These properties are: Degree of purity The degree of purity is of great significance when selecting a casting alloy to be used together with aluminium. This is because as purity increases so does corrosion resistance and ductility. These two properties affect the structure of the alloy created when combined with aluminium which is highly ductile and corrosive resistant (Zolotorevsky et al., 2010). This is best explained by aluminium-silicon casting alloys which are highly ductile and with a high corrosion resistance.
Strength The strength of raw materials used in aluminium casting alloys also dictates the strength of the cast alloys. This is because the cast alloy should possess characteristics of both aluminium and the other metal used in the casting process. This would then mean that the cast alloy should be stronger than the parent metals used in casting. The is evident with aluminium-magnesium alloys that are stronger when compared to aluminium and magnesium individually (Zolotorevsky et al., 2010) Ductile This refers to the ability of metal to deform when exposed to tensile stress.
Therefore, metals to be used for aluminium casting alloys should have the ability to be moulded into any given shape. Otherwise, metals with low ductility are not suitable for selection for aluminium casting alloys. This is evident with Silumin-Kappa which comprises of aluminium, silicon and magnesium. All these three raw materials are highly ductile which makes them suitable for production of automobile wheels (Hirsch et al., 2008) Fluidity This is also another factor that is given high priority in aluminium casting of alloy.
Fluidity refers to the ability of molten metal to flow or fill cavity accordingly. This is to mean that the molten metal should fill the cavity depicting the characteristics of the cavity. However, fluidity of material heavily depends on the how heat is transferred during solidification (Zolotorevsky et al,, 2010). Therefore, the metal to be combined with aluminium should be highly fluid but at the same time should have uniform heat transfer during solidification. This ensures that the molten material resembles the interiors of the cavity upon solidification.
Hot tearing and internal strains This refers to the presence of cracks on the cast during solidification of the molten material. This property is equally relevant as it determines the type of metal that is to be used during casting. This factor is dependent on the properties of the alloys when in the molten state and the casting process used. However, hot tearing occurs where solidification shrinkage of the alloy and its thermal deformation cannot be compensated during liquid flow (Hirsch, et al., 2008). Therefore, the most suitable raw material for casting should have a high resistance to hot tearing Casting process There are two main casting processes that are used for casting aluminium alloys.
Each of the process has its pros and con making it suitable compared to the other casting process. Sand casting process This process is used with small scale production of the cast and when casting prototypes upon which the final cast is to be based upon. This process involves the use of sand mould, which depicts the shape of the intended cast. The use of sand casting bears various benefits, but its flexibility is probably one of its main advantages. This is evident when there is a change of design on the intended cast.
In case of such an event, it is quite easy to dismantle the mould and create another mould depicting the changes in design. Additionally, the size of the grain and shape greatly influences the quality of the cast produced. Figure 1 shows a sand cast mould Fig. 1 Sand Cast Mould (PROSNA, Inc. 2009) Die casting This process, on the other hand, involves pushing the molten metal into a die cavity by the help of pumps, ram or simply pressure. This process is normally applied when the intended mechanical properties such as elongation and strength are high.
This process is further divided into two: low pressure gravity die process and high pressure die process (Zolotorevsky et al., 2010).
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