Will Stainless Steel React With Aluminium?

Stainless steel and aluminum are both widely used metals, but they can undergo galvanic corrosion when in contact. This occurs because aluminum is more chemically reactive than stainless steel and can corrode when exposed to moisture or certain electrolytes. To prevent galvanic corrosion, various strategies can be employed, such as using barrier layers between the metals, avoiding prolonged contact in corrosive environments, or selecting compatible materials for specific applications.

Imagine you build a super cool robot with shiny metal parts. You use something called stainless steel because it’s strong and won’t rust. But then you add some parts made of aluminum, another kind of metal. Will Stainless Steel React With aluminum? Sadly, sometimes they don’t play nicely together. They can start a secret battle that makes the aluminum weaker. We’ll learn why this happens and how to make sure your robot stays awesome! So keep reading to get proper guidance.

Stainless steel and aluminum seem like compatible metals, but don’t be fooled! When they come into contact, a process called galvanic corrosion can occur. This reaction causes the aluminum to deteriorate, potentially compromising the integrity of whatever you’re building.  Want to know the science behind this reaction? Read on!

Why Stainless Steel and aluminum Don’t Mix

The galvanic series is a chart that lists metals in order of their electrochemical reactivity. Metals that are further apart on the series have a greater potential for galvanic corrosion when they come into contact. Stainless steel is more “noble” than aluminum, meaning it’s less likely to corrode. Unfortunately, this means if you pair stainless steel with aluminum, the aluminum will become the anode and sacrifice itself, rapidly corroding to protect the stainless steel.

What Causes Stainless Steel to React With aluminum?

Stainless steel and aluminum seem like compatible metals, but don’t be fooled! When they come into contact, a process called galvanic corrosion can occur. This reaction causes the aluminum to deteriorate, potentially compromising the integrity of whatever you’re building.  Want to know the science behind this reaction? Read on!

Understanding Galvanic Corrosion

Before we dive into the specifics of stainless steel and aluminum, it’s crucial to understand the fundamentals of galvanic corrosion. This phenomenon occurs when two different metals are in electrical contact in the presence of an electrolyte, such as moisture or saltwater. The difference in electrode potentials between the metals drives an electrochemical reaction, leading to accelerated corrosion of the more reactive metal.

Here’s a simplified explanation of how galvanic corrosion works:

  • Electrode Potential Difference: When two dissimilar metals are in contact, they have different electrode potentials, which is a measure of their tendency to lose or gain electrons.
  • Anode and Cathode Formation: The metal with a higher electrode potential becomes the cathode, while the metal with a lower electrode potential becomes the anode.
  • Electron Flow: Electrons flow from the anode (the more reactive metal) to the cathode (the less reactive metal) through the metal-to-metal contact point.
  • Electrolyte Reaction: At the anode, the metal atoms lose electrons and go into the electrolyte solution as positively charged ions, causing corrosion.
  • Cathode Reaction: At the cathode, the electrons combine with oxygen and water from the electrolyte, forming hydroxide ions.

In the case of stainless steel and aluminum, their different positions in the galvanic series make them susceptible to this type of corrosion when in direct contact and exposed to an electrolyte. Stainless steel acts as the cathode, while aluminum becomes the anode and corrodes more quickly.

Factors That Influence Galvanic Corrosion of Stainless Steel and aluminum

While the potential for galvanic corrosion exists when stainless steel and aluminum are in contact, several factors can influence the extent and rate of the reaction. Understanding these factors is crucial for effective prevention and mitigation strategies.

1. Electrolyte Presence and Composition

The type of electrolyte present plays a significant role in galvanic corrosion. Saltwater, for instance, is a highly conductive electrolyte and accelerates the reaction compared to plain water. The concentration of salts and other dissolved ions in the electrolyte also impacts the corrosion rate.

2. Area Ratio

The relative surface areas of the anode (aluminum) and cathode (stainless steel) can influence the rate of galvanic corrosion. A larger cathode area compared to the anode area will increase the corrosion rate of the anode, as more electrons can flow from the smaller anode to the larger cathode.

3. Temperature

Temperature has a direct effect on the rate of galvanic corrosion. Higher temperatures generally increase the reaction rate, as the kinetic energy of the molecules in the electrolyte solution is higher, facilitating faster ion movement and electron transfer.

4. Metal Type and Alloy Composition

Not all stainless steel and aluminum alloys are created equal when it comes to galvanic corrosion. The specific alloy composition and microstructure can affect their positions in the galvanic series and, consequently, their susceptibility to corrosion. For example, some stainless steel grades like 316 are more resistant to galvanic corrosion than others, like 304.

It’s important to note that these factors often work in tandem, and their combined effect can significantly impact the severity of galvanic corrosion between stainless steel and aluminum.

