Increasing use of aluminum and magnesium in vehicles is giving automakers faster weight loss than even possible by Sweating to the Oldies with Richard Simmons.

Aluminum poundage will show a healthy boost again in the '97 model year, says the Aluminum Assn. The trade group says aluminum averages 252 lbs. (114 kg) in 1996 cars and 241 lbs. (109 kg) in light trucks, for an overall average of 247 lbs. (112 kg). The 1997 numbers are expected to be higher, based on booked business.

The association highly touts the 1996 estimates, prepared by Ducker Research, but many industry insiders with extensive product knowledge say they're far too high, especially for light trucks. Other estimates put the '96 average at 204 to 206 lbs. (92 to 93 kg). Still others say it's lower.

Insiders point out that there currently are no U.S.-made trucks with aluminum engine blocks, and a relatively low percentage are equipped with aluminum wheels, which makes the association's numbers difficult to believe.

Conversely, magnesium likely will enjoy a bigger percentage gain because it is coming off of a much smaller base. Experts predict magnesium use to increase 15% or 16% in '97 models, but total content still will be only about 6.5 lbs. (3 kg) per vehicle.

Byron Clow, executive vice president of the International Magnesium Assn., predicts all-industry demand for magnesium will climb by at least 154,000 tons (150,000 t) during the next five years.

One reason for aluminum's growth is that the cost of making parts from the light metal is dropping. One leading Ford Motor Co. materials scientist, Andy Sherman, says the cost gap between steel and aluminum is closing. He says that if process improvements continue, eventually the costs will be equal.

A new three-step light-alloy casting process similar to squeeze-casting may help the cause of aluminum and magnesium. Developed by Thompson Aluminum Casting Co. Inc. of Cleveland, metal compression forming (MCF) may be used for engine mounts in the 1998 model year by General Motors Corp.'s Delphi Automotive Chassis Div. An influx of Russian and Chinese magnesium also is exerting downward pressure on prices.

Despite cost improvements, magnesium still is an expensive solution. Ford is considering a change from magnesium back to steel in some pickup and sport/utility vehicle (SUV) seat components, citing high costs as the reason. GM reportedly has backed off one magnesium program for a light-truck component, but has gone ahead with others.

Sometimes weight savings may be worth the cost. Steven S. Wagner, market development manager for Alcoa Automotive Structures GmbH, estimates that automakers can save $4 for every pound of weight saved.

During the '97 model year, GM will use magnesium for a one-piece seat frame in some rear seats on its new U-body minivans and the cross-car instrument panel support beams on the Buick Park Avenue and Ultra. The all-new Oldsmobile Cutlass and Chevrolet Malibu will have one-piece magnesium steering column support brackets.

GM's EV1 electric cars feature numerous magnesium applications including seatcushion frames, steering-wheel armatures and cases and heat rails that protect battery connections.

In 1998, GM's Blazer, S-10, Jimmy and Sonoma will have magnesium IP pedal support brackets, and in '99 other light trucks will get similar treatment.

At Chrysler Corp., for 1997 the Jeep Cherokee and Dodge Dakota get one-piece steering-column support brackets made of magnesium. Ford also will switch from steel to magnesium for some seat assemblies in its Windstar minivan.

New Venture Gear Inc. (NVG), the GM-Chrysler joint venture, is said to be switching from aluminum to magnesium for 4-wheel-drive transfer system cases and covers for 1997 GM models. NVG's Chrysler transfer systems will be added by 1999, it's speculated.

While magnesium is making big percentage gains, aluminum's growth is measured in tonnage. Richard A. Schultz, director of Alcoa's worldwide automotive products, says he expects the average car to have 300 lbs. (136 kg) of aluminum by 2000 or 2001, and says the biggest growth area for the material is in engine blocks. "But exterior panels and suspension components are where the battles (with other materials) are being waged," he says.

Aluminum manufacturers and fabricators are bullish about the material's future in body structures after a decade of technical development. At first, aluminum-intensive vehicles (AIVs) were experimental or show cars. Now they're starting to roll off the assembly line. The GM EV1, Plymouth Prowler, Acura NSX, Jaguar XJ220 and Audi A8 each use aluminum for their basic load-bearing structures as well as most external skins.

When designing the A8, Audi engineers felt they could build a safer, stronger, lighter, more environmentally friendly and better-performing vehicle with an aluminum body.

U.S. aluminum supplier Alcan worked with the German luxury automaker for 10 years to develop the Audi Space Frame (ASF) concept. The ASF has produced 40 new patents and seven new aircraft-grade alloys, as well as numerous new designs, production techniques and supercomputer programs.

The A8's body uses a number of different types of extruded aluminum sections, vacuum-die-cast components and aluminum sheets in a range of thicknesses. Straight and curved extruded sections are connected by complex aluminum die castings at the highly stressed corners and joints.

Advances in the science of metallurgy were critical to the A8 body's success, as special high-strength aluminum alloys were created for sheet metal, extrusions and castings. New fastening methods were developed to join the body parts together.

The result is a cell-type structure that is 40% lighter than competitive steel units, has far fewer parts than traditional steel structures and offers 40% more structural rigidity than conventional unibody structures, says Audi. That contributes to the car's handling, responsiveness and vibration damping, and its quiet ride, says Audi, which also claims that the aluminum alloy outer panels are more dent-resistant than steel.

Despite these advances, aluminum still has a long way to go before it becomes as prevalent as steel and plastic on body panels. "Next year, one of each 10 cars made will have at least one aluminum body panel," says Alcoa's Mr. Schultz. "We've got a learning curve to go through with the stamping plants. They've been stamping steel for a long time."

Adds Mr. Wagner of Alcoa's German outpost: "We learned a lot in the development of the A8 body. We had to develop all new processes and had to create new alloys."

Beyond the high-profile Prowler and Audi, other significant aluminum applications coming for '97:

* The all-new Corvette becomes the first North American car to have both front and rear aluminum crossmembers. Corvette also will feature a drive-shaft made from aluminum metal matrix composite.

* Blocks and heads for GM's new Gen 3, 5.7L Corvette engine, replacing cast iron. The Gen 3 V-8 also features an aluminum oil pan and valve covers. Chevy Camaro and Pontiac Firebird engines will follow later.

* Steering knuckles, another aluminum growth area, on the GM minivans, Chevy Malibu, Olds Cutlass, Pontiac Grand Prix, Buick Regal and Olds Intrigue.

* Control arms on Buick's Park Avenue and Ultra.

* Hoods of GM's new front-drive minivans, representing the corporation's greatest use of aluminum sheet ever.

* Hoods of Park Avenue and Ultra, replacing steel.

* Hoods of Ford Expedition and Lincoln Navigator.

* Front crossmembers on Chrysler's '97 minivans were slated to go to steel, but the automaker decided to stay with aluminum.

* Radiators on the revamped Dodge Dakota pickup.

* Hayes Wheels is making aluminum spare wheels for GM's minivans. Most cars use inexpensive steel wheels for spares, but Hayes, through a new fabricating process, can apparently make cost-effective, lightweight aluminum spare wheels.

* Cylinder heads on Ford's newest truck engines.

* Cylinder block and heads in Honda's new V-6 engine (on the Acura CL in the U.S.).

Looking to 1998, aluminum is expected to be used for the hoods and rear crossmembers of the new Chrysler LH platform, as well as several other unique areas. Ford is said to be putting two major sheet aluminum panels on its entry-level luxury sports sedan, code-named DEW98, scheduled for 1999 intro.

Farther in the future, Ford is reported to be developing a new line of lightweight inline 4- and 5-cyl. engines with aluminum blocks. The engines could bow as early as 2001.