Light, strong, and corrosion-resistant aluminium is the ideal metal for shipbuilding.
It was first used for building a steam passenger boat in 1891. The boat named Le Migron was designed in Switzerland on the order of Alfred Nobel and was intended to carry 8 passengers. This was the first boat partially made of aluminium, which confirmed the very opportunity of using aluminium in shipbuilding.
It is notable that just three years later, in 1894, the Scottish shipbuilding yard Yarrow & Co presented a 58-m motor torpedo boat made of aluminium. This boat named ‘Falcon’ was manufactured for the navy of the Russian Empire. The boat reached a speed of 32 knots, a record for those times.
A year later, the aluminium boat ‘Defender’ won one of the most prestigious regattas in America (The America’s Cup), which was final proof of the advantage of the new metal. But in 1895 the cost of aluminium was 35 higher than the cost of steel, which hampered active use of the ‘light metal’. Another shortcoming was discovered later on: corrosion. Although it sounds strange today, it turned out that the yachts made of aluminium at the beginning of the century were exposed to severe corrosion in salt water. The service life of all these vessels turned out to be significantly less than that of similar vessels made of steel. Imperfect manufacturing processes and a lack of understanding of all aluminium properties and its capabilities hampered wide dissemination of this metal in shipbuilding. Engineers faced a complex problem which they managed to solve only a few decades later.
Throughout the years, steel was the most popular material in shipbuilding, leaving no alternative, due to its strength and low cost. Though steel has many advantages, its major drawback is its considerable weight. Construction of vessels with more and more carrying capacity made them bulky and led to poor control. For example, during the past century since 1910 the maximum weight of vessels increased more than twice: from 46,000 t (‘Titanic’) to 109,000 (‘Golden Princess’). The weight factor is very important in shipbuilding, because finally it determines the vessel speed and the transported payload weight. And the faster the vessels and the more weight they carry, the faster the return of investments in construction and the more profits received by ship owners. This was what motivated the studying of aluminium and its capabilities. It is known that using the ‘light metal’ allows reducing the ship weight by over 50%.
The first studies of aluminium alloy properties were initiated in the very beginning of the century, but only by the forties did the researchers who studied the issue of aluminium corrosion in seawater discover that adding a small amount of magnesium and silicon, made aluminium resistant to salt water. Alloy 5083 is considered the base alloy of the shipbuilders; it was registered by the Aluminium Association in 1954. Although this alloy is often called the ‘shipbuilding’ alloy, it is also widely used in many other industries. Alloy 5083 initially won popularity in shipbuilding thanks to its properties, such as high strength, corrosion resistance, good mouldability, and excellent welding characteristics.
By the 1960s, improvements in the technology, as well as reduction of the cost of aluminium led to extensive use of the ‘light metal’ in shipbuilding. Aluminium was used in manufacturing the shells of yachts, superstructure, masts, and port infrastructure. In the seventies, high-speed passenger vessels first appeared in Scandinavia - catamarans made of aluminium. Being light and quick, they proved their profitability and speed advantage, and became standard for passenger transportation for many years.
At present, aluminium alloys used in shipbuilding corrode 100 times slower than steel. During the first year of operation, steel corrodes at a speed of 120 mm/year, while aluminium – at a speed of 1 mm/year.
Therefore, aluminium vessels do not require such extensive care as steel vessels, which has an impact on the cost of their maintenance. As a rule, all sports vessels are made of aluminium, from the shell to the superstructures, which provides a significant gain in speed; shells of higher-capacity vessels are made of steel, while superstructures and other auxiliary equipment is made of aluminium alloys, reducing the total weight of the vessel and increasing its carrying capacity.
Until recently, alloy 5083 virtually had no competitors among other aluminium alloys. In 1995, Pechiney Co. (France) registered aluminium alloy 5383, which is an improved version of alloy 5083. The corrosion resistance of the metal was increased, and its impact strength was increased by 10%. These improvements potentially allow for a considerable reduction in the mass of welded vessels, and include the increase of the yield point of welded constructions by 15%. Together with the characteristics dealing with shaping, fold, cutting, and weldability, which are at least equal to the characteristics of alloy 5083, they make alloy 5383 very attractive for manufacturers of larger and high-speed vessels.
In 1999, Corus Aluminium Walzprodukte GmbH (Koblenz, Germany) registered aluminium-based alloy 5059 with the American Aluminium Association, which was called Alustar. This new alloy proved that aluminium can be stronger than steel. The alloy has the values of ultimate strength and yield point comparable with the corresponding values of low-alloy steel S235, AlCu4SiMg (AA2014). This alloy developed for the shipbuilding industry also has considerably improved strength characteristics compared to the traditional alloy 5083. The yield point before welding is increased by 26% and by 28% after welding (welding of heat-treated sheets H321/H116 made of AA5059 alloy grade).
Studies continue, and probably, very soon the scientists will present us even lighter and stronger aluminium alloys, which will allow manufacturers to create vessels and structures of the new generation.