* Magnesium sheets more difficult than steel or aluminum
* Costs for magnesium seen coming down as use expands -GM
* Widespread use still several years away -expert
DETROIT, Oct 23 (Reuters) - Engineers and scientists at General Motors Co believe they are making major strides toward lighter vehicles by developing a way to expand the use of magnesium in auto parts.
Making auto parts from magnesium sheets by heating the lightweight metal so it can be formed into precise, rigid shapes
will help GM and other automakers meet demanding U.S. fuel economy requirements, said GM metals researcher Jon Carter.
Magnesium auto parts formed by high pressure die casting are already common in cars and trucks, for steering wheels and other parts.
Using magnesium sheets to make auto parts could be a significant breakthrough for GM and eventually lead to much more magnesium in vehicles, said Dick Schultz, managing director of Ducker Worldwide and an expert on metals used in manufacturing.
GM is starting slow, using magnesium from sheet metal to make inner panels of doors and trunk lids.
Magnesium is 75 percent lighter than steel and 33 percent lighter than aluminum, said GM engineer Paul Krajewski. He said it also costs three to four times as much as aluminum, but wider use will encourage magnesium sheet metal producers to make more, which will bring down the costs.
"Magnesium will allow us to reduce the weight of certain sheet metal panels and thereby improve fuel efficiency and handling and overall performance," Carter said in a telephone interview.
GM will make about 50 vehicles, which will be sold to consumers, using the magnesium sheet process in the fourth quarter, but Carter would not indicate which model or models will be involved.
By 2020, magnesium will be able to take out 15 percent of the weight of a vehicle, leading to fuel savings of 9 percent to 12 percent, according to the U.S. Automotive Partnership.
The auto industry has been stamping steel sheets into trunk lids, hoods and door panels for more than 100 years.
Forming magnesium sheets into auto parts by heating them to 842 degrees Fahrenheit (450 degrees Celsius) is a slow process.
ROOM TEMPERATURE A GOAL
Manufacturers can stamp out steel auto parts at room temperature.
"The ultimate goal is to be able to one day stamp magnesium panels just like today we stamp steel panels at room temperature. We're not there yet," said Carter, but he added that magnesium sheet makers are working with new alloys that will allow the sheets to be formed at lower temperature.
So the use of magnesium sheets for auto parts in GM vehicles will be small in the near-term, but may expand as researchers and engineers speed the process.
GM's Detroit rivals Ford Motor Co and Chrysler Group are among automakers that currently use magnesium auto parts made by suppliers in their vehicles.
But those parts using magnesium, Schultz said, are not formed from magnesium sheets.
Schultz said the average passenger vehicle on the U.S. market has a weight of about 3,800 pounds, including 10 pounds from magnesium. Steel makes up 2,100 pounds of the weight of that average vehicle, and aluminum makes up 343 pounds.
GM began getting patents for the concept of using magnesium sheets back in 2002.
It was Carter who had a "slowly developing 'aha' moment" when he was working with a GM metal forming plant several years after that.
"We found that if we control the way we heat the sheet metal blank before it goes into the hot forming tool, it makes a world of difference in how the panel looks, how fast it can be formed and how to avoid making panels that have defects in them," said Carter.
Then it was back to the lab to see if this serendipitous discovery could be duplicated, he said.
The magnesium sheets are comprised of 96 percent magnesium, 3 percent aluminum and 1 percent zinc.
In the past few years, automakers have relied on more aluminum to make vehicles lighter.
"Aluminum has gotten much better through innovations. Magnesium is probably where aluminum was 25 years ago," said Schultz.
"Some of the existing infrastructure for making magnesium sheet dates back to World War Two when it was made for airplanes," said Krajewski. "We are now seeing an evolution of both the alloys and the material processing technology that can truly drive the costs down."
Carter and Krajewski estimate that developing magnesium alloys strong enough to make auto parts at room temperature, is still five to 10 years off.
GM has patents on the process for heating magnesium and for making it more resistant to corrosion. The company plans to license the technology to allow auto-parts suppliers to produce the magnesium inner panels, according to GM spokesman Kristopher Spencer.