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Stainless Steel & Aluminum: Why You Shouldn’t Use Them Together and Proper Precautions To Take If You Do

Why Can’t You Use Stainless Steel and Aluminum Together

Galvanic Corrosion

The combination of aluminum and stainless steel causes galvanic corrosion. In order to understand why you shouldn’t use stainless steel and aluminum together, we first need to understand how galvanic corrosion works. Galvanic corrosion is the transfer of electrons from one material (anode) to another (cathode). In addition to knowing what galvanic corrosion is, we also need to understand the technical terms that go along with it.

Here are all of the technical terms we will be using during this post:

  • Anode – material that is positively charged, electrons leave this material
  • Cathode – material that is negatively charged, electrons enter this material
  • Electrolyte – liquid that aids in the process of electron transfer
  • Corrosion/corrode – Destroy or weaken metal gradually

How It Works

Galvanic corrosion occurs when two materials (an anode and a cathode) come into contact with each other and an electrolyte. Electrolytes can be environmental factors such as humidity or rainwater. When these factors come into play, electron transfer will begin to occur. Depending on the level of resistance in an electrolyte, this transfer can happen much faster. This is why salt water, an electrolyte with a very low resistance, is a common factor when considering what product to use. Due to this, it is incredibly important to consider what material you are going to use in an environment.  When working with a marine, salt water environment, you even need to consider the type of stainless steel you are using.

There are multiple kinds of rust that can occur during the oxidization process. To find out more about them please read this blog post about Three types of rust that frequently occur.



Our Example

For the rest of our post, instead of referring to anode and cathode, we will be using the example of aluminum (anode) and stainless steel (cathode). When aluminum and stainless steel are used in an assembly together, the electrons from the aluminum will begin to transfer into the stainless steel. This results in the aluminum weakening. This weakened aluminum causes it to deteriorate at a much faster rate. This can lead to an extended life of the stainless steel. Note: Aluminum, if left on its own with the electrolyte, will still lose its electrons eventually, but having stainless steel present will significantly speed up this process.

The galvanic corrosion practice is actually commonly used in plating to create a sacrificial layer on top of another material. Zinc plated steel and black oxide are commonly used examples.

Exceptions

Each and every assembly is situational. As metal relies on its environmental factors to corrode, and there may be places where you can use some metals together without seeing these effects. If the environment is very dry, sheltered from weather and dirt then you, may try using metals together. However, in most situations the environment is not temperature and humidity controlled, rust will occur. Due to this, Albany County Fasteners recommends never using aluminum and stainless steel together. We also recommend using metals exclusively for maximum life.  Stainless with stainless, aluminum with aluminum, brass with brass.  Mixing metals can affect the strength of the application, the lifespan of the fasteners, the corrosion of the materials, etc.

The other situation in which these materials can be used together with little impact on rust prevention is if the cathode area is very small when compared to the anode area. For example, if the base material is a large sheet of aluminum, then using very small stainless steel screws will not dramatically decrease the life. Conversely, if you use aluminum to attach a large sheet of stainless steel, the aluminum life will be dramatically shortened.

Albany County Fasteners recommends the use of neoprene EPDM or bonding washers in between stainless fasteners and aluminum materials, the neoprene forms a barrier in between the metals, preventing corrosion.

Environmental Factors To Determine

Many factors need to be considered when choosing the correct material for your installation.

Factor Why It Matters
Duration of electrolyte contact The longer an electrolyte is in contact with aluminum and stainless steel, the more likely there is to be a transfer of electrons.
Electrolyte Resistance The lower the electrolyte resistance the easier it is for electron transfer to occur. Ex: salt water has a very low electrolyte resistance.
Stagnant Water Water that sits and takes a very long time to dissipate can lead to extended exposure to electrolytes.
Dirt Dirt (especially not in direct sunlight) can absorb an electrolyte and hold it for very long periods of time. This can result in increased exposure to the assembly if it is not kept clean.
Humidity/Fog Both are environmental factors that lead to increased water in the air. If the environment is prone to these factors, the exposure to electrolytes is considered to be extended
Crevices Crevices provide a catch for moisture (electrolyte) which can end up holding it against the materials for an extended period of time.



Noble Metals

If you decide that you need to use two different materials together, we recommend using an anode as the base material and making sure that it is significantly larger than the cathodes. Cathodes can also be called noble metals or metals that have a high resistance to oxidation (rust). We have compiled a list of noble metals below:

  • Gold
  • Iridium
  • Mercury
  • Osmium
  • Palladium
  • Platinum
  • Rhodium
  • Ruthenium
  • Silver

From Anode To Cathode

To mitigate the effects of galvanic corrosion even further, it is recommended to use materials that are less likely to cause electron transfer when exposed to each other and an electrolyte. The following list is a list of materials. *Note: the closer the two metals on this list, the less likely they will be to suffer from the negative effects of galvanic corrosion.

  • Magnesium
  • Magnesium Alloys
  • Zinc
  • Beryllium
  • Aluminum Alloys
  • Cadmium
  • Mild and Carbon Steel, Cast Iron
  • Chromium Steel (With Less Than Or Equal To 6% Chromium)
  • Active Stainless Steels (302, 310, 316, 410, 430)
  • Aluminum Bronze
  • Lead-Tin Solder
  • Tin
  • Active Nickel
  • Active Inconel
  • Brass
  • Bronze
  • Copper
  • Manganese Bronze
  • Silicon Bronze
  • Copper-Nickel Alloys
  • Lead
  • Monel
  • Silver Solder
  • Passive Nickel
  • Passive Inconel
  • Passive Stainless Steel (302, 310, 316, 410, 430)
  • Silver
  • Titanium
  • Zirconium
  • Gold
  • Platinum

How Can I Stop Galvanic Corrosion?

