Abstract: With the widespread use of aluminum-based copper, the amount of aluminum solder and aluminum wire has increased rapidly. The traditional ingot-extrusion-drawing process can no longer meet the production needs of aluminum wire. Currently, horizontal continuous casting With the drawing and scraping process and semi-continuous ingot, isothermal extrusion and continuous drawing process are the two leading production technologies. This article gives a more detailed overview of common aluminum welding wire production technology, compares the advantages and disadvantages of several processes, discusses the process improvement approach, and points out the development direction of aluminum welding wire. The research results show that the production efficiency of horizontal continuous casting and drawing and scraping is high, but the quality control is difficult. The quality of semi-continuous ingot, isothermal extrusion and continuous drawing process is stable, and the equipment investment is large. The application results show that in the actual production, the aluminum brazing material adopts the extrusion technology, and the aluminum welding wire adopts the horizontal continuous casting.
Keywords: aluminum solder; aluminum wire; horizontal continuous casting; semi-continuous ingot; isothermal extrusion; continuous drawing
CLC number: TG422 TG425
Foreword
Aluminum and its alloys are increasingly used in industrial production and social life. Due to its small specific gravity, good electrical conductivity, good castability, and excellent machinability, aluminum plays an important role in modern industrial materials. In aviation, aerospace, communications, automotive, electronics, home appliances, daily necessities, etc., in order to reduce weight, improve efficiency, and enhance aesthetics, aluminum-based copper and aluminum-based steel have made gratifying achievements. The achievement of these achievements depends to a large extent on the development of welding technology, especially brazing and argon-arc welding. It is of long-term significance to explore the manufacturing technology of aluminum argon arc welding, brazing and brazing, and argon arc welding. .
1 Aluminum solder manufacturing process
At present, there are mainly two kinds of aluminum solder manufacturing processes commonly used in industrial production: one is the ingot-extrusion-drawing process, which is mainly used for the production of brazing materials and some argon-arc welding wires; the other is the casting-linking. Cast - drawing, mainly for the production of argon arc welding wire.
Figure 1 is a flow chart of the ingot-squeeze-drawing process. Figure 2 is a flow chart of the casting process - continuous casting - drawing process. Both production processes have their merits.
2. Ingot casting of aluminum solder - extrusion - drawing process in the ingot of aluminum solder - extrusion - drawing process. The core technology is extrusion, extrusion temperature, extrusion speed, and extrusion deformation index are key parameters; preheating of ingots, preheating of molds, and mold design are also important aspects. Metal mold ingots and semi-continuous ingots are the mainstream in the way of obtaining ingots.
2.1 characteristics of extrusion technology
Among the many advantages of extrusion technology, the following two aspects are more favorable for the production of aluminum solder.
During the extrusion process, the extruded metal in the deformation zone can obtain a more intense and uniform three-directional compressive stress state than rolling or forging, which can fully exert the plasticity of the processed metal itself. Therefore, low-plastic, hard-to-deform metal can be processed by the extrusion method, which is difficult or even impossible to process by the rolling method and the forging method. For example, aluminum-silicon eutectic and aluminum-silicon-copper solder can be drawn after hot extrusion.
Extrusion processing flexibility is very large, only need to change the mold and other extrusion tools, you can produce a variety of shapes and varieties of products in a device, the replacement of the extrusion tool is simple and easy. This feature is particularly suitable for brazing materials with small batch sizes and many specifications.
Extrusion technology still has many problems to be improved. For example: large geometric waste loss, extrusion speed is much lower than the level of continuous casting speed, low production efficiency, slow market response, and large consumption of work tools.
2.2 Status and Prospects of Extrusion Technology
Extrusion technology rose at the beginning of the last century. In the 1920s, 200 tons of extrusion presses were introduced at the front desk. In 1941 Germany's Sehloeman produced 12,000 tons of extruders. At present, the larger extruder in use is the 27,000-tonne extruder of Renault, USA.
Since the advent of extrusion technology, the refinement and development of the extrusion process has never stopped. Cold extrusion, lubrication extrusion, isothermal extrusion, water-cooled die extrusion, continuous extrusion, rapid extrusion, jacket extrusion, hydrostatic extrusion Extrusion techniques such as die-squeezing, plane-die extruding, split-flow combined-die extruding, variable-section extruding, flat extruding, spiral extruding, wide-extrusion extruding, roll extruding, impact extruding, and quenching squeezing are emerging in an endless stream.
