[China Aluminum Industry Network] 1. Effect of alloying elements
Copper element
Aluminum-copper-alloyed Al rich in some 548, copper in the aluminum in the greater solubility of 5.65%, the temperature dropped to 302, the solubility of copper is 0.45%. Copper is an important alloying element. It has certain solid-solution strengthening effects. In addition, CuAl2 with ageing has a significant age hardening effect. The content of copper in aluminum alloys is generally 2.5% to 5%, and the copper content is 4% to 6.8%. The strengthening effect is better, so the copper content of some hard aluminum alloys is at this scale.
Aluminum-copper alloys can be rich in less silicon, magnesium, manganese, chromium, zinc, iron and other elements.
Silicon element
Al-Si alloys are rich in aluminum. Some have a eutectic temperature of 577, and silicon has a large solubility of 1.65% in solid solutions. Although the solubility decreases as the temperature decreases, the introduction of such alloys is generally not heat-treatable. Al-Si alloys have excellent forgeability and corrosion resistance.
If magnesium and silicon participate in the formation of aluminum-magnesium-silicon-based alloys in aluminum, the strengthening phase is MgSi. The mass ratio of magnesium to silicon is 1.73:1. When designing the Al-Mg-Si-based alloy composition, the matrix is ​​equipped with magnesium and silicon content in this portion. Some Al-Mg-Si alloys, in order to improve strength, participate in proper copper and join together with appropriate chromium to counteract the impact of copper on corrosion resistance.
Al-Mg2Si alloy-based alloys balance phase diagram Al-rich Mg2Si in aluminum, the greater the solubility of 1.85%, and the deceleration with the temperature decreases.
In the deformed aluminum alloy, silicon alone participates in aluminum and is limited to welding data. Silicon participates in aluminum and has certain strengthening effects.
Magnesium
Al-Mg alloy phase equilibrium phase diagram Al rich Although some of the solubility curves indicate, the solubility of magnesium in aluminum decreases with temperature, but in large industrial aluminum alloys, the magnesium content is less than 6%. The silicon content is also low, such alloys can not be heat-strengthening, but good weldability, corrosion resistance, and moderate strength.
Magnesium strengthens the aluminum significantly. For every 1% increase in magnesium, the tensile strength is probably increased by about 34MPa. If you participate in 1% or less of manganese, you can make up for the strengthening effect. Therefore, after adding manganese, the content of magnesium can be decreased, and the tendency of hot cracking can be reduced together. In addition, manganese can evenly precipitate Mg5Al8 compound and improve the corrosion resistance and welding function.
Manganese element
The Al-Mn alloy flat equilibrium phase diagram shows that at a eutectic temperature of 658, the large solubility of manganese in the solid solution is 1.82%. The alloy strength increases with the increase of solubility, and when the manganese content is 0.8%, the elongation reaches a large value. Al-Mn alloys have a right-and-error hardening alloy, that is, no heat treatment hardening.
Manganese can hinder the recrystallization process of aluminum alloys, increase the recrystallization temperature, and can significantly refine the recrystallized grains. The refinement of the recrystallized grains is mainly due to the effect of preventing the growth of recrystallized grains through the dispersed particles of the MnAl6 compound. Another effect of MnAl6 is that soluble iron can be dissolved to form (Fe, Mn)Al6 and reduce the harmful effects of iron.
Manganese is an important element of aluminum alloys. It can participate in the formation of Al-Mn binary alloys alone. It is more often joined with other alloying elements. Therefore, most aluminum alloys are rich in manganese.
Zinc element
Al-Zn alloy phase equilibrium diagram Aluminium Rich At some 275 hours, the solubility of zinc in aluminum is 31.6%, while at 125, its solubility drops to 5.6%.
Zinc alone participates in aluminum. Under the deformation conditions, the strength of the aluminum alloy is very limited. There is stress corrosion cracking and tendency together, which restricts its application.
Participation of zinc and magnesium together in aluminum constitutes a strengthening phase Mg/Zn2, and a significant strengthening effect is exerted on the alloy. When the content of Mg/Zn2 is increased from 0.5% to 12%, the tensile strength and yield strength can be significantly increased. Magnesium content exceeds that of the superhard aluminum alloys required to constitute the Mg/Zn2 phase. When the share of zinc and magnesium is controlled at 2.7, stress corrosion cracking resistance is large.
For example, Al-Zn-Mg based on the participation of copper elements, constitute Al-Zn-Mg-Cu alloy, base strengthening effect is greater in all aluminum alloys, is also an important aerospace, aviation industry, power industry aluminum alloy materials .
2. The influence of trace elements
Iron and silicon
Iron in Al-Cu-Mg-Ni-Fe wrought aluminum alloys, silicon is added as an alloying element in Al-Mg-Si series wrought aluminum and in Al-Si based electrodes and aluminum-silicon wrought alloys. In the base aluminum alloy, silicon and iron are common impurity elements, which have a significant effect on the function of the alloy. They mainly exist as FeCl3 and free silicon. When silicon is larger than iron, β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when iron is larger than silicon, α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the share of iron and silicon is not appropriate, it will cause cracks in the casting. When the iron content in the cast aluminum is too high, the casting will be brittle.
Titanium and boron
Titanium is a commonly used addition element in aluminum alloys and is joined in the form of Al-Ti or Al-Ti-B center alloys. Titanium and aluminum form a TiAl2 phase and become a non-conscious center during crystallization, which effects refinement of forging arrangement and weld arrangement. The critical content of titanium is about 0.15% when the Al-Ti alloy is subjected to a reaction. If boron is present, the deceleration is as small as 0.01%.
chromium
Chromium is an element commonly found in Al-Mg-Si, Al-Mg-Zn, and Al-Mg alloys. At 600° C., the solubility of chromium in aluminum is 0.8%, and it is substantially insoluble at room temperature.
