Pretreatment of Aluminum Extrusions: What You Need to Know

So, you’re thinking of painting or powder coating your extrusions. That’s great!

These finishes can give you a range of bright, vibrant colors, and they’ll make your project more visually appealing.

The last thing you want, though, is for your finish to not adhere properly. And you need to be aware that as soon as your profiles come off the extrusion press, they’re exposed to oxygen.

That oxygen causes some initial oxidation on their surface, and this greyish colored smut needs to be removed. If it isn’t, your paint or powder coat is going to be applied on top of it, and that will cause your coating to come off prematurely.

Enter pretreatment.

A good manufacturer will take the steps necessary to properly pretreat your profiles. That way, they can ensure paint or powder coat adhesion.”

Gary Teeling
General Manager, Gabrian International

What is Pretreatment?

Pretreatment is a process that your manufacturer goes through to remove all grease, oils and dirt from the aluminum surface. They need to do this before painting or powder coating to strengthen adhesion.

This process has multiple steps, and each one of them is important. So, doing a thorough job is what will ensure pretreatment success.

How many steps are there? That depends on the type of pretreatment you choose. The process also varies between manufacturers, but there are two basic types you should keep in mind.

The 2 Types of Pretreatment Coatings

There are two main types of pretreatment coatings. They are:

1. Chrome Conversion Coatings, and
2. Chrome-Free Coatings.

Chrome conversion coatings have been around for many decades. And chrome-free coatings are more recent. The difference between them is important to distinguish. So, let’s take a look at each one.

How Does the Pretreatment Process Work?

The pretreatment process will be different depending on whether the manufacturer is doing chrome conversion coating or chrome-free coating.

Different manufacturers will handle each of these in different ways, but pretreatment usually has between 5-10 steps. There are certain basic steps that are always there, though.

Essentially, your profiles will be dipped into a series of tanks. Inside each tank is a different solution. You will generally find tanks of cleaner, etchant, rinse, and the appropriate pretreatment coating.

Here’s an example of the basic process for each coating type. Again, additional steps may be added.

Chrome-Free Coating

1. Cleaner/Etchant
2. Rinse
3. Metal Cleaner/Deoxidizer
4. Rinse
5. Chrome-Free Coating

Once the profiles have gone through their succession of tanks, they need to be dried. It is very important that they be fully dried because any moisture on the surface will negatively impact paint or powder coat application.

Pretreatment is Important

Pretreating is an important step before painting or powder coating. It helps to get rid of surface contaminants that would cause your paint or powder coat to not adhere properly.

Traditionally, chrome conversion coatings have been the standard. But, in recent years chrome-free coatings have become prevalent. This is due to worker safety and environmental concerns.

The steps vary between processes, manufacturers and project requirements. But, they involve dipping your extrusions into a series of tanks.

So, keep in mind the importance of pretreatment and remember the difference between pretreatment types when talking to manufacturers.

Take a look at our aluminum extrusions page for more information about our services. We offer high-quality profiles from India with on-time delivery, and great service.