1.Effect of alloying elements

(1)The maximum solubility of Cu in Al is 5.65% when the al-rich part of Cu-al-Cu alloy is 548, and 0.45% when the temperature drops to 302. Copper is an important alloy element, which has a certain effect of solid solution strengthening. In addition, CuAl2 precipitated by aging has obvious effect of aging strengthening. The content of copper in aluminum alloy is usually in the range of 2.5% ~ 5% , and the strengthening effect is best when the content of copper is in the range of 4% ~ 6.8% . Aluminum-copper alloy can contain less silicon, magnesium, manganese, chromium, zinc, iron and other elements.

(2)At the EUTECTIC temperature of 577, the maximum solubility of silicon in solid solution is 1.65% . Although the solubility decreases with decreasing temperature, such alloys generally do not undergo heat treatment to strengthen. Al-si alloy has excellent casting properties and corrosion resistance. If MG AND SI are added to Al at the same time, the al-mg-si alloy is formed and the strengthening phase is Mgsi. The mass ratio of magnesium to silicon is 1.73∶1. When designing the composition of Al-Mg-Si alloys, the contents of MG and SI are proportionally distributed on the Matrix. In some Al-Mg-Si alloys, in order to improve the strength, a proper amount of copper is added, and a proper amount of chromium is added to counteract the adverse effect of copper on the corrosion resistance. The maximum solubility of Mg2si in Al-Mg2Si alloy is 1.85% , which is rich in Al-Mg2Si alloy in equilibrium phase diagram. In wrought aluminum alloys, the addition of silicon to aluminum alone is limited to welding materials, and the addition of silicon to aluminum also has a certain strengthening effect. 2. At the EUTECTIC temperature of 577, the maximum solubility of silicon in solid solution is 1.65% . Although the solubility decreases with decreasing temperature, such alloys generally do not undergo heat treatment to strengthen. Al-si alloy has excellent casting properties and corrosion resistance. If MG AND SI are added to Al at the same time, the al-mg-si alloy is formed and the strengthening phase is Mgsi. The mass ratio of magnesium to silicon is 1.73∶1. When designing the composition of Al-Mg-Si alloys, the contents of MG and SI are proportionally distributed on the Matrix. In some Al-Mg-Si alloys, in order to improve the strength, a proper amount of copper is added, and a proper amount of chromium is added to counteract the adverse effect of copper on the corrosion resistance. The maximum solubility of Mg2si in Al-Mg2Si alloy is 1.85% , which is rich in Al-Mg2Si alloy in equilibrium phase diagram. In wrought aluminum alloys, the addition of silicon to aluminum alone is limited to welding materials, and the addition of silicon to aluminum also has a certain strengthening effect.

(3)The equilibrium phase diagram of MG al-Mg alloy shows that the solubility of MG IN AL decreases with the decrease of temperature, but the content of MG in most industrial wrought AL alloys is less than 6% , and the silicon content is also low, this kind of alloy can not heat treatment strengthen, but weldability is good, corrosion resistance is good, and have medium strength. The strengthening effect of magnesium on aluminum is obvious. The tensile strength increases about 34MPa with 1% increase of magnesium. If below 1% manganese is added, it may supplement the strengthening effect. Manganese can reduce the content of magnesium and the tendency of hot cracking. In addition, manganese can make Mg5Al8 precipitate evenly and improve the corrosion resistance and weldability.

(4)The maximum solubility of manganese in solid solution is 1.82% at 658 eutectic temperature for the equilibrium phase diagram of Mn-al-Mn alloy system. The strength of the alloy increased with the increase of the solubility, and the elongation reached the maximum when the content of MN was 0.8% . Al-Mn alloy is a non-aging hardening alloy, that is, it can not be strengthened by heat treatment. Manganese can prevent the recrystallization process of aluminum alloy, increase the recrystallization temperature and refine the recrystallized grains. The refinement of recrystallized grain is mainly hindered by the dispersion particle of MNAL6 compound. Another function of MNAL6 is to dissolve impurity iron and form (Fe, MN) AL6 to reduce the harmful effect of iron. Manganese is an important element of aluminum alloy, which can be added separately to form Al-Mn binary alloy, and more often with other alloy elements, so most aluminum alloys contain manganese.