Chromium forms intermetallic compounds such as (CrFe)Al7 and (CrMn)Al12 in aluminum, prevents the nucleation and growth of recrystallization, has a certain strengthening effect on the alloy, and can also improve alloy resistance and reduce stress corrosion cracking susceptibility. . However, the meeting site increases the quench sensitivity, making the anodic oxide film yellow.
The increase of chromium in aluminum alloys generally does not exceed 0.35%, and decreases with the increase of transition elements in the alloy.
strontium
The ruthenium is an external active element and crystallographically can modify the behavior of the intermetallic phase. Therefore, the use of niobium element transformation process can improve the plasticity of the alloy and the final product quality. Because of the longevity, long-lasting effects, and reproducibility of defects, these years have replaced the use of sodium in Al-Si casting alloys. In the aluminum alloy used for kneading, 0.015%~0.03% niobium was added to make the β-AlFeSi phase of the ingot into a Chinese character α-AlFeSi phase, which reduced the ingot homogenization time by 60% to 70%, and improved the data mechanical function and plasticity. Processability; Improve the finished surface roughness. About 0.02%~0.07% niobium in high silicon (10%~13%) deformed aluminum alloy, it can reduce the primary crystal to a lower limit, and the mechanical function is also significantly improved. The tensile strength бb is improved from 233 MPa to 236 MPa. The yield strength б0.2 increased from 204 MPa to 210 MPa, and the elongation б5 increased from 9% to 12%. Joining the crucible in the hypereutectic Al-Si alloy can reduce the size of the primary crystal silicon particles, improve the plastic processing function, and can be smoothly hot-rolled and cold-rolled.
Zirconium element
Zirconium is also a common addition agent for aluminum alloys. In general, the participation amount of aluminum alloy is 0.1%~0.3%. ZrAl3 and ZrAl3 compounds are formed by aluminum, which can prevent the recrystallization process and refine the recrystallized grains. Zirconium can also refine the forging arrangement, but it is less effective than titanium. In the presence of zirconium, the effect of titanium and boron grain refinement is reduced. In Al-Zn-Mg-Cu alloys, because zirconium has less effect on quench sensitivity than chromium and manganese, zirconium is preferred to replace the recrystallization arrangement of chromium and manganese.
Impurity element
The rare earth elements participate in the aluminum alloy, so that when the aluminum alloy is cast, the components are overcooled, the grains are refined, the secondary crystal spacing is reduced, the gas and the gallium in the alloy are reduced, and the nodular phase tends to spheroidize. It can also reduce the external surface tension of the melt, increase the fluidity, and facilitate the casting into ingots, which has a significant effect on the process function. The amount of rare earths involved is about 0.1% at%. The increase of mixed rare-earth (such as La-Ce-Pr-Nd mixed) makes the critical temperature of Al-0.65%Mg-0.61%Si alloy formed by aging G?P region fall. Magnesium-containing aluminum alloys can stimulate the transformation of rare earth elements.
3. Influence of impurity elements
Vanadium constitutes a VAl11 refractory compound in an aluminum alloy, which refines the grain effect during the casting process, but is less effective than titanium and zirconium. Vanadium also has the effect of refining the recrystallization arrangement and increasing the recrystallization temperature.
Calcium has a very low solid solubility in aluminum alloys and forms a CaAl4 compound with aluminum. Calcium is a superplastic element of aluminum alloys, and aluminum alloys with about 5% calcium and 5% manganese have superplasticity. Calcium and silicon constitute CaSi, insoluble in aluminum, because the amount of solid solution of silicon is reduced, and the conductive function of industrial pure aluminum can be slightly improved. Calcium can improve the aluminum alloy cutting function. CaSi2 cannot strengthen the aluminum alloy by heat treatment. The trace amount of calcium facilitates the removal of hydrogen from the aluminum bath.
Lead, tin, and bismuth are low-melting metals that have little solid solubility in aluminum, slightly reducing alloy strength, but can improve cutting performance. Swelling in the condensation process is beneficial to feeding. Participation in high-magnesium alloys can avoid sodium brittleness.
锑 is primarily used as a tanning agent in forged aluminum alloys, and deformed aluminum alloys are rarely used. Replacing helium only in Al-Mg deformed aluminum alloys avoids sodium embrittlement. The niobium element participates in some Al-Zn-Mg-Cu alloys to improve the hot-pressing and cold-pressing process functions.
Niobium in the deformed aluminum alloy can improve the structure of the oxide film and reduce burning and noisiness during melting. Earthworms are toxic elements that can cause allergic poisoning. Thus, aluminum alloys that come into contact with foods and beverages cannot be rich in barium. The content of antimony in welding guess is generally controlled below 8μg/ml. The aluminum alloy used as the welding base also controls the content of niobium.
Sodium is almost insoluble in aluminum, with a large solid solubility of less than 0.0025%, and a low melting point of sodium (97.8°C). When sodium is present in the alloy, it adsorbs to the dendritic appearance or grain boundaries during the process of condensation, and the crystals are thermally processed. The sodium on the boundary constitutes the liquid adsorption layer. When brittle cracking occurs, it constitutes a NaAlSi compound, no free sodium is present, and no "sodium embrittlement" occurs. When the magnesium content exceeds 2%, magnesium is extracted from silicon, free sodium is separated, and "sodium embrittlement" occurs. Therefore, high magnesium aluminum alloys are not allowed to use sodium salt flux. The method of avoiding "sodium embrittlement" is chlorination, so that sodium constitutes NaCl and is discharged into the slag. Thallium is added to generate Na2Bi into the metal matrix; adding cerium to generate Na3Sb or adding rare earth can also have the same effect.
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