ORNL-led team developing breakthrough high-temperature, high-strength Al alloy for advanced light-duty engines
A team led by researchers from Oak Ridge National Laboratory (ORNL) is developing a lower-cost cast aluminum (Al) alloy capable of at least a 50 ˚C temperature increase over the current cylinder head alloys 319 and 356 for use in light duty engines. The new alloy is also targeting a better than 25% increase in strength at 300 ˚C compared to the older alloys at 250 ˚C, as well as excellent hot tearing resistance.
The work, led by Dr. Amit Shyam at ORNL, is part of a 4-year project consisting of a CRADA partnership with FCA and foundry giant Nemak. (Earlier post.)
|High-temperature, high-strength Al alloy project targets|
|Property||Cast aluminum baseline||Cast lightweight alloy target|
|Tensile strength||33 KSI||40 KSI|
|Yield strength||24 KSI||30 KSI|
|Shear strength||26 KSI||30 KSI|
|Endurance limit||8.5 KSI||11 KSI|
|Hot tearing resistance||Excellent||Excellent|
|High temperature performance||250 ˚C||300 ˚C|
|→Tensile strength||7.5 KSI||9.5 KSI|
|→Yield strength||5 KSI||6.5 KSI|
Having such a higher-temperature alloy for use in the head can be a game changer for light-duty engines, suggested Dr. J Allen Haynes, ORNL propulsion materials program manager. Higher-efficiency, down-sized, turbo-charged engines are already significantly increasing temperatures. Projected conditions for internal combustion engines in 2025 push light-duty engine exhaust temperatures into the low end of gas turbine regimes, Haynes said.
The increasing piston, cylinder, head, exhaust valve and turbocharger temperatures represent significant structural materials—and cost—challenges.
The 319 alloy has been used for more than 30 years, but has definite temperature limits; 356, which is more castable and has some thermal advantages, also has a lower temperature limit, Haynes said. Improved powertrain materials are a necessity for next generation ICEs.
The new alloys were enabled by recent microstructural discoveries, combined with first-principles modeling. The Oak Ridge team will be presenting 8 papers on the work on the new aluminum alloy at the upcoming TMS 2017 146th Annual Meeting in San Diego in February.
The work on the high-temperature Al alloy is one of a number of propulsion materials projects at the lab. ORNL has organized its propulsion materials work into four bins:
Materials for high-efficiency combustion engines. This includes turbo housings; turbo compressors; exhaust valve alloys; cast Al cylinder heads; advanced piston materials; work on high-temperature oxidation; friction wear and lubricants; coating and surface treatments; and the corrosion of Al in ethanol.
Materials for exhaust and energy recovery. This includes diesel particulate filters; exhaust gas recirculation; catalyst materials; thermoelectric materials; and high-temperature exhaust manifold materials.
Materials for electric and hybrid drive systems. This area includes improved organic dielectrics; high-temperature power electronics materials; non-rare-earth magnetic materials for electric motors; and high silicon steels for traction drive motors.
Other. Other includes advanced characterization; high-temperature oxidation; multi-scale computer modeling; testing standards; advanced alloys; and combustion and materials modeling.
A key and very valuable element in ORNL’s propulsion material work is the use of the Titan supercomputer to accelerate design of advanced materials via high performance computing. The ability to combine fundamental atomic level calculations in the context of applied research with the advanced experimental resources of the lab can results in developments such as the new Al alloy.
Developing a new material is often a very slow and expensive process. If you are a CEO and want to make investments and have a 2-3 year return on investments, materials are rarely going to meet that criteria. Many materials development cycles are 10-25 years, including bringing that to market. A very accelerated materials deployment from concept to deployment is 10 years. We are aiming to bring that cycle down to 5, 6, 7 years, maybe even less in some cases. It sounds like a really long time, but that’s almost a factor of two less than is typical. Materials development is expensive, high risk, it takes many years, and the payoff is a future event that may or may not fit your current manufacturing infrastructure.
[For companies] to develop new ones or to improve materials, that’s becoming rare. The national labs have an important opportunity to be able to come alongside industry and work together to identify and to accelerate solutions.—J. Allen Haynes