“The magnesium engine cradle is a breakthrough as a structural bearing component,” says executive director Mike Meloeny of Chassis/Powertrain for GM. “We’ve accomplished something here.
“The reduction in mass that we gain with this component helps the whole vehicle, for example, in terms of agility. It also illustrates that Corvette is still raising the bar. Collectors are already calling this a special car.”
This is important, too, because Corvette is America’s sports car – an icon. So when the engineers put together the next model, their work is examined by an entire industry.
Corvette had its first all-aluminium engine in 1969, and the company had also used the light metal for its engine cradle until now. The driver behind the magnesium cradle project was the US Council for Automotive Research, which worked with the US Department of Energy in identifying and resolving issues that limit opportunities for large-scale structural cast magnesium components.
“Magnesium was something we believed could be used to replace aluminium in the engine cradle, but it was still an unknown. We had to find out what we didn’t know,” says Meloeny.
He says that, firstly, engineers tried matching it with the aluminium design, but because magnesium is not as stiff as aluminium, some design changes had to be made. Furthermore, the company needed magnesium without creep, because “we couldn’t accept that in a structural member.”
A new high-temperature alloy produced by Hydro Magnesium was the solution to the material challenge. Not only does the AE44 alloy meet the advanced material properties in terms of temperature performance, it delivers corrosion resistance. The engine cradle is the first commercial use of such an alloy.
Hydro supplies the metal to its Canadian die-casting joint-venture company, Meridian Technologies, which is casting the component for Corvette. Compared to its aluminium predecessor, the 10.85-kilogram cradle provides mass savings of 30 to 35 percent.
“We wanted to give die-casters in the high-temperature arena more freedom in designing their parts,” says Hydro’s Lisabeth Riopelle. “The AE44 alloy is one of a family of alloys that can shorten product development time while providing good elongation properties, increased yield strength and better casting performance.”
Durability was another issue that needed to be resolved, says Meloeny. He smiles before reflecting on the testing process.
“We have thrown the book at this cradle,” he says. “We took the magnesium cradles through tests that were probably more thorough than anything we’ve done before with this type of component. And it performed just as well as the aluminium cradle. We’ll take these learnings for other potential applications.”
The main reason? Mass savings – and because Corvette always aims high.
“As mass becomes more and more critical,” says Meloeny, “you start to weigh your options. We want to keep Corvette on the edge – on the edge of controllability and powertrains – and mass is a key factor.
“This vehicle is matching all of that and gives it the character it has. We’ve pushed the envelope.”