(5)The solubility of zinc in aluminium is 31.6% at 275 and 5.6% at 125 for the al-rich part of the equilibrium phase diagram of Zn-al-Zn alloy system. The addition of zinc to aluminum has limited effect on the strength of aluminum alloy, and has the tendency of stress corrosion cracking, which limits its application. The Mg/Zn2 strengthening phase was formed by the addition of MG and MG in AL, which had obvious strengthening effect on the alloy. When Mg/Zn2 content was increased from 0.5% to 12% , the tensile strength and yield strength were increased obviously. The stress corrosion cracking (SCC) resistance of the superhard aluminum alloy with MG content exceeding that of Mg/Zn2 phase was the highest when the ratio of zn to Mg was about 2.7. For example, Al-Zn-Mg-cu alloy is formed by adding copper element on the basis of Al-Zn-Mg. The base strengthening effect of Al-Zn-Mg-cu alloy is the biggest among all aluminum alloys, and it is also an important aluminum alloy material in aerospace, aviation and electric power industries.

2.Micronutrient

(1) Iron and Silicon Fe-Si iron are added as alloying elements in Al-Cu-Mg-Ni-Fe wrought aluminium alloys, silicon in Al-Mg-Si wrought aluminium alloys and in Al-Si welding rods and Al-Si cast alloys, silicon and iron are common impurity elements, which have obvious influence on the properties of the alloy. They are mainly FECL3 and free silicon. When SI is larger than fe,-fesial3(or FE2SI2AL9) phase is formed, and when fe is larger than si,-fe2sial8(or FE3SI2AL12) is formed. When the ratio of iron and silicon is not appropriate, it will cause the casting crack, and when the iron content of cast aluminum is too high, it will make the casting brittle.

(2)Titanium and Boron Ti-B titanium are commonly used as additive elements in Al-Ti or al-Ti-B master alloys. The TIAL2 phase formed by Ti and AL becomes the non-spontaneous core during crystallization, which plays an important role in refining the casting structure and weld structure. The critical content of Ti is about 0.15% when the inclusion reaction takes place in Al-Ti alloys, and the reduction rate is less than 0.01% when boron is present.

(3)Common addition elements of CR CR CR 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 almost insoluble at room temperature. Chromium forms intermetallic compounds (CRFE) AL7 and (CrMn) AL12 in aluminum, which hinder the process of nucleation and growth of recrystallization, strengthen the alloy to some extent, improve its toughness and reduce its stress corrosion cracking sensitivity. But the venue increased quenching sensitivity, so that the anodic oxidation film was yellow. The amount of chromium added to aluminum alloy generally does not exceed 0.35% , and decreases with the increase of transition elements.

(4)Strontium SR is a surface active element. In crystallography, SR can change the behavior of intermetallic compounds. Therefore, modification with strontium can improve the plasticity of the alloy and the quality of the final product. In recent years, sodium has been replaced in Al-Si casting alloys due to the advantages of long effective time, good effect and reproducibility of SR modification. Adding 0.015% ~ 0.03% strontium into aluminium alloy for extrusion can change alfesi phase into Chinese character-AlFeSi phase in ingots, reduce the homogenization time of ingots by 60% ~ 70% , improve the mechanical properties and plastic workability of materials, and improve the Surface roughness of products. The addition of 0.02% ~ 0.07% SR to high SI (10% ~ 13%) wrought aluminum alloy can reduce the primary crystal to the minimum and improve the mechanical properties significantly. The tensile strength B increases from 233 MPA to 236 MPA, and the yield strength 0.2 from 204 MPA TO 210 MPA, elongation 5 increased from 9% to 12% . Adding strontium into hypereutectic Al-Si alloy can reduce the size of primary silicon particles, improve the plastic machinability, and can be successfully hot rolled and cold rolled.

