Corrosion

As the second most abundant metal on the planet, it comes as no surprise that aluminum is one of the most widely used metals. This highly versatile metal boasts a range of desirable characteristics and properties. Because of its popularity and widespread use, it’s imperative to have a clear understanding of the conditions that may shorten the lifespan of the metal, particularly aluminum corrosion. Let’s take a closer look at aluminum corrosion as well as how to prevent aluminum corrosion. 

Understanding Aluminum Corrosion 

Most metals naturally want to return to their original oxidized state. This conversion is called corrosion. However, the corrosion of any metal can substantially reduce its strength and cause partial fractures, cracks, and even total failure.

In the simplest sense, aluminum corrosion is the decay of aluminum molecules into its oxides. This results in the degradation of its chemical and physical properties. The severity and degree of corrosion that happens over time are based on material and the operating environment. 

Does Aluminum Rust?

Rusting, on the other hand, is a specialized form of corrosion that only iron and steel go through. Rust is the layman’s term for iron oxide, which is when steel or iron undergoes the process of oxidation.

In other words, rust is when the iron oxidizes and starts to flake off. This flaking then exposes fresh metal underneath, which then oxidizes, flakes, and constantly repeats. However, aluminum doesn’t rust. 

How Corrosion Resistant Is Aluminum?

Most experts on corrosion agree that aluminum resists corrosion well. Even so, it’s often necessary to protect it against corrosion based on the alloy, environment, application, and use of the aluminum component. 

• 1000-Series Aluminum: Aluminum grade 1100 is pure commercial aluminum. This material boasts excellent corrosion resistance and is typically used in food processing and chemical industries. 
• 3000-Series Aluminum: Alloy 3003 falls within this series and is undoubtedly the most widely used of all aluminum alloys. This is a pure, commercial-grade aluminum material enhanced by Manganese and Copper, which represents a 20% boost in strength. 3000-Series aluminum also offers excellent corrosion resistance. 
• 5000-Series Aluminum: Another very popular aluminum alloy is the 5052 alloy, which offers the highest strength of any non-heat-treatable grade. Alloy 5052 is widely used in marine atmospheres and environments with saltwater because of its remarkable corrosion resistance. 
• 6000-Series Aluminum: As one of the most versatile heat-treatable alloys, 6061 offers the trifecta of good strength, good aesthetics, and better corrosion resistance. On the other hand, Alloy 6063 is known as a structural alloy because of its great finishing, high tensile, and high corrosion resistance properties. 

While strain-hardenable alloys of 1000, 3000, and 5000 series and age-hardenable alloys of the 6000 series offer robust corrosion resistance, copper-containing alloys of 2000 and 7000 series are not sufficiently resistant to corrosion in humid environments. Because of this, these aluminum copper-containing alloys may require special treatment to prevent corrosion.

How to Prevent Aluminum Corrosion?

Aluminum corrosion can be a very serious problem, so you should take every necessary step to prevent corrosion of aluminum. A few of the top steps and best practices include:

1. Understand the Power of Choice. The first and most important thing you can do is to choose the right alloy. As a rule of thumb, 1000, 3000, and 5000 series aluminum will provide you with the highest level of resistance. 
2. Modify Surface Properties. Modifying the surface properties by applying chemical conversion coating, cladding, powder coating, anodizing, or boehmite coatings. 
3. Offer Protection. Knowing that certain environments can expedite corrosion, you can protect it by utilizing continuous protective coatings of lacquer or paint. 
4. Consider the Medium. You can minimize the effects of galvanic corrosion, which is caused by placing two dissimilar metals — such as steel and aluminum — next to each other. 

 Do you have questions about aluminum and aluminum corrosion? Email us at ProvenProductivity@bossard.com with any questions!

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Galvanic Corrosion in Carbon Fiber Materials

6 Types of Bolt Failure and How to Prevent It

The short answer is yes, aluminum does rust, although corrosion is a better technical term for what happens to this ubiquitous metal. The following are 10 types of corrosion that can affect aluminum.

