The future of aircraft metals appears bright

Features - Materials

Experts from Alcoa and Aleris discuss developments in metallurgy that are influencing the design and construction of aircraft and engines.

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February 19, 2016

Alcoa’s Eric Roegner shows off his company’s one-piece front turbofan frame casting for a General Electric GEnx engine.

ALCOA

Eric V. Roegner, COO, Alcoa’s Power & Propulsion and Titanium & Engineered Products (ATEP); and president, Alcoa Defense and ATEP; speaks to the company’s work with metals other than aluminum.

AM&D: How is Alcoa expanding its materials offerings in aerospace?

Eric Roegner: Alcoa has recently increased its portfolio of aerospace offerings – including those not made of aluminum. Alcoa’s downstream business is the Engineered Products and Solutions (EPS) group, and more than 80% of its products are made of materials other than aluminum.

Alcoa’s acquisition of RTI – now known as Alcoa Titanium & Engineered Products – expanded our reach into titanium and grew our portfolio of materials, including titanium-aluminides, increasingly used to manufacture lightweight, aerodynamic jet engine parts.

The largest business unit in EPS is Alcoa Fastening Systems and Rings – with the fasteners primarily made of titanium – that can hold different materials and enable lightning strike protection.

Alcoa Power and Propulsion (APP) makes some of the largest and most complex titanium, nickel, and aluminum structural castings. Additionally, APP makes investment castings for jet engines – the biggest portion is nickel airfoils in rotating parts in the hot section of engines. These are often single-crystal nickel airfoils with complex cooling channels inside with a lot of process technology on how to make them thin on the trailing edge, putting sophisticated cooling channels in the blade to put exactly the right amount of cooling where it’s needed, and advanced environmental-barrier or thermal-barrier coating systems.

Alcoa Forgings and Extrusions (AFE) produces a mix of engine forgings, including isothermal discs of powdered nickel forgings for the hot section of the engine; hollow, reverse-extruded and flanged shafts for the compressor section, such as the front spool that holds the fan and compressor discs; structural forgings, such as the titanium and aluminum bulkheads for the F-35 Joint Strike Fighter; and long and formed aluminum alloy extrusions for commercial and defense aerospace applications.

AM&D: What is Alcoa doing to help with the ramp-up needed in aircraft engine production?

ER: We work with customers, particularly in new technologies, in advance of a program. We can then ratchet up our capacity behind that investment in such a way that we are ready when the ramp comes.

We worked with Pratt & Whitney for more than seven years to develop a new application for aluminum-lithium for the Geared Turbofan (GTF) engine (for more about the GTF engine, see page 36). Together, we developed a new aluminum alloy forging for the front fan blade – usually made of titanium or carbon- fiber – for the Airbus A320neo. It allows the blades to be much thinner than those made with composites, making them 10% lighter, more aerodynamically efficient, and significantly lower in cost to produce.

AM&D: What other services are customers asking from Alcoa?

ER: Increasingly, customers are asking for a simplified supply chain, and want to buy a rough-machined or finish-machined part, and sometimes a finished and assembled part. These can be a titanium, aluminum, or nickel forging; an extrusion; investment casting; or sheet and plate. We can deliver a forging to machine shop, or we can deliver a finished, machined assembly.

AM&D: What do you see in the future of aircraft metals?

ER: Aluminum-lithium has been used in aerospace for more than 20 years. It started flying on the Airbus A380 fuselage 10 years ago, and on the wings seven years ago. Now it’s reached a level of maturity that it is designed into aircraft such as the Airbus A350, Boeing’s 787 and 777X. We started with one proprietary alloy and now we have three aluminum-lithium alloys aimed at different applications.

ATEP’s midstream and downstream capabilities complement Alcoa’s titanium investment casting and forging capabilities.

We see robust opportunity across all of the product forms to continue to work with customers and bring new technologies to market.

