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At last! The role of various elements in aluminum alloy
- At last! The role of various elements in aluminum alloy
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At last! The role of various elements in aluminum alloy
haomeialu > 02-09-2018, 03:25 AM
copper
The maximum solubility of copper in aluminum is 5.65%, and the solubility of copper is 0.45% when the temperature drops to 302. Copper is an important alloy element, which has certain solid solution strengthening effect, and CuAl2 has obvious aging effect. The copper content in aluminum alloy is usually 2.5% ~ 5%, and the copper content is the best when 4%~6.8%, so the copper content of most hard aluminum alloy is in this range. Aluminum copper alloy can contain less silicon, magnesium, manganese, chromium, zinc, iron and other elements.
silicon
The maximum solubility of silicon in solid solution was 1.65% when the eutectic temperature of Al - Si alloy was 577. Although solubility decreases with temperature, such alloys are generally not heat-treatable. Aluminum silicon alloy has excellent casting performance and corrosion resistance. If magnesium and silicon are added to aluminum to form the aluminum magnesium silicon alloy, the enhanced phase is MgSi. The mass ratio of magnesium and silicon is 1.73:1. When designing the composition of al-mg-si alloy, the content of magnesium and silicon is configured on the base. Some of the al-mg-si alloys, in order to increase the strength, add a moderate amount of copper, and add a moderate amount of chromium to offset the adverse effects of copper against corrosion.
The maximum solubility of Mg2Si in al-mg2si alloy is 1.85% in aluminum, and decreases with the decrease of temperature. In the deformed aluminum alloy, the silicon alone is limited to the welding material, and the addition of silicon to aluminum has certain strengthening effect.
magnesium
Al - Mg alloy system equilibrium phase diagram rich aluminum part though the solubility curve shows that the solubility of magnesium in aluminium greatly decreases with temperature drop, but in most of the deformation of industrial aluminum alloy, magnesium content are less than 6%, and silicon content is low, this kind of alloy can't heat treatment to strengthen, but good weldability, corrosion resistant, with moderate intensity. Magnesium's reinforcement to aluminum is obvious, with each increase of 1% magnesium, the tensile strength is about to increase by about 34MPa. If you add less than 1% of manganese, you may be reinforcing. Therefore, manganese can decrease the content of magnesium and reduce the tendency of thermal cracking. Besides, manganese can also precipitate the Mg5Al8 compound and improve the corrosion resistance and welding properties.
Manganese element
The maximum solubility of Mn in the solid solution was 1.82% when the eutectic temperature was 658. The strength of alloy increases with the increase of solubility, and when the manganese content is 0.8%, the elongation reaches the maximum. Al-mn alloy is non - aging hardening alloy, which is non - heat - treatment hardening. Manganese can prevent the recrystallization process of aluminum alloy, improve recrystallization temperature, and can significantly refine the recrystallization grain. The refinement of recrystallized grains is mainly an obstacle to the growth of recrystallized grains by the dispersion of MnAl6 compounds. Another function of MnAl6 is to dissolve impurities iron, forming (Fe, Mn) Al6, reducing the harmful effects of iron. Manganese is an important element of aluminum alloy. It can be added to form al-mn binary alloy separately, and more is added with other alloy elements, so most aluminum alloys contain manganese.
zinc
The solubility of Zn in aluminum was 31.6%, while at 125, the solubility decreased to 5.6%. Zinc alone is added to aluminum, and the strength of aluminum alloy is very limited under the condition of deformation. Meanwhile, stress corrosion cracking and tendency are also present, thus limiting its application. Zinc and magnesium were added to the aluminum to form the strengthening phase Mg/Zn2, which had a significant strengthening effect on the alloy. When Mg/Zn2 content increased from 0.5% to 12%, the tensile strength and yield strength were significantly increased. The content of magnesium is higher than that of the superhard aluminum alloy required to form Mg/Zn2 phase. The ratio of zinc and magnesium is controlled at about 2.7, and the stress corrosion cracking resistance is the largest. If copper is added on the basis of al-zn-mg, it will form al-zn-mg-cu alloy, and the base strengthening effect is the largest in all aluminum alloys, and is also an important aluminum alloy material in aerospace, aviation industry and electric power industry.
Iron and silicon
Iron in Al - Cu - Mg - Ni - Fe in the forging of aluminum alloy, silicon in Al - Mg - Si is wrought aluminium and in Al - Si electrode and aluminum silicon alloy casting, all of the alloy elements and in its aluminium alloy, silicon and iron is a common impurity elements, have obvious influence on performance of alloy. They mainly exist in FeCl3 and free silicon. When the silicon is greater than the iron, it forms the beta -FeSiAl3(or Fe2Si2Al9) phase, while the iron is greater than the silicon, forming the alpha-fe2sial8 (or Fe3Si2Al12). When the ratio of iron and silicon is not at that time, it will cause cracks in the castings, and when the iron content in cast aluminum is too high, the casting will be brittle.