The development of extrusion technology is advancing with each passing day, and research on new processes such as superplastic extrusion, liquid extrusion and semi-solid extrusion has made encouraging progress.
2.3 Tooling Design and Manufacturing
With the development of extrusion technology, the design of the tool and die has developed into a new discipline.
Extrusion tool molds include mold frames, mold sleeves, extrusion cylinders, extrusion shafts, extrusion pads, extrusion dies, mold supports, and the like. Mold is the basic tool to ensure product shape, size and precision, and it is also one of the more important factors to ensure the quality of the product inside and outside, affect the extrusion speed and extrusion force. Reasonable mold structure, shape and size can, to a certain extent, control the internal structure and mechanical properties of the product.
The mold design and manufacturing must meet the extrusion process requirements. At the same time, the service life of the extrusion mold is a concern. The selection of mold materials, heat treatment and surface treatment processes, structural design, machining and electrical processing, and use and maintenance are the main factors affecting the life of the mold.
2.4 extrusion of aluminum solder
The blanks of non-ferrous metal welding wire are usually obtained by ingot extrusion. Among them, copper wire (band) and part of aluminum wire (band) are often produced by large-scale non-ferrous metal processing plants. Due to the small production volume of welding materials, production quality The large fluctuations bring a lot of inconvenience to the production organization. The copper-phosphorus solder, silver-based solder and part of aluminum-based solder are produced by professional solder manufacturers. The production is often squeezed by 100--800 ton hydraulic presses.
Aluminum-magnesium and aluminum-manganese welding wires are two types of welding wires that are better extruded. The extrusion performance of aluminum-silicon argon-arc welding wires is acceptable. The extrusion speed of aluminum-silicon solder is low and the efficiency is low. Al-Si-Cu and Al-Si-Cu Zinc is two types of solder that are more difficult to squeeze.
In the production of aluminum solder, low production efficiency, long production cycle, and high proportion of recycled materials are the main reasons affecting economic efficiency.
2.5 Application of Extrusion in Solder Production
Extrusion processing occupies a special position in the production of brazing materials because extrusion technology has long been widely used by domestic and foreign solder manufacturers. The use of extrusion technology to produce solder is more suitable for multi-species and small-batch features than other pressure processing methods. With the continuous advancement of science and technology, people are constantly researching and developing a variety of solder molding techniques. These technologies have good prospects for application, but it is not yet possible to replace extrusion molding. There are two reasons why extrusion is dominant in solder molding. One is the long-term habit of thinking that solder production has been used for extrusion; the second is the technical reliability and stability of extrusion processing. Maturity.
3 Casting of Aluminum Solder - Continuous Casting - Drawing Process
3.1 The performance and requirements of horizontal continuous casting equipment
A complete set of reliable and reliable continuous casting equipment is the key to the aluminum alloy solder melted into filament. The equipment for casting and continuous casting must meet the requirements for adjustment of process parameters in the production process. At the same time, it should also be suitable for the characteristics of small batch production of aluminum solder. The specific technical requirements are:
The detection and control of the liquid level of the insulation package is regulated by an adaptive system.
Furnace volume is compatible with production volume.
In order to accurately control the melt temperature, the holding furnace uses infrared ceramic heating elements to heat up, thermocouples measure the temperature, and the thyristor regulates pressure to achieve thermal equilibrium.
The furnace body is adapted to work at the same time with multiple crystallizers; the cooling intensity of primary and secondary cooling is adjustable.
The pull-out device uses a DC motor equipped with a cycloidal speed reducer as a power source. The speed control of the motor uses a PWM control circuit, and a chain drive is used to achieve multi-head pull. The number of heads for aluminum-manganese welding wire can reach 32 heads. The finer the diameter of the drawn wire drawing, the more favorable it is for drawing. However, if the fine wire diameter brings about a reduction in the drawing speed, it is better to use 4 to 6 mm in half.
3.2 Cost and Reliability of Automatic Control Systems
Aluminum welding wire continuous casting process, drawing speed, melt temperature control and the height of the liquid surface to use adaptive control technology, the use of PLC integrated control technology can be reliably achieved braking control. Manually open-loop controlled equipment is also used in production, but its production stability is poor.
