As tough new fuel economy regulations loom, automakers are scrambling to make their cars' powertrains - that's the engine, batteries, and transmission - as efficient as they can possibly be.
But that won't be enough to meet the new standard of 49 miles per gallon average by 2025.
Cars will also have to be lighter, because in general, the lighter the car is, the less fuel it requires to move down the road.
So, automakers are looking at ways to use more aluminum and magnesium in their cars.
Magnesium is the lightest metal that is still "structural," according to Stephen Logan, a senior technical specialist at Chrysler.
But there are some daunting obstacles to increasing the use of magnesium parts. Logan says it's a lot more complicated to weld magnesium to steel and aluminum than just pulling out a blowtorch.
"When they have different crystalline structures, they don't just weld together. You can't just provide heat and get them to join together."
Logan says there are some non-traditional welding techniques - friction stir welding and impact welding - that hold promise. But the processes are expensive and difficult to adopt with the millions of vehicles being produced.
Another obstacle is corrosion.
"When you join dissimilar materials, you have something called galvanic corrosion," says Logan, "which is essentially one metal causing the other to corrode."
Weld a part made of magnesium to one made of steel, and the steel will cause corrosion in the magnesium part.
Chrysler recently received a $587,000 grant from the Department of Energy to research and develop better techniques for welding magnesium to aluminum and high-strength steel.
Chrysler already has a lot of expertise in using the metal. The Viper's cowl is the largest part made of magnesium of any passenger vehicle in the world. The Jeep Wrangler spare tire carrier is also made of magnesium.
Related DOE grants also went to the University of Michigan. It got $600,000 for research on temperature changes in advanced magnesium alloys.
Ford Motor Co. received $1.5 million to develop new welding techniques and $350,000 to adapt new lubricants for use in vehicles (a joint Army-Department of Energy project).
General Motors was given $1.3 million to develop new methods of joining aluminum to high-strength steel.
Michigan State University received $599,999 to demonstrate bonding and repair of dissimilar materials using thermoplastic adhesives (joint Army-DoE project).