There are a few steps you can take if you MUST use these materials together.

  1. Add an insulator between the two materials so they no longer connect. Without that connection, the transfer of electrons cannot occur. Well Nuts are a commonly used fastener to help separate materials that can suffer from galvanic corrosion.
  2. Use materials with the same potential. Metals with the same corrosion resistance are typically ok to use together.
  3. If you are in a situation where only one of the materials will come into contact with an electrolyte then transfer of electrons will not occur.
  4. If there is a coating on the cathode it can prevent the transfer through increased resistance.
  5. Consider your environment before installing. Choose materials that will work for your environment.
  6. Coat or paint your assembly (completely) so that the electrolyte cannot make contact with the materials
  7. Use neoprene EPDM or bonding washers as a barrier in between the metals.

If you’re curious about the types of materials we offer and more about them, check out our Materials Reference Guide.

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Star Drive Deck Screws have Arrived!

Stainless Steel Star Drive Deck Screws

Also Known as Torx, 6lobe, and Hexalobular Drive

 
stainless steel deck screws

Star Drive Deck Screws are here by popular demand! Star Drive Deck Screws are functionally the same as our standard Square Drive Deck screws, however they feature an unconventional drive style that offers many installation benefits including higher torque possibilities and more resistance to cam out than a conventional style like Phillips or slotted.
The “Star” drive style for screws (like many things in the industry!), goes by many names including Torx, 6lobe and Hexalobular and is characterized by having a fastener recess with six points of contact which allow for these benefits.

Star Drive Deck Screw


Stainless Steel Deck Screws in all drive styles feature a notched Type 17 point to help cut into the wood or composite boards being installed, as well as sharp cutting threads for stronger retention. Stainless Steel Deck Screws are used primarily in outdoor applications due to the corrosion / rust resistant properties of the metal, making them a good choice for long-lasting applications.




For more information on Deck Screws in both Star Drive and Square Drive and to browse our selection visit our Decking Fasteners section today!


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Stainless Steel Security Socket Set Screws

 

Stainless Steel Tamper Proof Socket Set Screws

18-8 Stainless Steel Pin-In Set Screws

Socket Set Screws in this selection are driven with a special hex key or allen wrench designed to accommodate the hex drive with a central pin (pin-in). This pin prevents tampering with the fastener after assembly because it cannot be driven by a standard bit or hex key. Socket Set Screws are also referred to as Grub Screws, or simply Set Screws. Stainless Steel Set Screws are used in applications where a flush surface is key. Because they are headless fasteners, this property also adds a level of security to the screw, since it is resistant to gripping devices and anything besides the corresponding bits. 

Socket Set Screws, Grub Screws
Set screws are commonly used in pulleys, tracks, manufacturing, surfboard fins, handles and grips. Tamper proof screws are commonly seen in public areas because removal of the fasteners will be difficult, if not impossible without the correct bit. Because of this, they are commonly found in public restrooms, safes, hotels, campgrounds, jails and food processing areas. Stainless Steel tamper proof screws are ideal because the corrosion and rust resistance of the metal makes these screws suitable for long-lasting applications.


Shop Tamper Proof Set Screws Today!

 

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Fasteners 101

Looking for more information on Fastener Nomenclature, Standards, Finishes and more?

We are proud to announce the launch of Fasteners 101 – The Official Fastener Information Page of Albany County Fasteners.

Check it out today for information on fastener varieties, drives and materials with more content added regularly.

Fasteners 101

Check out Fasteners 101 Today

Black Oxide Fasteners

Albany County Fasteners is proud to announce our expanding black oxide fasteners line, as well as offering custom black oxide fastener orders. With this announcement, we would also like to share some information with our customers and subscribers about the process, and what exactly makes a black oxide fastener.

On stainless steel (particularly for us in stainless steel fasteners), black oxide fasteners are 18-8 or
Black Oxide Socket Cap Screws

304 grade stainless steel fasteners that have undergone a conversion coating process to alter certain qualities of the material, most notably the color. The chemical treatment process has a greater effect than this coloring however, in that it also adds a mild corrosion and abrasion resistance to the fastener.

 
The Black oxidation process for stainless steel consists of a series of chemical baths in a mixture of caustic, oxidizing and sulfur salts. Before the part is dipped into a hot bath of a solution of these materials, it is first dipped in an alkaline cleaner, and then water to ensure a surface free of debris. After the piece is treated in this manner, the fastener has porous qualities. This is then finished by infusing the material with oil or wax to add the corrosion and abrasion resistant qualities.
To achieve maximum corrosion and abrasion resistance, the black oxide is infused with wax during the process and complies with military specifications as a Class 4 finish. The enhanced protection, as well as the sleek black finish are why these fasteners are used. Our Stainless Steel Black Oxide Fasteners undergo this chemical process in order to achieve the black oxide properties.
Black Oxide Lock Washers
 
The benefits of this process are that the fastener becomes more durable, with an insignificant altering of the fastener’s dimensions.
 

 

Black Oxide fasteners are used commonly in the jewelry industry, the automotive industry on both cars and motorcycles, as well as in knife builds, firearm builds and in small machines. This process can be applied to any stainless steel fastener available on our website making the possibilities virtually endless.
Black Oxide Machine Screw Nuts
 

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