What is an aluminum pipe

What is an aluminum pipe?

Aluminum pipe is a kind of non-ferrous metal pipe, which is made of pure aluminum or aluminum alloy by extrusion into a hollow metal tubular material along its longitudinal full length.

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Classification of aluminum pipes

Aluminum pipes are mainly divided into the following types:
According to the shape, it is divided into square pipe, round pipe, patterned pipe, special-shaped pipe and universal aluminum pipe.
According to the extrusion method, it is divided into seamless aluminum pipe and ordinary extruded pipe.
According to accuracy, it is divided into ordinary aluminum pipe and precision aluminum pipe. Precision aluminum pipe generally needs to be reprocessed after extrusion, such as cold drawing, fine drawing and rolling。
By thickness: ordinary aluminum pipe and thin-wall aluminum pipe。
Performance: corrosion resistance, light weight.

Characteristics of aluminum pipes

  • It is a kind of high-strength hard aluminum, which can be strengthened by heat treatment. It has medium plasticity in annealing, rigid quenching and thermal state, and good spot welding. When gas welding and argon arc welding are used, the aluminum pipe tends to form intergranular cracks;
  • The machinability of aluminum pipe after quenching and cold work hardening is good, but it is poor in annealing state. The corrosion resistance is not high. Anodizing and painting methods or aluminum coating on the surface are often used to improve the corrosion resistance. It can also be used as mold material.

Advantages of aluminum pipe

  • The advantages of welding technology: the welding technology of thin-walled copper aluminum pipe suitable for industrial production is known as a world-class problem, and it is the key technology of replacing copper with aluminum for the connecting pipe of air conditioner.
  • The advantage of service life: from the perspective of the inner wall of the aluminum pipe, since the refrigerant does not contain water, the inner wall of the copper aluminum connecting pipe will not be corroded.
  • Energy saving advantages: the lower the heat transfer efficiency of the connecting pipeline between the indoor unit and the outdoor unit of the air conditioner, the more energy-saving, or the better the thermal insulation effect, the more power-saving.
  • Excellent bending performance, easy to install and move.

Surface treatment of aluminum pipe

  • Chemical treatment: oxidation, electrophoretic coating, fluorocarbon spraying, powder spraying, wood grain transfer printing;
  • Mechanical treatment: mechanical wire drawing, mechanical polishing, sand blasting.

Application of aluminum pipe

Aluminum pipes are widely used in all walks of life, such as automobile, ship, aerospace, aviation, electrical appliances, agriculture, electromechanical, home, etc. aluminum pipes are everywhere in our life.

Use of aluminum pipes with different alloys and different processing processes

Aluminum pipe is widely used in the electronic industry because of its light weight, good strength, easy processing, good conductivity and other characteristics. Different alloys and different processing processes are suitable for different products. Nowadays, most aluminum alloys are represented by the international four digits.

  • 1. The amount of aluminum is not less than 99%, which belongs to pure aluminum, relatively soft and good conductivity;
  • 2 series has high copper content and high hardness, and is often aviation aluminum;
  • 3 Series manganese, rust proof, good weldability and good ductility, also known as rust proof aluminum;
  • 4 series alloy has high silicon content and has the characteristics of heat resistance and wear resistance;
  • 5 series has high magnesium content, also known as aluminum magnesium alloy, which is characterized by low density, high tensile strength and high elongation;
  • 6 series is aluminum magnesium silicon alloy with high strength, good processability and good surface treatment performance.
  • Processing technology of aluminum.

Aluminum processing technology includes rolling aluminum plate, hot extrusion profile, fine drawing aluminum pipe after extrusion, continuous cold extrusion aluminum pipe, reverse extrusion seamless pipe, etc. Hot extrusion can produce various shapes of complex profiles with high production efficiency. It is widely used in industrial and civil products.
However, the tolerance of hot extruded profiles is generally large. If you want aluminum pipe products with high precision, you can add cold processing and fine drawing later, which can not only improve the dimensional accuracy, but also greatly enhance the strength and hardness of products for profiles that cannot be strengthened by aging, such as 1060 and 3003 aluminum pipes. Of course, processing costs have also increased. Therefore, we should choose appropriate alloy and processing technology according to different uses and requirements of products, and do not blindly pursue accuracy

