What is aluminum alloy
What is aluminum alloy?
Aluminum alloy is an alloy based on aluminum and added with a certain amount of other alloying elements. It is one of the light metal materials. In addition to the general characteristics of aluminum, aluminum alloys also have some specific characteristics of alloys due to the different types and quantities of alloying elements. The density of aluminum alloy is 2.63 – 2.85g/cm and has high strength（σb is 110 – 650MPa), the specific strength is close to that of high alloy steel, and the specific stiffness is higher than that of steel. It has good casting performance and plastic processing performance, good electrical and thermal conductivity, good corrosion resistance and weldability. It can be used as structural materials. It is widely used in aerospace, aviation, transportation, construction, electromechanical, lightweight and daily necessities.
Aluminum alloy is one of the most widely used non-ferrous structural materials in industry, which has been widely used in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industry. With the rapid development of science and technology and industrial economy, the demand for aluminum alloy welded structural parts is increasing day by day, which makes the research on the weldability of aluminum alloy in-depth. The wide application of aluminum alloy promotes the development of aluminum alloy welding technology. At the same time, the development of welding technology expands the application field of aluminum alloy. Therefore, the welding technology of aluminum alloy is becoming one of the research hotspots.
Name, composition and application of commonly used structural etchants for aluminum and aluminum alloys
|1||Dilute sodium hydroxide aqueous solution||
Sodium hydroxide 15-25g,
Time: 1 – 4min
|The macrostructure of aluminium and its alloys is shown|
|2||0.5% hydrofluoric acid aqueous solution||
Hydrofluoric acid 0.5ml,
distilled water 100ml
Time: 10 – 40min
|It is suitable for most aluminum and aluminum alloys. Compounds containing Fe and Ni are brown yellow and Si is dark red|
|3||Sodium hydroxide aqueous solution||
Sodium hydroxide 10-15g,
distilled water 100ml
Temperature: 50 – 70 ℃,
Time: about 5 seconds
|Exposure of grain boundaries of aluminum and aluminum alloys|
|4||25% nitric acid aqueous solution||
distilled water 75ml,
nitric acid 25ml
Temperature: 70 ℃,
|It is suitable for most aluminum and aluminum alloys, especially for aluminum alloys containing copper|
Classification of aluminium and aluminium alloys
Wrought aluminum alloy
Aluminum alloy with high strength, high specific strength and suitable for plastic forming.
Wrought aluminum alloy can be divided into:
- Industrial pure aluminum
- Non strengthening aluminum alloy by heat treatment
- Aluminum alloy strengthened by heat treatment
Cast aluminum alloy
It is suitable for filling the mold in molten state to obtain aluminum alloy with certain shape and size.
Cast aluminum alloy is divided into:
- Al Si alloy
- Aluminum copper alloy
- Aluminum magnesium alloy
- Al Zn Alloy
Grades of aluminium and aluminium alloys
According to the content of aluminum and other elements in aluminum alloy:
- (1) Pure aluminum: pure aluminum is divided into high-purity aluminum, industrial high-purity aluminum and industrial pure aluminum according to its purity. The welding is mainly industrial pure aluminum. The purity of industrial pure aluminum is 99.7% to 98.8%, and there are six brands, such as l1.l2.l3.l4.l5.l6.
- (2) Aluminum alloy: aluminum alloy is obtained by adding alloying elements to pure aluminum. According to the processing characteristics of aluminum alloys, they can be divided into deformation aluminum alloys and casting aluminum alloys. Wrought aluminum alloy has good plasticity and is suitable for pressure machining.
Wrought aluminum alloys can be divided into antirust aluminum (LF), hard aluminum (ly), super hard aluminum (LC) and forged aluminum (LD) according to their performance characteristics and applications. Cast aluminum alloys can be divided into aluminum silicon system (Al Si), aluminum copper system (Al Cu), aluminum magnesium system (Al Mg) and aluminum zinc system (Al Zn).
The main aluminum alloy grades are: 1024.2011.6060, 6063.6061.6082.7075
|Pure aluminum (aluminum content not less than 99.00%)||1XXX|
|Aluminum alloy with copper as the main alloy element||2XXX|
|Aluminum alloy with manganese as the main alloy element||3XXX|
|Aluminum alloy with silicon as the main alloy element||4XXX|
|Aluminum alloy with magnesium as the main alloy element||5XXX|
|Aluminum alloy with magnesium and silicon as main alloying elements and Mg2Si phase as strengthening phase||6XXX|
|Aluminum alloy with zinc as the main alloy element||7XXX|
|Aluminum alloy with other alloy elements as main alloy elements||8XXX|
|Spare alloy set||9XXX|
- The first digit of the brand indicates the alloy system (main alloy element).