3.3 Thermal balance
The temperature control of the melt is achieved by the balance between the heating capacity of the heating element and the heat dissipation of the system. At the end of the addition of the metal liquid and drawing, the system is shocked by step heat and is in a transient instability state.
In the production, the undercooling of the welding wire is generally stabilized by the use of an isothermally added molten metal and a technical solution for changing the withdrawal speed.
3.4 Productivity
Since the diameter of the continuous casting wire blank is small, and the melt drawing speed is also limited, in practical applications, the production efficiency is bound to be limited. At present, the more advanced technology is to increase the number of drawn wires and adopt a multi-head simultaneous drawing and drawing technique.
There is no "deformation texture" in the brazing material obtained by the melt drawing, which has a certain influence on the cold forming processing efficiency in the subsequent production. Without adding any influence on the performance of solder, adding titanium, boron, and grain refinement technology can improve the pass processing rate.
3.5 Solder Chemical Composition Control
Welding materials are precision alloys, the chemical composition of which allows for small fluctuations in the amplitude; the more detrimental to compositional control is the presence of volatile, oxidative, and easily depleting elements (eg, zinc) in the solder. The above two factors make the control of the main component of the solder important and difficult.
In production, it is inevitable to use recycled waste, which makes the control of trace elements and impurity elements challenging.
In production practice, half is based on the theory of mathematical statistics to control the main components and impurity elements, and adopts the method of sample analysis before final product to determine whether it is qualified or not.
3.6 Control of microstructure of solder
Casting - continuous casting - the segregation of components in the drawing process is unavoidable, and the focus of quality control lies on how to reduce and eliminate it.
The more common forms of segregation in horizontal continuous casting are: specific gravity segregation, dendrite segregation, grain boundary segregation, and regional segregation.
The specific gravity segregation is due to the large difference in the specific gravity between the components in the molten metal, which results from the floating or sinking of the solute when the heat-retaining package and the cooling are slow. The related factors include the properties of the solder, the cooling rate, the specific gravity of the primary crystal, the shape and size, and the casting process. If the alloy solution is allowed to stand for a long time before drawing, serious segregation of the specific gravity will occur.
Dendritic segregation is particularly prominent in solid solution alloys with large solid-liquidus differences. The cause of this is the result of the selective crystallization of the alloy within the solidification temperature range, which results in different concentrations of the successively formed crystalline components. The dendrite segregation of some solders is very serious.
Grain boundary segregation causes low-melting point matter to accumulate in the grain boundary. Since the grain boundary segregation cannot be eliminated by homogenization annealing, the damage can be extended to the hot cracking and grain boundary corrosion of the brazed joint after brazing.
Regional segregation has positive segregation and segregation. It is worth noting that regional segregation also exists in the ingot-extrusion brazing process.
In production practice, the following measures are generally used to prevent or reduce segregation: deteriorating treatment, stirring the melt, lowering the temperature, increasing the cooling intensity, strengthening the secondary water cooling, and subsequent diffusion annealing.
3.7 Drawing and Scratching of Aluminum Solder
In the plastic processing technology of aluminum solder, single wire drawing machine, looper wire drawing machine, pulley wire drawing machine, straight wire drawing machine and straight wire drawing machine all have applications. At present, the in-line drawing machine has high production efficiency and good product quality.
Aluminum solder surface treatment process ultrasonic cleaning; hot concentrated alkali solution cleaning concentrated nitric acid photochemical, and then washed with water; scraping skin fine scraping silk skin technology. Among them, the fine scraping technology is more advanced, mainly in the cleanliness of the wire surface, and the resistance to atmospheric corrosion is better than that of concentrated alkali cleaning.
4 Conclusion
(1) At present, the manufacture of aluminum brazing alloys uses ingot-extrusion-drawing process. The quality of semi-continuous ingot casting, isothermal extrusion and continuous drawing process is stable, but the equipment investment is large.
(2) Casting - continuous casting - The drawing process begins to be applied in the production of aluminum argon arc welding wire. Horizontal continuous casting and drawing and scraping process have high production efficiency, but quality control is difficult.
(3) The straight-in drawing and scraping process is an advanced process for improving the production efficiency of aluminum solder and ensuring the quality of aluminum solder products.
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About the author: Zhang Qiang, born in 1973, engineer, is mainly engaged in welding material processing work.
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