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    October 25, 2022

    What is PAA + BR127 Primer?


    When you design a manufactured part, the priorities are often to make it long-lasting, strong, and prepared for outdoor use. This has led to a whole host of different finishing steps and material selections to achieve the perfect characteristics.

    One of the finishing options that Rapid Axis supports is a combination of PAA and BR127 Primer. Even though you might not have heard of these, there’s a very good chance you’ve come across parts with this coating. In this guide, we’ll explain what PAA and BR127 are, their benefits, and where you might see them used.

    What Is PAA?

    PAA stands for Phosphoric Acid Anodize. The sole purpose of this treatment is to prepare a surface for an application of BR127.

    PAA is a specialized surface treatment. It doesn’t result in a decorative finish or any change in material characteristics that make a part more durable, corrosion resistant, or temperature resilient. Instead, it ensures the aluminum surface will accept the BR127 treatment and create a chemical bond between the two.

    If you want to think of this process generally, you can imagine a two-step adhesive. First, you would combine the two mixtures of the epoxy together before applying it to the parts you want to bond. In this example, PAA and BR127 would be the two mixtures.

    Without PAA, the BR127 application would not appropriately spray on. You’ll find uneven sections and a lack of durability as the coating falls off. With PAA, the aluminum’s surface is changed so it will accept and bond to the BR127, resulting in a longer-lasting and more uniform coating.

    What Is BR127?

    BR127 is the brand name of a modified epoxy primer that works as an anti-corrosion primer. It is strictly used on aluminum as a protective coating, but it can be used on virtually any grade or type of aluminum.

    It works by chemically bonding to the metal. Once bonded, it prevents hydrolysis which is the scientific reason why oxidation starts in the first place. The water won’t be able to break down the surface of the metal, meaning that rust won’t form.

    It gets applied as a spray coating which is convenient, since it means that you can apply BR127 to parts of any size and geography. The downside of traditional electroplating is that the full part needs to be submerged in a vat of liquid. You can only plate parts that are small enough to fit into the container.

    With BR127, the application can be done in roughly the same way that a car is painted, regardless of the part’s size.

    Benefits of BR127

    To better understand why people use BR127, let’s discuss some of its major benefits. Remember, this coating requires a treatment of PAA before any of these benefits are true.

    Prevents Corrosion

    Above everything else, BR127 is great at preventing corrosion. After all, that’s the main purpose of this primer.

    Since the epoxy primer chemically bonds to the aluminum, you’ll find that the preexisting rust will not mature and future rust will be prevented. 

    Thin Application

    We offer BR127 application anywhere from 0.001” to 0.010”, which is smaller than the thickness of an eyelash.

    With a low-profile coating, you can still hit your tolerances and assemble your part without issues.

    High-Temperature and Low-Temperature Operation

    Officially, BR127 is rated to perform from -67 to 300 degrees F. That means you can take the part from Montana’s winter to California’s summer without any issues.

    The operational temperature refers to what temperature range the BR127 coating will stay intact. If it gets too hot or cold, it can start to crack and fall apart.

    Environmentally Resistant Coating

    A BR127 coating is highly durable and very environmentally resistant. This is a general term that defines how well a part can withstand scratching, dust, pollution, UV, temperature, and the ability to handle airborne chemicals and particles.

    To put it simply, BR127 can be used outdoors without any issues. This is why it’s the preferred coating for aerospace vessels and airplanes — vehicles that are constantly exposed to the elements.

    Common Applications for BR127

    In the aerospace industry, BR127 has become a standard. The claim is that nearly every commercial aircraft created since BR127 was invented has been coated in this primer.

    If you’re in a situation where you need corrosion resistance that’s low-profile, long-lasting, and highly durable, then BR127 might be right for you. As long as your part is aluminum, there’s a good chance it can be applied since we use a spray applicator.


    Now you know that BR127 is an aluminum coating that uses PAA to prepare the surface. This coating is used on most commercial airplanes and it’s durable, corrosion-resistant, performs in a wide variety of temperatures, and it’s able to withstand different environments.

    If you want to have your own BR127-coated part for your operation, reach out to our team at Rapid Axis today. Our professional machine shop has all the finishing steps you’ll need to get the most out of each part. Get a free quote today.

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