An aluminum-scandium alloy developed by RUSAL, the Russian aluminum producer, was recently approved for use in the shipbuilding industry by Russian authorities. The new alloy is lighter and stronger than alternatives, which will lead to fuel savings for commercial vessels.
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The materials and methods allowed for shipbuilding in Russia are regulated by the Russian Maritime Register of Shipping, a marine classification society based in Saint Petersburg, Russia.
The Register updated its Rules for the Classification and Construction of Sea-Going Ships and Rules for Technical Supervision During the Construction of Ships and Manufacture of Materials and Products for Ships to include RUSAL’s aluminum-scandium alloy 1581 (Al-Mg-Sс) in relevant sections of the rules, including the requirements for welded joints.
Aluminum-Scandium Solutions for Automotive, Aerospace, and Now Shipping
RUSAL launched a new range of aluminum-scandium products in April 2021, dubbed “ScAlution.” The materials in the range exploit the technological, physical, and mechanical qualities of aluminum-scandium alloys to provide a lightweight alternative to aluminum alloys commonly used in the automotive manufacturing, aerospace, and (now) shipping industries.
Aluminum-scandium alloys were first developed in Russia during the Cold War. The novel materials were used to manufacture missiles and the famous MIG fighter jets.
Scandium is the first transition element, and as such it occupies an intermediate position between typical rare-earth elements and lightweight metallic elements. This makes it an ideal candidate for alloying with aluminum.
Adding a relatively small amount of scandium in an aluminum alloy has numerous benefits, as demonstrated in the extensive research that has been performed on the material.
The most significant of these benefits is a major increase in strength, with some studies finding increments of up to 100 MPa per 0.1 wt% of scandium added to an aluminum alloy. Such high strength is attributed to fine spherical L12 aluminum-scandium dispersoids, which typically measure just 10 nm in diameter.
Scandium works as a solid solution hardener, so aluminum-scandium alloys act as both precipitation hardeners and recrystallization inhibitors at once. The material is also a favorable nucleation site for strengthening phases.
Alongside increased strength, adding scandium to an aluminum alloy also improves or stabilizes the material’s ductility. This feature combines with aluminum scandium’s strong resistance to recrystallization to enable the creation of superplastic alloys that can form at strain rates up to 10− 2 s− 1.
Magnesium in aluminum-scandium alloys developed by RUSAL also gives the material a lower density than other alloys.
Finally—and significantly for applications in the shipping industry—aluminum-scandium also resists corrosion better than other alloys.
What Are The Applications for Aluminum-Scandium?
Overall, aluminum-scandium alloys feature high strength, ductility, weldability, corrosion resistance, and low density.
Combined, these features make the material ideal for aerospace and automotive manufacturing – usually in sheet and plate forms. Windmill blades and sporting goods like bicycle frames, baseball bats, and golf clubs are also often made with aluminum scandium.
The new regulation for RUSAL’s aluminum-scandium alloys in the Russian shipbuilding industry will also bring these benefits to the sector.
Barriers to Wider Adoption of Aluminum-Scandium Alloys
While aerospace components, commercial vessels, and sporting goods are worlds apart in terms of engineering requirements and scale, they share one thing in common: all three represent relatively high-end markets for materials.
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Aluminum-scandium alloys are prevented from wide-scale adoption due to the high cost of scandium.
Scandium is present in most rare-earth and uranium compound deposits, but only a handful of mines worldwide extract scandium from these ores. This is due to the higher value for other rare-earth materials present in these ores.
On top of this, metallic scandium is relatively complex to prepare. Scandium oxide must be converted to scandium fluoride, and then reduced using metallic calcium.
Metallic scandium was only first extracted from ore in 1937, and applications for the material were not developed until the 1970s.
That is when Russian researchers discovered the positive effects of scandium on aluminum alloys. To this day, scandium is only really used in aluminum alloys. The global trade for the material (sold as scandium oxide) is limited to between 15 and 20 tons sold each year.
Demand for scandium oxide is much higher, however. There is a clear demand for between 22.5 and 30 tons of scandium oxide each year, all to satisfy the demand for aluminum-scandium alloys.
Production and demand have both been rising sharply in light of all of this. Only three mines in the world produced scandium oxide in 2003, in Ukraine, China, and Russia. Since then, two more mines have started producing the material, both in the Philippines. A new mine in Nebraska, US, could produce up to 95 tons of scandium oxide each year if it gets the funding needed for development (around $1 billion).
The price of scandium is rising sharply. Small quantities of metallic scandium ingot rose from $107 per gram to $134 per gram between 2015 and 2019. In the same period, the price of a gram of scandium oxide rose 20% from $4 to $5.
References and Further Reading
“An Overview Of Aluminium-Scandium (AlSc).” (2014) AZO Materials. Available at: https://www.azom.com/article.aspx?ArticleID=10670.
Dorin, T. et al. (2018). “Aluminium Scandium Alloys.” In Fundamentals of Aluminium Metallurgy. Woodhead Publishing. Available at: https://doi.org/10.1016/B978-0-08-102063-0.00012-6.
Kareta, N. (2021). “RUSAL's Aluminium-Scandium Alloy Included in the Russian Maritime Register of Shipping.” Spotlight Metal. Available at: https://www.spotlightmetal.com/rusals-aluminium-scandium-alloy-included-in-the-russian-maritime-register-of-shipping-a-1058709/.