The most harmful impurities
Iron It is considered one of the most harmful impurities aluminum. This is especially noticeable in the manufacture of cast aluminum alloys for casting in a metal mold and a sand mold. Iron along with aluminum and other alloying elements, such as manganese, copper, magnesium and silicon form a phase intermediate iron, that significantly reduce the mechanical properties of the final product.
Iron, aluminum scrap
The main pollution iron aluminum It occurs during the melting of aluminum scrap, which is mixed with an iron bar. Moreover, Aluminum scrap may itself contain a high concentration of iron. It belongs, for example, to waste aluminum casting alloys under pressure. To minimize the problem of pollution of aluminum scrap iron, aluminum industry employs rigorous scrap sorting before loading it into a melting furnace. This involves manual sorting, magnetic sorting, electromagnetic sorting and so-called "air knife" for sorting crushed scrap particle density.
Разбавлять вторичный алюминий первичным?
By simple reduction of iron in aluminum dilution is its primary aluminum. Often, however, it is not profitable.
Iron-containing particles in liquid and solid aluminum
In conventional solidification of aluminum-silicon casting alloys typically begins to harden the first aluminum phase. Other components of the alloy remains liquid accumulate in the areas between the grains of the primary phase. Загрязнение железом может приводить к изменениям в порядке затвердевания фаз: первыми появляются частицы железосодержащей промежуточной фазы, and only then crystallization occurs alumina grains. When these particles are formed before aluminum, they are free to grow and so grow up in the rough crystals, surrounded by a liquid phase.
Effect of manganese at an iron removal efficiency
In the casting of aluminum alloys typically used to reduce the aluminum silicon melt viscosity. Alloys of aluminum-iron-silicon has a relatively high solubility of iron in liquid phase even after removal of the primary crystals, containing iron. therefore, for reducing the iron content in the liquid phase in the alloy added manganese, which transforms the system aluminum-iron-Kremin in aluminum-iron-manganese-silicon.
The addition of manganese gives the change in the solidification mechanisms, facilitating release of intermediate phases, containing iron, as well as reduction of the residual concentration of iron in the liquid phase to acceptable limits for casting alloys. The molten aluminum is maintained at an intermediate temperature between the formation of the intermediate phase and the appearance of aluminum. Separating the solid phase from the liquid by filtration of the melt occurs at this temperature.
The process of removing iron from aluminum
The efficiency of manganese additives on the kinetics of formation of primary phases during solidification of the aluminum alloy casting provides a method for removing iron by precipitation of the intermediate phases, followed by filtration through a ceramic filter. However, the easier and cheaper it can not be called. Nonetheless, it makes it possible to use scrap aluminum from any source, regardless of the original content in the iron, for applications, which require low iron content, such as aluminum casting molds or sand molds.
Каждый состав вторичного алюминиевого расплава требует определенного количества добавок марганца и кремния (до состава литейных сплавов) для достижения высокой эффективности удаления железа. The amount of added manganese depends on the content of iron in the melt.
Удаление железа из алюминия производят в четыре этапа (рисунок):
1) добавление в расплав марганца и, if necessary, кремния;
2) контролируемое охлаждение расплава для выделения в расплаве частиц промежуточной фазы Al(FeMn)Si;
3) отстаивание расплава для осаждения железосодержащих частиц на дно печи;
4) фильтрование расплава через керамический фильтр.
Figure – Scheme process of removing iron from aluminum
Materials Transactions, Vol. 47, No. 7 (2006)