Aluminum Workshop: Aluminum-scandium alloys—Strong yet scarce

Q: I’ve seen various references to aluminum-scandium (AlSc) alloys. Apparently, the addition of scandium makes aluminum alloys stronger. But I never see these alloys used in common welded fabrication. Why? Can I weld them?

A: The major aluminum companies experimented with Sc additions to a lot of different aluminum alloys in the 1980s and 1990s. Scandium is a very potent grain refiner that can increase yield and tensile strengths of an alloy up to 30 percent, depending on the alloy itself. It also prevents recrystallization in the heat-affected zone (HAZ) of welds, which minimizes the deterioration in mechanical properties in the HAZ that we commonly see when heat-treatable aluminum alloys (like 6061) are welded. Sounds great, right? So why don’t we see AlSc alloys everywhere?

The answer is simple. Scandium is very rare, with only three mines in operation and only about 4,500 lbs. produced worldwide each year. Because of its scarcity, the current price of Sc is around $70 per gram. That’s about $32,000 per lb. Even though we add only about 0.3 percent Sc to the alloys, the addition makes any of the common alloys prohibitively expensive. So don’t expect to see common extrusions or plate made from AlSc alloys in everyday fabrication.

However, AlSc alloys are commonly used in one specific market—high-performance sporting goods. High-end aluminum baseball bats and very high-end bicycle frames are often made from AlSc alloys. Why? Well, there are some real performance advantages in these applications. There’s also the prestige factor of being able to say you have the best, most expensive item available.

Can you weld AlSc alloys? Well, the end is welded onto baseball bats (although this isn’t a structural weld) and bicycle frames are welded. However, the answer really is that it depends. Some aluminum alloys which have Sc additions are weldable. Some are not.