Aluminum Versus Iron
Aluminum castings started making
significant inroads on iron castings almost as soon as the price of aluminum
began to make it economically feasible, albeit a stretch. Momentum changed
dramatically with the implementation of mandatory fuel economy standards for
light vehicles.
CAFÉ
legislation was passed in 1975, not to reduce what was already recognized as
high levels of pollution created by automobiles, but to address the 1973 Arab
oil embargo. The rules were challenged, plaintiffs were granted extensions and
economic issues delayed comprehensive implementation until the mid-1980’s. The
standards continue to tighten with the EPA requiring vehicles to meet a target
of 63 grams of carbon dioxide equivalent per mile in model year 2025. It is
most conveniently and understandable when expressed in miles per gallons but
that is not the correct form.
Taking
weight out of vehicles is one of the easiest ways to meet EPA regulations.
Aluminum is a very good way to take weight out. Initially, iron castings
including engine blocks, heads, intake manifolds and transmission housings were
converted to aluminum. In addition, steel wheels were largely replaced by cast
aluminum wheels. In 1975, aluminum content in light vehicles was about 80
pounds. In 2012, aluminum content rose
to an average of 343 pounds. About 85% of that weight is in the engines (130
pounds), wheels (67 pounds), transmission and drive chain(70 pounds) and
radiators (32 pounds). Eighty percent of engine blocks are aluminum, 99% of
cylinder heads, 100% of radiators and transmissions and 70% of road wheels are
aluminum. Small percentages of aluminum castings are used in suspension
arms/links (14%), bumper beams (17%), steering knuckles (27%) and hoods (30%).
The 263
pound of aluminum added to vehicles from 1975 to 2012 came at the expense of
765 pounds of iron castings.
It is
generally accepted in the automotive industry that $2 in additional vehicle
cost is reasonable to reduce weight by one pound. Ford Motor’s 2015 F150 Pickup
is the first “all aluminum” vehicle. There is about $1000 in added cost due
just to the use of aluminum. While the use of aluminum in light vehicles will
continue to grow only a small portion will be aluminum castings. Most of the
growth in the use of aluminum will be extrusions and sheet.
Most
reports compare iron and aluminum castings based either on tons (weight) or
sales dollars. Neither makes any sense in the comparison. Iron weighs 491
pounds per cubic foot and aluminum weight 169 pounds per cubic foot. A
comparison based on weight substantially understates the volume of aluminum
cast relative to iron. In 2012, the average aluminum casting sold of $2.358 per
pound compared to $.641 for ductile iron, a multiple of 3.7 times the price of
ductile iron. A comparison based on sales dollars overstates the importance of
aluminum.
An
“apples to apples” comparison is a comparison of the cubic feet cast.
As the
chart shows, aluminum is a larger share of the market than recognized when
weight is used as a comparison. Several factors impact the volumes cast in any
one year. For both iron and aluminum, automotive is the “900 pound gorilla.” In
2012, 8.9% of gray iron castings were for automotive, 12.2% for ductile iron
and 30.5% for aluminum. In die casting aluminum, fully 55% of production is for
automotive applications. The significant drop in aluminum production that began
in 2008 and started to reverse in 2010 was due to the drop in automotive
production.
Each of
the iron alloys and aluminum alloys have properties that can determine which is
best in a particular application. There are times the materials are
interchangeable with reasonable or no modification to the part design. As proof
of this, consider the conversions of iron castings in automotive to aluminum.
When the materials are substantially interchangeable, price becomes the
determining factor. Aluminum is a preferable material from the standpoint of
ease of processing.
A
hypothetical casting weighing one pound in iron (.34 pounds in aluminum) that
can be made identically in both iron and aluminum would cost $.641 in ductile
and $.802 in aluminum. The price of aluminum is trending very slowly downward.
When the cost of aluminum drops another 25%, the materials will be cost
competitive. Aluminum is a much more prevalent element than iron in the earth’s
surface. A breakthrough in processing technology that lowers primary aluminum
cost could bring a dramatic price drop. Also, aluminum is very easily recycled.
As more primary aluminum is put into use and products reach the end of their
life cycle and are reprocessed the supply of secondary aluminum will increase.
An increased supply of secondary aluminum will put downward pressure on
material costs.
There
do not appear to be any imminent breakthroughs in primary aluminum processing.
The price of secondary aluminum is moving very slowly. It will be some time
before aluminum, as a material in itself, is price competitive with iron.
There
are certain categories of castings where there is no comparison between iron
and aluminum castings. Aluminum castings top out at 3,500 pounds with a few
somewhat larger. Iron castings top out at 200,000 pounds in the United States
and even larger in Europe and China.
