Introduction
Aluminum is one of the most popular materials in the contemporary design and construction due to its benefits such as high strength to weight ratio, corrosion resistance, ease of shaping, and aesthetically pleasing look. These qualities have made it to have immense increase in usage in almost every field within various industries over the past few years which speaks about its importance in today’s world.
Although pure aluminum has some useful properties, its uses are somewhat limited in practical application. It is usually alloyed with silicon, magnesium, and manganese to create materials that have enhanced and particular properties for different applications. This process creates a number of different grades of aluminum alloys that have different physical and chemical characteristics, which makes them suitable for use.
The aluminum alloys are mainly categorized into two broad categories based on the process of manufacturing; the wrought aluminum alloys and the cast aluminum alloys. These two types are manufactured through different industrial processes that define their characteristics in the solid form of the final product. In this article, we will explain the classification criteria of aluminum alloys, their distinctive key physical properties, and most frequent uses.
An Overview of Wrought Aluminum
Wrought aluminum alloys are those aluminum alloys that are formed through mechanical working while in the solid state. This category includes a vast majority of aluminum uses, about 85% of all aluminum used. The working of the metal by rolling, extrusion, forging, and drawing etc., alters the grain structure of the metal and in most cases improves its strength and other mechanical characteristics. Different types of aluminum alloys are classified by a four-digit number, where the first digit refers to the primary alloying element, and the second digit refers to the particular alloy or the aluminum purity in case of the 1xxx series, which makes it easier for the professionals to determine their main properties and the areas of their application.
An Overview of Cast Aluminum
Different from wrought aluminum, cast aluminum alloys are made by pouring liquid aluminum into molds of the intended shape. This method is especially useful for the creation of geometries and intricate parts of the model. Cast alloys contain more silicon than the wrought alloys and this makes them to have better flow characteristics when being cast. They are also numbered with a four-digit system, but with a decimal point after the first three digits to indicate it’s a cast alloy. Although wrought alloys are much more durable, for some applications, flexibility in design is far more beneficial which is provided by cast alloys.
Wrought vs. Cast Aluminum: Key Differences
Wrought and cast aluminum are both vital materials in the current manufacturing industries, but they differ in terms of composition, processing, and performance.
Alloying Elements
The first difference is based on the elements used in the alloys and their percentages.
Wrought alloys are produced by proper combination and proportioning of elements such as copper, manganese, silicon, magnesium and zinc to obtain the desired mechanical properties like strength, ductility and corrosion resistance. The elements chosen for cast alloys are those that enhance their castability, especially silicon, but other elements are also added to fine-tune the properties of the alloy.
Fabrication Methods
As mentioned earlier, wrought aluminum is that aluminum which is shaped in its solid state by processes such as rolling to produce sheets, aluminum extrusion to produce profiles or forging to produce three dimensional shapes. Cast aluminum, on the other hand, is formed in a mold cavity when it is in a molten state and then solidifies. This difference in fabrication has implications on the achievable shapes, the grain structure of the metal and the strength properties.
Structural and Performance
In a broad sense, wrought aluminum alloys are stronger, more ductile, and have better fatigue resistance compared to cast alloys of the same elements due to mechanical working processes through which the grain structure is aligned. Though cast alloys may be weaker, they are more suitable for applications which require greater geometric complexity due to their ability to be designed with intricate features.
Wrought Aluminum Series
Wrought aluminum has a distinct four-digit designation which indicates its primary alloying element, the following are the wrought aluminum alloy series:
1000
The 1xxx series is of commercially pure aluminum with aluminum content of 99% and above. These alloys have high corrosion resistance, but they also exhibit poor corrosion resistance in certain environments. They have high thermal and electrical conductivity, are suitable for heat sinks, and have good workability. They are commonly employed in applications where such characteristics are desirable, for instance in chemical processing equipment, electrical conductors, and decorative trim.
Two noteworthy grades in this series are: 1050, which has very high ductility and is used in applications such as spun hollowware. There is 1100, which is characterized by good formability and weldability in most of the general sheet metal uses and fin stock.
2000
Copper is the main alloying element in the 2xxx series, which is present in an amount of between 2.2% and 6.8%. These alloys are usually characterized by high strength and are normally heat-treatable. They are widely employed in aerospace industries and other areas of high mechanical stress. Nevertheless, they are less resistant to corrosion as compared to other aluminum alloys.
