Aluminum is usually the first choice of metal when designing a new product. This metal is lightweight, durable, and useful in a wide range of industrial applications. It is strong, highly malleable, and recyclable which makes it environmentally friendly. One common form is cast aluminum which is employed when creating sturdy and useful components.
Is cast aluminum pure aluminum? The answer to this question is a resounding NO. Cast aluminum is an alloy that contains other elements to improve its mechanical properties. While the use of pure aluminum is limited, cast aluminum has important characteristics which make it indispensable. This article explains what cast aluminum is, the reasons why cast aluminum is not the same as pure aluminum, and the different ways you can cast aluminum.
What is Cast Aluminum
Cast aluminum is a component produced using one out of the many casting techniques. It involves melting aluminum metal and pouring it into a mold that contains the negative impression of the final shape. You then leave it to cool and solidify before ejecting the final casting. After ejection, the next step is to trim off all excesses and carry out the required post-processing operations.
Furthermore, aluminum casting is popular for many manufacturing reasons. It is lightweight yet strong and helps to increase fuel efficiency in the automotive and aerospace sectors. Aluminum castings have excellent corrosion resistance properties which makes them useful in harsh environments and demanding applications. Additionally, it is easy to further machine-cast aluminum components to add designs and features.
Is Cast Aluminium Pure Aluminum
No, cast aluminum is not the same as pure aluminum. Cast aluminum is an alloy that contains aluminum in conjunction with other elements such as silicon, magnesium, zinc, and copper. Each of these elements plays a unique role in improving the overall mechanical properties of the alloy. On the other hand, pure aluminum is made up of over 99% aluminum content.
The physical properties of cast aluminum and pure aluminum are also different. Pure aluminum is soft, and highly malleable with remarkable corrosion resistance properties. Conversely, cast aluminum is stronger and more durable. However, the lower aluminum content in cast aluminum makes it more susceptible to corrosive attacks.
Because of their many differences, the way you use cast aluminum and pure aluminum also differ. Pure aluminum has applications in areas where corrosion resistance is needed such as in packaging industries. It is also useful in electrical wiring and lightweight structural components. Cast aluminum, on the other hand, is ideal for applications requiring high strength and rigidity such as engine components, electrical enclosures, and medical devices.
Why Use Alloyed Aluminum in Casting
Aluminum alloys are more suitable for casting when compared to pure aluminum. The following are the reasons you should opt for alloyed aluminum when casting structures
Improved Mechanical Properties
The various alloy elements play a huge role in improving the mechanical properties of aluminum. For instance, the presence of copper, nickel, and magnesium increases strength and hardness. Furthermore, zinc metal permits precipitation hardening of the aluminum alloy.
Better Castability
Alloyed Aluminum is relatively easy to cast. They fill the mold evenly and solidify without any defects. This property is more pronounced with aluminum-silicon alloys. The presence of silicon allows the molten metal to flow freely to produce reliable components. However, the use of silicon and aluminum alone is not advisable. Other elements such as magnesium should be present to make the alloy heat treatable.
Thermal Conductivity
The thermal conductivity of cast aluminum components is top-notch. These parts allow the free flow of heat from one point to another. The ability to dissipate heat effectively makes them useful in manufacturing radiators and heat exchangers. Furthermore, aluminum alloys containing copper and silicon are thermally stable. Their properties remain unchanged even at extreme temperatures.
Corrosion Resistance
The undebatable corrosion resistance properties of alloy aluminum also make it suitable for casting. Cast aluminum forms a stable oxide layer when in corrosive environments. This protective layer prevents further oxidation and degradation. This feature makes cast aluminum suitable for use in harsh environments.
Common Methods to Cast Aluminium Alloys
There are several casting methods available for aluminum alloys. Each technique has unique benefits that make it suitable for different applications. The following are the most common methods to cast aluminum alloys
Sand Casting
Sand casting is a common process you can use to produce aluminum components. It has been around for many years and continues to evolve. The sand casting operation begins with creating the mold pattern and placing it in the sand. You then set up the gating system and remove the mold pattern as the sand takes its shape. Thereafter, melt the aluminum metal and pour it inside the mold cavity. As the metal cools and solidifies, break open the mold to remove the final casting.
Sand casting is versatile and can produce complex shapes and intricate designs. It has a low cost and is affordable for small and medium-scale businesses. However, this technique is less precise and the final parts have a limited surface finish.
Pressure Die Casting
As the name implies, you carry out the process of pressure die casting under pressure. Pressure die casting can either be high-pressure die casting (HPDC) or low-pressure die casting (LPDC). HPDC is the recommended type for casting aluminum alloys. It takes place under pressure ranging from 1,500 to 25,000 PSI.
High-pressure die casting is fast and comes with a high production rate. Additionally, you can use it when casting walls as thin as 0.4 mm. HPDC products include gearbox casings, high-production imaging equipment, and cross-car beams.
Gravity Casting
Gravity casting is another way you can cast aluminum parts. Here, the molten metal fills the mold under the force of gravity without any external force or pressure. This feature allows for consistent filling of the mold cavities to produce high-quality components. Before carrying out gravity casting, it is important to preheat the mold to avoid thermal shock and damage.
Gravity casting is a permanent mold casting method where the steel and iron molds are reusable. It produces consistent and repeatable parts with a smooth finish. However, this technique is slow because the molten metal is poured gradually under gravity.
Vacuum-Assisted Casting
Vacuum casting uses silicon molds to produce accurate and precise components. The process of vacuum casting begins with placing the mold in a vacuum chamber. You then use the vacuum to draw the molten metal inside the silicone mold. This helps to remove air bubbles and produce denser parts.
The vacuum-assisted casting comes with design flexibility and allows you to create intricate details such as undercuts and ribs. It has a low tooling cost and the surface finish of the final parts is top-notch. However, vacuum casting has some size constraints and there is a limit to the number of times you can use the silicone mold.
Conclusion
Novices and those new in manufacturing may confuse cast aluminum with pure aluminum. These two concepts stand alone and are not the same. Cast aluminum, one of the many forms of fabricated aluminum, is an alloy. The different alloying elements are added to improve the strength, hardness, and workability properties of pure aluminum. They also help to enhance thermal conductivity and improve corrosion resistance properties.