Titanium and boron
Titanium is a commonly used additive element in aluminum alloy, and is added in the form of al-ti or al-ti-b intermediate alloy. Titanium and aluminum form TiAl2 phase, which becomes the non-spontaneous core of crystallization, and the function of the cast structure and weld organization is refined. The critical content of titanium was about 0.15% when the al-ti alloy was produced. If boron existed, the reduction was small to 0.01%.
chromium
The addition of chromium in al-mg -Si, Al-Mg-Zn and Al-Mg alloys. In 600 ℃, chrome aluminum solubility of 0.8%, when the room temperature basically insoluble. (CrFe) Al7 and chromium in aluminium (CrMn) Al12 intermetallic compounds, such as hinder recrystallization nucleation and growth process, the alloy has certain reinforcement, also improve alloy toughness and reduce the stress corrosion cracking sensitivity. However, the sensitivity of quenching was increased, and the anodic oxide film was yellow. The addition of chromium in aluminum alloy is generally not more than 0.35%, and decreases with the increase of transition element in alloy.
strontium
Strontium is a surface active element, and strontium can change the behavior of intermetallic compounds in crystallography. Therefore, the modification can improve the plasticity and final product quality. In recent years, the use of sodium in al-si alloy has been replaced by the advantages of long time, good effect and good reproducibility. For extruded aluminum alloy, 0.015%0.03% strontium was added to make the ingot-alfesi phase change into the han-type, which reduced the uniformity of ingots by 60% and 70%, and improved the mechanical properties and plasticity of the materials. Improve surface roughness of products. For the deformation of high silicon (10% 13%), adding 0.02% 0.07% strontium aluminium alloy elements can make the crystal to reduce to a minimum, at the beginning of mechanical properties was also significantly increased, tensile strength б b from 233 mpa to 233 mpa, yield strength б 0.2 from 204 mpa to 210 mpa, elongation б 5 increased from 9% to 9%. The addition of strontium in the eutectic al-si alloy can reduce the size of the initial silicon particles and improve the plastic processing properties, which can be successfully rolled and cold rolled.
zirconium
Zirconium is also a common additive in aluminum alloys. In the aluminum alloy, the addition of 0.1%-0.3%, zirconium and aluminum ZrAl3 compounds can inhibit the recrystallization process and refine the recrystallized grains. Zirconium can also refine casting tissue, but less than titanium. When zirconium is present, it reduces the effect of titanium and boron refining grains. In al-zn-mg-cu alloy, zirconium is suitable to replace chromium and manganese to refine the recrystallization structure due to the effect of zirconium on quenching sensitivity than chromium and manganese.
Rare earth elements
The rare earth elements are added to the aluminum alloy, so that the aluminum alloy can be melted in the process of cooling, refining the grain, reducing the spacing of the secondary crystals, reducing the gas and inclusion in the alloy, and making the inclusions tend to spherify. It can also reduce the surface tension of melt, increase fluidity, and be beneficial to casting ingot, which has obvious influence on process performance. The amount of rare earth added is about 0.1%at%. The addition of mixed rare earth (la-ce-pr -Nd, et Al.) made Al-0.65 Mg-0.61%Si alloy aging G? The critical temperature in P area is reduced. Magnesium - containing aluminum alloy can stimulate the metamorphism of rare earth elements.
The impurity elements
Vanadium formed VAl11 refractory compound in aluminum alloy, and refined grain function in the process of melting, but less than titanium and zirconium. Vanadium also has the effect of refining and recrystallization and increasing the temperature of recrystallization.
Calcium is very low in solid solubility in aluminum alloy, forming CaAl4 compound with aluminum, calcium is the superplastic element of aluminum alloy, about 5% calcium and 5% manganese aluminum alloy has superplasticity. Calcium and silicon are formed and are insoluble in aluminum. As a result of reducing the solid solubility of silicon, the conductivity of industrial pure aluminum can be slightly improved. Calcium can improve the cutting performance of aluminum alloy. CaSi2 does not enhance heat treatment of aluminum alloys. Trace calcium helps to remove hydrogen from aluminum.
Lead, tin and bismuth elements are low melting point metals. They have a low solubility in aluminum and slightly reduce the strength of alloy, but can improve the cutting performance. The bismuth expansion in the solidification process is beneficial to the retraction. The addition of bismuth in the high magnesium alloy prevents the sodium brittle.
Antimony is mainly used as metamorphant in casting aluminum alloy, and deformed aluminum alloy is seldom used. Bismuth is only used in Al-Mg deformed aluminum alloy to prevent sodium brittleness. Antimony elements were added to some Al-Zn-Mg-Cu alloys to improve the performance of hot and cold pressing.
Beryllium can improve the structure of the oxide film and reduce the loss and inclusion during melting. Beryllium is a toxic element that can cause allergic intoxication. Therefore, it is not possible to contain beryllium in the aluminium alloy exposed to food and beverages. The amount of beryllium in the welding material is usually controlled below 8. G /ml. The aluminium alloy used for welding the substrate should also control the content of beryllium.
Almost don't dissolve in sodium in aluminum solid solubility is less than 0.0025%, the largest of the low melting point of sodium (97.8 ℃), sodium exist in the alloy, adsorption on the surface of the dendrite in the process of solidification or grain boundary, hot working, sodium form liquid adsorption layer on the grain boundary, produce brittle cracking, NaAlSi compound formation, no free sodium exist, does not produce sodium "fragile". When the magnesium content exceeds 2%, magnesium takes the silicon, precipitates out the free sodium and produces "sodium brittle". Therefore, magnesium alloys are not allowed to use sodium salt flux. The method of preventing "sodium embrittlement" has the method of chlorination, which causes the sodium to form NaCl into the slag, adding bismuth to produce Na2Bi into the metal matrix. Adding antimony to Na3Sb or adding rare earth can also play the same role.