Aluminium is perfect for many applications that require a strong, lightweight metal. Aluminium has the greatest ratio of strength to weight of any of the metals. There are a number of types of screws that can be used with aluminium. The most common problem with using any type of screw in aluminium is corrosion where the screw meets the aluminium. There are ways to prevent this corrosion to assure that the screws stay in place and look good for many years.
Types of Screws
Aluminium screws can be used with aluminium applications. Stainless steel is the most common screw to use with aluminium. Galvanised screws and aluminium bronze also work well in certain environments. Aluminium bronze is composed of aluminium mixed with other metals, such as iron, nickel, manganese and silicon. Aluminium bronze is commonly used in highly corrosive environments, such as in marine applications. Aluminium bronze usually contains between 5 per cent and 12 per cent aluminium in the blend. Titanium screws are also compatible with aluminium applications. Screws made from zinc and zinc mixtures will work with some lightweight aluminium applications that are not under high-stress conditions.
Corrosion where screws meet the aluminium 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 aluminium 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 aluminium and steel or iron.
To help prevent corrosion between a screw and aluminium, drill the proper size hole before inserting the screw. Pre-drilling the hole will prevent the protective oxide from being stripped from the aluminium 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 aluminium 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 aluminium. Even if you are using protective sealants or washers, you will still need to pre-drill holes before inserting the screw into the aluminium.
Depending on the type of project and the conditions to which the screws will be regularly exposed, stainless steel, aluminium, aluminium bronze and titanium screws are the best options for screws that are compatible with aluminium.