Aluminum Alloys.

Aluminum alloys are used primarily because of their low weight, the ease with which they can be formed and fabricated, and their corrosion resistance in many atmospheric and immersion environments. They are not, however, resistant to corrosion in many marine environments and are subject to crevice corrosion, pitting, and in some alloys, stress corrosion cracking. The alloys are also very subject to galvanic corrosion as they have an anodic potential with respect to most other metals.

1000 Series Aluminum Alloys.

This series of alloys are essentially unalloyed aluminum. While they have fairly good corrosion resistance as compared to other aluminum alloys, they have relatively low strength. They are subject to crevice corrosion and pitting.

2000 Series Aluminum Alloys.

This series of alloys are alloys of aluminum and copper. These alloys are relatively high in strength and are widely used in the aerospace industry. The corrosion resistance of these alloys is inferior to most other aluminum alloys.

3000 Series Aluminum Alloys.

This series of alloys are alloys of aluminum and manganese. Their corrosion performance is roughly comparable to the 1000 series alloys.

5000 Series Aluminum Alloys.

This series of alloys are alloys of aluminum and magnesium. The are relatively low in strength and cannot be heat treated to obtain higher strengths. Their corrosion performance in most environments is superior to other aluminum alloys with the exception of the 1000 series. They are, however,, subject to both pitting and crevice corrosion, particularly in marine applications.

6000 Series Aluminum Alloys.

This series of alloys are alloys of aluminum, magnesium, and silicon. They are relatively high in strength and can be heat treated to obtain higher strengths. Their corrosion performance in most environments is somewhat inferior to the 5000 series alloys but is acceptable in many applications. They are subject to both pitting and crevice corrosion.

7000 Series Aluminum Alloys.

This series of alloys are alloys of aluminium and zinc. They are heat treatable to obtain high strengths. Their corrosion performance in chloride containing environments application is inferior to other aluminium alloys. If they are used, care must be used to control crevice and pitting attack unless the effects of these forms of attack are not functionally significant. Some of the 7000 series alloys are subject to stress corrosion cracking when heat treated to high strength levels.

Cast Aluminium Alloys.

Of the cast aluminium alloys, alloy A-356 has the best overall balance between mechanical properties, castability, and corrosion resistance and is the most commonly used aluminium casting alloy for corrosion service. Its corrosion performance is comparable to the 6000 series wrought alloys.