1. Uniform Corrosion appears as pits that measure one micrometer in diameter, producing a constant decrease in thickness over the entire surface of the metal. This corrosion typically appears in highly acidic or alkaline media with dissolution rates ranging from a few micrometers per hour to a few micrometers per year.
2. Pitting Corrosion puts unevenly shaped depressions on the surface of the aluminum due to contact with liquid media such as surface water, seawater, and humid air. The corrosion pits are covered with white gelatin made from alumina. 
3. Trans-Granular and Intergranular (Intercrystalline) Corrosion is microscopic, affecting metals at the granular level. This type of corrosion often reduces the mechanical properties of aluminum that leads to the destruction of components. Propagation of intergranular corrosion usually begins as pits.
4. Exfoliation Corrosion selectively affects the planes that run parallel to the direction of the rolling or extrusion. The thin sheets of metal between these planes peel off, which gives rise to the term “exfoliation.” 
5. Stress Corrosion combines a corrosive environment with mechanical stresses, such as bending. By themselves, each of these factors does not affect the aluminum. But putting them together causes problems. Creating alloys with high mechanical strength can reduce stress corrosion.
6. Filiform Corrosion affects only lacquered aluminum, making the surface look different. It is a superficial attack, measuring only a few tens of microns. It starts from coating defects like scratches, holes, or cut edges, and usually appears only after several years.
7. Waterline Corrosion, as the name implies, occurs at the part of the metal that is just below the surface of water. It happens due to the difference in aeration between the surface of the liquid and the area directly underneath it.
8. Cavitation happens when the hydrodynamic pressure is greater than the vapor pressure of a moving liquid. Gas bubbles inside the liquid, which then crash against the metal at high speed, producing rounded cavities. Because the natural oxide film is destroyed, the aluminum suffers when the film is constantly torn and reformed. This type of corrosion usually happens within a few hours or days, depending on the speed and temperature of the liquid. Externally hardening the metal can help resist this type of corrosion.
9. Erosion happens due to moving media such as a flowing liquid, which produces scratches and undulations in the aluminum that match the direction of the flow. Among the ways of reducing erosion are controlling the speed of the fluid, using corrosion inhibitors, or streamlining the shape of the aluminum to minimize turbulence.
10. Microbiological Corrosion in aluminum is caused by certain types of bacteria in an organic carbon source. These bacteria transform organic substances into carbon dioxide, organic acids, and metabolites that are released into the environment. The environment and not the bacteria corrode the aluminum. One way to prevent this corrosion is to use disinfectants that dissolve in water or other liquid.

Want more information on aluminum corrosion in fasteners or other applications? Please contact us at ProvenProductivity@bossard.com.

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Galvanic Corrosion in Carbon Fiber Materials

6 Types of Bolt Failure and How to Prevent It

Corrosion is a problem when it comes to metal. Once your masterpiece is exposed to the elements, eventually rust or corrosion will set in, so this is something you are going to have to take into consideration. Thinking about corrosion before it becomes a problem is often a good strategy.

There are a few different types of corrosion you could run into. Check out what they are and how to prevent them:

Uniform Corrosion
The first, and most common type, is uniform corrosion. This type of corrosion has a reddish color that covers your fastener. The way to prevent uniform corrosion is to choose the right plating and coating option for your project.

Galvanic Corrosion
Another type of corrosion is called galvanic corrosion. Galvanic corrosion occurs when two different metals are electrically connected through a conductive solution. This can be prevented by using metals with similar corrosion potentials, by insulating or separating the materials from each other, or by applying coatings to both materials.

Crevice Corrosion
Crevice corrosion occurs in any small cracks or crevices in a fastener. These spaces have the possibility of retaining moisture, which can lead to corrosion. To prevent this from happening, you will want to use washers sparsely and try to make sure all joint surfaces are as smooth as possible, so as not to create spaces for crevice corrosion to occur.

Pitting Corrosion
This type of corrosion consists of holes that penetrate inward in a certain area of material. It often occurs because the surface is exposed to chemicals. To prevent pitting corrosion, choose a material that is most appropriate for the conditions it will be in.

Stress Corrosion Cracking
Stress corrosion cracking occurs when the materials are subject to tensile stress and a corrosive environment. In order to prevent stress corrosion cracking, try to reduce the stress being put on your materials, and choose your materials wisely.

Those are many of the types of corrosion. Before putting together your next project consider this list to reduce the risk of corrosion. If you have any questions, contact us at ProvenProductivity@bossard.com.

To find some corrosion resistant cables click here.

As much as we all hate to admit it, mistakes sometimes occur when designing or maintaining our projects. Bossard Proven Productivity is here to make sure you are aware of the risks of metal-to-metal corrosion and how to prevent rust.

Visually, corrosion is harmful to the appearance and surface of an item. More importantly, it can cause structural damage if it isn’t discovered and prevented from the very beginning.

In order to understand how to fix your problem, you have to know what kind of corrosion you’re dealing with and what causes it.

How does metal-to-metal corrosion happen? In the simplest words, the contact between different metals causes accelerated galvanic corrosion to occur in one of those metals, while the other remains protected. To prevent this, you don’t want a large cathode surface in contact with a small anode surface.

