The 3000 series aluminum coil alloy is an aluminum alloy with manganese as the main alloying element, and it is an aluminum alloy that cannot be strengthened by heat treatment. Its high plasticity, good welding performance, strength is higher than 1000 aluminum alloy, and the corrosion resistance is similar to 1000 aluminum alloy, is a medium strength aluminum coil alloy with good corrosion resistance, its wide use, large amount.
The role of alloying elements and impurity elements in 3000 series aluminum coil
- Manganese: Manganese is the only main alloying element in 3××× aluminum alloy, its content is generally 1.0%~1.6%, the strength, plasticity and process performance of the alloy is good, manganese and aluminum can generate MnAl6 phase. The strength of the alloy increases with the increase of Mn content. When w (Mn) >1.6%, the strength of the alloy increases. However, due to the formation of a large number of brittle compound MnAl6, the alloy is easy to crack when deformed. The recrystallization temperature of the alloy increases with the increase of w (Mn). Due to the large supercooling capacity, the alloy produces a large intrachrystalline segregation during rapid cooling crystallization. The concentration of manganese is low in the central part of the dendrites, but high in the edge part. When there is obvious manganese segregation in the cold processing products, coarse grains are easily formed after annealing.
- Iron: Iron can dissolve in MnAL6 to form (FeMn) Al6 compounds, thereby reducing the solubility of manganese in aluminum. Adding w(Fe)=0.4% ~0.7% to the alloy, but to ensure that w(Fe+ Mn)≤1.85%, can effectively refine the grain after annealing of the sheet, otherwise, the formation of a large number of coarse sheet (FeMn) Al6 compounds, will significantly reduce the mechanical properties and process properties of the alloy.
- Silicon: Silicon is a harmful impurity. Silicon and manganese form a complex ternary phase T(Al12Mn3Si2), which can also dissolve iron, forming a quaternary phase (Al, Fe, Mn, Si). If both iron and silicon are present in the alloy, α(Al12Fe3Si2) or β(Al9Fe2Si2) are formed first.Phase, will destroy the beneficial effects of iron. Therefore, the w(Si) in the alloy should be controlled to be < 0.6%. Silicon can also reduce the bath solubility of manganese in aluminum, and the effect is greater than that of iron. Iron and silicon can accelerate the decomposition process of manganese from supersaturated solid solution during thermal deformation, and can also improve some mechanical properties.
- Magnesium: A small amount of magnesium (w(Mg)≈0.3%) can significantly refine the grain after annealing of the alloy, and slightly improve its tensile strength. But it will also damage the surface gloss of the annealed material. Magnesium can also be an alloying element in Al-Mg alloy, adding w(Mg)=0.3%~1.3%, alloy strength increase, elongation (annealed state) reduced, so the development of Al-Mg-Mn alloy.
- Copper: The w(Cu) in the alloy is 0.05%~0.5%, which can significantly improve its tensile strength. However, containing a small amount of copper (w(Cu) =0.1%), it can reduce the corrosion resistance of the alloy, so the w(Cu) in the alloy should be controlled to be <0.2%.
- Zinc：When w(Zn) < 0.5%, the mechanical properties and corrosion resistance of the alloy are not significantly affected. Considering the weldability of the alloy, the limit of w(Zn) < 0.2% is adopted.