Eck Industries Inc. has teamed with military- and specialty-vehicle axle manufacturer AxleTech International to deliver lightweight cast components made from A206 aluminum alloy, including a new steering knuckle that saves about 60 lb (27 kg) per axle on a military vehicle (the specific truck, OEM, and vehicle details could not be disclosed).
The 30-lb (13.5-kg) aluminum knuckle, production of which started in June, cuts in half the weight of its iron counterpart. (There are two knuckles per axle—thus, the 60-lb savings.)
“One challenge is package space, to engineer a robust knuckle and still have room to integrate all the adjacent components,” shared Andrew Halonen, Sales Engineer for Eck Industries. “The 206 aluminum alloy is superior to other cast aluminums in strength, fatigue, toughness, and bolt retention, thus making it a great choice for these applications. And, the weight savings is significant.”
The challenge of converting from steel to aluminum owes to the two materials’ mechanical properties; since steel is stronger and stiffer than aluminum, the aluminum component needs to be “beefed up,” meaning it needs to be thicker in the areas that are load-carrying, Halonen explained. “The aluminum component will be larger in size or thickness, yet it may often be 50% lighter,” he said.
The 206 aluminum is said to deliver high specific strength, be very tolerant to damage, perform well at elevated temperature, and offer attractive ballistic properties. Considering the high-strength T7 temper, the typical ultimate tensile strength is 58 ksi (400 MPa), the typical yield strength is 48 ksi (331 MPa), and the typical elongation is 5%, according to Halonen. Working closely with the foundry, the premium properties of this temper are 60 ksi (414 MPa), 50 ksi (345 MPa), and 7% respectively. For the high toughness T4 temper, the typical properties are 55 ksi (379 MPa) tensile, 36 ksi (248 MPa) yield, and 10% ductility, he noted.
Since 206 aluminum contains about 4.5% copper, the density is slightly higher than such alloys as A356 at 0.101 lb/in3 (2.80 g/cc). “The addition of copper helps it retain its properties at elevated temperatures,” said Halonen. “Typical cast aluminum alloy properties are reduced at temperatures exceeding 300ºF for a long period of time; however, 206-T4 held for four hours at 390ºF was 50 ksi tensile, 45 ksi yield, and 3% ductility.”
“With high-strength aluminum, we are helping customers convert transfer cases, differential cases and carriers, hubs, and steering knuckles to aluminum from iron,” said Halonen. “The strength and stiffness differences are definitely a challenge; depending on the suspension configuration and the vehicle weight, it may be feasible to convert control arms as well.”
Eck Industries is currently working with several axle manufacturers to design, develop, and test lightweight components for heavy trucks, mainly military trucks because of the weight challenge involved with vehicle armoring, said Halonen. On vehicles of large axle loads, the company has the following 206 aluminum components in development, with subsequent weight savings per axle:
• Hubs – approximate savings of 60 lb/axle
• Brake calipers – approximate 30 lb/axle
• Differential case – approximate 45 lb (20.5 kg)/axle
• Differential carrier – approximate 70 lb (32 kg)/axle.
“Considering all of these components, there is the opportunity to reduce axle weights by hundreds of pounds,” said Halonen. “Other applications in development include fifth wheels and structural equipment mounts, especially those located high on the vehicle. Removing weight high on the vehicle helps reduce the center of gravity, which will reduce the likelihood of tipping.”
Even though aluminum alloys can handle the rigors of many heavy-duty component applications, there is one very good reason why their adoption has been slow: cost. “On a per-pound basis of raw material, aluminum is $1.20-1.80/lb while ductile iron is about $0.70-$1.00/lb,” Halonen shared.
He believes that the market challenges in the trucking market—namely, high fuel prices, reduced stopping distances, and additional emission equipment weight—will drive the growth of such robust, lightweight materials.
The perception of aluminum as being a “lightweight”—in the sense of lacking the robustness to perform capably in such demanding applications—also handicaps the material. “Our biggest challenge is to convince the design engineer to consider the material,” Halonen admitted. “Then, the process of evaluation with CAD and analysis tools is straight-forward, and many times, we will know whether or not it will be feasible before a part is even made.”
Eck Industries has a number of alloy development programs in progress. “We have developed a process to cast aluminum alloys that were developed for wrought or extruded processes, yet we would like to incorporate the benefits of a net shape casting,” Halonen explained. “One material is 6063, which is often used for heat sinks. We can cast 6063 in production today. A second wrought alloy is 7075, which is very strong yet is cost-effective. We have cast flat plates with very good properties and will next experiment with more detailed geometry. 7075 should be available for production products within a year.”
The company is also working with University of Wisconsin-Madison and Oshkosh Corp. to develop nano-reinforced 206 aluminum, with the goal of achieving high strength and high ductility. “While the full benefits of the nano-composite work will be three to five years out, some benefits like enhanced ductility and improved castability will be incorporated into production parts by the end of 2012,” he said.
Eck Industries has been casting high-strength 200 series aluminum alloys since the early 1980s. The flagship applications—production of which began more than 30 years ago—are the final drive housings and covers on the M2 Bradley Fighting Vehicle made by BAE Systems, delivering a savings of 1000 lb (454 kg) in comparison to the original cast-iron design. Similar housings are used on the amphibious AAV7. Also, 206 aluminum has been in production for decades on the M1 Abrams for components on the transmission and trunnions, valves, rings, and steering components.