Thanks mostly to a growing number of engine and driveline parts on high-volume light trucks, use of aluminum in 1999 models built in North America is expected to soar to a new high, taking ever deeper bites out of cast iron's dwindling piece of the automotive pie.

American Metal Market estimates '99 models built in North America will have an average of 235 lbs. (107 kg) of aluminum per vehicle, up 5% or about 12 lbs. (5.4 kg) from last year's average. That's one of the largest year-to-year gains ever, the trade paper asserts. Meanwhile, cast iron content is diving and is expected to drop another 14 or 15 lbs. (6.3 to 6.8 kg) in '99, AMM reports.

BMW AG's new '99 3-Series, for instance, replaces cast iron with aluminum on the block of its 2.5L and 2.8L 6-cyl. engines for a weight savings of 51 lbs. (23 kg). Forged aluminum lower arms replace previous steel arms on the 3-Series' front suspension; the upper strut mount has been switched to aluminum from steel, as has the brake shield.

BMW says aluminum parts now make up 21.3% of total suspension weight, or 132 lb. (60 kg). The entire suspension system weighs in at 602 lb. (273 kg). It would have been 26 lbs. (12 kg) heavier if it were built entirely of steel, BMW says. The lighter suspension - and lower unsprung weight - benefits handling and ride, particularly on rough roads.

Industry sources say much of the gain in North America for '99 is the result of General Motors Corp. and Chrysler Corp. using aluminum instead of cast iron for the cylinder heads of their new, high-volume light-truck V-8 engines, which debut on new vehicles such as GM's GMT800 full-size pickups and Chrysler's Grand Cherokee. But an impressive array of other parts also are being switched to aluminum this model year, including suspension systems, differential cases, steering knuckles and other components. An increasing number of cars are offered with aluminum wheels as standard equipment, and that's jacking up aluminum poundage as well.

One of the most significant aluminum showcases to emerge during the '99 model year will be Ford Motor Co.'s Lincoln LS sport sedans. While technically 2000-model cars, they are expected to debut early next year sporting aluminum hoods, decklids and fenders. Detroit-based automakers haven't used aluminum for fenders in decades, although Ford toyed with the idea for current Taurus/Sable models.

In addition to numerous aluminum body panels, the new Lincoln sport sedans also will be fitted with all-aluminum engines, suspension control arms, steering knuckles, differential carriers and chassis crossmembers.

Nevertheless, supplier sources suggest Ford engineers did not originally set out to make the new platform - known as DEW98 - quite so aluminum-intensive. Instead they set out to make two versions of a sport sedan that would "out-BMW BMW" in performance and handling, but they ran into weight problems early on. Engineers reportedly have been desperately trying to take weight out ever since. But the cars still reportedly are heavier than comparable BMWs.

Japanese transplant automakers also are contributing to the aluminum boom by launching several new aluminum engine programs. Toyota Motor Mfg. North America's new engine plant in Buffalo, WV, will soon start up, and Honda of America Mfg. Inc. (HAM) is expanding production of aluminum-intensive engines and transmissions.

Switching engine blocks from cast iron to aluminum is not quite a no-brainer, though. In 1996, BMW ran into problems in the U.S. when it began to convert iron-blocked I-6 and V-8 engines to aluminum. Because BMW wanted to enjoy the full weight-saving benefits of aluminum-block construction, it spurned the commonly accepted - but rather lowbrow, by BMW standards - practice of fitting cast-iron cylinder liners in the aluminum blocks to enhance durability.

Instead, BMW engineers opted for Nikasil, a fancy process in which a high-silicon-content cylinder-bore "insert" is placed in the block casting mold; when the aluminum is injected into the mold, the insert melts, but leaves a high-silicon surface right where you want it: on the cylinder bores.

BMW hadn't factored-in high-sulfur U.S. gasoline, though. The Nikasil coating didn't hold up to the effects of heavily sulfured gasoline - and quite a few BMW production engines gave their lives in the prove-out. For the I-6s in the 3- and 5-Series, the Bavarians briefly switched back to iron. This year, aluminum returns - but with the more pedestrian cast-iron liners.

There are alternatives to Nikasil that are more sulfur-resistant, including Alusil and Lokasil (both aluminum/silicon processes); Porsche AG uses Lokasil for its all-aluminum engines. But BMW 3-Series director and product line manager Wolfgang Zeibart admits all these processes are expensive - thus the move to iron liners for the new, '99 3-Series aluminum 6-cyl. engines.

The liner/surface-coating camps each make good points. Makers of higher-priced, premium vehicles tend to prefer the higher-tech, cylinder-coating approach. Yet for smaller engines, using iron liners often negates a goodly portion of the weight saved in the switch to an all-aluminum block. This aspect was underscored when General Motors Corp. converted the block of the old LT1/LT4 V-8 to aluminum in creating the new LS1 V-8. Engineers kept iron cylinder liners.

John Juriga, the lead GM Powertrain engineer for the LS1, summed it up in an interview in '97: "We've seen some problems others have had with Nikasil and other coatings," he said. "The cast-in liners are a good, reliable method; the weight penalty really isn't that great."

AMM and other industry sources cite other significant aluminum applications for the coming model year, among them:

n The hoods and rear crossmembers on Chrysler's 300M and LHS.

n The lower front control arms, knuckles and brake calipers in the Olds Alero and Pontiac Grand Am.

n Lift gates and heat shields on GM's GMT800 full-size pickups.

n Cases, valve bodies and covers on GM's 4L60E automatics.

n Aluminum also is replacing magnesium in transfer cases of the 4-wheel-drive systems of Ford's F-150 pickups and compact SUVs.

Despite aluminum's growth, few experts believe it will soon dominate more traditional materials such as steel.

Richard Shultz, a veteran of both the steel and aluminum industries currently serving as project consultant for Bloomfield Hills, MI-based Ducker Research, says lightweight aluminum alloy components - to a lesser extent magnesium - will proliferate long-term. But steel and cast iron will continue to play major roles, near-term, he says.

How big a role? Mr. Shultz says it's possible that aluminum can achieve a weight saving of 300-plus lbs. (135 kg) in most standard-sized cars by the early 2000s, about 75% of which would be in the form of underhood applications like transmissions, transmission cases, engine blocks and cylinder heads. The remaining 25% to 30% most likely would come from aluminum wheels, hoods, deck lids, space frames, underbody crossmembers and body panels.

The latter application is subject to innovative technology in the production and stamping of sheet aluminum, and improved structural integrity as well as dent-resistance.

The mix, he says, is critical if automkers are to meet increasingly stringent CAFE requirements which, in turn, could help them satisfy stiff Environmental Protection Agency emissions mandates. - with Fran Smith