Aluminum ranks high among metals used in manufacturing for its low density, anti-corrosiveness, and high thermal and electrical conductivity. However, not all forms of aluminum are identical. The differences between cast aluminum and wrought aluminum(often simply referred to as “aluminum”)are pivotal to the understanding of their properties, applications, and manufacturing processes.
What is Cast Aluminum?
Cast aluminum is aluminum that has been melted and poured into a mold for a desired shape. The casting process is divided into four steps:
Melting: Preparation commences with aluminum in a furnace to bring the melting point temperature to 660°C or 1220°F.
Molding: The molten aluminum is poured into a mold many times previously, designed using sand, metals, or other materials.
Cooling: The solidification process enables the aluminum to settle into the mold.
Finishing: The part is separated from the mold, and any extra material is removed: castings are often trimmed of sprues or flash and will generally be followed by secondary processes such as machining, polishing, or coating.
Aluminum casting processes include die casting, sand casting, investment casting, and permanent mold casting, each with its advantages and disadvantages.
What is Aluminum?
Aluminum is wrought aluminum and has been mechanically worked into the final form by processes including rolling, extrusion, forging, and drawing.
Heating: Aluminum is heated to obtain malleability.
Shaping: Afterward, aluminum is shaped by rolling it in sheets, extruding it into profiles, or forging it into complex shapes.
Cooling: Frequently by quenching to develop the required mechanical properties.
Finishing: These may involve additional treatments, such as annealing, tempering, or surface finishing.
Wrought aluminum is usually stronger and more ductile than cast aluminum for the work that aligns the grain structure and reduces porosity.
Mechanical Properties
Strength: Cast aluminum generally has lower tensile strength than wrought aluminum. The casting process can introduce defects such as porosity, inclusions, and uneven grain structures that act to degrade the properties of the material.
Working processes re-align grain structures in wrought processes and provide for a more homogeneous and stronger material.
Ductility: Cast aluminum is less ductile, being more susceptible to cracking under some stress. Again, this can be attributed to the presence of defects and a coarse grain structure typical for cast materials. Working processes re-align grain structures in wrought processes and provide for a more homogeneous and stronger material.
Hardness: The hardness of cast aluminum can vary widely depending on which alloy and casting process is used. Some cast aluminum alloys can be quite hard there generally, but still less hard than wrought aluminum.
Fatigue Resistance: Cast aluminum has reduced fatigue resistance because of the existence of internal defects that can work as stress concentrators.
Surface Finish and Aesthetics
Surface Finish: Cast aluminum generally has a rougher surface finish than wrought aluminum. Such surfaces require additional machining or polishing to get smooth surfaces. The mechanical working process brings more uniform surfaces to wrought aluminum, which may then be polished or anodized to further improve the look.
Aesthetics: Cast aluminum parts lend themselves to a more “cast” appearance that usually shows grain patterns and has visible surface imperfections. This is a most-desired case for some applications that purposely require rugged or industrial looks.
Cost and Manufacturing Considerations
Cost: Cast aluminum is cheaper to manufacture compared to wrought aluminum and extrusion, especially for complex shapes. The casting methods allow stylistically complex forms to take place with minimal machining so that overall costs can be reduced in the long run. And every one of the processes like rolling, extrusion, or forging tends to be more energy- and time-intensive in wrought aluminum.
Manufacturing Speed: The casting process works best for larger numbers of parts in terms of speed, especially when casting methods like die casting are used. Production of wrought aluminum parts could be considerably slower, specifically for wrought aluminum parts with complex shapes that involve multiple steps of mechanical working.
Tooling: Quite costly initially, to create molds for casting; however, the cost per part drops dramatically once the mold is created. The tooling for wrought aluminum processes–like dies for extrusion or forging–would also be expensive, but in cases where strong, high-performance components are required, costs would often be justified.
Alloy Considerations
Both cast and wrought aluminum can be alloyed with other elements to improve properties. Common alloying elements include copper, magnesium, silicon, and zinc.
Cast Aluminum Alloys
A356: An alloy that finds wide use in the manufacture of castings, characterized by good strength, ductility, and corrosion resistance properties. It is often used in automotive and aerospace applications.
A380: Another widely used cast aluminum alloy that is best defined by its excellent fluidity and pressure-tightness, making it perfect for die casting.
Wrought Aluminum Alloys
Aluminum alloy 6061: A vastly used wrought aluminum alloy with good mechanical properties as well as usable weldability. The structural application of this alloy is highly performed.
Aluminum alloy 7075: A high-strength wrought aluminum alloy that is often used in aerospace applications because of its great ratio of strength to weight.
Environmental Considerations
While the cast and wrought aluminum can be recycled, this work does have a positive influence on the sector of sustainability. However, wrought aluminum uses more energy, due to the additional mechanical working processes. Cast aluminum, while less energy-intensive to produce, may require more post-casting machining, which can offset some of the energy savings.
Future Trends
New-generation cast and wrought aluminum is driven by the demand for lightweight materials in the automotive and aerospace industries. Advanced methods in the technology of casting such as vacuum casting and squeeze casting, are accruing quality improvements and strength enhancements in cast aluminum parts. There are also many new developments in the structural processing of wrought aluminum, as well as friction stir welding and additive manufacturing, which make possible new designs of lightweight, high-strength components.
Conclusion
In summary, the final decision on the choice of cast or wrought aluminum must depend on the particular application for which it is intended. Cast aluminum is best suited for those applications where the primary considerations are the cost and the ability to form complex shapes in relatively high volumes; wrought aluminum is more suited to high-strength applications requiring ductility and a good surface finish.
