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Use of aluminum alloy (2000-3000 words)
First, rust-proof aluminum alloy

Rust-proof aluminum alloys include aluminum-magnesium alloys, aluminum-manganese alloys and industrial pure aluminum. See Table 6-2 for the brand and chemical composition of antirust aluminum alloy.

The main performance of this aluminum alloy is excellent corrosion resistance, so it is named rust-proof aluminum alloy, abbreviated as rust-proof aluminum. In addition, it has good plasticity and weldability, and is suitable for pressure processing and welding. This alloy can not be strengthened by heat treatment, and its mechanical properties are relatively low. In order to improve its strength, it can be strengthened by cold working. However, due to the poor processing technology of antirust aluminum, it is suitable for making cold deformed parts such as welded pipes, containers and rivets.

1. Al-Mg alloy

In the chemical composition of aluminum-magnesium alloy, magnesium is the main component of the alloy, and a small amount of other elements such as manganese and titanium are added.

The effect of magnesium content on the mechanical properties of the alloy is that with the increase of magnesium content, the strength and plasticity of the alloy also increase accordingly. However, when the magnesium content in the alloy exceeds 5%Mg, the stress corrosion resistance of the alloy decreases; When the magnesium content exceeds 7%, the plasticity of the alloy decreases and the weldability becomes worse. This may be related to the increase of magnesium content and the segregation tendency of the alloy during liquid phase crystallization. Due to the non-equilibrium crystallization of the alloy, brittle β(Mg2Al3) phase appears in the alloy structure, which leads to the deterioration of the properties of Al-Mg alloy. It is pointed out that β(Mg2Al3) phase is not found in 5A02 and 5A03 alloys with low magnesium content. With the increase of magnesium content, a small amount of β(Mg2Al3) phase can be seen in 5A05, while in 5A06 alloy, the number of β(Mg2Al3) phase increases correspondingly due to the increase of magnesium content.

Adding a small amount of manganese (0.3% ~ 0.8%) to Al-Mg alloy can not only improve the corrosion resistance of the alloy, but also improve the strength of the alloy. A small amount of titanium or vanadium mainly plays the role of grain refinement, and a small amount of silicon can improve the weldability of the alloy.

Iron, copper and zinc are harmful impurity elements in aluminum-magnesium antirust aluminum, which will deteriorate the corrosion resistance and technological properties of the alloy, so their contents should be strictly controlled.

In Al-Mg alloys, although magnesium has great solubility in solid aluminum and changes greatly with temperature, the transition phase β' formed during aging of Al-Mg alloys has no lattice relationship with the quenched matrix, and its aging strengthening effect is very small, so all Al-Mg alloys with rust-proof aluminum content less than 7% do not adopt aging treatment to improve their strength.

In order to improve the strength of aluminum-magnesium antirust aluminum, cold working and hardening can be used to improve its strength. However, after cold working and hardening, the strength, especially the yield strength, of aluminum-magnesium series antirust aluminum with high magnesium content decreased obviously, while the elongation increased significantly with the increase of room temperature. Moreover, this softening phenomenon is more obvious with the increase of magnesium content and alloy deformation degree. In order to prevent high magnesium antirust aluminum from softening after cold working, it should be stabilized after cold deformation, that is, heated to 150℃ for 3 hours to stabilize its mechanical properties at room temperature.

2. Aluminum-manganese antirust aluminum

The common alloy brand in aluminum-manganese antirust aluminum is 3A2 1. Manganese is the main component of the alloy, and the alloy with manganese content in the range of 1.0% ~ 1.6% has high strength, high plasticity, weldability and excellent corrosion resistance. When the manganese content exceeds 1.6%, a large number of brittle compounds MnAl6 are formed. Although the strength is improved, the plasticity of the alloy is obviously reduced, and the working performance of pressure working becomes worse. Therefore, the manganese content in antirust aluminum generally does not exceed 1.6%.

Iron and silicon are the main impurities in the alloy. Iron reduces the solubility of manganese in aluminum and can be dissolved in MnAl6 to form (FeMn)Al6, which is a hard and brittle insoluble phase. Practice has proved that a small amount of iron in the alloy can refine the microstructure of the alloy, but when the iron content is too high, a large amount of (FeMn)Al6 phase will be formed, which will significantly reduce the mechanical properties and technological properties of the alloy and the casting performance, so its content should be strictly controlled, generally below 0.6%.

