There are many reasons why aluminum is the material of choice for custom extrusions. The natural corrosion resistance of aluminum, plus the ability to prevent corrosion through design makes it a very valuable metal material for many different industries. Custom aluminum extrusions count on the ability of the finished product to resist different types of corrosion, especially if the unique properties of the metal are considered in the initial design.
The Pros and Cons of Aluminum
In most environments, untreated aluminum has a very good resistance to corrosion. The natural corrosion resistance of aluminum exists because of the way that aluminum spontaneously forms a thin oxide layer that prevents oxidation. Unlike the oxide layers that are found on other types of metals, aluminum oxide is impermeable and is strongly adhered to the metal.
If the oxide layer is damaged mechanically, it will begin to repair itself right away. It is because of this extremely beneficial oxide layer that aluminum is the metal of choice for many products. However, the oxide layer is not perfect. It is perfectly stable when in a pH range of 4-9, but in environments that are strongly alkaline or acid, it will corrode rather quickly, as if it didn’t have that layer of protection at all.
Of course the other reason why aluminum is the metal of choice for custom extrusions is because it is more malleable and easy to force through the steel dies in order to create the unique and specific shapes that are ordered. Silver City Aluminum purchases billet from several different suppliers, using aluminum materials that are 99.9 percent recyclable. To create the custom aluminum extrusions, the metal is pushed through the die with approximately 10,000,000 pounds of pressure.
Common Types of Corrosion
There are three major types of corrosion that metal workers and manufacturers have to consider when creating products or materials from aluminum. Those three types include galvanic corrosion, crevice corrosion and pitting.
- GALVANIC – Galvanic corrosion can occur when there is metallic contact and an electrolytic bridge between two different metals. The way it works is that the least noble metal will become the anode and suffer from galvanic corrosion, while the most noble metal will become the cathode and becomes protected against galvanic corrosion. Aluminum is the least noble metal in most combinations with other metals, posing a greater risk of galvanic corrosion than other typical metals used in structural construction. However, the risk of this occurring is minimal. Galvanic corrosion does not occur in dry, indoor atmospheres, but is most likely in areas that border the sea, where carbon steel, copper and stainless steel can all cause galvanic corrosion with aluminum materials.
- PITTING – Pitting is the most common type of corrosion that affects custom aluminum extrusions and other aluminum materials. However, it can only occur where an electrolyte, such as water or moisture, is present, which contains dissolved salts or chlorides. Small pits begin to appear in the surface of the metal. In the open air, these pits are just a small fraction of the overall thickness of the metal, however underground in water or soil, penetration of pitting will be thicker.
- CREVICE – Crevice corrosion is the type of corrosion that can occur in the narrow crevices of custom aluminum extrusions. This is definitely one of those types of issues where you can prevent corrosion through design. The likelihood of crevice corrosion occurring in well-designed custom aluminum extrusions is very small, however in marine atmospheres or on vehicles, water can collect in the crevices between aluminum surfaces, leading to a superficial corrosion known as water staining. The water source is condensation, which can form when cold materials are taken into a warm location. Simply the change between night and day can cause crevice condensation to occur when the aluminum is stored outdoors.
A fourth type is also common, but much less common with aluminum alloys than with other types of metal. Stress corrosion is a more unique type of corrosion that can lead to the formation of cracks. This is present primarily in high-strength alloys that are subjected to prolonged periods of tensile stress while in the presence of a corrosive medium. Stress corrosion does not typically occur in aluminum alloys.
How to Prevent Corrosion Through Design
Once you gain an understanding of how and why custom aluminum extrusions experience corrosion, it becomes easy to figure out how to prevent corrosion through design. For example, simply keeping aluminum away from metals that are more noble can prevent most instances of galvanic corrosion. However, that is not always possible. Mixed metal materials are often used, especially in manufacturing, industrial and other types of professional situations.
- GALVANIC – Manufacturers who want to prevent corrosion through design with galvanic corrosion need to consider where and how the custom aluminum extrusions will be used. Due to the natural corrosion resistance of aluminum, galvanic corrosion will not occur in dry, indoor temperatures and rural atmospheres are not conducive to it either. When different metals are used in combination, galvanic corrosion can still be prevented through electrical insulation that breaks all contact between the metals. Paint can be used to prevent an electrolytic bridge from forming between the metals in large constructions where insulating would be difficult.
- PITTING – Because pitting is usually so minimal, it is more of an aesthetic issue than a functional problem. Pitting is more frequent and severe on aluminum that has not been treated, so surface treatment through anodizing, painting or coating will counteract pitting and prevent corrosion through design. Cleaning treated aluminum regularly just by rinsing it with water should help maintain the corrosion protection. Never use alkaline detergents to clean treated aluminum. Creating custom aluminum extrusion with design profiles that will dry quickly and easily to prevent build-up of alkaline materials will also help to prevent corrosion through design.
- CREVICE – Sealing compounds and double-sided tapes can be used before joining together two components to prevent water from getting into the gaps. This is a simple and easy approach to prevent corrosion through design for custom aluminum extrusions. Taking it a step further, screws and rivets can sometimes be replaced with adhesive bonding to counteract the formation of crevices in the custom aluminum extrusions.
High-Quality Custom Aluminum Extrusions at Silver City Aluminum
Contact Silver City Aluminum for all of your custom aluminum extrusions and fabrication needs. We pride ourselves in our dedication to provide our clients with the best standards of quality control and service. We strive to provide a superior custom product that will exceed all of your expectations.
We keep our focus on the application of the product itself and consider all of the specifics relating to its intended use. As a result, we are able to help our clients create finished custom aluminum extrusions that meet their needs and requirements. Give us a call today to find out more about our custom aluminum extrusions and related services. We provide our services to businesses right here in Southeastern Massachusetts and all around the world.