8 Elements Affecting Casting Aluminum Alloy
1. The influence of copper
Copper is an important alloying element and has a certain solid solution strengthening effect. In addition, CuAl2 precipitated by aging has a remarkable aging strengthening effect. The copper content in aluminum sheets is usually between 2.5% and 5%, and the copper content is best at 4% to 6.8%. Therefore, the copper content of most hard aluminum alloys is in this range.
2, the influence of silicon
Al-Mg2Si alloy alloy equilibrium phase diagram The maximum solubility of aluminum-rich Mg2Si in aluminum is 1.85%. And the deceleration is small with the decrease of temperature. In the deformed aluminum alloy, silicon is added to the aluminum plate alone and is limited to the welding material, and the silicon is also added to the aluminum to have a certain strengthening effect.
3. The influence of magnesium
The strengthening of magnesium by aluminum is remarkable. For every 1% increase in magnesium, the tensile strength is about 34 MPa. If 1% or less of manganese is added, it may supplement the strengthening effect. 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 precipitate the Mg5Al8 compound on average, improving corrosion resistance and welding performance.
4, the influence of manganese
The maximum solubility of manganese in the solid solution is 1.82%. The strength of the alloy increases with increasing solubility. When the manganese content is 0.8%, the elongation reaches a maximum. The Al-Mn alloy is a long-term age hardening alloy, that is, it cannot be heat-treated.
5. The influence of zinc
Al-Zn alloy equilibrium phase diagram The solubility of zinc in aluminum is 31.6% at 275, while the solubility at 125 is reduced to 5.6%. Zinc is added to aluminum alone. Under the premise of deformation, the progress of the strength of the aluminum alloy is very limited, and there is a tendency of stress erosion cracking, which limits its application.
6, the impact of iron and silicon
Iron In the Al-Cu-Mg-Ni-Fe-based wrought aluminum alloy, silicon is added as an alloying element in Al-Mg-Si-based wrought aluminum and in Al-Si-based welding rods and aluminum-silicon forged alloys. Among the base metals, silicon and iron are common impurity elements and have a significant effect on the alloy function. They are mainly present as FeCl3 and free silicon. When silicon is larger than iron, a 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 to silicon is not correct, it will cause cracks in the casting. If the iron content in the cast aluminum is too high, the casting will be brittle.
7, the influence of titanium and boron
Titanium is an additive element commonly used in aluminum alloys and is added in the form of an Al-Ti or Al-Ti-B master alloy. Titanium forms a TiAl2 phase with aluminum, which becomes a non-spontaneous core during crystallization, which acts to refine the forged structure and the weld structure. When the Al-Ti alloy is subjected to a package reaction, the critical content of titanium is about 0.15%, and if boron is present, the retardation is as small as 0.01%.
8, the impact of chromium and bismuth
Chromium forms an intermetallic compound such as (CrFe)Al7 and (CrMn)Al12 in an aluminum plate. The nucleation and growth process that hinders recrystallization has a certain strengthening effect on the alloy, and can also improve the toughness of the alloy and reduce the sensitivity of stress corrosion cracking. However, the quenching sensitivity is increased and the anodized film is yellow. The addition amount of chromium in the aluminum alloy generally does not exceed 0.35%, and decreases as the transition element in the alloy increases. Addition of 0.015% strontium extruded to 0.03% strontium aluminum alloy in the ingot β-AlFeSi form with Chinese characters into α-AlFeSi phase. It reduces the average aging time of the ingot by 60%~70%, improves the mechanical properties and plastic workability of the material, and improves the roughness of the surface of the product. For high-silicon (10%~13%) deformed aluminum alloy, adding 0.02%~0.07% antimony element can reduce the primary crystal to a minimum and improve the mechanical function. The tensile strength бb is improved from 233 MPa to 236 MPa, the yield strength σ 0.2 is increased from 204 MPa to 210 MPa, and the elongation б5 is increased from 9% to 12%. The addition of yttrium to the hypereutectic Al-Si alloy can reduce the size of the primary silicon particles, improve the plastic working function, and smoothly perform hot rolling and cold rolling.