Aluminum-manganese series antirust aluminum is not aged because of its poor aging strengthening effect. The heat treatment of 3A2 1 alloy products is mainly annealing. However, when 3A2 1 alloy is annealed, it is easy to produce coarse grains, which leads to rough surface or cracks in semi-finished alloy during drawing or bending. In order to obtain fine-grained 3A2 1 alloy products, the heating rate during annealing should be increased or 0.4% iron should be added to the alloy to refine the alloy structure. Or homogenize the ingot and anneal at 600-620℃ to eliminate the serious segregation of manganese within and between grains. So as to obtain uniform and fine grains and improve the machinability of pressure machining.

Second, hard aluminum alloy.

Al-Cu-Mg alloy is an early and widely used aluminum alloy. It has a strong aging strengthening effect and high hardness and strength after aging treatment, so Al-Cu-Mg alloy has always been called hard aluminum alloy. In addition, this alloy has excellent machinability, and can be processed into semi-finished products such as plates, bars, pipes, wires, profiles, forgings, etc., and is widely used in national economy and national defense construction.

The main alloying elements of hard aluminum alloy are copper and magnesium, in addition to manganese and some impurity elements such as iron, silicon, nickel and zinc. The brand and chemical composition of hard aluminum alloy are shown in Table 6-2.

Different brands of hard aluminum alloys have different chemical compositions and different performance characteristics. Hard aluminum with low copper and magnesium content has low strength and high plasticity; Hard aluminum with high copper and magnesium content has high strength and low plasticity. The relationship between the composition and mechanical properties of hard aluminum alloy is determined by the strengthening phase formed in the alloy. The different ratio of copper to magnesium in hard aluminum alloy leads to different strengthening phases, and its strengthening phases and strengthening effects are also different. When the magnesium content is low, the main strengthening phase is θ phase (CuAl2). When the magnesium content increases, θ phase decreases, forming S (Al _ 2cumg) phase with greater strengthening effect and certain heat resistance. With the further increase of magnesium content, T(Al6CuMg4) phase and β(Al3Mg2) phase with poor strengthening effect are formed one after another. When the ratio of copper to magnesium is constant, the higher the total amount of copper and magnesium, the more strengthening phases and the greater the strengthening effect.

In addition to copper and magnesium, a certain amount of manganese is added to the hard aluminum alloy. Manganese can improve the corrosion resistance of hard aluminum and refine the alloy structure. Quenching is to dissolve manganese in solid solution, so that the strength of quenched hard aluminum can be improved by 30~70MPa. However, when the manganese content is too high, the plasticity is obviously reduced, so the manganese content in hard aluminum alloy is controlled at 0.3% ~ 1.0%. In addition, manganese can also improve the heat resistance of hard aluminum and weaken the harmful effect of impurity iron. The content of manganese in hard aluminum alloy is controlled at 0.3% ~ 65438 0.0%.

Iron is a harmful element in hard aluminum. It can not only form intermetallic compound FeAl _ 3 with aluminum, reducing the plasticity and corrosion resistance of the alloy, but also capture copper from the alloy, forming insoluble compound Cu _ 2 FeAl _ 7, reducing the number of strengthening phases θ and S, and reducing the aging strengthening effect. In addition, iron can form coarse brittle compounds with silicon, manganese and other elements, which makes the process performance worse. Therefore, the iron content in hard aluminum alloy is generally controlled below 0.5%.

Silicon also exists as an impurity in hard aluminum. When the iron content in the alloy is low, silicon and magnesium preferentially form Mg2Si compound, which consumes a part of magnesium and reduces the strengthening phase S(Al2CuMg). Thereby reducing the natural aging strengthening effect of hard aluminum. Silicon has little effect on the plasticity of duralumin. On the contrary, when iron exists in the alloy, the Fe _ 2Sial2 phase is formed between silicon and iron, which can reduce the effect of harmful elements to form coarse flake (Femn) Al _ 22 phase. The content of silicon in hard aluminum is generally controlled at 0.5% ~ 0.7%.

Nickel is also a harmful impurity in hard aluminum alloy. Nickel can form AlCuNi insoluble compounds with copper, thus reducing the number of strengthening phases θ(CuAl2) and S(Al2CuMg) and reducing the aging strengthening effect of hard aluminum, so the nickel content should be limited below 0. 1%.

As an impurity, zinc exists in hard aluminum, which has no effect on the mechanical properties of hard aluminum at room temperature, but it needs to be strictly controlled to reduce the thermal hardness of hard aluminum and increase the tendency of cracking during welding.

