The eight major elements that affect the performance of aluminum alloys are metal elements such as vanadium, calcium, lead, tin, bismuth, antimony, beryllium, and sodium. Due to the different uses of aluminum coils and the addition of elements during processing, these Impurity elements have different melting points, different structures, and different compounds formed by aluminum, so the impact on the properties of aluminum alloys is 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, 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 is small with the decrease in 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 is limited to welding materials. There is also a certain strengthening effect.
3. Metal elements: the influence of magnesium
The strengthening effect of magnesium on aluminum coils is significant. For every 1% increase in magnesium, the tensile strength of the aluminum alloy coil increases by about 34MPa.
If less than 1% manganese is added, the strength of the aluminum coil may be enhanced. Therefore, the addition of manganese can reduce the magnesium content, and at the same time reduce the tendency of hot cracking. In addition, manganese can also make the Mg5Al8 compound precipitate evenly, and improve the corrosion resistance and welding performance of aluminum coils.
4. Metal elements: the influence of manganese
The maximum solubility of manganese in a solid solution is 1.82%. The strength of the alloy increases continuously with the increase of solubility. When the manganese content in the aluminum coil is 0.8%, the elongation reaches the maximum value. Al-Mn alloy is a long and short-age hardening alloy, that is, it cannot be strengthened by heat treatment.
5. Metal elements: the influence of zinc
The addition of zinc to aluminum alone has a very limited improvement in the strength of the aluminum alloy under the premise of deformation. At the same time, there is a tendency to stress corrosion cracking, which limits its application.
6. Metal elements: the influence of iron and silicon
Iron is added as an alloying element in Al-Cu-Mg-Ni-Fe series wrought aluminum alloys, silicon in Al-Mg-Si series wrought aluminum, Al-Si series electrodes, and aluminum-silicon forged alloys. Silicon and iron are common impurity elements in aluminum alloys, and they have a significant impact on the properties of the alloy.
They mainly exist as FeCl3 and free silicon. When the silicon is larger than the iron, the β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when the iron is larger than the silicon, the α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the proportion of iron and silicon is not right, it will cause cracks in the casting, and if the iron content in cast aluminum is too high, the casting will be more fragile.
7. Metal elements: the influence of titanium and boron
Titanium is also a commonly used additive element in aluminum alloys, and it is added in the form of Al-Ti or Al-Ti-B master alloy. 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 weld structure.
When the Al-Ti alloy produces a package reaction, the critical content of titanium is about 0.15%, and if there is boron, it is reduced to about 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 sensitivity of stress erosion cracking.
However, it will increase the quenching sensitivity and make the anodized film yellow. The amount of chromium added to aluminum alloys generally does not exceed 0.35%, and it decreases with the increase of transition elements in the alloy. Strontium adds 0.015% to aluminum alloys for extrusion. %~0.03% strontium, the β-AlFeSi in the ingot will change into α-AlFeSi, which reduces the average time of the ingot by 60%~70%. It can improve the material mechanical properties, plasticity, and processability of aluminum coils, and improve the surface roughness of aluminum alloy products.
Adding 0.02%~0.07% strontium element to high-silicon (10%~13%) deformed aluminum alloy can reduce the primary crystal to a minimum, and the mechanical function is also significantly improved. The tensile strength бb increased from 233MPa to 236MPa and the yield strength б0.2 increased from 204MPa to 210MPa, elongation б5 increased from 9% to 12%.
Adding strontium to Al-Si alloy can reduce the size of primary silicon particles, improve the plasticity and processing performance of aluminum coils, and can smoothly process aluminum coils for hot rolling and cold rolling.