Why should aluminum pipes be oxidized

The oxidation of aluminum pipe refers to a material protection technology, also known as surface anodizing, which forms an oxide film on the surface of aluminum pipe through external anodic current in electrolyte solution. After anodizing, the corrosion resistance, hardness, wear resistance, insulation and heat resistance of aluminum pipe materials or products are greatly improved. The most anodized metal material is aluminum. Anodizing of aluminum pipes is generally carried out in acidic electrolyte with aluminum as anode. In the process of electrolysis, the anion of oxygen reacts with aluminum to produce oxide film. The film is not fine enough at the beginning of formation. Although there is a certain resistance, the negative oxygen ions in the electrolyte can still reach the aluminum surface and continue to form an oxide film. With the increase of film thickness, the resistance increases and the electrolytic current decreases. At this time, the outer oxide film in contact with the electrolyte is chemically dissolved. When the rate of oxide formation on the aluminum surface is gradually balanced with the rate of chemical dissolution, the oxide film can reach the maximum thickness under this electrolytic parameter. The outer layer of the anodic oxide film of aluminum is porous and easy to absorb dyes and colored substances, so it can be dyed and improve its decoration. After hot water, high temperature steam or nickel salt sealing treatment, the corrosion resistance and wear resistance of the oxide film can be further improved. In addition to aluminum, magnesium alloy, copper and copper alloy, zinc and zinc alloy, steel, cadmium, tantalum, zirconium and other metals with surface anodizing treatment in industry.

What is the difference between aluminum alloy pipe and aluminum pipe?

Aluminum pipe and aluminum alloy pipe are still common metal pipe fittings in daily life. People may know what their use attributes are when they are separated, but the concept may be vague when they are put together. In fact, not only individuals can’t distinguish them, but most of them can’t be distinguished when they are put together. Today, Xinlianchang aluminum small series will help you distinguish the difference between the two.
Aluminum pipe is a kind of high-strength hard aluminum, which can be strengthened by heat treatment. It has medium plasticity in annealing, rigid quenching and thermal state, and good spot welding. When gas welding and argon arc welding are used, aluminum pipe tends to form intergranular cracks; The machinability of aluminum pipe after quenching and cold work hardening is good, but it is poor in annealing state. The corrosion resistance is not high. Anodizing and painting methods or aluminum coating on the surface are often used to improve the corrosion resistance.

The density of aluminum alloy pipe is low, but the strength is relatively high. It is close to or higher than high-quality steel. It has good plasticity and can be processed into various profiles. It has excellent conductivity, thermal conductivity and corrosion resistance. It is widely used in industry, and the usage is only second to that of steel. Aluminum alloy pipe can use heat storage to obtain good mechanical properties, physical properties and corrosion resistance.

Heat treatment technology of aluminum pipe

Aluminum tube heat treatment technology is a process in which the metal workpiece is heated to a suitable temperature in a certain medium, maintained at this temperature for a certain time, and then cooled at different speeds. Heat treatment of aluminum tube is one of the most important processes in material production. Compared with other processing processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but endows or improves the service performance of the workpiece by changing the internal microstructure of the workpiece or the chemical composition of the surface of the workpiece. It is characterized by improving the internal quality of the workpiece, which can not be observed by the naked eye.
Heat treatment technology aluminum tube refers to annealing, normalizing, quenching (solid solution) and tempering (aging):

  • (1) Annealing refers to heating the workpiece to an appropriate temperature, adopting different holding time according to the material and the size of the workpiece, and then cooling slowly. Its purpose is mainly to reduce the hardness of the material and improve the plasticity, so as to facilitate subsequent processing, reduce residual stress and improve the uniformity of microstructure and components. Annealing can be divided into recrystallization annealing, stress relief annealing, spheroidization annealing, complete annealing and so on.
  • (2) Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to annealing, but the microstructure is finer. It is often used to improve the cutting performance of materials, and sometimes used for the final heat treatment of some parts with low requirements.
  • (3) Quenching refers to the rapid cooling of the workpiece in water, oil or other inorganic salt, organic aqueous solution quenching medium after heating and insulation.
  • (4) After quenching, the material is an unbalanced structure, which is usually very hard and brittle. It needs to be kept warm for a long time at a temperature higher than room temperature and then cooled. This process is called tempering (aging).