Hard aluminum alloys can be divided into three types according to the content and properties of alloying elements: low-strength hard aluminum, such as 2A0 1, 2A03, 2A 10 and other alloys; Medium strength hard aluminum, such as 2A 1 1 alloy; High strength hard aluminum, such as 2A 12 alloy.

1. Low strength duralumin

This hard aluminum alloy has low magnesium content (2A 10) or low copper and magnesium content (2A0 1). Its main strengthening phase is θ(CuAl2) phase, so its aging strengthening effect is small, its strength is low, its plasticity is high, and its aging hardening speed is slow. After aging strengthening, it has high shear resistance and is suitable for riveting materials.

2. Medium strength hard aluminum

Medium strength hard aluminum is also called standard hard aluminum. The contents of copper and magnesium in these alloys are relatively high. In Figure 6-9 (such as 2A 1 1 alloy), it is located to the left of α(Al)+θ(CuAl2)+S(Al2CuMg) phase, and the main strengthening phase is also θ(CuAl2) phase, followed by S(Al2CuMg) phase. However, the total amount of copper and magnesium is higher and the amount of magnesium is lower, so it has higher strength and better plasticity. After annealing, the process performance is good, and it can be used in cold bending, stamping and other processes. Good welding performance and moderate corrosion resistance. The machinability is poor in the annealed state, but it is good in the age hardening state. Mainly used as a structural member with medium load.

3. High strength hard aluminum

In order to improve the strength and yield limit of hard aluminum alloy, on the basis of medium strength hard aluminum alloy, the content of copper and magnesium is increased at the same time or the content of magnesium is increased alone to form high strength hard aluminum alloy. Such as 2A 12 alloy. It is located on the right side of α(Al)+θ(CuAl2)+S(Al2CuMg) phase region in Figure 6-9. The main strengthening phase is S(Al2CuMg) phase, followed by θ(CuAl2) phase. Because the natural aging strengthening effect of S phase is stronger than that of θ phase, 2A 12 alloy has higher strength, yield limit and good heat resistance than 2A 1 1, but its plasticity and some technological properties are poor. 2A 12 alloy is a kind of high strength hard aluminum alloy which is widely used in industry.

The corrosion resistance of hard aluminum alloy is much worse than that of antirust aluminum, especially in seawater. Therefore, all hard aluminum alloy parts that need to work in corrosive environment should be plated with a layer of high-purity aluminum to improve their corrosion resistance. However, the mechanical properties of aluminized hard aluminum after heat treatment are lower than those without aluminizing.

Quenching and heating of hard aluminum are very sensitive to overheating. In order to obtain supersaturated solid solution with maximum solid solubility, the ideal quenching temperature of 2A 12 alloy is 500 3℃, but it is difficult to achieve it under actual production conditions, so the commonly used quenching temperature of 2A 12 alloy is 495 ~ 500℃.

Hard aluminum alloy quenching plus artificial aging has a greater tendency of intergranular corrosion than quenching plus natural aging, so natural aging is generally used except for parts working at high temperature. Relationship between natural aging and mechanical properties of 2A 12 alloy after quenching.

The quenching cooling rate has a great influence on the strength and corrosion resistance of hard aluminum alloy. When the quenching cooling rate is low, a large number of strengthening phases, such as θ(CuAl2) phase, precipitate along the grain boundary during quenching, which reduces the strengthening effect of natural aging and increases the tendency of intergranular corrosion. Therefore, when quenching hard aluminum alloy, the faster the cooling speed, the better on the premise of ensuring no deformation and no cracking. For 2A 1 1 and 2A 12 alloys, the quenching cooling rate is not less than 20℃/s and 14℃/s respectively, and the quenching medium is usually water.

Third, superhard aluminum alloy

Al-Zn-Mg-Cu alloy is an aluminum alloy with the highest strength at room temperature at present. Its strength reaches 500~700 MPa, which is higher than that of high-strength hard aluminum 2A 12 alloy (400~430 MPa), so it is called superhard aluminum alloy. The brand and chemical composition of superhard aluminum alloy are shown in Table 6-2. In superhard aluminum alloy, the main alloying elements are zinc, magnesium and copper, and sometimes a small amount of elements such as manganese, chromium and titanium are added.

Zinc and magnesium are the main strengthening elements in the alloy, and η(MgZn2) and T(Al2Mg3Zn3) strengthening phases are formed in the alloy. The solubility of both of them in aluminum changes greatly, and they have obvious aging strengthening effect. However, when the content of Zn and Mg is too high, although the strength of the alloy is high, the plasticity and stress corrosion resistance are reduced.

