment (3)
Classification of steel

Steel is an alloy with iron and carbon as the main components, and its carbon content is generally less than 2.11%. Steel is an extremely important metal material in economic construction.

Steel is divided into two categories: carbon steel (referred to as carbon steel) and alloy steel according to its chemical composition. Carbon steel is an alloy obtained by smelting pig iron. In addition to iron and carbon as its main components, it also contains a small amount of impurities such as manganese, silicon, sulfur, and phosphorus. Carbon steel has certain mechanical properties, good process properties, and low price. Therefore, carbon steel has been widely used. However, with the rapid development of modern industry and science and technology, the performance of carbon steel can no longer fully meet the needs, so people have developed various alloy steels. Alloy steel is a multi-element alloy obtained by adding some elements (called alloying elements) purposefully on the basis of carbon steel. Compared with carbon steel, the performance of alloy steel has been significantly improved, so it is increasingly widely used.

Due to the wide variety of steel materials, in order to facilitate production, storage, selection and research, steel materials must be classified. According to different purposes, chemical composition and quality of steel, steel can be divided into many categories:

1. Classification by purpose

According to the purpose of steel, it can be divided into three categories: structural steel, tool steel, and special performance steel.

Structural steel: 1. Steel used for various machine parts. It includes carburized steel, quenched and tempered steel, spring steel and rolling bearing steel.

2. Steel used as engineering structure. It includes A, B, special steel and ordinary low alloy steel springs in carbon steel.

Tool steel: steel used to make various tools. According to different uses of tools, it can be divided into cutting tool steel, die steel and measuring tool steel.

Special performance steel: steel with special physical and chemical properties. Can be divided into stainless steel, heat-resistant steel, wear-resistant steel, magnetic steel, etc.

2. Classified by chemical composition

According to the chemical composition of steel, it can be divided into two categories: carbon steel and alloy steel.

Carbon steel: According to carbon content, it can be divided into low carbon steel (carbon content ≤0.25%); medium carbon steel (0.25%<carbon content<0.6%); high carbon steel (carbon content ≥0.6%) .

Alloy steel: According to the content of alloying elements, it can be divided into low alloy steel (total content of alloying elements≤5%); medium alloy steel (total content of alloying elements=5%-10%); high-alloy steel (total content of alloying elements> 10%). In addition, according to the different types of main alloying elements contained in steel, it can also be divided into manganese steel, chromium steel, chromium nickel steel, chromium manganese titanium steel and so on.

3. Classified by quality

According to the content of harmful impurities phosphorus and sulfur in steel, it can be divided into ordinary steel (phosphorus content ≤0.045%, sulfur content ≤0.055%; or phosphorus and sulfur content ≤0.050%); high-quality steel (phosphorus and sulfur content ≤ 0.040%); high-quality steel (phosphorus content ≤0.035%, sulfur content ≤0.030%).

In addition, according to the type of smelting furnace, steel is divided into open hearth steel (acid open hearth, basic open hearth), air converter steel (acid converter, basic converter, oxygen top-blown converter steel) and electric furnace steel. According to the degree of deoxidation during smelting, steel is divided into boiling steel (with incomplete deoxidation), killed steel (with relatively complete deoxidation) and semi-killed steel.

When naming steel products, steel mills often combine the three classification methods of use, composition, and quality. For example, the steel is called ordinary carbon structural steel, high-quality carbon structural steel, carbon spring steel, high-quality carbon tool steel, alloy structural steel, alloy tool steel, etc.

Mechanical properties of metal materials

The performance of metal materials is generally divided into two categories: process performance and use performance. The so-called process performance refers to the performance of metal materials under the specified cold and hot processing conditions in the processing and manufacturing process of mechanical parts. The process performance of metal materials determines its adaptability in the manufacturing process. Due to the different processing conditions, the required process performance is also different, such as casting performance, weldability, forgeability, heat treatment performance, machinability, etc. The so-called performance refers to the performance of metal materials under the conditions of use of mechanical parts, which include mechanical, physical, and chemical properties. The performance of the metal material determines its use range and service life.

In the machinery manufacturing industry, general mechanical parts are used in normal temperature, normal pressure and non-strongly corrosive media, and each mechanical part will bear different loads during use. The ability of metal materials to resist damage under load is called mechanical properties (or mechanical properties).

The mechanical properties of metal materials are the main basis for the design and selection of parts. The nature of the applied load is different (such as tension, compression, torsion, impact, cyclic load, etc.), and the required mechanical properties of the metal material will also be different. Commonly used mechanical properties include: strength, plasticity, hardness, impact toughness, multiple impact resistance and fatigue limit. The various mechanical properties will be discussed separately below.

1. Strength

Strength refers to the ability of metal materials to resist damage (excessive plastic deformation or fracture) under static load. Since the load acts in the form of tension, compression, bending, shearing, etc., the strength is also divided into tensile strength, compressive strength, bending strength, and shear strength. There is often a certain connection between various strengths, and tensile strength is generally used as the most basic strength indicator in use.

2. Plasticity

Plasticity refers to the ability of metal materials to produce plastic deformation (permanent deformation) without damage under load.

3. Hardness

Hardness is a measure of the hardness of metal materials. At present, the most commonly used method for measuring hardness in production is the indentation hardness method, which uses an indenter of a certain geometric shape to press into the surface of the metal material to be tested under a certain load, and the hardness value is determined according to the degree of indentation.

Commonly used methods include Brinell hardness (HB), Rockwell hardness (HRA, HRB, HRC) and Vickers hardness (HV).

4. Fatigue

The strength, plasticity, and hardness discussed above are all indicators of the mechanical properties of metals under static load. In fact, many machine parts are working under cyclic loads, under which conditions the parts will fatigue.

5. Impact toughness

The load acting on the machine at a very large speed is called impact load, and the ability of metal springs to resist damage under impact load is called impact toughness.

Quenching of steel

Quenching is to heat the steel to above the critical temperature, keep it for a period of time, and then quickly put it in the quenching agent to make its temperature drop suddenly, and rapidly cool it at a rate greater than the critical cooling rate to obtain an imbalance dominated by martensite The heat treatment method of the organization. Quenching can increase the strength and hardness of steel, but reduce its plasticity. Quenching agents commonly used in quenching are: water, oil, alkaline water and salt solutions.