- The third and fourth digits of the brand name represent the identification of alloys with different chemical compositions.
- The second letter of the brand indicates the modification of the original pure aluminum or aluminum alloy, and the last two digits indicate that the last two digits of the brand identify different aluminum alloys in the same group or indicate the purity of aluminum.
- 1×××: the last two digits of the series brand are expressed as percentage points of the lowest aluminum content. For example, 1050,1070 indicates that the aluminum purity is more than 99.50% and 99.70% respectively. The second letter of the brand indicates the modification of the original pure aluminum.
- 2××× – 8×××: the last two digits of the series brand have no special significance and are only used to distinguish: different aluminum alloys in the same group. The second letter of the brand indicates the modification of the original pure aluminum.
*Status of aluminium and aluminium alloys:
- Code F×× Is: free machining status;
- O×× As: annealing state;
- H××As: work hardening state;
- W×× As: solid fusion heat treatment state;
- T×× Is: heat treatment state (different from F, O and H States).
*H×× Subdivision status of: the first digit after H indicates the basic handler to obtain this status, as shown below.
- H1: simple work hardening state;
- H2: work hardening and incomplete annealing state;
- H3: work hardening and stabilization state;
- H4: work hardening and painting state h.
The second digit after H indicates the work hardening degree of the product. For example, 0 – 9 represents that the work hardening degree is getting harder and harder.
*Rolling of aluminum alloy plate and strip: according to the rolling temperature, it can be divided into hot rolling, warm rolling (medium temperature rolling) and cold rolling. According to the arrangement of rolling mills, it can be divided into single stand rolling, semi continuous rolling and continuous rolling.
Characteristics of aluminum and aluminum alloy (aluminum profile)
Compared with other metal materials, aluminum and aluminum alloys have the following characteristics:
1. Low density
The density of aluminum and aluminum alloy is close to 2.7g/and about 1/3 of that of iron or copper.
2. High strength
Aluminum and aluminum alloys have high strength. After a certain degree of cold working, the matrix strength can be strengthened, and some brands of aluminum alloys can also be strengthened by heat treatment.
3. Good conductivity
The electrical and thermal conductivity of aluminum is second only to silver, copper and gold.
4. Good corrosion resistance
The surface of aluminum is easy to naturally produce a layer of dense and firm Al2O3 protective film, which can well protect the matrix from corrosion. Through artificial anodizing and coloring, cast aluminum alloy with good casting performance or deformed aluminum alloy with good processing plasticity can be obtained.
5. Easy processing
After adding certain alloying elements, cast aluminum alloy with good casting properties or deformed aluminum alloy with good processing plasticity can be obtained.
Application of aluminum alloy
Aluminum alloy has the characteristics of low density, good mechanical properties, good processability, non-toxic, easy recovery, excellent conductivity, heat transfer and corrosion resistance. It is widely used in marine industry, chemical industry, aerospace, metal packaging, transportation and other fields.
Aluminum alloy is the main material for making aircraft. Compared with mild steel for automobile, aluminum alloy has expensive price and low density, with a relative density of 2.8. Compared with mild steel with a relative density of 7.8, it is about one-third lighter. Although the strength difference is not much, for aircraft, light material is the most important, with strong corrosion resistance and convenient processing. Therefore, aluminum alloy is the most ideal material for aircraft.
Duralumin can manufacture rivets, aircraft propellers and high-strength parts on aircraft according to its different alloy element content; Superhard aluminum is a kind of hard aluminum containing zinc. Its hardness and strength are higher than that of hard aluminum. Different kinds of superhard aluminum are used to manufacture various structural parts and high load parts. It is one of the important materials in the aviation industry.
2. Marine industry
Aluminum and aluminum alloys are more and more widely used in the shipbuilding industry, ranging from motor boats to 10000 ton oil tankers, from offshore hovercraft to submarine, from civil to military, from fishing ships to marine mining ships. Aluminum alloys with excellent comprehensive performance are used to produce ship shells, support structures, supporting facilities, pipelines, etc.
The application of aluminum alloy in marine industry can reduce the overall weight of the ship, improve the running speed of the ship, and resist the corrosion of seawater to the ship. Aluminum alloys used in marine industry are mainly aluminum copper alloy, aluminum magnesium alloy and aluminum silicon alloy. Aluminum copper alloy is widely used in ships in China and Russia, but its poor seawater corrosion resistance hinders its development in the shipbuilding industry. Aluminum magnesium alloy is mainly used for hull shell, water pump conduit, pump shell and base support, with grades of 5083, 5086, 5456, 5466, etc. Aluminum silicon alloy has moderate structural strength, good fluidity and strong filling capacity. It is easy to produce parts with high density and complex structure, such as high-pressure valve, cylinder block, pump, reducer housing, turbine blade, etc.