Adding a certain amount of copper into the alloy can improve the stress corrosion resistance of superhard aluminum, and copper can form θ(CuAl2) and S(Al2CuMg) to supplement and strengthen the alloy, thus improving the strength of the alloy. However, when the copper content exceeds 3%, the corrosion resistance of the alloy decreases, so the copper content in superhard aluminum alloy should be controlled below 3%.

Adding manganese and chromium to superhard aluminum can improve the strength of the alloy in quenching state and the effect of artificial aging strengthening, and at the same time improve the stress corrosion resistance of the alloy.

Both iron and silicon are harmful impurities. Iron and manganese form an insoluble complex compound phase, which reduces the mechanical properties of the alloy and makes the riveting performance worse. Silicon takes magnesium away from the alloy to form Mg2Si phase, which reduces the number of main strengthening phases η(MgZn2) and T(Al2Mg3Zn2) in the alloy and reduces the aging strengthening effect. When iron and silicon exist at the same time, the influence on the properties of superhard aluminum alloy is less than that when they exist alone. For example, the contents of iron and silicon are both below 0.5%. In fact, it has no effect on the mechanical properties of the alloy.

The main strengthening phases of 7A04 alloy are η phase and T phase, followed by S phase. If the content of zinc, magnesium and copper is slightly increased on the basis of 7A04 alloy, for example, in the structure of 7A06 alloy, the number of η phase and T phase increases, while the number of S phase decreases, the alloy has stronger aging strengthening effect, so 7A06 alloy has higher strength than 7A04 alloy after heat treatment, and Rm can reach 600~700 MPa.

Compared with hard aluminum, the quenching temperature range of ultra-hard aluminum is wider. For alloys with 6% zinc and less than 3% magnesium, the quenching temperature is 450 ~ 480℃. However, the quenching temperature should not exceed 480℃, otherwise the corrosion resistance of the alloy will be reduced. When the alloy is quenched, the quenching transfer time should be shortened as much as possible to prevent the precipitation of copper-containing phase and reduce the aging effect of the alloy.

The heat treatment of superhard aluminum is different from that of hard aluminum. The natural aging time of superhard aluminum is very long, and it takes 50 ~ 60 days to achieve the maximum strengthening effect. In addition, naturally aged superhard aluminum has a greater tendency to stress corrosion than artificially aged aluminum, so artificially aged superhard aluminum is treated. In order to further improve the stress corrosion resistance of the alloy, staged artificial aging can be used, that is, aging at 120℃ for 6 hours, and then aging at 160℃ for 3 hours to further eliminate internal stress.

If superhard aluminum is air-cooled after annealing, it will have quenching effect. Therefore, the annealing cooling speed is not easy to be too fast, generally not exceeding 30℃/h, and it is cooled with the furnace to 150℃ and discharged for air cooling.

The main disadvantage of superhard aluminum alloy is poor corrosion resistance. In order to improve the corrosion resistance of the alloy, the surface of the general plate contains an aluminum coating of 1%Zn. In addition, although the room temperature strength of ultra-hard aluminum is much higher than that of hard aluminum, its heat resistance is not as good as that of hard aluminum. When the temperature rises, the solid solution in superhard aluminum alloy decomposes rapidly, and the strengthening phase gathers and grows, which makes the strength drop sharply. Therefore, superhard aluminum alloy should not work above 120 ~ 130℃. Ultra-hard aluminum is mainly used as a structural member with high stress.

Fourthly, forging aluminum alloy.

Al-Mg-Si-Cu alloy has excellent forging process performance and is mainly used to manufacture forgings with complex shapes, so it is called forged aluminum alloy. See Table 6-2 for the brand and chemical composition of wrought aluminum alloy.

Wrought aluminum alloy is developed on the basis of Al-Mg-Si alloy. Mg2Si compound can be formed by adding magnesium and silicon into aluminum. The solid solubility of Mg2Si compound in aluminum is very large, and it drops sharply with the decrease of temperature. When Mg2Si phase precipitates from supersaturated solid solution, it causes serious lattice deformation, so Mg2Si phase is an extremely effective strengthening phase. However, Mg2Si phase has a certain tendency of natural aging strengthening. If it is not aged immediately after quenching, the effect of artificial aging strengthening will be reduced. In order to make up for this strength loss, copper and a small amount of manganese are added to the Al-Mg-Si system.

