Aluminium casting alloys Essay Example

9Aluminium Cast Alloys

Aluminium Cast Alloys

Institute

Aluminium Cast Alloys

Introduction

Aluminium is widely used in the world today compared to any other metal in the world. This can be attributed to the fact that aluminium exist in large quantities, in the world, thereby making it affordable. Additionally, the physical and chemical properties of aluminium make it suitable for various industries. This has made aluminium one of the favourite metals used when coming up alloys and casting of metals. This is based on the fact that aluminium readily combines with other metals thereby forming strong and reliable alloys. Aluminium cast alloys are one of the most common alloys which is attributed to the properties added by aluminium to the cast. This is evident in industries such as aerospace and kitchen wares that use aluminium as the main raw material for their finished products. However, aluminium cast alloys always depend on the physical and chemical of the other metal that is to be combined with aluminium to form an alloy. This is because with correct raw materials it is easier to come up with an alloy that is capable of withstanding its intended objective (ASM International, 2009). This paper looks at the various aluminium cast alloys in relation to their physical and chemical properties. Additionally, the paper looks at the process used in coming up with aluminium based alloys. This paper also looks at the commercial use of aluminium cast alloys, and whether they are economical compared to other alloys.

Selection of raw materials

As earlier stated, aluminium possesses some of the most favourable physical and chemical properties making it one of the most used metal in coming up with alloys. Some of the physical properties exhibited by aluminium include: aluminium is outstandingly light when compared to other commonly used metal. This comes in handy aerospace industry as this affects the motion of the planes. Additionally, the lightness of aluminium helps save energy, which translates to it being economical when compared with other metals (ASM International, 2009).It is also important to note that addition of other metals does not affect the density of aluminium, thus making it a suitable raw material for alloys. Thermal conductivity also makes aluminium based alloys standout compared to other alloys. This is attributed to the fact that aluminium is a very good thermal conductor. In addition to these, it has a high thermal conductivity when compared to metals such as copper thus making it suitable for environments that experience high temperatures such cooking utensils and car radiators. Additionally, aluminium has a high corrosion resistance when compared to other metal as a result of a tenacious film of oxide. This makes aluminium suitable for shipping companies as ships are constantly exposed to corrosive elements. These properties make aluminium a suitable raw material for the creation of cast alloys to be used for various commercial purposes. (Hirsch et al., 2008). However, there are certain properties that the metals to be used for alloy casting have to possess. 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)

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

aluminium casting alloys

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). In low pressure die casting, the molten metal flow upward using low pressure. The molten metal the fills a cavity at a fixed rate thereby reducing instances whereby air pockets are formed. The process also involves the use of overpressure bar, which helps in reducing the formation of deformities as a result of shrinking during solidification. This process is commonly used in casting symmetrical objects. The high pressure die casting, on the other hand, employs the use of high pressure on the molten metal while filled in a cavity. This process is the most used method when dealing with aluminium alloy. This is attributed to the fact that it results in casts that are of very high quality (Kaufman, 2008). Figure 2 and 3 shows both low pressure die cast process, and high pressure die casting process

aluminium casting alloys 1

Fig. 2 Low Pressure Die Cast process (European Aluminium Association, 2013).

aluminium casting alloys 2

Fig. 3 High Pressure Die cast process (Engineer Student, 2011).

Significance aluminium cast alloys

Aluminium alloys play a significant role in any industry as they are seen a cheaper and effective alternatives when compared to other metals. This is evident in the aerospace industry where aluminium alloys form most of the metallic parts of a plane. The reason behind this is the fact that aluminium alloys are not only light but also strong. Therefore, this allows planes to remain airborne with little stress while at the same time carry loads. The lightness of the plane also allows it travel faster covering longer distances while using less fuel. The thermal conductivity and corrosion resistance have made aluminium alloys the most preferred cooking utensils. This is because aluminium is resistant to high temperatures thereby making it suitable for cooking. The ductility of aluminium alloys also make them suitable casting alloys when compared to other metallic alloys. This is because aluminium alloys can be moulded into any shape without compromising their chemical and physical properties (ASM International, 2009). Therefore, this shows that aluminium alloys are of great significance to the world,and it is practically impossible to do without them

Conclusion

In conclusion, it is quite evident that aluminium allows play a significant role in the world as they are of great economical value. However, the selection of the best aluminium alloy is dependent on the chemical and physical properties of the raw materials used. Additionally, it is quite evident that due to the high ductile properties of aluminium alloys they are easily moulded into intended shapes. This is achieved by use of the various casting processes. Each process bears its own advantages making it preferred to other process.

References

ASM International (2009). Casting Design and Performance. Ohio: ASM International.

Engineer Student (2011). Die Casting. Retrieved from www.engineerstudent.co.uk/Images/die_casting_diagram_large.png

European Aluminium Association (2013). Aluminium Casting Techniques — Sand Casting and Die Casting Processes. Retrieved from http://www.azom.com/article.aspx?ArticleID=1392

Hirsch, J., Skrotzki, B. &Gottstein, G. (2008). Aluminium Alloys. New Jersey: John Wiley & Sons.

Kaufman, J.G. (2008). Properties of Aluminium Alloys: Fatigue Data and the Effects of Temperature, Product Form, and Processing. Ohio: ASM International.

PROSNA, Inc. (2009). Sand Casting. Retrieved from http://www.prosna.com/sand-casting-process.html

Zolotorevsky, V.S., Belov, N.A. & Glazoff, M.V. (2010). Casting Aluminium Alloys. Amsterdam: Elsevier.