Automotive applications for aluminum have increased every year for the past 40 years. The forecast for the next 10 years is an average increase of 12 Pounds Per Vehicle (PPV) per year. This is an overall forecast, which includes both castings and wrought aluminum materials for the body panel applications. Ever since the launch of the 2015 all-aluminum Ford F150 body structure, the body-structure applications have catapulted to the top position for automotive aluminum applications. Even though the earlier Tesla model S had an all-aluminum body structure, it was the higher volume mass-market production for the F-150 truck that set the stage for competing against traditional steel structures.
Source: The Road Ahead: Aluminum Content Growth Surge (2017 Ducker Study Webinar). https://www.drivealuminum.org/research-resources/the-road-ahead-aluminum-content-growth-surge-2017-ducker-study-webinar/
Automotive Commodity Categories
When we look at the overall use of aluminum castings as the metal supply industry would prefer, we can see that the predominate categories are:
- Transmission & Driveline Housings.
- Road Wheels.
- Body Structures.
- Cylinder Heads.
- Engine Blocks.
With each of these general applications for aluminum castings, the demand is high enough for each category that entire factory complexes are set up to manufacturing these castings in the most efficient, there by most competitive, way possible.
Road Wheel Commodity – Characteristics
From an engineering perspective, lighter wheels can improve handling and fuel economy by reducing unsprung mass, allowing suspension to follow the terrain more closely and thus improve grip. However, due to stress modeling and design safety factors, the reality is that not all commercial OEM alloy wheels are lighter than what their steel equivalents would be. So, the demand in aluminum alloy wheels is generally attributed to being able to satisfy a consumer demand for style and appearance. During the rapid increase in demand during the early 2000’s, a common style for early aluminium alloy wheel designs imitated the crossed spokes of a wire wheel. It was a heavy design, but the intricate and bold design appearance was far more desirable than any sort of wheel cover alternative.
While aluminum alloy wheels are in demand for their cosmetic appearance, an unprotected alloy wheel is highly susceptible to oxidation because it isn’t corrosion-resistant. Therefore an aluminum alloy wheel casting must be be sealed with paint or a plasma vapor deposition (PVD) coating. Even with these surface protections, aluminum wheels will eventually start to corrode after 5 years. Although refurbishment of appearance is possible at a cost, after 5 years the wheel is generally functional. Unfortunately, aluminum alloy wheels are more difficult to repair than steel wheels when bent, but their higher price usually makes repairs cheaper than replacement.
At the end of life, the aluminum alloy wheel still has a lot of value in the scrap supply. As long as the wheel is only aluminum and doesn’t contain ferrous inserts at the lug nut locations, most scrap yards will pay up to 50% of the aluminum market price because it can be directly recycled.
Road Wheel Castings
The cast-aluminum road wheel commodity is almost entirely produced by the Vertical Low Pressure die casting process. Most of the plants producing road wheels are vertically integrated with value streams beginning with raw materials:
- Aluminum melting (new ingots, remelting of scrap and machining chips), degassing, delivery and oxide removal.
- Casting with Vertical Low Pressure.
- Triming of rough casting.
- Machining, including chip reclamation.
- Packing for shipment.
Each casting commodity has a particular value stream that optimizes the competitiveness for the OEM. While the road wheel production value stream listed above is found in the most competitive operations, the automotive OEM companies purchase the wheels from Tier 1 companies.
Aluminum Road Wheels
Wheel castings are a specialized commodity such that every manufacturing location is considered a vertical manufacturing unit:
- Aluminum melting
- Casting with Vertical Low Pressure machines
- Automated X-ray inspection
- Machining operations with in-plant chip reclamation
- Automated Leak Testing prior to paint
- Automated paint lines with furnace curing
- No-touch handling between manufacturing steps
- OEM delivery with scratch-proof packing materials
Unlike road wheels, most automotive OEM’s will machine their engine block and cylinder head castings in house. While the block and head castings are typically produced at a Tier 1 location, the final machining is almost always owned by the OEM.
The first F-150 models to have aluminum body panels came with the thirteenth generation design which first debuted on the 2015 model year.
All models 2015 and newer have aluminum construction for the cab and box areas.
The lighter weight of the aluminum body allowed Ford to package a new standard 2.7L V-6 engine provided a significantly improved fuel economy, while still providing 8,500 lbs of trailer towing capacity.
Aluminum Usage in Automotive
In the 2015 Ducker Worldwide study illustrated above, the NA market for new automotive vehicle sales was posted at 17.46 million units, which has been consistent for many prior years. With this total amount of vehicle sales, the following metrics related to aluminum apply:
Aluminum = 6.9 billion lbs.
- Engine parts = 33%
- Transmission = 19%
- Wheels = 16%
- Body & Closures = 11%
The most significant trends developing after the 2015 study is an increase in aluminum castings associated with Body Stuctures and electric driveline parts. These new automotive casting commodities create new applications for casting producers, however they also have unique requirements. For instance, the body structure castings need to be joined to other sheet metal parts. Therefore the body structure parts need to have material properties conducive to Self Piercing Riveting (SPR) methods or welding by Cold Metal Transfer (CMT).
Vehicle Structure Castings:
Thin walled, high ductility aluminum alloys with refined microstructures:
- Thin walls require cavity thermal control.
- High elongation for riveting assembly.
- Paint for improved adhesive bonding.
- Weldable alloys and high vacuum in cavity.
- In-plant testing for material properties.
Electric Power Train Castings:
Thin to moderate walled, high ductility alloys with unique features for removing heat.
- High elongation for absorbing impact energy.
- Complex internal cores or other features.
- Challenging design requirements from new community of engineers.