8 metal elements that affect the properties of aluminum alloys
Aluminum has many excellent properties, but it is often necessary to add other metals to improve performance during processing. Which metals can affect the properties of aluminum alloys? There are
There are eight metal elements such as vanadium, calcium, lead, tin, bismuth, antimony, beryllium, and sodium.
Due to the different uses of the finished aluminum coil, the elements added during the processing of these impurity elements have different melting points, different structures, and different compounds formed by aluminum, so their effects on the properties of aluminum alloys are also different.
1. Metal elements: the influence of copper elements
Copper is an important alloying element and has a certain solid solution strengthening effect. In addition, the 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 the best when the copper content is 4%-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 system alloy equilibrium phase diagram The maximum solubility of Mg2Si in aluminum in the aluminum-rich part is 1.85%, and the deceleration decreases with the decrease of temperature. In the deformed aluminum alloy, the addition of silicon to the aluminum plate is limited to welding materials, and the addition of silicon to aluminum There is also a certain strengthening effect.
3. Metal elements: the influence of magnesium
The strengthening of magnesium to aluminum is remarkable. For every 1% increase of magnesium, the tensile strength increases by about 34MPa. If less than 1% manganese is added, the strengthening effect may be supplemented. Therefore, after adding manganese, the magnesium content can be reduced, and the tendency of hot cracking can be reduced at the same time. In addition, manganese can make the Mg5Al8 compound precipitate evenly, and improve 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 continuously with the increase of solubility, and the elongation reaches the maximum value when the manganese content is 0.8%. Al-Mn alloys are long and short age-hardening alloys, that is, they cannot be strengthened by heat treatment.
5. Metal elements: the influence of zinc
The solubility of zinc in aluminum is 31.6% when the aluminum-rich part of the Al-Zn alloy system is 275, and its solubility drops to 5.6% when it is 125. When zinc is added to aluminum alone, the improvement of the strength of the aluminum alloy is very limited under the premise of deformation, and there is a tendency of stress corrosion cracking and cracking, thus limiting its application.
6. Metal elements: the influence of iron and silicon
Iron is added as an alloying element in Al-Cu-Mg-Ni-Fe wrought aluminum alloy, silicon in Al-Mg-Si wrought aluminum, and in Al-Si series welding rod and Al-Si wrought alloy. In other aluminum alloys, silicon and iron are common impurity elements, which have a significant impact on the performance of the alloy. They exist mainly as FeCl3 and free silicon. When silicon is larger than iron, the β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when the iron is larger than silicon, α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the ratio of iron and silicon is not correct, it will cause cracks in the casting, and when the iron content in the cast aluminum is too high, the casting will become brittle.
7. Metal elements: the effect 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 a non-spontaneous core during crystallization, and plays a role in refining forging structure and weld structure. When the Al-Ti-based alloy has a clathrate reaction, the critical content of titanium is about 0.15%, and if there is boron, the deceleration is as small as 0.01%.
8. Metal elements: the influence of chromium and strontium
Chromium forms intermetallic compounds such as (CrFe)Al7 and (Crum)Al12 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 of the venue increases, making the anodic oxide film yellow. The addition of chromium in the aluminum alloy generally does not exceed 0.35%, and decreases with the increase of transition elements in the alloy. Strontium is added to the aluminum alloy for extrusion by 0.015%. ~0.03% strontium, so that the β-AlFeSi phase in the ingot becomes a Chinese character-shaped α-AlFeSi phase, which reduces the average time of the ingot by 60% to 70%, improves the mechanical properties of the material and the plastic workability; improves the surface roughness of the product.
For high silicon (10%~13%) deformed aluminum alloys, adding 0.02%~0.07% strontium element can reduce the primary crystal to the minimum, and the mechanical properties are also significantly improved. The tensile strength бb is improved from 233MPa to 236MPa, and the yield strength б0.2 increased from 204MPa to 210MPa, elongation б5 increased from 9% to 12%. The addition of strontium to the hypereutectic Al-Si alloy can reduce the size of the primary crystal silicon particles, improve the plastic working performance, and can smoothly hot-roll and cold-roll.
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