The elements that have great influence on the properties of aluminum alloy are copper (Cu), magnesium (mg), silicon (SI), iron (FE), manganese (MN), nickel (Ni), zinc (Zn), chromium (CR), calcium (CA).
Advantages: solid solution strengthening and aging strengthening effect, the strengthening effect * good when copper content is 4% to 6.8%, so the copper content of most hard aluminum alloy is in this range. The increase of copper content, the fluidity, tensile strength and hardness of the alloy are improved, and the mechanical properties are improved and the cutting property is better.
Disadvantages: reduce corrosion resistance and shape, and increase the tendency of thermal cracking.
2. Magnesium (mg):
Advantages: to improve tensile strength and yield * limit, and to improve the machinability of alloy.
Disadvantages: Mg2Si will make the casting brittle.
3. Silicon (SI):
Advantages: improve the casting properties of the alloy, silicon and aluminum can form solid solution, improve the high temperature molding property of the alloy, reduce shrinkage, and have no tendency of thermal cracking. The binary aluminum base alloy has high corrosion resistance. The tensile strength, hardness, cutting property and high temperature strength are improved, and the elongation is reduced. Silicon is also the main component to improve the flow performance, and good fluidity can be obtained from eutectic to hypereutectic.
Disadvantages: the hard point of free silicon is easy to appear in the crystalline silicon (SI), which makes the cutting property worse, and the high silicon aluminum alloy has a serious corrosion effect on the casting crucible.
4. Iron (FE):
Advantages: the adhesion of aluminum alloy to the mold is very strong, especially when the iron content is below 0.6%, that is, it is difficult to demould. When the iron content is more than 0.6%, the sticking mode phenomenon will be greatly reduced.
Disadvantages: when the content of iron in aluminum alloy is too high, iron exists in the alloy with the sheet or needle like structure of feal3, fe2al7 and Al Si Fe, which forms metal compounds and forms hard spots. The structure will also reduce mechanical properties, increase the thermal cracking, and make the casting brittle. When the content of iron (FE) is over 1.2%, the fluidity of alloy is reduced, the quality of casting is damaged, and the life of metal components in die casting equipment is shortened.
5. Manganese (MN):
Advantages: the strength of alloy increases with the increase of solubility. When the manganese content is 0.8%, the elongation reaches a large value. Manganese (MN) can prevent recrystallization process of aluminum alloy, increase recrystallization temperature and refine recrystallization grain significantly. The refinement of recrystallized grains is mainly through the dispersion particle of mnal6 compounds, which can hinder the growth of recrystallized grains. Another role of mnal6 is to dissolve the impurity iron (FE), form (Fe, Mn) al6, which makes the lamellar or needle like structure formed by iron in aluminum alloy become fine crystal structure, reducing the harmful effect of iron.
Disadvantages: segregation can be caused when manganese content is too high.
6. Nickel (Ni):
Advantages: it has the tendency of increasing tensile strength and hardness, which has a great influence on corrosion resistance.
Disadvantages: reduce corrosion resistance and thermal conductivity.
7. Zinc (Zn):
Advantages: adding zinc and magnesium into aluminum at the same time, forming the strengthening phase mg/zn2, which has obvious strengthening effect on the alloy.
Disadvantages: there is a tendency of stress corrosion cracking.
8. Chromium (CR):
Advantages: chromium (CR) forms intermetallic compounds such as (CrFe) AL7 and CrMn al12 in aluminum, which hinders the nucleation and growth process of recrystallization, and has a certain strengthening effect on the alloy, and also improves the toughness of the alloy and reduces the sensitivity of stress corrosion cracking.
Disadvantages: increase quenching sensitivity.
9. Calcium (CA):
Advantages: calcium has low solid solubility * in aluminum alloy, and caal4 compound is formed with aluminum. Calcium is also superplastic element of aluminum alloy. About 5% calcium and 5% manganese aluminum alloy have superplasticity. Calcium and silicon form casi2, which is insoluble in aluminum. Because of the decrease of solid solution of silicon, the conductivity of pure aluminum can be improved slightly. Calcium can improve the cutting performance of aluminum alloy. The trace calcium is beneficial to the removal of hydrogen in aluminum solution.
Disadvantages: casi2 can not strengthen the heat treatment of aluminum alloy.
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