As can be seen from the above definition, whether annealing, normalizing, quenching or tempering, the workpiece shall be heated, insulated and cooled during heat treatment. Therefore, in metal heat treatment, heating speed, holding time and cooling speed become the most important process parameters in heat treatment process.
Among the “four fires”, quenching and tempering (aging) are most closely related, and they are often used together. However, in actual production, in order to save cost and improve production efficiency, on-line quenching is often used to replace quenching furnace quenching and natural aging is used to replace tempering for products with low performance requirements. For example, when extruding aluminum alloy 6061 aluminum pipe, due to the low quenching sensitivity of these alloys, silicon and magnesium dissolve quickly above the solid solution temperature. Therefore, supersaturated solid solution with large solid solution can also be obtained by air-cooled quenching when the outlet temperature of extruded material is higher than the solid solution temperature.

Welding of aluminum pipe and aluminum products

Aluminum pipe and aluminum alloy have unique physical and chemical functions. Its appearance is silver gray, low density, low resistivity and large linear expansion coefficient. Because aluminum has a face centered cubic structure, there is no change in isomerism and “ductility brittleness”, it has excellent low temperature resistance and can maintain excellent mechanical function at low temperature. In addition, aluminum and aluminum alloys also have excellent corrosion resistance, high specific strength (intensity/density), and excellent reflectivity to heat and light. No spark and no magnetism during grinding.
Aluminum pipe and aluminum alloy are very simple to process and form. It can be made into a variety of products by casting, rolling, stamping, wire drawing, pressing, drawing and rolling. It can also be made into products of different shapes by hammering, forging and kneading. Aluminum and aluminum alloys are easy to machine and have high processing speed, which is also one of the important elements of using aluminum parts. The change range of mechanical function, electrochemical function, chemical or paint finishing of aluminum is also wide.
The melting point of pure aluminum is 660 ℃. The melting point of aluminum alloy changes between 482 ℃ – 660 ℃ with the different alloy elements. When aluminum and aluminum alloys are heated from room temperature to melting state, there is no color change, which makes it difficult to judge whether they are close to the melting point.
The mechanical function of aluminum pipe and aluminum alloy changes with its purity. The higher the purity, the lower the strength and the higher the plasticity. For example, the minimum tensile strength of industrial pure aluminum hot rolled plate is between 70-110mpa, the tensile strength of industrial high-purity aluminum is only 50MPa, and the tensile strength of aluminum magnesium alloy is more than 170Mpa. Another characteristic of aluminum and aluminum alloys is that the tensile strength decreases with the increase of temperature; When the temperature decreases, the tensile strength increases and the elongation increases.
Compared with steel, aluminum has high thermal conductivity and requires high heat input during welding. Preheating is required when welding large sections. When resistance welding is used, compared with welded steel parts, aluminum needs larger current and shorter welding time to accurately control welding parameters because of its high conductivity. Because aluminum is non-magnetic, when DC welding is used, the arc will not blow off. Therefore, it can be used as a welding baffle and fixture.
Aluminum pipe and aluminum alloy, when exposed to air, will soon form a strong adhesive and heat-resistant oxide film. Before welding, it is necessary to carefully remove this oxide film, so that the matrix and filler metal can fuse well during welding; In fiber welding, the solder has good fluidity. The oxide film can be removed by solvent or by the effect of welding arc in lazy atmosphere, perhaps by mechanical or chemical methods.
The existence of oxide film also has a protective effect on aluminum pipe and aluminum alloy. Due to its fine arrangement and strong binding force with aluminum, it can prevent the continuous oxidation of aluminum metal and protect the metal from damage. Moreover, the higher the purity of aluminum, the more favorable the corrosion. Due to the existence of impurities, in addition to affecting the adhesion between oxide film and metal, it may also lead to other forms of corrosion. According to this feature of the oxide film, aluminum is often used as the storage container for the media that can promote the formation of the oxide film and do not work with it, such as nitric acid and wax acid, while the media that can damage the film, such as hydrochloric acid, alkali and table salt, can quickly damage the oxide film and corrode aluminum, which is a fierce corrosive agent for aluminum, Therefore, aluminum cannot be used as a container for the storage of such media.
Although many difficult factors will be encountered in the welding process of aluminum pipe and aluminum alloy, aluminum and aluminum alloy have some unparalleled advantages compared with other materials such as copper. Therefore, aluminum and aluminum alloy welding products are increasingly widely used in aviation, aerospace, cars, machinery manufacturing, electronics, chemical industry, light industry, railways and other aspects. China has a vast territory and abundant resources, aluminum resources are very rich, and the cost of development and utilization is low. Aluminum and aluminum alloy welding has a very promising future in China.

Source: China Aluminum Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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