3. Application in chemical industry
Aluminum has good thermal conductivity. Aluminum and aluminum alloys are widely used in the production of heat exchange equipment in chemical equipment, storage tanks resistant to concentrated nitric acid corrosion, adsorption filters, fractionators, pipelines and many linings. Cast aluminum alloy has good fluidity, strong mold filling ability, small shrinkage, not easy to form cracks, good corrosion resistance (aluminum oxide and silicon dioxide protective film can be formed on its surface), light weight and good mechanical properties. It is widely used to manufacture corrosion-resistant parts with complex structure, such as cylinders, pipe fittings, valves, pumps, pistons, etc. Aluminum has many special uses in chemical production. Aluminum does not produce sparks, and aluminum alloy can produce containers containing easily volatile substances; Aluminum is non-toxic, will not cause food deterioration, will not affect the appearance of goods and will not corrode goods. Therefore, aluminum alloy is widely used to make relevant equipment in food chemical industry.
4. Application in metal packaging industry
Aluminum alloy can be used for metal packaging, which has the following excellent characteristics: good mechanical properties, light weight, high compressive strength, durability, easy to store and transport goods; Good barrier performance, can block the damage of sunlight, oxygen and humid environment to articles, and can prolong the shelf life of articles; Good texture and aesthetic feeling. Aluminum alloy is used as packaging, with unique metallic luster, good touch feeling and beauty, so as to improve the quality of goods; Non toxic, easy to recycle, recyclable, saving resources and reducing environmental pollution. Aluminum alloy is widely used in beer, beverage and other food cans, mostly in stamping and drawing structure. Aluminum foil utensils are beautiful, light and good heat transfer. They are used in the packaging of fast food. They have the effects of fresh preservation, taste preservation and non-toxic. They are used by more and more food industries. The aluminum alloy metal hose can be extruded and deformed, and the contents can be used after extrusion. It is simple and convenient. It is commonly used in the packaging of paste cosmetics.
5. Application in other industries
Aluminum alloy has high specific strength, light weight, good fluidity, strong filling capacity, good corrosion resistance and low melting point. It is widely used in tractor, locomotive parts, electronic products, medical devices, building decoration and other industries. Aluminum alloy has excellent ductility and is widely used in daily necessities industry and food industry. In the field of power transmission, aluminum alloy conductor has attracted more and more attention because of its low cost, light weight, good corrosion resistance, heat transfer, easy conductivity and wear resistance. In the field of power transmission, aluminum alloy is used the most, and up to 90% of high-voltage conductor materials are aluminum products. Al Si alloy can be used as a good deoxidizer to reduce the sensitivity of steel to subcutaneous bubbles, deoxidize steel and improve the quality of steel. The market consumption of Al Si alloy is large, and the national annual demand is up to one million tons.
I. JISA.A1000 series – pure aluminum series
- 1. 1060 as a conductive material, IACS guarantees 61%, and 6061 wire is used when strength is required.
- 2. 1085,1080,1070,1050,1N30,1085,1080,1070,1050 – good formability and surface treatment, and its corrosion resistance is the best among aluminum alloys. Because it is pure aluminum, its strength is low. The higher the purity, the lower the strength. Daily necessities, aluminum plate, lighting appliance, reflector, decoration, chemical industry container, heat sink, solution wiring, conductive material.
- 3. 1100,1200al general purpose aluminum with purity of more than 99.0% is slightly white after anodizing, which is the same as the above. General utensils, heat sink, bottle cap, printing board, building materials and heat exchanger assembly 1n00 – strength is slightly higher than 1100, good formability, and its chemical characteristics are the same as 1100.
II. Daily necessities 2000 series – alxcu series
- 1. 2011 fast cutting alloy, good machinability and high strength. But the corrosion resistance is poor. When corrosion resistance is required, 6062 series alloy volume shaft, optical components and screw head shall be used.
- 2. 2014,2017,2024 contains a large amount of Cu, which has poor corrosion resistance, but high strength. It can be used as structural materials. Forgings can also be used for aircraft, gears, oil, pressure components and axles.
- 3. After solid solution heat treatment, 2117 is used as hinge nail material, which is an alloy to delay the aging rate at room temperature.
- 4. 2018,2218 alloy for forging. It has good forging property and high high temperature strength. Therefore, it is used for forgings requiring heat resistance. It has poor corrosion resistance, such as cylinder head, piston and VTR cylinder.
- 5. 2618 alloy for forging. High temperature strength is superior, but corrosion resistance is poor. Piston, die for rubber forming, general heat-resistant components.
- 6. 2219 has high strength, good low and high temperature characteristics, excellent solubility, but poor corrosion resistance. Cryogenic vessels, aerospace machines. 7. 2025 alloy for forging. Good forging property and high strength, but poor corrosion resistance. Propeller, magnetic barrel. 2n01 – alloy for forging. It has heat resistance and high strength, but poor corrosion resistance. Aircraft engine, oil pressure components.
