Aluminum alloys can be divided into cast aluminum alloys and wrought aluminum alloys according to their composition and technological properties. Wrought aluminum alloys can be divided into four categories according to their service performance and technological performance: rust proof aluminum, duralumin, super duralumin and forged aluminum.
1. Rust proof aluminum
The main alloy elements of rust proof aluminum are manganese and magnesium, belonging to Al Mn and Al Mg system alloys. This aluminum alloy belongs to the aluminum alloy that cannot be strengthened in time. After forging and annealing, it is a single-phase solid solution with high corrosion resistance and good plasticity. Manganese can improve the strength of aluminum alloy in aluminum through solution strengthening, but its main role is to improve the corrosion resistance of aluminum alloy. The second phase Mnal6 in A1 Mn system alloy is close to the chemical property of aluminum, so manganese alloy has good corrosion resistance. The corrosion resistance of aluminum alloy is less damaged by magnesium, which has a good solution strengthening effect.
Rust proof aluminum has strong pressure processing ability, and can be processed by cold pressing to produce processing strengthening. It has good weldability and poor cutability (because it is too soft). Rust proof aluminum is used to manufacture corrosion resistant and small stressed parts, such as oil pipes, oil tanks, willow nails, etc.
2. Hard aluminum
The duralumin is basically an AU Cu Mg alloy, with a small amount of manganese added to copper and magnesium. In addition to the solid solution strengthening effect, the strengthening stages of CuA12 (ー phase) and Al2CuMg (S phase) are also formed. Manganese is mainly added to improve the corrosion resistance of the alloy, and also has a certain effect of solution strengthening, but the precipitation tendency of manganese is small, so it does not participate in the timely process. All kinds of duralumin can be strengthened in time; The higher the content of copper and magnesium in the alloy, the more significant the timely strengthening effect is, the higher the strength is, but the plasticity and corrosion resistance are reduced. According to the alloying degree of the alloy Mechanical and technological properties: duralumin can be divided into willow joint duralumin (2A01, 2A10), medium strength duralumin (2Al1), separated strength duralumin (2A12, 2A06), heat resistant duralumin (2A02), etc.
Duralumin is the most widely used deformed aluminum alloy in the aviation industry. it has strong hardening ability and the strength after heat treatment can reach 500 mpa.
The corrosion resistance of duralumin is very poor, especially in seawater. This is because it contains higher steel, and the electrode potential of copper solid solution and compound is more likely to cause intergranular corrosion than the grain boundary.
3. Super hard aluminum
Super hard aluminum is mainly Al Cu Mg Zn system, such as 7A04. In addition to ー phase and S phase, there are also MgZn2 (ー phase) and Al2Mg3Zn3 (T phase). Room temperature strength after quenching and aging treatment.
It can exceed 600 mpa and is a deformed aluminum alloy with strength. The disadvantages of this alloy are poor fatigue resistance, sensitive to stress concentration, obvious stress corrosion tendency, and lower heat resistance than duralumin.
4. Forged aluminum
Wrought aluminum belongs to Al Mg Si Cu system and Al Cu Mg Ni Fe system alloys. Although there are many kinds of alloy elements in this aluminum alloy, the content of each element is small, so it has good thermoplasticity. It is suitable for manufacturing various aviation forgings, especially large forgings with complex shapes. Mg2Si, Al2Cumg, Cual2 and other compounds can be formed in the alloy. When human iron and nickel are added, the service temperature of the alloy can be increased, so it is called heat-resistant forged aluminum alloy. Common forged aluminum alloys include 6A02.2A50.2B50 and 2A14. The supply state is generally quenching and artificial aging.
For aluminum alloys that need to work at temperature separation, a small amount of transition elements such as manganese, chromium and germanium are usually added Titanium, dissolved in the matrix, can greatly increase the recrystallization temperature. When the second phase of diffusion precipitates, it can effectively prevent the recrystallization process and grain growth. The recrystallization temperature is also an indicator of heat resistance.
The excessive content of alloy elements in wrought aluminum alloy will seriously reduce the process plasticity and corrosion resistance of the alloy, and even make the pressure processing of the alloy difficult. Therefore, the content of w (Cu) in wrought aluminum alloys generally does not exceed 5%, w (Mg) does not exceed 2.5% - 5%, w (Zn) 3% - 8%, and w (Si) 0.5% - 1.2%. Iron, silicon and other elements are harmful impurities in wrought aluminum alloys.
Most wrought aluminum alloys have good malleability and can be used to produce forgings of various shapes and types. Aluminum alloy satin pieces can be produced by existing forging methods, including free forging. Die forging. Xu Forging. Roller forging. Cylinder pressure. Rotary pressure. Ring rolling and extrusion, etc. The flow stress of aluminum alloy changes obviously with the composition, and the flow stress value of each alloy is about twice of the value (that is, the difference of required forging load is about twice); Some low strength aluminum or aluminum alloys, such as 1100 (equivalent to industrial pure aluminum 1200) and 6A02, have lower flow stress than carbon steel. The flow stress of 7075 (LC4), 7049 (LC6) and other high-strength aluminum alloys is significantly higher than that of carbon steel. The flow stress of other aluminum alloys, such as 2219 (LY16), is very similar to that of carbon steel. As an alloy, aluminum alloy is generally considered to be more difficult to forge than carbon steel and many alloy steels. However, compared with nickel or cobalt alloys and titanium alloys, aluminum alloy is obviously easier to forge, especially when isothermal die forging technology is used.
Wrought aluminum alloys can be divided into three categories according to technological plasticity and mechanical properties. It belongs to low strength. High plasticity alloys include 6A02, 3A21, 5A02, 5A03, 5A05 and industrial pure aluminum; Medium strength and plastic alloys include: 2A14, 2B50, 2A70, 2A80, 2A02, 2A06, 2A11, 2A16, 2A17, 5A06, etc; It belongs to high strength. Low plasticity alloys include 2A14, 2A12, 7A04, etc. The figure shows the forgeability comparison of 10 representative aluminum alloys in aluminum alloy forging production. Its relative malleability is based on the deformation string produced by each energy absorbing unit pier of 10 alloys in their respective forging temperature range. At the same time, it also considers the difficulty of meeting specific deformation requirements and the tendency of cracks. It can be seen from the figure that the forgeability of various aluminum alloys increases with the increase of temperature, but the influence of temperature on various alloys is different. For example, the malleability of 4032 alloy with free silicon content is very sensitive to temperature changes, while the high-strength Al Zn Mg Cu series 7075 and other alloys are least affected by temperature. The malleability of various aluminum alloys in the figure varies greatly. The basic reason is that the different kinds and contents of alloy elements in various alloys strengthen the properties of phases. The quantity and distribution characteristics are also very different, which seriously affects the plasticity and resistance to deformation of aluminum alloys. Some wrought aluminum alloys, such as 1100 and 3003 (LF21), are far away from the alloys listed in the figure, but their application in forging production is limited because they cannot be strengthened by heat treatment. Another characteristic of aluminum alloy related to its malleability is poor fluidity. The so-called fluidity refers to the ability of alloy to fill the forging die cavity under the action of external force. It mainly depends on the deformation resistance and external friction coefficient of the alloy. The smaller the deformation resistance and external friction coefficient, the better the fluidity. At the forging temperature, the deformation resistance of high-strength aluminum alloy is greater than that of steel, and the external friction coefficient is larger, so the fluidity of aluminum alloy is poor.