ALERIS

Dr. Matthias Miermeister, manager, field engineering global aerospace, Aleris Rolled Products Germany, discusses his company’s new aluminum-magnesium-scandium alloy.

AM&D: What are the properties of Aleris’ new aluminum-magnesium-scandium alloy?

Matthias Miermeister: When Boeing introduced the 787 Dreamliner and Airbus the A350, everyone thought the next generation of planes would be made of composites, but we have to say now that is not so. For example, Boeing’s 777X will have composite wings but a metallic fuselage. We have the fourth generation of aluminum-lithium alloys where the lithium content has been reduced significantly, which offers more weight savings from density reduction. Aleris has co-developed with Airbus an alloy of aluminum-magnesium-scandium (AlMgSc) – designated AA5028 – which offers an even lower density than aluminum-lithium.

AM&D: How much lower?

MM: AlMgSc is 4% lighter than 2024 aluminum, the most-used aircraft alloy today.

AM&D: How was AlMgSc developed?

MM: The AlMgSc technology started more than 15 years ago with a German government-funded program in which Airbus participated, along with Aleris and other companies. Airbus wanted us to continue to develop AlMgSc. The first reason was its low density and lighter weight, and the second, Airbus is interested in welding technology. The A380 features laser welded panels in the lower fuselage based on 6000 series aluminum. A big advantage is that compared to typical metal fuselage, stringers are riveted to the skin. When you laser weld, you don’t need a stringer foot to put the rivet through, so you save about 30% of the stringer material. Additionally, laser welding speed is much faster than riveting.

With AlMgSc, you take a flat sheet and a straight stringer and weld it, then put it into an oven at 325°C for two hours. You get nearly 100% of the strength back. It’s an annealing process. Once customers become aware of this, they believe the material can be used for applications with elevated temperatures, such as wing leading-edges heated with anti-icing devices or engine nozzle inlet lips. We are supporting this research and development activity, but our main focus target for the time being is fuselage sheet.

AM&D: Can it be substituted in new or existing aircraft?

MM: It is a full one-to-one replacement for 2024 aluminum. You can take out the 2024 and put in AlMgSc, and you have 4% weight savings without any design change.

AM&D: Any aircraft types in particular?

MM: It would not be suitable for a large-diameter fuselage, twin-aisle aircraft, where other materials would lead to a lighter design, but it would be perfect for a single-aisle airliner such as a Boeing 737 or Airbus A320. AlMgSc together with an aluminum-lithium stringer could lead to the lightest design.

Aleris’ Matthias Miermeister highlights features of his company’s aluminum-magnesium-scandium fuselage sheet.

AM&D: How much scandium is in the alloy? Is it expensive?

MM: The scandium component of AlMgSc is around 0.15% to 0.20% as the limits registered with the Aluminum Association.

Years ago, the main source was the Ukraine, but now there are sources for scandium in Russia, China, Australia, Canada, and even the United States.

Scandium is not rare; it is only a matter of production to get enough. AlMgSc is more expensive than 2024 aluminum, but it’s more cost effective than aluminum-lithium – which requires special casting processes and making sure that the scrap is not mixed with other alloys. Also, many aluminum-lithium alloys have silver that makes them relatively expensive.

However, the manufacturing process for AlMgSc is the same as for other aluminum alloys. Aleris can cast ingots and roll to plate or sheet. AlMgSc sheets are typically produced in gauges between 1.6mm and 7.0mm (0.063" and 0.275") and supplied in annealed condition.

AM&D: What is AlMgSc’s maturity level?

MM: It is not flying yet. It has almost a technology readiness level of six (TRL 6), which means ready for qualification. We are waiting for a program to pick up this technology to get it into flight status.

Alcoa Inc.

www.alcoa.com

Aleris International Inc.

www.aleris.com

About the author: Eric Brothers is senior editor of Aerospace Manufacturing and Design. He can be reached at ebrothers@gie.net or 216.393.0228.