III 3000 series – alxmn series
- 1. The strength of 3003,3203 is about 10% higher than 1100, and its formability, solubility and corrosion resistance are good. General utensils, heat sink, cosmetic board, photocopier drum, marine materials.
- 2. 3004,3104 has higher strength than 3003, superior formability and good corrosion resistance. The strength of aluminum tank, lamp cap, roof plate, color aluminum plate 3 and 3005,3005 is about 20% higher than that of 3003, and the corrosion resistance is also better. Building materials, color aluminum plate.
- 4. The strength of 3105,3105 is slightly higher than that of 3003, and other characteristics are similar to that of 3003. Building materials, color aluminum plate, bottle cap.
IV 4000 series – alxsi series
- 1. 4032 has good heat resistance, abrasion resistance and low coefficient of thermal expansion. Piston, cylinder head.
- 2. 4043 has less solidification shrinkage and is treated with sulfuric acid anodizing, showing a natural gray color. Dissolving wiring, building panel.
V 5000 Series – alxmg series
- 1. The strength of 5005 is the same as that of 3003, with good processability, solubility and corrosion resistance. The modification processing after anodizing is good, which is commensurate with the color of 6063 shape material. Interior and exterior decoration for construction, interior decoration for vehicles and interior decoration for ships.
- 2. 5052 is the most representative alloy with medium strength. It has good corrosion resistance, solubility and formability, especially high fatigue strength and good seawater resistance. General sheet metal, ships, vehicles, buildings, bottle caps, honeycomb plates.
- 3. 5652 restricts the impure elements of 5052 and inhibits the separation of hydrogen peroxide. Other characteristics are about 20% higher than 5052 in strength with 5052 and hydrogen peroxide containers 4 and 5154. Other characteristics are the same as 5052 and pressure vessel
- 5. 5254 limits the impure elements of 5154 and inhibits the decomposition of hydrogen peroxide. Other properties are the same as 5154.
- 6. The strength of the 5454 is about 20% higher than that of the 5052, and its characteristics are roughly the same as those of the 5154, but its corrosion resistance in vicious environment is better than that of the 5154. Car wheels.
- 7. 5056 has excellent corrosion resistance, cutting and working surface modification, good anodizing and dyeing. Camera body, communication machine components, zipper.
- 8. 5082 has similar strength to 5083 and good formability and corrosion resistance. Tank cover.
- 9. The strength of 5182 is about 5% higher than that of 5082, and other characteristics are the same as that of 5082. Tank cover.
- 10. 5083 alloy for fusion construction. It is the highest strength corrosion-resistant alloy in practical non heat treated alloys and is suitable for solution bonding structures. Ships, vehicles, low temperature vessels and pressure vessels with good seawater resistance and low temperature characteristics.
- 11. 5086 has higher strength than 5154. It is a non heat treatment fusion structure alloy with good seawater resistance. Ship, pressure vessel and magnetic disc 5n01 – the strength is the same as that of 3003, and the anodizing treatment after brilliant treatment can have high brilliance. Good formability and corrosion resistance. Kitchen supplies, cameras, decorations, aluminum 5n02 hinge nail alloy, with good seawater resistance.
Ⅵ 6000 series – alxmgxsi series
- 1. 6061 heat treated corrosion resistant alloy. T6 treatment can have a very high endurance value, but the strength of the fusion interface is low. Therefore, the extrusion alloy used in 6n01 for screws, hinged nails, ships, vehicles and land structures has the middle strength of 6061 and 6063. It has good extrusion, stamping and quenching properties. It can be used as a large thin meat material with complex shapes, with good corrosion resistance and fusion properties. Vehicles, land structures, ships.
- 2. 6063 is a representative extrusion alloy with lower strength than 6061 and good extrudability. It can be used as a shape material with complex section shape. It has good corrosion resistance and surface treatment. It is used in buildings, highway guardrails, high hurdles, vehicles, furniture, household appliances and decorations
- 3. 6101 high strength conductive material. 55% IACS guaranteed wires.
- 4. 6151 has excellent forging processability, corrosion resistance and surface treatment. It is suitable for complex forging products. Mechanical and automotive components 5 and 6262 have better corrosion resistance and surface treatment than 2011, and their strength is the same as 6061. Camera body, oxidizer assembly, brake assembly and gas appliance assembly.
VII 7000 series – alxznxmg series
- 1. 7072 electrode has low potential. It is mainly used for anti-corrosion covering leather materials. It is also suitable for heat sink of heat exchanger. Aluminum alloy sheet leather, heat sink.