In Al-Mg-Si-Cu system, the main function of manganese is not only to prevent coarse grains during crystallization annealing, but also to increase the upper limit of quenching temperature of the alloy, thus improving the strength of the alloy in quenching state. Adding copper can significantly improve the hot working plasticity and heat treatment strengthening effect, and can also inhibit the extrusion effect and reduce the anisotropy caused by adding manganese.

The main phases of Al-Mg-Si-Cu forged aluminum alloy are A, Mg2Si and W(Cu4Mg5Si4Alx). When the copper content in the alloy is high, there are also θ(CuSi2) and S(Al2CuMg) phases.

During the heat treatment of forged aluminum alloy, Mg2Si and W(Cu4Mg5Si4Alx) phases, which are the same as * * * *, precipitate slowly at room temperature, and it is difficult to achieve the maximum strengthening effect during natural aging, so artificial aging must be adopted.

The same disadvantage of heat treatment of forged aluminum alloy is that the residence time at room temperature after quenching cannot be too long, otherwise the artificial aging strengthening effect will be obviously reduced. Moreover, the longer the residence time, the worse the strengthening effect of artificial aging. Therefore, wrought aluminum alloy should be aged immediately after quenching.

casting aluminium alloy

Casting aluminum alloy should not only have certain service performance, but also have excellent casting process performance. The alloy with * * * crystallizing point has the best castability, but there are a lot of hard and brittle compounds in the alloy structure at this time, which leads to the sharp increase of alloy brittleness. Therefore, not all casting alloys actually used are * * * crystal alloys, but the content of alloy elements is higher than that of wrought aluminum alloys.

According to GB/T8063- 1994 standard, the brand of cast aluminum alloy is represented by "ZAl ++ symbol of main elements and percentage+symbol of auxiliary elements and percentage+symbol of auxiliary elements and percentage ...".

The code name of cast aluminum alloy is expressed by the first letter "ZL" of the Chinese phonetic alphabet of "Zhu" plus three digits. The first digit indicates alloy type: 1 indicates aluminum-silicon alloy; 2 represents an aluminum-copper alloy; 3 represents aluminum-magnesium alloy; 4 represents an aluminum-zinc alloy; For example, ZL 1 10 means no. 10 aluminum-silicon casting aluminum alloy, that is, aluminum-silicon casting alloy.

Al-Si alloy has excellent fluidity, small casting shrinkage and linear expansion coefficient, excellent weldability, corrosion resistance and sufficient mechanical properties. However, the alloy has low density and is suitable for making castings with low density and complex shape.

In a simple binary aluminum-silicon alloy, a multi-element aluminum-silicon alloy formed by adding some strengthening elements is called a special aluminum-silicon alloy.

1. Simple aluminum-silicon alloy

Simple binary Al-Si alloy (ZL 102) is an alloy with silicon content of 1 1% ~ 13%. The structure after casting is composed of coarse acicular silicon and aluminum-based solid solution and a small amount of plate-like primary silicon. Due to the existence of coarse acicular crystalline silicon in the structure, the mechanical properties of the alloy are not high, the tensile strength Rm is not greater than 140 MPa, and the elongation A is not less than 3%.

If 2% ~ 3% modifier is added to the alloy liquid before pouring, the microstructure can be refined. Commonly used modifiers are 2/3NaF+ 1/3 NaCl or 25% NaF+62.5%NaCl+ 12%KCl mixture, which are poured into the mold after being evenly stirred.

After modification, the tensile strength Rm of ZL02 alloy reaches 180MPa, and the elongation A reaches 8%. Although Al-Si alloy modification can refine the microstructure and improve the mechanical properties, the modifier sodium is easy to react with the gas in the alloy melt, resulting in casting defects such as pores (also known as pinholes) in the modified aluminum alloy castings. In order to eliminate this casting defect, refining and degassing must be carried out before pouring, which makes the casting process complicated. Therefore, at present, alloys with silicon content less than 7% ~ 8% are generally not modified.

After modification, the mechanical properties of simple Al-Si alloy are improved. However, the strength of pure Al-Si alloy is not high because the solid solubility of silicon in aluminum changes little and the diffusion speed of silicon in aluminum is very fast, so it is easy to precipitate from solid solution and grow up, so it can not play a strengthening role in aging treatment. In order to further improve the mechanical properties of Al-Si alloy, alloying elements such as copper and magnesium are often added to form an aging strengthening phase, which is strengthened by heat treatment to further improve the mechanical properties and expand its application scope.