Preventing Galvanic Corrosion Between Stainless and aluminum

preventing galvanic corrosion between stainless and aluminum

While galvanic corrosion is a concern when using stainless steel and aluminum together, several effective strategies can help prevent or minimize the risk. Here are some common methods:

1. Insulation and Physical Separation

One of the most straightforward ways to prevent galvanic corrosion is to prevent direct metal-to-metal contact between stainless steel and aluminum. This can be achieved by using insulating materials, such as plastic washers, gaskets, or coatings, to physically separate the two metals.

For example, when using stainless steel fasteners with aluminum components, insulating washers or sleeves can be used to prevent direct contact between the fastener and the aluminum surface.

2. Protective Coatings and Platings

Applying protective coatings or platings to either the stainless steel or aluminum surface can also help prevent galvanic corrosion. These coatings act as a barrier, preventing electrical contact between the two metals and isolating them from the electrolyte.

Common coating options include:

  • Paints and varnishes: Applying a high-quality paint or varnish can provide a physical barrier between the metals.
  • Conversion coatings: These chemically-formed oxide layers, such as anodizing for aluminum, can enhance corrosion resistance.
  • Metallic platings: Plating one metal with a more noble metal, like cadmium or zinc, can shift its position in the galvanic series, reducing the potential for corrosion.

3. Alloy Selection

Choosing stainless steel and aluminum alloys that are closer together in the galvanic series can minimize the driving force for galvanic corrosion. For example, using a more noble stainless steel grade like 316 (with higher chromium and nickel content) in combination with a less reactive aluminum alloy can reduce the potential difference between the metals.

4. Proper Design and Drainage

Effective design can also help mitigate galvanic corrosion risks. Avoiding crevices or areas where moisture can accumulate and ensuring proper drainage are crucial. Additionally, minimizing the area ratio between the anode and cathode can help limit the corrosion rate.

5. Cathodic Protection

In some cases, cathodic protection techniques can be employed to control galvanic corrosion. This involves connecting the metal that needs protection (in this case, aluminum) to a sacrificial anode made of a more active metal, like zinc or magnesium. The sacrificial anode corrodes preferentially, protecting the aluminum from corrosion.

When Galvanic Corrosion Between Stainless and aluminum Can’t Be Avoided

In certain applications, particularly in the marine or offshore industries, it may not be possible to completely avoid contact between stainless steel and aluminum components. In such scenarios, it’s crucial to plan for and mitigate the effects of galvanic corrosion proactively.

Here are some strategies to consider when galvanic corrosion betweensteel grades is unavoidable:

  • Thorough Planning and Design: During the design phase, carefully consider the potential for galvanic corrosion and incorporate preventative measures from the outset. This may involve selecting more corrosion-resistant alloys, optimizing drainage, or incorporating sacrificial anodes.
  • Regular Inspections and Maintenance: Implement a rigorous inspection and maintenance program to monitor for signs of corrosion and take corrective action as needed. This may involve replacing corroded components or applying protective coatings.
  • Corrosion Monitoring Techniques: Employ corrosion monitoring techniques, such as electrical resistance probes or linear polarization resistance measurements, to detect and quantify corrosion rates in real-time.
  • Overdesign and Plan for Replacements: In critical applications where failure is not an option, it may be necessary to overdesign components and plan for periodic replacements to account for anticipated corrosion rates.
  • Cathodic Protection Systems: In severe environments, like offshore platforms or ships, installing impressed current or sacrificial anode cathodic protection systems can help mitigate galvanic corrosion on a larger scale.

It’s important to note that preventing galvanic corrosion between stainless steel and aluminum may not always be feasible or cost-effective. In such cases, a proactive approach to mitigating its effects and planning for component replacements or repairs is essential for maintaining operational safety and structural integrity.

FAQs:

Q: Can I use stainless steel screws with aluminum?

A: While technically possible, it’s highly discouraged unless preventative measures are implemented. If you must do so, isolation techniques (washers, coatings) are vital.

Q: Does the surface area matter?

 Yes! A small stainless steel fastener on a large aluminum sheet is worse than vice-versa. The larger the anode’s (aluminum) surface area relative to the cathode (stainless steel), the faster corrosion will occur.

Q: Are there any safe combinations?

Some aluminum alloys are less susceptible to galvanic corrosion. Also, some stainless steel grades are closer to aluminum on the galvanic series, reducing the severity of the reaction. Always research compatibility before combining.

Conclusion:

Stainless steel and aluminum do unfortunately interact, leading to a process called galvanic corrosion. This means the aluminum can corrode when in direct contact with stainless steel, especially in moist or salty environments. To protect your metals, consider isolating them with paint, coatings, or washers. If you must use them together, remember that larger aluminum surfaces are less severely impacted by this reaction.

While galvanic corrosion is a concern, various strategies can be employed to prevent or mitigate its effects. These include physical separation using insulating materials, applying protective coatings or platings, selecting compatible alloys, incorporating proper design and drainage, and implementing cathodic protection systems.

Do you have any experience with galvanic corrosion between stainless steel and aluminum? Share your stories and tips in the comments below! Alternatively, if you’re facing a design challenge involving these metals, feel free to contact us for expert advice.

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