- 2. 7075 aluminum alloy is one of the alloys with the highest strength, but its corrosion resistance is poor. The coating material with 7072 can improve its corrosion resistance, but the cost is increased. Aircraft and ski poles 7050, 7050 are alloys that improve the quenchability of 7075. They have good stress corrosion cracking resistance. They are suitable for 7N01 fusion structure alloys for thick plates, forged aircraft and high-speed rotating bodies. They have high strength. Moreover, the strength of the fusion part can be returned to the strength close to the base metal when placed at room temperature. Corrosion resistance is also very good. Vehicles, other land structures and aircraft.
- 3. 7003 extrusion alloy for fusion structure has slightly lower strength than 7N01, but good extrudability. It can be used as a large shape material with thin meat. Other properties are roughly the same as 7N01. Outer ring of vehicle and locomotive wheel.
Manufacturing process of aluminum alloy
Aluminum alloy is obtained by refining raw aluminum and recovered aluminum obtained by electrolysis, and then adding elements to it.
The process of electrolytic raw aluminum is to extract alumina from bauxite by Bayer method, and then electrolytic aluminum by ERU hall method.
Electrolysis is an application of electrochemistry. The so-called electrolysis is a process in which the electrolytic cell is driven by electric energy and the product is separated by the oxidation-reduction reaction on the cathode or cathode of the electrolytic cell. These products are useful to us.
The principle of electrolytic aluminum smelting is the same. But electrolytic aluminum uses a special electrolyte, not an aqueous solution. Aluminum cannot be obtained by electrolysis in aqueous solution. The method of electrolytic melting alumina is adopted. Alumina (alumina) is an ionic compound. It is usually solid. Ions cannot move easily in solids. Only when they are heated above the melting point and melted into liquid, can ions migrate between cathode and anode under the drive of electric field to form ionic conductors. However, the melting point of alumina is very high. Before heating it to melting, most of the structural materials used to make electrolytic cells, such as steel, are melted first. Therefore, it should be dissolved in a suitable solvent to form a special solution. The solvent used is cryolite and sodium hexafluoroaluminate. In this way, the working temperature of electrolytic aluminum can be reduced below 1000 ℃ (generally 950 ℃ – 970 ℃).
Heat treatment and quenching process of aluminum alloy
The heat treatment of aluminum alloy is to select a certain heat treatment specification, control the heating speed to rise to a certain corresponding temperature, hold it for a certain time and cool it at a certain speed to change the structure of the alloy. Its main purpose is to improve the mechanical properties of the alloy, enhance the corrosion resistance, improve the processing function and obtain the dimensional stability.
It is well known that for steels with high carbon content, high hardness and low plasticity can be obtained immediately after quenching. However, it is not the case for aluminum alloy. After quenching, the strength and hardness do not increase immediately, but the plasticity does not decrease, but increases. However, when the quenched alloy is placed for a period of time (e.g. 4 – 6 days and nights), the strength and hardness will be significantly improved, while the plasticity will be significantly reduced. The phenomenon that the strength and hardness of aluminum alloy increase significantly with time after quenching is called aging. Aging can occur at room temperature, called natural aging, or in a temperature range higher than room temperature (such as 100 – 200 ℃), called artificial aging.
Age hardening of aluminum alloy is a very complex process. It depends not only on the composition and aging process of the alloy, but also on the defects caused by shrinkage in the production process, especially the number and distribution of vacancies and dislocations. At present, it is generally believed that age hardening is the result of the segregation of solute atoms to form hardening zone.
The size and quantity of hardening zone depend on quenching temperature and quenching cooling rate. The higher the quenching temperature, the greater the vacancy concentration, the more the number of hardened zone and the smaller the size of hardened zone. The larger the quenching cooling rate is, the more vacancies are fixed in the solid solution, which is conducive to increasing the number of hardening zone and reducing the size of hardening zone.
A basic characteristic of precipitation hardening alloy system is the equilibrium solid solubility varying with temperature, that is, the solid solubility increases with the increase of temperature. Most aluminum alloys that can be strengthened by heat treatment meet this condition.
Basic knowledge of aluminum and aluminum alloy heat treatment
1. Function of heat treatment of aluminum and aluminum alloy
Aluminum and aluminum alloy materials are heated to a certain temperature and held for a certain time to obtain the expected product microstructure and properties.
2. Main methods and basic principles of heat treatment of aluminum and aluminum alloys
(1) Basic principle of heat treatment of aluminum and aluminum alloys
Annealing: the product is heated to a certain temperature and held for a certain time, and then cooled to room temperature at a certain cooling rate. Through atomic diffusion and migration, the structure is more uniform, stable and internal stress is eliminated, which can greatly improve the plasticity of the material, but the strength will be reduced.