2. Magnesium-containing special Al-Si alloy

If a proper amount of magnesium is added to Al-Si alloy, Mg2Si phase can be formed, and its solid solubility in α solid solution decreases significantly with the decrease of temperature. Solution treatment can dissolve all α solid solutions, and aging treatment can produce obvious strengthening effect. However, when the addition of magnesium is too high, there is still some undissolved excess phase Mg2Si after solution treatment, which makes the alloy brittle.

Commonly used special Al-Si alloys are ZLl04, ZL0 1 etc. For example, the composition of ZL 104 alloy is marked in the position shown in the figure, and the equilibrium structure at room temperature is α solid solution, (α+ Si) binary * * * crystal precipitated from α solid solution and Mg2Si phase. After heat treatment, the tensile strength Rm reached 240 MPa and the elongation was 3.6%. High casting, welding and corrosion resistance.

3. Special Al-Si alloy containing copper

Adding copper to Al-Si alloy can form θ (CuAl2) strengthening phase, and the strength of the alloy can be further improved by heat treatment. The commonly used special Al-Si alloy containing copper is ZL 107 alloy. After heat treatment, the tensile strength of ZL 107 is 260MP and the elongation is 3%.

4. Special Al-Si alloy containing copper and magnesium

A multicomponent alloy formed by simultaneously adding copper and magnesium to an Al-Si alloy. In addition to Mg2Si, CuAl2 and other phases, there are also strengthening phases such as Al2CuMg and W(AlxCu4Mg5Si). Commonly used alloys are ZL 103, ZL 105, ZL 1 10, etc. Multi-element special Al-Si alloy has high mechanical properties after heat treatment, and can be used as internal combustion engine parts, such as cylinder block, cylinder head and crankcase.

Two. Al-Cu cast alloy

Al-Cu casting alloy is characterized by high heat resistance, which is the highest alloy among all cast aluminum alloys. Its high temperature strength increases with the increase of copper content, while the shrinkage and the tendency to form cracks decrease. However, due to the increase of copper content, the brittleness of the alloy increases, so the copper content of cast aluminum platform gold generally does not exceed 14%. The biggest disadvantage of Al-Cu alloy is poor corrosion resistance, which decreases with the increase of copper content.

The properties and characteristics of cast Al-Cu alloy are different with different copper content, and their uses are also different. The alloy with copper content of 4% ~ 5% has the best heat treatment strengthening effect, high strength and plasticity, but poor castability. For example, ZL203 alloy is suitable for making castings with simple shape and high strength requirements. The alloy with medium copper content (about 8% ~ 10%) has poor heat treatment strengthening effect, but good castability. For example, ZL202 alloy is suitable for casting large castings with complex shapes but low requirements for strength and plasticity. Alloys with high copper content have high heat resistance and excellent castability. Suitable for casting castings with complex shapes and high temperature operation, such as pistons of automobile and motorcycle engines.

Three. Al-Mg casting alloy

Al-Mg casting alloy has the lowest density (2.55), the best corrosion resistance and the highest strength (the tensile strength can reach 350MP). However, due to the wide crystallization temperature range, poor fluidity and large porosity tendency, its casting performance is not as good as that of Al-Si alloy, and it is easy to form oxide slag inclusion during melting and casting, which complicates the casting process. In addition, due to the low melting point and low thermal strength of the alloy, the working temperature does not exceed 200℃.

Commonly used Al-Mg casting alloys are ZL30 1 and ZL302 alloy. ZL30 1 alloy consists of α solid solution and its precipitated Mg5Al8 phase. Because the aging treatment of Al-Mg alloy does not go through GP zone stage, but directly precipitates Mg5Al8 phase, the aging strengthening effect is poor, and the corrosion resistance and plasticity of the alloy decrease strongly. Therefore, ZL30 1 alloy is often used in the quenched state. After solution treatment, the tensile strength Rm of ZL30 1 alloy reaches 350MPa and the elongation reaches 10%. Al-Mg casting alloy is often used to manufacture important parts and joints with simple appearance, which can withstand impact, vibration load and seawater or atmospheric corrosion.

Four. Al-Zn casting alloy

The solubility of zinc in aluminum is very high, and the limit solubility is 32%. Adding more than 10% zinc to aluminum can significantly improve the strength of the alloy, so the aluminum-zinc casting alloy has higher strength and is the cheapest casting aluminum alloy, and its main disadvantage is poor corrosion resistance.

