Eight major metal elements that affect the performance of aluminum alloys
The eight major elements that affect the properties of aluminum alloy are: vanadium, calcium, lead, tin, bismuth, antimony, beryllium and sodium and other metal elements, due to the different uses of the finished aluminum coil in the processing process, these impurity elements due to the different melting points, different structures and compounds formed by aluminum are also different, so the impact on the properties of aluminum alloy is also different.
1. Metallic elements: the influence of copper elements
Copper is an important alloying element, which has a certain solution strengthening effect, and 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 best when the copper content is 4%~6.8%, so the copper content of duralumin alloy in most departments is in this range.
2. Metallic elements: the influence of silicon elements
The maximum solubility of Mg2Si in aluminum is 1.85%, and the deceleration is small with the decrease of temperature.
3. Metallic elements: the influence of magnesium
The strengthening of magnesium to aluminum is significant, and for every 1% increase in magnesium, the tensile strength increases by about 34MPa. If less than 1% manganese is added, it may increase the strengthening effect. Therefore, the addition of manganese can reduce the magnesium content, and at the same time can reduce the tendency of hot cracking, and manganese can also make the Mg5Al8 compound evenly precipitate, improve the corrosion resistance and welding function.
4. Metallic elements: the influence of manganese elements
The maximum solubility of manganese in solid solutions is 1.82%. The strength of the alloy increases with the increase of solubility, and the elongation reaches the maximum value when the manganese content is 0.8%. Al-Mn alloy is a long-term age-hardening alloy, that is, it cannot be strengthened by heat treatment.
5. Metallic elements: the influence of zinc
The solubility of zinc in aluminum is 31.6% at 275, while the solubility of zinc decreases to 5.6% at 125. Zinc alone is added to aluminum, and the progress of aluminum alloy strength under the premise of deformation is very limited, and there is stress erosion cracking and tendency, which limits its application.
6. Metallic elements: the influence of iron and silicon
Iron is added as alloying elements in Al-Cu-Mg-Ni-Fe forged aluminum alloys, silicon in Al-Mg-Si forged aluminum and Al-Si electrodes and aluminum-silicon forged alloys. They are mainly found in the form of FeCl3 and free silicon. When silicon is greater than iron, the β-FeSiAl3 (or Fe2Si2Al9) phase is formed, and when iron is greater than silicon, α-Fe2SiAl8 (or Fe3Si2Al12) is formed. When the ratio of iron and silicon is not right, it will cause cracks in castings, and when the iron content in cast aluminum is too high, it will cause brittleness in castings.
7. Metallic elements: the influence of titanium and boron
Titanium is a commonly used additive element in aluminum alloys, which 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 weld structure. The critical content of titanium is about 0.15% when the Al-Ti alloy is encapsulated, and the deceleration is as small as 0.01% if boron is present.
8. Metallic elements: the influence of chromium and strontium
Chromium forms intermetallic compounds such as (CrFe)Al7 and (CrMn)Al12 in aluminum plates, which hinders the nucleation and growth process of recrystallization, strengthens the alloy to a certain extent, and can also improve the toughness of the alloy and reduce the susceptibility to stress erosion cracking. However, the venue increases the quenching sensitivity, so that the anodized film is yellow, the addition of chromium in the aluminum alloy is generally not more than 0.35%, and decreases with the increase of transition elements in the alloy, strontium adds 0.015%~0.03% strontium to the aluminum alloy for extrusion, so that the β-AlFeSi phase in the ingot becomes the Chinese character α-AlFeSi phase, which reduces the average time of the ingot by 60%~70%, and improves the mechanical function and plastic processability of the material; Improve the roughness of the surface of the product. For high silicon (10%~13%) deformed aluminum alloy, the addition of 0.02%~0.07% strontium element can reduce the initial crystal to a minimum, and the mechanical function is also significantly improved, the tensile strength бb is improved from 233MPa to 236MPa, the yield strength б0.2 is increased from 204MPa to 210MPa, and the elongation б5 is increased from 9% to 12%. The addition of strontium to the supereutectic Al-Si alloy can reduce the size of the primary crystalline silicon particles, improve the plastic processing function, and enable smooth hot and cold rolling.