- ① Ingot homogenization annealing: keep warm at high temperature for a long time, and then cool at a certain speed (high, medium, low and slow), so as to homogenize the chemical composition, structure and properties of the ingot, which can improve the plasticity of the material by about 20%, reduce the extrusion force by about 20%, increase the extrusion speed by about 15%, and improve the surface treatment quality of the material at the same time.
- ② Intermediate annealing: also known as local annealing or inter process annealing, it is to improve the plasticity of materials, eliminate the internal processing stress of materials, and keep them warm for a short time at a lower temperature, so as to facilitate continuous processing or obtain a combination of certain properties.
- ③ Complete annealing: also known as finished product annealing, it is held at a higher temperature for a certain time to obtain the softened structure in the state of complete recrystallization, with good plasticity and low strength.
Solution quenching: heat the heat treatable and strengthened aluminum alloy material to a higher temperature and keep it for a certain time, so that the second phase or other soluble components in the material can be fully dissolved into the aluminum matrix to form a supersaturated solid solution, and then maintain the supersaturated solid solution to room temperature by rapid cooling. It is an unstable state because it is in a high-energy state, Solute atoms may precipitate at any time. However, at this time, the plasticity of the material is high, and the cold working or straightening process can be carried out.
- ① On line quenching: for some alloy materials with low quenching sensitivity, solid solution can be carried out at high temperature during extrusion, and then quenched with air cooling (T5) or water mist cooling (T6) to obtain certain microstructure and properties.
- ② Off line quenching: some alloy materials with high quenching sensitivity must be reheated to a higher temperature in a special heat treatment furnace and maintained for a certain time, and then quenched into water or oil with a transfer time of no more than 15 seconds to obtain a certain structure and performance. According to different equipment, they can be divided into salt bath quenching, air quenching, vertical quenching and horizontal quenching.
(2) Aging: when the material after solution quenching is maintained at room temperature or higher temperature for a period of time, the unstable supersaturated solid solution will decompose, and the second phase particles will precipitate (or precipitate) from the supersaturated solid solution and distribute in α( Al) around the aluminum grain, resulting in strengthening, which is called precipitation (precipitation) strengthening.
Natural aging: some alloys (such as 2024, etc.) can produce precipitation strengthening at room temperature, which is called natural aging.
Artificial aging: some alloys (such as 7075, etc.) precipitate at room temperature without obvious strengthening, but the precipitation strengthening effect is obvious at higher temperature, which is called artificial aging.
Artificial aging can be divided into under aging and over aging.
- ① Under aging: in order to obtain certain properties, lower aging temperature and shorter aging time are controlled.
- ② Over aging: aging at higher temperature or holding for a long time in order to obtain some special properties and better comprehensive properties.
- ③ Multistage aging: in order to obtain some special properties and good comprehensive properties, the aging process is divided into several stages. It can be divided into two stages and three stages.
(3) Regression treatment: in order to improve plasticity, facilitate cold bending or correct geometric tolerance, the quenched and aged products can be restored to the new quenched state after heating at high temperature for a short time, which is called regression treatment.
Quenching cooling rate of aluminum alloy
The cooling rate of aluminum alloy quenching furnace must ensure that the supersaturated solid solution is fixed and does not decompose. Prevent the precipitation of strengthening phase and reduce the mechanical properties after quenching and aging.
Therefore, the faster the cooling rate during quenching, the better. However, the greater the cooling rate, the greater the residual stress and residual deformation of quenched products. Therefore, the cooling rate should be determined according to different alloys and products of different shapes and sizes.
The quenching of general alloys is highly sensitive to the cooling rate, and the cooling rate should be large. For example, the quenching cooling rate of 2A11 and 2A12 alloys should be above 50 ℃ / s, while 7A04 alloy is very sensitive to the cooling rate, and its quenching cooling rate should be above 170 ℃ / s.
For products with different shapes and sizes, different cooling rates should be adopted, which is usually realized by adjusting the temperature of quenching medium. For simple shape, small and medium-sized bars, room temperature water quenching can be used (water temperature is generally l0 – 35 ℃). For profiles with complex shape and large wall thickness difference, water quenching at 40 – 50 ℃ can be used.
For products that are particularly prone to deformation, the water temperature can even be raised to 75 – 85 ℃ for quenching. The test shows that the mechanical properties and corrosion resistance of quenched products decrease with the increase of water temperature.
The common quenching medium of aluminum alloy quenching furnace is water. Because the viscosity of water is small, the heat capacity is large, the heat of evaporation is fast, the cooling capacity is strong, and the use is very convenient and economical.
However, its disadvantage is that the cooling capacity decreases after heating. The cooling of quenched and heated products in water can be divided into three stages: the first stage is film boiling stage. When the hot product just comes into contact with cold water, an uneven superheated steam film is immediately formed on its surface. It is very firm and has poor thermal conductivity, which reduces the cooling speed of the product.
