Aluminum VS. Copper-Brass Radiator: Corrosion Susceptibility
Now that we understand the factors that allow a radiator to exchange heat from the coolant to the air as well as the differences in construction of an aluminum radiator and a copper-brass radiator, it’s time to take a look at how well they resist corrosion.
Let’s face it, no matter how well you maintain your car, parts are going to wear out. There’s not much point in using parts that are going to wear out faster than others. This is where some pretty heated debate can come in between aluminum and copper-brass. Before we get to the differences between the two, let’s look at some of the similarities.
Environments with a lot of salt are disastrous to both types of radiators. Whether you live near the coast or are driving all winter on salted roadways, you have to take extra care with your radiator (as well as the rest of your car). Salt encourages oxidation of metal, which causes metal to rust. If you operate your vehicle in a salty environment, chances are you know just how problematic this can be.
While both types of radiator are adversely affected by salt, they also both form their own protective oxide skin. You can think of this “skin” as a thin layer of corrosion that helps prevent further corrosion. It is spontaneously formed when the metal is exposed to air. One minor difference between the two skins is aluminum’s skin is transparent and does not affect the look of the radiator where as copper turns brownish-red then green. Since the green color of copper is considered an eye-sore, copper-brass radiators are traditionally painted. Depending on the type of paint used, this can reduce the radiators ability to transfer heat. There is a major difference between strength of these skins, but we’ll get to that in a moment.
Regardless of which radiator you have, you must use the proper type of antifreeze and distilled water. Antifreeze contains many different additives to help keep the cooling system clean, maintain proper pH, and inhibit corrosion. As a quick note on antifreeze, never mix different types of antifreeze together and make sure that you use the antifreeze that your system is designed for. For more info on antifreeze, read our “Do I Need Antifreeze in Warm Weather?” and “Can I Mix Different Types of Antifreeze?” articles. We’ll get into some more details regarding corrosion and your coolant in a minute.
So both types of radiators are destroyed by salt heavy environments (as most metals are), they both develop their own protective oxidized skin, and they require distilled water and the proper antifreeze. Now that we know the similarities, let’s look at the differences between the two.
Differences in Corrosion Susceptibility
Aluminum’s Oxide Layer
While both metals form a protective skin, the protective oxide layer that forms on aluminum is impressively strong. Even though the layer is extremely thin (as little as 1 nanometer), it is impermeable (meaning fluid cannot pass through it) and adheres strongly to the parent metal. In addition to this, if the layer of oxide is scratched off, it is repaired immediately in most environments. Because aluminum’s corrosion resistance is so good, it is added to brass alloys to make them stronger and more resistant to corrosion. That says a lot in itself.
Galvanic Corrosion (often referred to as “Electrolysis”)
Before we start this discussion, we need to clear up one misnomer. When most people talk about galvanic corrosion in radiators, they use the term “electrolysis.” Electrolysis is a different type of reaction than galvanic corrosion, but the term “electrolysis” has been used so long that most people don’t realize it is incorrect.
Electrolysis is a method of using a direct electrical current to force a chemical reaction. It is commonly used in commercial application to separate metals out of ore. Electrolysis can happen in your cooling system, but only if a stray electrical current is somehow connected to the system (a bare wire touching the radiator). Galvanic corrosion is more likely to occur than electrolysis.
Galvanic corrosion occurs when an anode metal is in contact with a cathode metal through an electrolyte solution. The anode metal will dissolve and collect on the cathode metal producing an electrical charge as well as destroying the anode metal. This is how a battery works, but is quite destructive to a cooling system. The coolant can act as an electrolyte solution, particularly when tap water is used instead of distilled water and your antifreeze is not changed at the proper intervals. The additives in antifreeze that help protect against corrosion will breakdown which is why your antifreeze must be changed on a regular basis.
Galvanic corrosion requires dissimilar metals, and if you remember from our previous segment, Construction Differences, a brazed aluminum radiator is all aluminum where as a copper-brass radiator contains copper, brass, and a lead/tin solder. This solder makes a copper-brass radiator more susceptible to galvanic corrosion than aluminum.
If you know a little about the chemistry of aluminum and copper, you may be aware that copper has a higher nobility than aluminum. A metal’s “nobility” determines whether or not it will corrode when in an electrolyte solution with a dissimilar metal; however, in our case, this is a bit misleading. Copper may have a higher nobility than aluminum, but that simply means it is not the metal that will corrode. Instead, copper will attract the metal that does corrode, which will be the lead/tin in the solder since it has less nobility than copper and brass. When galvanic corrosion does occur, the solder holding the copper-brass core and headers together will deteriorate creating leaks and weak spots within the core.
Since modern vehicles and parts are designed for aluminum components, there is significantly less risk of galvanic corrosion with an aluminum radiator. If you are a die-hard copper-brass radiator fan, you may be tempted to replace the stock aluminum radiator with a copper-brass radiator. This would be an expensive mistake. While your copper-brass radiator would not be at risk of corrosion, all of the aluminum components that your coolant touches will be at significant risk of galvanic corrosion. That’s because, as we mentioned before, aluminum has less nobility than copper; therefore, it will corrode preferentially to the copper-brass. Needless to say, this means expensive repairs to your engine and other components.
While there are a few similarities to resisting corrosion between both aluminum and copper-brass radiators, there are some significant differences due to how each is constructed.
Radiator is all aluminum thanks to the brazing process, which reduces the risk of corrosion.
Protective oxide layer is highly resistant to corrosion and self repairing. Aluminum is added to many alloys to enhance corrosion resistance.
Most modern vehicles are designed for aluminum parts, reducing the risk of galvanic corrosion.
Radiator is composed of dissimilar metals due to the solder, which increases risk of corrosion.
Protective oxide layer is not as resiliant as aluminum’s, thus aluminum is often added to some brass alloys to improve corrosion resistance.
Most modern vehicles are not designed for copper-brass, increasing the risk of galvanic corrosion.
Due to the number of dissimilar metals in a copper-brass radiator, it significantly increases the risk of corrosion in a cooling system. Even if it isn’t the radiator itself that corrodes, it can cause other metal components in the system to corrode. Combining that with the fact that most vehicles and parts are designed around aluminum components, an aluminum radiator has less risk of corrosion than copper-brass.
This segment of our discussion has a significant impact on our over-all look at aluminum vs. copper-brass, but we did allude to the fact that you still have to maintain your antifreeze at regular intervals regardless of which radiator you use. So perhaps there are some differences in maintenance requirements that we need to look at. We’ll tackle exactly that in Part 4 of our discussion.
Aluminum VS. Copper-Brass Discussion Points
Use the links below to follow the discussion or jump ahead. While the purpose of a radiator is straight forward, some of the manufacturing and servicing considerations are not. If you found this discussion helpful, please share it with others.