One of the best examples of the series is 2024 aluminum that is known for its high strength to weight ratio that makes it a popular material for aircraft fuselage, marine equipment, and wing frame. Another important grade is 2017, which is also widely used in aerospace applications for such parts as rivets and structural members, where good machinability is also desirable.
3000
Manganese is the major alloying element in the 3xxx series, which is usually incorporated in a range of 0.3-1.5%. These alloys have good formability and moderate strength, about 20% higher than the 1xxx series. They are widely used in uses like general sheet metal work, utensils used in cooking and in pressure vessels.
One of the most popular grades in this series is the 3003 aluminum, which has good formability and corrosion resistance, and is widely used in roofing, sidings, and manufacturing of chemical storage tanks, as well as in various architectural applications, but it cannot handle high temperatures.
4000
Silicon is the main alloying element in the 4xxx series with the content of between 3.6% and 13.5%. These alloys have a low melting range and good flow characteristics, which makes them ideal for welding and brazing. They are also employed in construction and as welding filler metals.
Some of the alloys in this series are also characterized by good strength and wear resistance. One of the most popular is 4043 aluminum, which is used as a welding filler for aluminum and is particularly suitable for heat-treatable base alloys.
5000
In the 5xxx series, magnesium is the most significant alloying element, which may be present in an amount of between 0.05% and 5.5%. These alloys are highly weldable and possess good corrosion resistance especially in marine applications. They have medium to high tensile strength and are applied in ships, storage tanks, and pressure vessels.
Among the 5000 series alloys, 5052 aluminum is particularly strong and easily weldable, which is why it is used in the construction of marine vessels and pressure vessels. In addition, 5083 aluminum has much higher the highest strength and excellent performance in severe corrosive conditions, often used in shipbuilding and offshore structures.
6000
The 6xxx series contains magnesium (0.35% to 1.5%) and silicon (0.2% to 1.8%) as the main alloying elements. These are heat treatable and possess good strength, weldability, heat treatability, and corrosion resistance. These are used in architectural extrusions, bicycle frames, automotive parts and in furniture.
Aluminum 6061 is one of the most popular alloys from this series due to its satisfactory characteristics and a wide range of applications in various structures. Accompanying it is 6063 aluminum which is used in extrusionsaluminum extrusion applications where surface finish is important, for instance in windows and door frames.
7000
Zinc is the main alloying element in the 7xxx series, which is usually between 0.8-8.2% and can be combined with magnesium and copper. These are the strongest aluminum alloys and are widely used in aerospace constructions, sports equipment, and military equipment. It may have lower corrosion resistance as compared to other series.
Aluminum 7075 is well known for its performance and is used in aircraft fittings and gears. Another alloy is 7050 aluminum that has similar strength to 7075 but has better stress corrosion cracking resistance making it ideal for use in aircraft fuselage skins and wing planks.
Cast Aluminum Series
The same pattern applies to cast aluminum alloys where the first digit represents the primary alloying element, here are the various cast aluminum alloy series:
1xx.x
Like the wrought 1000 series, the 1xx.x cast series are primarily aluminum casting alloys that have good corrosion resistance and electrical conductivity but low strength.
They are widely used for chemical equipment and in applications where high electrical or thermal conductivity is needed, for instance in certain electrical parts and heat exchangers.
2xx.x
Copper is the main alloying element in this series. These alloys can reach high strength and are frequently exposed to heat treatment. But they are not very resistant to corrosion in most cases. The high strength attainable in this series makes them ideal for structural castings in aerospace and military applications where strength is a critical factor although most of these applications require protection coatings in various environments.
3xx.x
These alloys contain silicon with copper and/or magnesium. It is easy to cast, strong, and has a high degree of resistance to corrosion. Due to its high castability, this series is ideal for complex castings that are used in automotive parts such as engine blocks and cylinder heads, as well as aerospace structural parts.
4xx.x
Silicon is the main alloying element in the 4xx.x cast series. These alloys are characterized by their good flow characteristics during casting and are commonly employed in applications that require high wear resistance. They are ideal for pistons, pump housings and other parts that are prone to frictional forces due to their wear resistance.
5xx.x
Magnesium is the primary addition in the 5xx.x cast series, these alloys are known for their good casting fluidity and are often used in applications that require good wear resistance. Due to their wear resistance, they are used in pistons, pump housings and other parts that are exposed to frictional loads.
7xx.x
Zinc is the primary alloying component.These alloys are strong and can be heat treated to improve their characteristics. Because of their strength, they are used in aerospace structural parts and high stress parts where weight is a major consideration.