The second stage is bubble boiling stage. When the vapor film is destroyed, the liquid near the metal surface will produce violent boiling and strong heat exchange. The third stage is the heat convection stage. The circulation of cooling water, or the product swings left and right, or moves up and down, increases the convective heat exchange between the product surface and water, so as to improve the cooling speed.
According to the above analysis, in order to quickly break through the first stage, step by step cooling and ensure uniform cooling of quenched products, compressed air pipes need to be installed in the quenching water tank for mixing, and the products should swing properly after entering the water tank.
In addition, in order to ensure that the water temperature will not rise too much, the quenching tank shall have sufficient capacity (generally more than 20 times the total volume of quenched products). Moreover, the cooling water shall have a circulating device.
In addition to adjusting the water temperature to control the quenching cooling rate of aluminum alloy quenching furnace, different solvents can also be added to the cooling water to adjust the cooling capacity of the water.
Usually, the polyethylene alcohol aqueous solution is used as the cooling medium. At the same time, the concentration of polyethylene alcohol aqueous solution can be adjusted to control the cooling rate of product quenching. Generally, products that are easy to deform are often quenched with this aqueous solution of polyethylene alcohol.
What is the difference between air cooling and water cooling quenching of aluminum alloy profiles
The quenching of aluminum alloy is from high temperature to low temperature. For example, the steel blade should be quenched in water before it is hard and sharp. The quenching of aluminum also includes water cooling quenching and air cooling quenching.
6063 aluminum profile for construction is quenched by air cooling. The quenched aluminum profile is aged in the aging furnace for a certain time. The internal crystallization of aluminum profile is rearranged, and the mechanical strength is significantly improved. Among all metal alloys, only aluminum alloy has aging state.
The forming temperature of aluminum alloy extruded profile is 460 – 500 degrees. Generally, the temperature after quenching is 200 degrees. The state of artificial aging after high temperature extrusion and solution heat treatment (quenching) is air cooling (T5); The state of cooling through the high-temperature extrusion process and then artificial aging is water cooling (T6).
As the saying goes: T5 is air-cooled after extrusion. T6 is water-cooled after extrusion, and its hardness is improved after water quenching. It’s that simple. However, if the aluminum material needs to be pulled and bent, try not to T6.
Some people think that the difference between T5 and T6 is only the difference of cooling speed, not the difference of air cooling and water cooling. If the cooling speed of air cooling is large enough, it can also achieve T6 effect. On the contrary, if the cooling speed of water cooling is not large enough, it can only be T5 effect!
In fact, T6 status can be quenched online (water cooling or strong air cooling) or offline (quenched in quenching furnace), but it should be determined according to customer requirements and product varieties and specifications.
In actual production, no matter which production process is adopted, the key is to meet the mechanical strength requirements of the aluminum profile product.
Hardness has little to do with air cooling speed and water cooling speed.
The better the cooling effect is, the better the hardness will be after aging. Why are there T5 and T6? Because the size of T5 air-cooled products will not deform, T5 will be selected for almost all profiles such as doors and windows. T6 is a profile with relatively thin water-cooled thickness, which will deform in case of water, especially those with openings are easy to deform in case of water.
Of course, you can also use floating water in the form of water, that is, the spray way of water. Of course, the effect of the product after water is much better than that of air cooling. 6063-T5 is between 10-13, and 6063-T6 can reach more than 13.
Why is aluminum alloy difficult to electroplate?
As a widely used metal material, aluminum needs metal surface treatment in order to have better performance. In most cases, aluminum materials will be anodized instead of electroplating. Electroplating on aluminum and aluminum alloy is much more difficult and complex than electroplating on steel, copper and other metal materials. The main reasons are as follows.
- 1. Aluminum and aluminum alloys have high affinity for oxygen and are easy to form oxide film. Once this oxide film is removed, a new oxide film will be produced in a very short time, which will seriously affect the adhesion of the coating.
- 2. The electrode potential of aluminum is very negative. When immersed in electroplating solution, it is easy to replace with metal ions with positive potential, which affects the adhesion of coating.
- 3. The expansion coefficient of aluminum and aluminum alloy is larger than that of other metals, so it is not suitable for electroplating in the range of large temperature change. The difference of expansion coefficient between aluminum and aluminum alloy coating and other metal coatings will cause large stress, so that the bonding force between coating and aluminum and aluminum alloy is not strong.
- 4. Aluminum is an amphoteric metal, soluble in acid and alkali, and unstable in both acidic and alkaline electroplating solutions.
- 5. Aluminum alloy die castings have sand holes and pores, which will leave plating solution and hydrogen, easy to bubble, and reduce the adhesion between the coating and the base metal.
