Aluminum coil and strip are available in dozens of different alloys. Why? Simply because various applications require different properties to meet specific performance needs. In order to make sure the product performs and lasts as intended, it’s critical to choose the alloy best suited for the item. Despite there being many options, the most common alloys are summarized below. These are the ones that are all around us – used in construction, automotive, aerospace and countless consumer products.
In order to choose the most suitable alloy of aluminum, you must first determine the needs for your application. Do they include strength? Corrosion resistance? Perhaps formability or weldability? Once these are determined, you’ll need to match those requirements to a specific alloy’s properties and typical uses. Other considerations, such as cost and availability, will also be factors in the decision.
Key Alloy Performance Characteristics
Let’s take a closer look at the key characteristics and how they relate to selection:
- Strength – It’s well known that aluminum alloys are significantly stronger and therefore more durable when compared to pure aluminum. However, strength varies greatly between different alloy series.
- Highest Strength – The 7xxx series (alloyed with zinc, like 7075) offers superior strength for high-stress applications. These are typically used for very demanding aerospace and defense applications.
- High Strength – The 2xxx series (alloyed with copper, like 2024) provides high strength along with fatigue resistance, which makes it another popular choice for aerospace applications.
- Medium-to-high Strength – The versatile 6xxx series (alloyed with magnesium and silicon, like 6061) offers a good balance of strength, weldability, and corrosion resistance. This makes these alloys most suitable for structural components.
- Heat Treating – Note that the 7XXX, 6XXX, and 2XXX series can also be heat-treated into a T-temper condition, in some cases rivaling the strength of steel.
- Medium Strength Alloys – typically include those in the 1XXX, 3XXX, and 5XXX alloy ranges. These alloys will have various degrees of strength depending on the temper. For example, H18 temper (full hard), would have more inherent strength than H12 (1/4 hard) of the same alloy, gauge and width aluminum strip.
- Learn more about Aluminum Alloy designations here
- Corrosion Resistance – All aluminum naturally forms a protective oxide layer that resists corrosion. But it’s important to note that some alloys offer better resistance than others. Particularly important for intense chemical or marine environments.
- Excellent Resistance – The 1xxx series (pure aluminum, like 1100) and 5xxx series (alloyed with magnesium, like 5052 and 5083) offer excellent resistance to corrosion. These alloy will perform best in saltwater and chemical environments.
- Poor Resistance – High-strength 2xxx alloys have poor corrosion resistance due to the copper content. Their resistance is improved by protective coatings.
- Weldability – The ability to be joined by welding varies widely among aluminum alloys and determines how easily complex parts can be fabricated.
- Good Weldability – The 1xxx, 3xxx, and 5xxx alloys offer excellent to good weldability. The 5xxx alloys are the go-to for high-strength, heavy-duty applications such as shipbuilding. These alloys may also be suitable for roll forming and welding applications, depending on the specifics of the job.
- Poor Weldability – The 2xxx and 7xxx series, which are high-strength, are sensitive to cracking during welding, and are not recommended.
- Formability – high formability alloys are quite malleable. They can be easily bent, shaped, or drawn without cracking. The 1xxx, 3xxx, and 5xxx series, which are not heat-treatable, typically offer much better formability than heat-treatable alloys. Formability is also highly dependent on the final temper of the strip, as well as how it was produced. Technical factors such as grain size and structure need to be considered. This is especially true of demanding deep draw applications , or where very tight radius bends are required. We suggest consulting with your supplier’s metallurgists to discuss the production process and help make an informed alloy and temper selection.
- Heat Treatability – Alloys are classified as heat-treatable or non-heat-treatable with their own properties as follows:
- Heat-treatable alloys (2xxx, 6xxx, and 7xxx) can be strengthened and hardened through thermal processes (called T-temper)
- Non-heat-treatable alloys (like 1xxx, 3xxx, and 5xxx) are strengthened through cold working (typical rolled tempers of aluminum strip such as H12, H14, H16, H18, and O)
- Cost and availability – Common alloys like 1100, 3003 and 5052 are widely available and cost-effective, while some specialty alloys are more expensive. Consider total cost-efficiency over a product’s lifespan, which includes maintenance and replacement costs. Consider also your choice of aluminum coil supplier. Can they offer:
- Trials or samples of strip for testing
- Metallurgical assistance
- Any size order
Other Selection Considerations
Some other things to consider in your aluminum alloy selection:
Additional Processing – Does your aluminum coil application require some additional processing? For instance, should the aluminum be tension leveled or painted? Other aluminum alloy applications require it be pre-anodized, or perhaps have a layer of strippable PE / plastic coating. Discuss these requirements early on, as the additional processing will help determine the underlying aluminum alloy required. Keep in mind that some alloys brighten and anodize quite well, while other alloys chemistry makes for poor anodizing surface conditions.
> Learn more about aluminum toll processing including leveling, sheeting, painting and anodizing
Sourcing? Does your application call for any guidelines regarding the source country of your aluminum? Does the use need to meet standard guidelines such as DFARS or USMCA?
Conclusion
Aluminum is extremely versatile and used for so many applications across almost every industry. Having many flavors available means the right alloy is available to meet the exact demands of your particular application. In order to make the optimal selection, you must balance multiple factors. In addition to the production process being used, these include mechanical properties, corrosion resistance, and formability or weldability. By understanding the specs and trade-offs, engineers can identify the one that delivers the necessary performance at the most reasonable price.