the fluidity of aluminum

Metal fluidity

Fluidity - this is a purely foundry term and it differs from the general scientific term "fluidity". In ordinary science, "fluidity" is a quantity, reverse viscosity and, so, it can be accurately measured numerically.

Foundry fluidity (also called "casting fluidity") is defined as the distance, on which the liquid metal penetrates into the cavity of the casting mold during metal casting, including, at aluminum casting. Therefore, fluidity is not absolute, relative magnitude.

When molten aluminum enters the mold cavity, then during this flow it loses its thermal energy. Finally, aluminum begins to solidify and stops flowing at some point in the cavity.

zhidkotwkuchest-alyuminiya-neobxodimostFigure 1 - For such complex castings with thin elements, a high degree of metal fluidity is required

Influence of casting technology on metal fluidity

The main factors, affecting the fluidity of the metal, They are as follows.
1) Initial metal temperature.
2) Power of heat extraction from the melt by the material of the casting mold, including the effect of thermal insulation coatings on the mold.
3) Kinetic energy of metal. Gravity casting (chill casting) and sand casting rely on the flow of metal from top to bottom under its own weight. Low and high pressure casting is used in different ways, adjustable pressure for, to make the metal flow into the mold.
4) Metal purity, that is, the presence of impurities in the alloy also has a great effect on the fluidity of the metal (figure 2).

zhidkotekuchest-alyuminiya-filtrFigure 2 - Influence of filtration of aluminum melt on its fluidity

The role of metal fluidity in casting

1) Insufficient fluidity can lead to incomplete filling of the mold and indistinct repetition of the shape of the product.
2) Excessive fluidity can result in metal penetration through the sand mold or excessive metal splashing as it travels through the casting channels.
3) In practice, the fluidity of the metal is controlled by the choice of the alloy, melt temperature and mold temperature.
4) Deterioration in metal fluidity may be an indication of contamination..
5) You can expect a change in the fluidity of the metal with a change in the content of impurities, the introduction of additives for grain refinement or alloy modification.

Spiral fluidity test

The spiral sample is the pouring of metal into a spiral sand mold (Figure 3). It is the oldest method for assessing the fluidity of a metal.. The metal is poured into a mold at a carefully controlled temperature and the length is measured, which metal went through.

zhidkotekuchest-spiralnaya-probaFigure 3 - Diagram of a spiral fluidity test

Vacuum fluidity test

The essence of a vacuum fluidity test is as follows (figure 4). Ceramic or quartz tube connects to the vacuum system. This pipe is dipped into the tested melt at a given temperature. The height of the rise of the metal is judged on its fluidity.

zhidkotekuchest-vakuumnaya-probaFigure 4 - Scheme of a vacuum sample for fluidity

Influence of alloying elements on aluminum fluidity

The effect of the alloying elements (copper and silicon) content in aluminum on the fluidity is shown in the figure 5.

zhidkotekuchest-alyuminiya-legirovanieFigure 5 - Dependence of aluminum fluidity
from silicon and copper content

Influence of modifiers (strontium) on the fluidity of aluminum, grain grinders (titanium, titanium / boron) and impurities (iron) shown in the figure 6.

zhidkotekuchest-alyuminiya-legiruyushchie-elementyFigure 6 - Influence of changes in impurity content on the fluidity of aluminum alloy A320, alloying elements and modifying additives

Effect of aluminum purity on its fluidity

The fluidity of aluminum is very sensitive to its purity level, as seen from the picture 7.

zhidkotekuchest-chistogo-alyuminiyaFigure 7 - A sharp decrease in the fluidity of pure aluminum with an increase in the total content of impurities

A source: European Aluminium Association, 2002

More about sand casting of aluminum:

Aluminum Alloy Casting: Properties, Processes And Applications – J. Gilbert Kaufman, Elwin L. Rooy