8xx.x
Tin is the main alloying element in the 8xx.x cast series. These are less frequently used and are mainly used in special bearing applications because of their good bearing properties and wear resistance.
Popular Aluminum Types for Sheet Metal Fabrication
In choosing aluminum for sheet metal fabrication, certain grades of aluminum alloys are more suitable in terms of strength, corrosion resistance, and ease of working. Here are some of the most frequently used aluminum grades in fabrication:
| Property | Aluminum 1100 | Aluminum 3003 | Aluminum 5052 | Aluminum 6061 |
| Composition | 99.0% min Al | 96.8-99.0% Al, 1.0-1.5% Mn | 95.7-97.7% Al, 2.2-2.8% Mg, 0.15-0.35% Cr | 95.8-98.6% Al, 0.8-1.2% Mg, 0.4-0.8% Si, 0.15-0.4% Cu, 0.04-0.35% Cr, 0.15-0.40% Mn |
| Strength (MPa) | 125 | 130 | 210 | 290 |
| Hardness (HB) | 30 | 40 | 60 | 95 |
| Corrosion Resistance | Excellent (in atmospheric environments) | Good (in atmospheric environments) | Excellent (especially in marine environments) | Good (but needs coating in aggressive environments) |
| Weldability | Excellent (all methods) | Good (all methods) | Good (needs preheating) | Good (TIG, MIG) |
| Machinability | Excellent (easy to machine) | Good (easy to machine) | Fair (requires harder tools) | Good (needs high-performance tools due to higher strength) |
Note: All the data provided are based on typical reference values and actual performance may vary depending on the batch of the alloy, the manufacturing process and the operating environment. It is advisable to refer the most recent information from the supplier’s technical documentation.
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Key Factors for Choosing the Right Aluminum Type
Selecting the right aluminum alloy is essential for ensuring optimal performance and durability of the final product. Here are the key factors to consider:
Application Requirements
The intended use of the final product is the most critical factor. If the product will be exposed to harsh environments, such as moisture or chemicals, choosing a corrosion-resistant alloy is crucial. For applications requiring high strength, such as aerospace or automotive, alloys with higher tensile strength like 6061 or 7075 are ideal.
Strength-to-Weight Ratio
Aluminum is known for its excellent strength-to-weight ratio, but this varies between different alloys. For industries like aerospace, where weight reduction is critical, alloys like 7075 are favored due to their high strength-to-weight ratio. General applications may require alloys such as 6061, which balance strength and weight, providing cost-effective solutions without sacrificing performance.
Corrosion Resistance
If the application involves exposure to moisture, chemicals, or saltwater, choosing an alloy with good corrosion resistance is paramount. Alloys like 5052 in the 5xxx series offer excellent resistance to saltwater and harsh chemicals, making them perfect for marine environments. For less demanding outdoor applications, alloys like 1xxx and 3xxx offer good corrosion resistance at a lower cost.
Machinability
The ease with which an aluminum alloy can be machined is an important consideration for manufacturing processes. Alloys like 6061 are easy to machine, allowing for precision and faster production. High-strength alloys such as 7075, however, require specialized tools and techniques, potentially increasing manufacturing costs.
Weldability
If welding is required for the fabrication process, the weldability of the chosen aluminum alloy is crucial. Some alloys, such as the 5xxx and 6xxx series, are generally considered more weldable than others, like the 2xxx and 7xxx series, which may require specific welding procedures.
Cost
The cost of different aluminum alloys can vary significantly. It’s essential to balance the required performance characteristics with the budgetary constraints of the project. While alloys like 7075 offer high performance, they come at a premium. If budget is a concern, alloys like 1100 or 3003 may be better suited for less demanding applications.
Industry Standards
Depending on the industry, there may be specific regulations or standards that the material must meet. For example, aerospace components require alloys that comply with stringent regulations to ensure safety and performance.
Conclusion
The world of aluminum is far more nuanced than a simple glance might suggest. From the workhorse alloys used in everyday products to the high-performance materials that power aircraft, each grade of aluminum possesses a unique combination of properties that makes it suitable for specific applications.
Understanding the differences between wrought and cast aluminum, as well as the unique characteristics of various alloy series and grades, is essential for making the right choice. Engineers and manufacturers who are familiar with these properties can make more informed decisions, ensuring that the aluminum selected meets the specific requirements of the project. This knowledge leads to better quality products and more efficient production processes.
