Aluminum and its alloys have been extensively used for structural applications with success. Aluminum resists corrosion from the atmosphere if there is an absence of narrow crevices. Many statues erected, over a hundreds of years ago, have not deteriorated badly which is in contrast with aluminum cables used in seawater. The corrosion resistance of aluminum is due to its tendency to form a compact oxide layer over the surface. The oxide formed offers a high resistance to corrosion. The normal surface film present in air is about 1 nm thick. The film thickness increases at the elevated temperature. The film growth is more rapid in water than in oxygen.
aluminium alloys are corrosion resistant in atmosphere, but often have poor corrosion resistance when submerged in aqueous environments. Aluminum corrosion resistance is also often only high in a restricted range of pH. For example, data has been published6 that shows aluminum corrosion rates are very low when the chemical stream pH is between approximately 4 and 7, but the corrosion rates are very high when the pH is either below 4 or above 7.
1xxx
Alloy 1100: Aluminum grade 1100 is commercially pure aluminum. It has excellent corrosion resistance and is common in the chemical and food processing industries. Otherwise, it is a soft and ductile metal with excellent workability. You’ll find alloy 1100 frequently in applications that require forming. It can be welded with any method, but it is non-heat-treatable.
3xxx
Alloy 3003: Alloy 3003 is the most common of the aluminum alloys. It is pure, commercial-grade aluminum with a 20% boost in strength thanks to the addition of Manganese and Copper. It also has excellent corrosion resistance, workability, and can be welded or brazed, drawn or spun.
5xxx
Alloy 5052: 5052 is also a very popular alloy because it has the highest strength of any of the non-heat-treatable grades. It is especially common in marine and saltwater atmospheres because of its resistance to corrosion. It has excellent workability and is easily drawn or formed into complex shapes.
6xxx
Alloy 6061: 6061 is the most versatile of the heat-treatable alloys, including corrosion resistance, workability when annealed, and weldability. You’ll find alloy 6061 in products and applications that require a trifecta of good appearance, better corrosion resistance, and good strength.
Alloy 6063: 6063 is usually known as an architectural alloy because of its high tensile, great finishing, and high corrosion-resistant properties. You’ll find 6063 in interior and exterior architectural settings and trims. It is frequently anodized.
The Aerospace Industry (2xxx & 7xxx)
In the aerospace industry, there’s a need for both high strength and high corrosion resistance. For this reason, the aerospace industry is generally confined to the 2xxx and 7xxx series of aluminum. We get around the reduced corrosion resistance of alloyed aluminum in these series through alclad liners that are pure aluminum and alloyed to the stronger aluminum alloy underneath. The pure aluminum gives the plane the corrosion resistance that’s needed without compromising the strength of the structural aluminum.
Alloy 2011: Alloy 2011, otherwise known as Free Machining Alloy (FMA), is known for its high mechanical strength and excellent machining, which is why you see it in complex and detailed parts. If this alloy is machined under high-speed, it will produce fine chips, but they’re easily removed.
Alloy 2014: Alloy 2014 is copper-based with very high strength and excellent machining. You’ll find it in many structural aerospace applications because of its high corrosion resistance.
Alloy 2024: Alloy 2024 is very commonly used because of its combination of high strength and excellent fatigue resistance. You’ll find it wherever products require a good ratio of strength to weight. But, it’s corrosion resistance is fairly low, so you’ll often see it with either an anodized surface (see below) or with Alclad.
Alloy 7075: Of all of the aluminum alloys, 7075 is one of the highest strength alloys. Like 2024, it has an excellent ratio of strength to weight and is used in parts that will undergo high stress. 7075 can be formed when annealed and then heat-treated if needed.
