When it comes to aluminum alloys, most grades provide good appearance and corrosion resistance. However, to achieve optimal results, the anodizing process is necessary. Anodizing increases the amount of aluminum oxide on the surface of an aluminum substrate. This increases the part/component’s ability to withstand corrosion. It can also change its appearance.
There are lots of different aluminum alloys and grades on the market that can be anodized, but some are better than others.
The aluminum alloys that are most ideal for the anodizing process are the 5XXX, 6XXX, and 7XXX Series. Why? Because the anodizing process can sometimes change the size of the aluminum oxide layer on aluminum alloys. This coating may provide less than optimal protection on some alloys. Additionally, some alloys may result in an undesirable color, like dark grey, yellow, or brown colors after the anodizing process.
For this article, I’d like to focus on the difference between the 5052 & 3003 aluminum alloys. Plus, I’ll touch on why it’s easier to anodize certain aluminum alloys like 6061 & 5052—and more difficult to anodize 3003 & 2024. First, I’ll cover the main alloy series to provide you with some background.
1XXX Series – This series includes pure aluminum. Aluminum in this series can be anodized resulting in a layer of aluminum oxide that has a clear and shiny sheen. However, since pure aluminum is soft, anodized aluminum is damaged relatively easily and it lacks good mechanical properties compared to other aluminum alloys.
2XXX Series – This series is aluminum alloyed with copper. With copper embedded into these alloys, it makes the aluminum alloy stronger and harder than the 1XXX Series. Copper improves the mechanical properties of aluminum, but it also makes these alloys bad choices for anodization. When anodized, this series normally leaves an oxide layer that is yellowish in color and not appealing visually. Finally, this option provides poor corrosion protection for the underlying aluminum alloy.
3XXX Series – In this series, aluminum is alloyed with manganese. You’ll get good protection with manganese-alloyed aluminum substrates, but you’ll also get an ugly brown finish. This brown color is different in certain aluminum grades and substrates. This means it’s really difficult to maintain a consistent color in your components during the assembly process.
4XXX Series – The 4XXX series is aluminum alloyed with silicon. It provides good protection after the anodizing process. However, the 4XXX series results in a dark gray color that may not be visually appealing for your application.
5XXX Series – Like the 3XXX Series, this series is also alloyed with manganese. After the anodization process, the alloys in this series provides a clear, strong oxide layer making them great for anodizing. These alloys are sometimes replaced with a 4XXX series alloy for welding filler metal. That’s because the weld color closely matches the rest of the anodized aluminum assembly.
6XXX Series – This series was developed for aluminum alloyed with silicon and magnesium. Both of these alloys are great choices for anodizing. The oxide layer after anodizing is transparent and provides superior protection. This series of alloys have ideal mechanical properties and can be anodized easily, this is the option used most frequently for structural applications.
7XXX Series – This series uses zinc as the main alloying element. It anodizes readily, and the resulting oxide layer is clear and provides superior protection. However, if zinc levels get too high the oxide layer can turn the component brownish in color after anodization.
The difference between 5052 & 3003
Common alloys used in the industry are 3003 aluminum sheet and 5052 aluminum sheet. This is because they are the most specified alloys in the aluminum industry. However even minor changes in these alloy’s composition makes a big difference when it comes to the properties and end-uses required.
3003 is normally alloyed with Manganese (Mn) and the primary alloy ingredient for 5052 is Magnesium (Mg). 3003 is an alloy of Magnesium, Copper, Silicon, Iron, and Zinc. 5052 is an alloy of Silicon, Copper, Manganese, Magnesium, Chromium, and Zinc.
Mechanical Properties of 3003 & 5052
The mechanical properties of 3003 & 5052 shows that even the smallest changes in alloying composition make a considerable difference when it comes to tensile strength. 3003 H14 has an ultimate tensile strength range of 20 – 26 KSI, a yield of 21, an elongation of 8.3%, and a Brinell hardness of 40, while 5052 H32 has an ultimate tensile strength range of 31 – 38 KSI, a yield of 28, an elongation of 12%, and a Brinell hardness of 60.
Differences in Forming & Fabricating
3003 aluminum is fairly pliable while providing decent corrosion resistance and workability. It’s also moderately strong and it’s weldable. However, 5052 aluminum is stronger and offers better corrosion resistance, good drawing, good formability, and it’s also weldable.
3003 is widely viewed as a very practical general-purpose aluminum for moderate strength applications. Our customers usually choose 3003 aluminum because of its great workability and drawing characteristics. 3003 can also be welded and brazed using all industry methods and it has great corrosion resistance.
5052 is tough, easily worked, and extremely corrosion-resistant. It’s known industry-wide as the strongest non-heat-treatable aluminum sheet and plate in use. 5052 is also versatile and costs less making it one of the most serviceable alloys. This option provides superior drawing properties and a high rate of work hardening. Many customers in the marine industry choose this alloy due to its ability to resist saltwater corrosion, where it’s used in multiple applications from parts and components to exterior finishes.
Common applications for 3003 aluminum alloys include hardware, tanks, general sheet metal fabrication and chemical equipment. Common end-users of 5052 include high strength sheet metal fabricators, appliance manufacturers, the automotive and marine industry, as well as food service and medical equipment manufacturers.
3003 & 5052 are very similar in chemical composition, but as I’ve explained previously they have substantial differences. For many applications these alloys can be used interchangeably, especially in sheet metal work.
Why it’s easier to anodize certain alloys like 6061 and 5052
The 6XXX series was created for aluminum alloyed with magnesium and silicon. These alloys are excellent candidates for anodizing because the oxide layer that follows the anodizing process is transparent and offers excellent protection. The 6XXX series alloys offer excellent mechanical properties and are readily anodized, that’s why they are normally used for structural applications.
The 5XXX series is alloyed with manganese. When anodized, the alloys in the 5XXX series have a resulting oxide layer that is also strong and clear. This makes them excellent candidates for anodizing. With that said, there are some important things to consider when applying the anodizing process on the 5XXX series alloys. For instance, certain alloying elements such as manganese and silicon need to be kept within a certain composition range, so the anodizing process selected is critical. These alloys are frequently substituted with a 4XXX series alloy for welding filler metal because the resulting weld is not a different color than the rest of the anodized aluminum assembly.
Why it’s more difficult to anodize alloys like 3003 and 2024
Aluminum alloyed with manganese is also typical in the 3XXX Series. While the anodized layer offers good protection for the manganese-alloyed aluminum substrate, it does create a visually undesirable brownish color. Also, this brown color sometimes differs from substrate to substrate and especially from grade to grade. This makes it difficult to keep a similar color across a 3XXX series aluminum assembly.
The 4XXX series is made up of aluminum alloyed with silicon. Anodized 4XXX material is well protected by the aluminum oxide layer created from the anodizing process. However, it is important to know that the 4XXX series results in a dark gray color that also lacks in aesthetic appeal. 4XXX alloys are most often used to weld other alloys such as 6XXX, but if these welded assemblies are anodized, it’s important to note that the weld metal will not match the color of the base metal.
Aerospace Metals has over 30 years of specialized experience in metal finishing, anodizing, and plating. Our team of professionals consistently produce the best quality aluminum alloy component parts complete or manufactured, whether it’s plated or anodized.
For more information about our services and our state-of-the-art equipment, check out our website at www.aerospacemetalsllc.com.