The commonly used Al-Zn casting alloy is ZL40 1 alloy. Because of its high silicon content (6.0% ~ 8.0%), this alloy is also called special Al-Si alloy containing zinc. Adding proper amount of Mn, Fe and Mg to the alloy can significantly improve the heat resistance of the alloy. It is mainly used for manufacturing automobile, airplane parts, medical machinery and instrument parts with complex structure and shape whose working temperature does not exceed 200℃.

V. Heat treatment characteristics and codes of cast aluminum alloy.

Except Al-Si alloy ZL 102 and Al-Mg alloy ZL302, all other cast aluminum alloys can be strengthened by heat treatment.

Compared with wrought aluminum alloy, cast aluminum alloy has coarse structure, serious intragranular segregation and coarse acicular compounds. In addition, the shape of the casting is also very complicated. Therefore, the heat treatment of cast aluminum alloy has the characteristics of heat treatment of common deformed aluminum alloy, and the quenching heating temperature is generally higher and the holding time is longer, generally around 15 ~ 20 hours. Secondly, due to the complex shape and uneven wall thickness of castings, high temperature water (60 ~ 100℃) is generally used as quenching cooling medium to prevent deformation and cracking during quenching. In addition, in order to ensure the corrosion resistance, microstructure, properties and dimensional stability of castings, all castings that need aging treatment are generally artificially aged.

According to the working conditions and performance requirements of castings, different heat treatment methods can be selected. Ability knowledge point 6 heat-resistant aluminum alloy

First, the alloying of heat-resistant aluminum alloy

The alloying of heat-resistant aluminum alloy is similar to that of heat-resistant steel, and the thermal strength is improved mainly by solid solution strengthening, over-phase strengthening and grain boundary strengthening.

1. solid solution strengthening

The solid solution strengthening of heat-resistant aluminum alloy requires that the added alloy elements and the solid solution formed have high thermal strength without significantly reducing the melting point of the alloy, so as to ensure that the alloy has a high recrystallization temperature. Secondly, the addition of alloying elements can increase the binding force between atoms and slow down the diffusion process of atoms and the decomposition rate of solid solution. Heat-resistant aluminum alloys are usually alloyed with various alloying elements. The addition of these alloying elements usually rarely lowers the melting point of the alloy. Most of them are transition group elements with melting point higher than that of aluminum, and commonly used alloy elements are manganese, iron, copper, lithium and rare earth elements.

2. Excessive phase strengthening

Heat-resistant aluminum alloys are mostly multiphase alloys. A certain amount of residual phase with good heat resistance is indispensable for heat-resistant aluminum alloys. The residual phase with high melting point, complex composition and structure and weak interaction with solid solution in * * * has high thermal stability at high temperature. The surplus phases with good thermal stability in aluminum alloys are A 12CuMg(S), A6Cu3Ni (T), Al.xCu, 4Mg5Si4(W (W), AI2FeSi, etc.

3. Grain boundary strengthening

Adding titanium, zirconium and rare earth elements to aluminum alloy can effectively strengthen grain boundaries. In particular, rare earth elements can react with various impurity elements in aluminum to remove impurities at grain boundaries, purify grain boundaries and improve the creep resistance of grain boundaries, thus significantly improving the heat resistance of aluminum alloys.

Second, the heat-resistant aluminum alloy brand

Heat-resistant aluminum alloys can be divided into heat-resistant deformed aluminum alloys and heat-resistant cast aluminum alloys according to different processing characteristics. Commonly used heat-resistant deformation aluminum alloys are: 2A02, 2A 16, 2A 17, 2A70, 2A80, 2A90, etc. Commonly used heat-resistant cast aluminum alloys are ZL 1 10, ZL 108, ZL 109, 1. Heat-resistant deformation aluminum alloy.

1). Heat-resistant hard aluminum alloy

Heat-resistant hard aluminum alloy is Al-Cu-Mn alloy, and commonly used alloys are 2A02, 2A 16 and 2A 17. Copper and manganese are important components of this alloy. The alloy with copper content of 6.0% ~ 6.5% has higher recrystallization temperature, so it has higher heat resistance. At the same time, CuAl2 strengthening phase can be formed by adding copper, and the alloy can be strengthened by artificial aging. The main elements to ensure the heat resistance of the alloy are that the diffusion coefficient of manganese in aluminum is small, the diffusion speed of copper in aluminum is reduced, the decomposition of α solid solution is slowed down, and the tendency of strengthening phase aggregation and growth at high temperature is reduced. When the manganese content in the alloy is 0.4% ~ 0.5%, fine dispersed T (CuMn2Al 12) phase can be formed, which improves the heat resistance of the alloy. However, when the manganese content exceeds 1.2%, the number of T phases and the phase interface increase, which accelerates the diffusion process and reduces the heat resistance of the alloy. Therefore, the manganese content in heat-resistant hard aluminum alloy should be controlled at 0.4% ~ 0.8%.

