Types of Screws

• Aluminum screws can be used with aluminum applications. Stainless steel is the most common screw to use with aluminum. Galvanized screws and aluminum bronze also work well in certain environments. Aluminum bronze is composed of aluminum mixed with other metals, such as iron, nickel, manganese and silicon. Aluminum bronze is commonly used in highly corrosive environments, such as in marine applications. Aluminum bronze usually contains between 5 percent and 12 percent aluminum in the blend. Titanium screws are also compatible with aluminum applications. Screws made from zinc and zinc mixtures will work with some lightweight aluminum applications that are not under high-stress conditions.
  
  

Corrosion

• Corrosion where screws meet the aluminum can be caused by moisture, corrosive liquids, heat and friction. Applications that are exposed to salt water are particularly vulnerable to corrosion. The stress caused by friction can loosen screws, allowing moisture to penetrate the connection and lead to corrosion. Structures that remain immobile, such as aluminum roofs, experience less stress that leads to corrosion than applications with moving parts. Corrosion can also be caused by a reaction between different types of metals, such as aluminum and steel or iron.
  
  

Preventing Corrosion

• To help prevent corrosion between a screw and aluminum, drill the proper size hole before inserting the screw. Pre-drilling the hole will prevent the protective oxide from being stripped from the aluminum and the threads of the screw --- this helps prevent corrosion. In applications where it is not necessary to countersink the screws, a washer made of nylon or other synthetic material can help prevent the friction that leads to corrosion. Sealants are available commercially that will help protect the surface between the screw and aluminum from the friction and moisture that leads to corrosion. Teflon or silicon can be used as insulators to prevent corrosion between different types of screws and aluminum. Even if you are using protective sealants or washers, you will still need to pre-drill holes before inserting the screw into the aluminum.
  
  

Best Options

• Depending on the type of project and the conditions to which the screws will be regularly exposed, stainless steel, aluminum, aluminum bronze and titanium screws are the best options for screws that are compatible with aluminum.