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.
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).
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.
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.
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.
Influence of modifiers (strontium) on the fluidity of aluminum, grain grinders (titanium, titanium / boron) and impurities (iron) shown in the figure 6.
Effect of aluminum purity on its fluidity
The fluidity of aluminum is very sensitive to its purity level, as seen from the picture 7.
A source: European Aluminium Association, 2002