To prevent this type of corrosion from happening, electrically insulate the two metals from each other. If there is no contact, then the reaction will not occur.

Ultimately, it’s up to you to choose fasteners carefully during the initial stages of the design process to avoid chances of corrosion from the start. Choosing metals that have similar electropotentials can prevent the headache of metal-to-metal corrosion. Plating is another way to use more noble metals that better resist corrosion.

Read our blogs on the surface treatment processes to find out how Bossard products are treated for minimal corrosion.

We are dedicated to contribute to the success of our customers. Explore our website for more information about how our products can help you in your next design project.

Do you have stories about corrosion? Share your corrosion problems and questions with us at ProvenProductivity@bossard.com. We would love to hear from you! For more information about Bossard and tips about fasteners and design, check out the rest of our blogs at provenproductivity.com and subscribe to get regular updates!

Just a few weeks ago, the topic of galvanic corrosion was discussed at length on this blog. One aspect of galvanic corrosion that was not mentioned in that post was how the use of carbon fiber materials would affect preventative measures against corrosion.

Why Carbon Fiber?

Carbon fiber is attractive to engineers and manufacturers because it possesses a high specific strength. The specific strength is the ratio of a material’s yield strength to its mass density.

Manufacturers find carbon fiber materials ideal for their applications because of their low crack growth, lighter weight and general cost effectiveness in mass production. The most popular use of carbon fiber is within the aerospace and automobile industries.

The Problem with Carbon Fiber

The issue with using carbon fiber materials for fastener applications is that carbon fiber is electrically conductive, thus making it more susceptible to galvanic corrosion. When coupled with a fastener, bolt or nut, the situation worsens. Aluminum and plain steel, when coupled with a carbon composite, are both highly susceptible to galvanic corrosion.
Galvanic corrosion with carbon fiber materials has been an issue for decades, but experts have yet to produce a universal solution for the problem.

Your Best Solutions

Extensive testing has shown that coupling the carbon composite with titanium and its alloys – rather than aluminum or plain steel – is your best chance of limiting galvanic corrosion. Stainless steel is also less susceptible to galvanic corrosion when coupled with carbon fiber materials, but that also runs the risk of suffering pitting or crevice corrosion.

As the use of carbon fiber materials becomes more prevalent in fastener applications with products from bigHead® and BCT®*, understanding the role it plays in galvanic corrosion going forward has become even more important. To learn more about galvanic corrosion in fastener applications with carbon fiber materials, contact Bossard at ProvenProductivity@bossard.com.

*BCT® is a registered trademark owned by BBA srl Italy

When choosing a corrosion protection for hardware one must be aware of the environment and any environmental restrictions the assembly may be subject to as well as the amount of corrosion the assembly will be exposed to.

In February 2003, the European Union adopted the “Restriction of Hazardous Substances Directive” or RoHS, as it is commonly referred to. The RoHS directive aims to restrict certain dangerous substances commonly used in electronic equipment. This practice has now been accepted worldwide by the medical, food, farm implement and auto industries, as well.

The following are the most common corrosion protections:

Hot Dip Galvanizing
Heavy zinc layer, usually 80-100 microns thick with the minimum practical thickness around 40 microns. Applied by dipping parts into molten zinc, this process is not recommended for higher strength grades. It is difficult to maintain thread tolerances and usually means over tapping the threads of the nut or female mating part. However, this is an excellent choice for outdoor use, such as highway construction.

Electrolytic Plating
The most common method for commercial hardware. Several different metals can be used with the most common being zinc. Other metals could be nickel, copper, etc. When used on fasteners with property class 10.9 (Grade 8) and case hardened fasteners such as tapping and thread forming screws, the risk for hydrogen embrittlement increases. The plating thickness may vary from 3-15 microns.

Mechanical Plating
An alternative to electro plating that can be used on materials sensitive to hydrogen embrittlement. It is simply a method of blasting the fasteners with very small pigments and a carrier, causing a fusing of plating metal (zinc, nickel, aluminum etc.) to the fastener surfaces. The thickness is about the same as for electro plating.

Coatings
The most common being manganese or zinc often used in high strength applications. Recent developments in engineering class coatings promises to solve hydrogen embrittlement but also improves the control of lubricity, which is very important in controlling torque tension relations.

Each type of corrosion has its own advantages and disadvantages. That’s why it is import to understand the environmental and mechanical requirements for each application before deciding on a finish. To learn more about how to determine the best plating for your environment, contact Bossard at ProvenProductivity@bossard.com.