The eight major elements that affect the performance of aluminum alloys are: vanadium, calcium, lead, tin, bismuth, antimony, beryllium, sodium and other metal elements. These impurity elements are the elements added during the processing depending on the purpose of the finished aluminum coil. Due to the different melting points, different structures and different compounds formed by aluminum, the effects on the properties of aluminum alloys are also different.
1. Metal element: the influence of copper element
Copper is an important alloy element and has a certain solid solution strengthening effect. In addition, CuAl2 precipitated by aging has a significant aging strengthening effect. The copper content in the aluminum plate is usually 2.5%-5%, and the strengthening effect is best when the copper content is 4% to 6.8%, so the copper content of most hard aluminum alloys is in this range.
2. Metal elements: the influence of silicon
Al-Mg2Si alloy series alloy equilibrium phase diagram The maximum solubility of Mg2Si in aluminum in the aluminum-rich sector is 1.85%, and the deceleration is small with the decrease of temperature. In deformed aluminum alloys, the addition of silicon alone to the aluminum plate is limited to welding materials, and the addition of silicon to aluminum It also has a certain strengthening effect.
3. Metal elements: the influence of magnesium
The strengthening of aluminum by magnesium is remarkable. For every increase of 1% of magnesium, the tensile strength will increase by about 34MPa. If adding less than 1% manganese, the strengthening effect may be added. Therefore, after adding manganese, the magnesium content can be reduced, and the hot cracking tendency can be reduced at the same time. In addition, manganese can also precipitate the Mg5Al8 compound evenly, improving the corrosion resistance and welding performance.
4. Metal elements: the influence of manganese
The maximum solubility of manganese in solid solution is 1.82%. The strength of the alloy increases with the increase in solubility, and the elongation reaches the maximum when the manganese content is 0.8%. Al-Mn alloy is long and short age hardening alloy, that is, it cannot be strengthened by heat treatment.
5. Metal elements: the influence of zinc
Al-Zn alloy system equilibrium phase diagram The solubility of zinc in aluminum is 31.6% at 275 in the aluminum-rich section, and its solubility drops to 5.6% at 125. Zinc alone is added to aluminum, and the improvement of aluminum alloy strength is very limited under the premise of deformation, and there is stress corrosion cracking and tendency, which limits its application.
6. Metal elements: the influence of iron and silicon
Iron in Al-Cu-Mg-Ni-Fe series wrought aluminum alloy, silicon in Al-Mg-Si series forged aluminum and Al-Si series electrode and aluminum-silicon forging alloy are all added as alloying elements. Among base aluminum alloys, silicon and iron are common impurity elements, which have a significant impact on the performance 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 ratio of iron and silicon is not right, it will cause cracks in the casting, and if the iron content in the cast aluminum is too high, the casting will be brittle.
7. Metal elements: the influence of titanium and boron
Titanium is a commonly used additive element in aluminum alloys and is added in the form of Al-Ti or Al-Ti-B master alloys. Titanium and aluminum form the TiAl2 phase, which becomes the non-spontaneous core during crystallization, and plays a role in refining the forging structure and the weld structure. When the Al-Ti alloy produces a clad reaction, the critical content of titanium is about 0.15%. If boron is present, the deceleration is as small as 0.01%.
8. Metal elements: the influence of chromium and strontium
Chromium forms (CrFe)Al7 and (CrMn)Al12 intermetallic compounds in the aluminum plate, which hinders the nucleation and growth process of recrystallization, has a certain strengthening effect on the alloy, and can also improve the toughness of the alloy and reduce the susceptibility to stress corrosion cracking . However, the quenching sensitivity is increased at the venue to make the anodic oxide film yellow. The amount of chromium added to the aluminum alloy is generally not more than 0.35%, and it decreases with the increase of transition elements in the alloy. Strontium adds 0.015% to the aluminum alloy for extrusion ~0.03% strontium, the β-AlFeSi phase in the ingot becomes the Chinese-shaped α-AlFeSi phase, which reduces the averaging time of the ingot by 60%~70%, improves the mechanical performance and plastic workability of the material; improves the surface roughness of the product . For high silicon (10%~13%) wrought aluminum alloy, adding 0.02%~0.07% strontium element can reduce the primary crystals to a minimum, and the mechanical performance is also significantly improved. The tensile strength бb is increased from 233MPa to 236MPa, and the yield strength is б0.2 increased from 204MPa to 210MPa, elongation б5 increased from 9% to 12%. Adding strontium to the hypereutectic Al-Si alloy can reduce the size of primary silicon particles, improve the plastic processing performance, and can smoothly hot-roll and cold-roll.
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