Adding a small amount of titanium to the alloy can refine the microstructure of the alloy, increase the recrystallization temperature of the alloy, and thus improve the heat resistance of the alloy. However, when the titanium content exceeds 0.2%, the heat resistance of the alloy will decrease, so the titanium content should be controlled at 0. 1% ~ 0.2%.

2A 17 alloy is an alloy with 0.25% ~ 0.45% Mg added on the basis of 2A 16. Magnesium can improve the room temperature strength of the alloy, which is beneficial to improve the heat resistance of the alloy at 150 ~ 250℃, but it makes the weldability of the alloy worse, which should be controlled below 0.5%.

Heat-resistant hard aluminum is mainly used to manufacture semi-finished products for extrusion and die forging, and parts that work at 200 ~ 300℃, such as compressor blade disks or welded containers that work at normal temperature and high temperature.

2). Heat-resistant forged aluminum alloy

Heat-resistant deformation aluminum alloy belongs to aluminum-copper-magnesium-iron-nickel series alloy, and aluminum-copper-magnesium-iron-nickel series alloy belongs to heat-resistant deformation aluminum alloy. Commonly used brands are 2A70, 2A80 and 2A90 alloys. S(A 12CuMg) is the main heat-resistant phase in this kind of alloy, so the number of S(A 12CuMg) phase in the alloy should reach the limit. Therefore, the copper content in the alloy should be relatively reduced, while the magnesium content should be appropriately increased to ensure the maximum number of S(A 12CuMg) phases, thus obtaining excellent heat resistance.

When iron and nickel are added to the alloy at the same time in the ratio of 1: 1, FeNiAl9 can be formed, which has a good effect on improving the heat resistance of the alloy. However, when iron or nickel is added to the alloy alone, the heat resistance of the alloy decreases.

Heat-resistant deformation aluminum alloy not only has good heat resistance, but also has small thermal expansion coefficient, good thermal conductivity and good processability. It can be processed into various bars, forgings and structural parts working at 150 ~ 225℃.

2. Heat-resistant cast aluminum alloy

Piston is an important component for transmitting energy in an engine. It bears high temperature and pressure and moves back and forth at high speed. Therefore, as a piston material, it requires not only low density and good thermal conductivity, but also excellent heat resistance and wear resistance and good processing technology. Piston aluminum alloy is a typical heat-resistant cast aluminum alloy. On the basis of binary Al-Si alloy ZL 102, a certain amount of copper, magnesium, nickel, manganese and rare earth elements are added to form a multi-element Al-Si casting alloy. Among them, ZL 1 10 and ZL 108 of Al-Si-Cu-Mg-Ni system and ZL 109 of Al-Si-Cu-Mg-Ni system are the most commonly used heat-resistant cast aluminum alloys, which are mainly used to manufacture pistons.

CuAI2 _ 2, Mg2Si and W(Al 5mg 5 Cu 4 Si 4) phases can be formed by adding copper and magnesium to Al-Si alloy, which plays a strengthening role. However, if the magnesium content is too high, there will be coarse excess Mg2Si, which will make the alloy brittle and increase its availability. Manganese can improve the heat resistance of alloy. Its diffusion coefficient in solid solution is very small. When the alloy solidifies, manganese remains in the solid solution, which plays a role in solid solution strengthening and improves the stability of the solid solution at high temperature, thus improving the heat resistance of the alloy. Manganese can also form T(CuMn2Al 12) phase with high temperature hardness, which significantly improves the thermal hardness of the alloy. Nickel can form thermally hardened AI3Ni or [(Cuni) 2Al3 phase in the alloy, which improves the thermal strength of the alloy. In the structure of ZL 109 alloy, the main phases are α, Si, Mg2Si, AI3Ni, etc.

The heat treatment of heat-resistant aluminum alloy must ensure high microstructure and performance stability at working temperature. Therefore, heat-resistant aluminum alloys are artificially aged after solution treatment.