How metallic elements affect the properties of aluminum alloy?
The eight elements that affect the properties of aluminum alloy are: vanadium, calcium, lead, tin, bismuth, antimony, beryllium and sodium.
Due to the different uses of the finished aluminum coil, the elements added in the processing process will lead to the melting point of the finished aluminum alloy, the structure is different, and the compounds formed by aluminum are different, so the impact on the performance of the aluminum alloy is not the same.
- Copper
Copper is an important alloying element and has a certain solid solution strengthening effect. In addition, CuAl2 precipitated by aging has a remarkable strengthening effect of solution and aging treatment. The copper content in the aluminum plate is usually 2.5%-5%, and the strengthening effect is best when the copper content is 4%-6.8%, so the copper content of most duralumin alloys is in this range.
- Silicon
In aluminium rich of Al-Mg2Si alloy phase equilibrium diagram, the maximum solubility of Mg2Si in aluminum is 1.85%, and the deceleration goes down with the decrease of temperature. In wrought aluminium alloy, silicon added to aluminum plate alone is limited to welding materials, and silicon added to aluminum also has a certain strengthening effect.
- Magnesium
The strengthening of magnesium on aluminum is significant. While the tensile strength increases by about 34MPa for every 1% increase in magnesium. If less than 1% manganese is added, the strengthening effect may be supplemented. Therefore, the addition of manganese will reduce the content of magnesium, while reducing the hot cracking tendency. In addition, manganese can also make Mg5Al8 compound average precipitation, improve the corrosion resistance and welding function.
- Manganese
The maximum solubility of manganese in solid solution is 1.82%. The strength of the alloy increases with the increase of solubility. The elongation reaches the maximum when the manganese content is 0.8%. Al-Mn alloy long and short age hardening alloy, that is, can not be strengthened by heat treatment.
- Zinc
In the Al-Zn alloy system, the solubility of zinc in aluminum is 31.6% at 275 degrees Celsius, and the solubility drops to 5.6% at 125 degrees Celsius. When zinc is added to aluminum alone, the strength of aluminum alloy under deformation is very limited, and there is a risk of stress erosion cracking tendency, which limits its application.
- Iron
Iron in Al-Cu-Mg-Ni-Fe series wrought aluminium alloy, silicon in Al-Mg-Si series wrought aluminium alloy and in Al-Si series welding rod and aluminum-silicon wrought aluminium alloy, are added as alloying elements. In other aluminum alloys, silicon and iron are common impurity elements, which have a significant effect on the alloy function. They exist mainly as FeCl3 and free silicon. When the content of silicon is greater than iron, the β-FeSiAl3(or Fe2Si2Al9) phase is formed, and when the content of iron is greater than silicon, the α-Fe2SiAl8(or Fe3Si2Al12) phase is formed. When the proportion of iron and silicon content is not appropriate, it will cause cracks in the casting. When the iron content in cast aluminum is too high, the casting will be brittle.
- Titanium & boron
Titanium is a common addition to aluminum alloys in the form of Al-Ti or Al-Ti-B intermediate alloys. The TiAl2 formed by titanium and aluminum becomes the non-spontaneous core during crystallization, which plays the role of refining the forging structure and weld structure. When the Al-Ti alloy produces the pack reaction, the critical content of titanium is about 0.15%, and if there is boron, the deceleration is as small as 0.01%.
- Chromium & Strontium
During the reaction process, chromium forms intermetallic compounds such as (CrFe)Al7 and (CrMn)Al12 in the aluminum plate, which impedes the nucleation and growth process of recrystallization, has a certain strengthening effect on the alloy, and can improve the toughness of the alloy and reduce the sensitivity of stress erosion cracking. However, it will increase the quenching sensitivity and make the anodic oxide film yellow. The addition of chromium in aluminum alloys generally does not exceed 0.35%, and decreases with the increase of transition elements in the alloy. By adding 0.015%~0.03% strontium to aluminum alloy for extrusion, the β-AlFeSi phase in the ingot becomes α-AlFeSi phase, reducing the average casting time by 60%~70%, strengthening the mechanical function and plastic workability of the material, and improving the surface roughness of the product.