Therefore, aluminum cannot be plated by electroplating. This is the same reason that electrolytic salt water can not get metal sodium, but sodium hydroxide. Therefore, aluminum alloy needs to be coated by anodic treatment.
Anodizing of aluminum alloys
Principle of anodic treatment
Anodizing is a process in which aluminum or aluminum alloy is placed in the electrolyte with an anode and an oxide film is formed on its surface by electrolysis. The cathode in the device must be materials with high chemical stability in electrolytic solution, such as lead, stainless steel, aluminum, etc. The principle of aluminum anodizing is essentially the principle of water electrolysis. When the current passes through, hydrogen is released on the cathode; On the anode, the precipitated oxygen is not only molecular oxygen, but also atomic oxygen and ionic oxygen, which are usually expressed as molecular oxygen in the reaction. Aluminum as an anode is oxidized by the oxygen precipitated on it to form an anhydrous oxide film. Not all the generated oxygen acts with aluminum, and some will precipitate in gaseous form.
Purpose of anodizing
The original intention of anodic treatment is antioxidant treatment, but due to the rapid change of science and technology, the anodic treatment process is becoming more and more colorful. After dye dyeing treatment, dyes can be selected according to different uses and product grades, and then color matching and dyeing treatment can be carried out. Therefore, it is mostly used in high-grade aluminum products, such as gold pens, cosmetics, hearing aids, optical instruments, jewelry and 3C products. Therefore, in addition to strengthening its functionality, it can show its color and brightness on the surface of various products, so as to increase the charm of commodity sales.
Advantages of anodic treatment
Generally, aluminum alloy is easy to oxidize in the air. Although the natural oxide layer has a certain passivation effect, the oxide layer will still be damaged and peeled off as a result of long-term exposure;
Therefore, the purpose of anodic oxidation treatment is to quantitatively and forcibly form an oxide layer on the product surface by electrochemical method, so as to prevent further natural oxidation of aluminum and increase the mechanical properties (functionality) of the surface; Another purpose is to produce various colors and enhance beauty (decoration) through different back reactions.
Classification of anodic oxidation
Classification by process
- 1. Natural Color Anodizing
- 2. Black anodizing
- 3. Oxidation of other colors (blue oxidation, red oxidation, gold oxidation, etc.)
B. Hard anodizing
- 1. Hard oxidation of natural color (the color of oxide film presents different colors according to the material)
- 2. Black hard oxidation (hard oxidation dyeing black)
Classification by substrate
1. Anodizing of extruded aluminum 2. Anodizing of die cast aluminum
Characteristics of anodic oxidation
Color of natural oxide film
Aluminum products do not dye after conventional anodizing, showing the color of the product oxide film itself, which is not always colorless. Different aluminum materials show slightly different colors.
- 1100-pure aluminum: transparent and colorless
- 3003-aluminum manganese: light yellow
- 3004-aluminum manganese: transparent and colorless
- 4043-aluminum silicon: gray
- 5052-aluminum magnesium: transparent and colorless
- 6061-aluminum magnesium zinc: milky yellow with gray
- 6063-aluminum magnesium zinc: light yellow
- 7072-aluminum zinc: transparent, colorless and striped
- ADC12-cast aluminum: brown gray, hairy, macular (silicon)
- ZL105-cast aluminum: brown yellow
Color of natural hard oxide film
Aluminum products do not dye after hard anodizing, showing the color of the oxide film itself. Different aluminum materials show great color differences. From yellow to brown to gray to black, the thicker the film, the darker its color will be.
Fig. 1 appearance color of hard oxide film of different materials
Oxidation characteristics of die cast aluminum
- 1. Compared with extruded aluminum, the impurity content of die-casting aluminum is much higher (for example, ADC12, silicon content is 9.5-12.5%, copper content is 1.5-3.5%).
- 2. There is release agent on the surface.
- 3. These impurities cannot be removed by conventional chemical pretreatment.
Therefore, if the oxide film layer is formed on the surface of such material, there will be uneven, irregular, spotted, variegated and other phenomena. Moreover, because silicon is not conductive, the overall conductivity of the product becomes poor. Under the same oxidation conditions, the appearance of the film will be much worse than that of extruded aluminum (as shown in the figure below). This is also the characteristic of die casting aluminum oxidation.
Fig. 2 appearance of die cast aluminum after oxidation
The general oxidation process of extruded aluminum is as follows:
Figure 3 extrusion aluminum oxidation process
The general oxidation process of die cast aluminum is as follows:
Figure 4 die casting aluminum oxidation process
See here, the new people should have a general grasp of the anodizing process and application, and will gradually refine the details in the follow-up, so that we can have a better understanding of it.
Source: China Aluminum Alloy 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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