As just about anyone who know anything about engines will tell you, the cylinder head is forced to cope with some of the toughest, most grueling conditions any engine part will ever be subjected to. The cylinder head on a conventional internal combustion engine is tasked with channeling fresh intake charge – often pressurized by a turbo or supercharger – into the cylinder; carrying hot, spent exhaust gases out to the exhaust manifold or headers; and sealing with the block to provide an air- and water-tight chamber where compression and combustion can take place.
In the course of all that, the component is exposed to staggeringly high temperatures and pressures that demand not only the best, most exacting of manufacturing techniques, but a strong, durable material to match. And as automakers have increasingly started to turn to downsizing and turbocharging as a means to produce an ideal mix of efficiency and performance, the demands made of production cylinder heads have only grown.
Now, Fiat Chrysler Automobiles has announced that it’s helped craft a new aluminum alloy ideal for use in high-strung turbocharged engines, capable of withstanding more heat than either of the aluminum alloys most often used today: grades 319 and 356. Working with the federally-funded Oak Ridge National Laboratory in Tennessee and casting supplier Nemak, FCA has helped to create an alloy called “16HT”, or “ACMZ”.
The selling point: where 319 and 356 are often significantly weakened by temperatures above 200°C (392°F), ACMZ can reliably withstand temperatures as high as 300°C (572°F) while still maintaining its strength, and it only costs 7 percent more than competing alloys. The key: using copper instead of silicon as the strengthening agent.
Aluminum alloys containing copper are nothing new, but they have a tendency to crack after casting, during solidification. But Oak Ridge’s advanced facilities allowed FCA and its partners to crack the code by studying what happens on an atomic level as an alloy cools. The team used Oak Ridge’s “Titan” supercomputer – the seventh-most-powerful in the world – to virtually test 50 never-before-proposed recipes for a copper-containing aluminum alloy, narrowing the field down to seven promising candidates within 24 months.
“The Titan and [Integrated Computational Material Engineering] let the team focus only on truly promising candidates instead of spending time on trial and error,” says FCA Senior Manager of Advanced Powertrain Engineering Gregg Black. “It’s like ‘Star Wars’ stuff for us, creating new alloys in the computer without having to pour it.
“When we focused on copper, other people in the industry almost laughed us off, saying we’d never be able to cast that,” he says. “We knew there was competition, including other teams working at Oak Ridge National Labs, but we outperformed everyone on this.”
The alloy known as “ACMZ” is the result of a three-year, $3.5-million project sponsored by the federal government. The material can be cast and machined using existing technologies, and it could allow automakers like FCA to utilize higher boost pressures/compression ratios on their turbocharged engines for stronger performance out of a smaller package.