(5) Zirconium Element Zr-Zr is also a common additive for aluminum alloys. Generally, the addition of 0.1% ~ 0.3% zirconium and aluminum into aluminum alloy forms ZrAl3 compound, which can hinder the recrystallization process and refine the recrystallized grains. Zirconium can also refine the cast structure, but the effect is smaller than titanium. In the presence of Zr, the refinement effect of Ti and B is decreased. In Al-Zn-Mg-Cu Alloy, zirconium has less effect on quenching sensitivity than chromium and manganese, so zirconium should be used instead of chromium and manganese to refine recrystallized structure.

(6)The inclusion of Re in aluminum alloy can make the aluminum alloy subcool, refine the grain, reduce the secondary grain spacing, reduce the gas and inclusion in the alloy, and make the inclusion tend to spheroidize. It can also reduce the melt surface tension, increase the fluidity, is conducive to casting into ingots, has a significant impact on the process performance. It is better to add about 0.1% of each kind of rare earth. The addition of mixed rare earth (La-Ce-Pr-Nd, etc.) makes al-0.65% mg-0.61% SI alloy aged g? The critical point of the P zone is decreasing. Aluminum alloys containing magnesium can stimulate the metamorphism of rare earth elements.

3.Influence of impurity elements

Vanadium forms VAl11 refractory compound in aluminum alloy, which plays an important role in grain refinement during melting and casting, but less important than titanium and zirconium. Vanadium can also refine the recrystallization structure and increase the recrystallization temperature. Calcium has very low solid solubility in aluminum alloy, and forms CAAL4 compound with aluminum. Calcium is also a superplastic element of aluminum alloy. Calcium and silicon form Casi, which is insoluble in aluminum. The conductivity of industrial pure aluminum can be improved slightly by reducing the solid solution of silicon. Calcium can improve the cutting performance of aluminum alloy. CASI2 can not strengthen aluminum alloy after heat treatment. Trace amounts of calcium are beneficial to the removal of hydrogen from Molten Aluminum. Lead, tin and bismuth are low melting point metals, which have low solid solubility in aluminum and slightly reduce the strength of the alloy, but can improve the cutting performance. Bismuth expands during solidification, which is beneficial to feeding. Adding Bismuth to high magnesium alloys prevents sodium embrittlement. Antimony is mainly used as a modifier in cast aluminium alloys, but deformed aluminium alloys are rarely used. Replacing Bismuth only in Al-Mg wrought aluminum alloys prevents sodium embrittlement. Antimony is added to some Al-Zn-Mg-Cu alloys to improve the processing properties of hot and cold pressing.

Beryllium in wrought aluminum alloy can improve the structure of oxide film and reduce the burning loss and inclusion during melting and casting. Beryllium is a toxic element that can cause anaphylactic poisoning. Therefore, beryllium should not be present in aluminium alloys in contact with foods and beverages. Beryllium content in welding materials is generally controlled below 8 g/ml. The content of beryllium should also be controlled in aluminium alloys used as welding substrates. Sodium is almost insoluble in aluminum, the maximum solid solubility is less than 0.0025% , the melting point of sodium is low (97.8 °C) , when sodium is present in the alloy, it is adsorbed on the surface of dendrite or grain boundary during solidification, brittle cracking occurs when the formation of NAALSI compounds, the absence of free sodium, do not produce "sodium brittle. ". When the content of magnesium exceeds 2% , magnesium takes away silicon, precipitates free sodium and produces "sodium embrittlement" . Therefore, sodium salt flux is not allowed to be used in high magnesium aluminum alloy. Sodium embrittlement can be prevented by chlorination of sodium into the slag, adding bismuth to form Na2bi into the metal matrix, adding antimony to form NA3SB or adding rare earth. 

Source: China Aluminum Net

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