Material Innovations
Nanocomposite debuts on GM vehicles
 The step-assist on the 2002 GMC Safari represents a first for the exterior application of a TPO-based nanocomposite. |
The 2002 Chevrolet Astro and GMC Safari midsize vans are the first vehicles to use an advanced thermoplastic olefin nanocomposite on an exterior application, according to General Motors Corp., but not the last. About the vehicles' optional step-assist—a running board designed to help people enter and exit a vehicle—GM Executive Director of Science for R&D Alan Taub said, "This is the first of several applications we're investigating."
GM and three supplier partners—Basell, Southern Clay Products, and Blackhawk Automotive Plastics, Inc.—worked to bring the TPO-based nanocomposite to production. Basell, the world's largest producer of polypropylene resins for plastics, provides the resin and processing technology for the new nanocomposite. Marking an unprecedented occurrence for the automaker and its outside suppliers, GM, Basell, and Southern Clay Products (a provider of specialty additives based on smectite materials) have a mutual confidentially agreement; information is trade-secret-protected, rather than patented, since it "would be difficult to do reverse engineering," said Taub.
The technology breakthrough deals with how the very thin flakes of a clay filler are peeled apart. "The greater the extent of exfoliation, the thinner the particles are, and a greater surface area is available for interaction with the polymer matrix, resulting in better performance," Taub explained. When properly exfoliated, these layered materials have dimensions on the order of 1 nm (0.04 µin) thick by 100-1000 nm (3.94-39.4 µin) long.
In the 2001 model year, 8000 units of the Astro and Safari were sold with an optional step-assist molded by Blackhawk. The low-volume application choice is intentional for the new nanocomposite. "We're doing mold trials on rocker panels, which may be the next step for a higher-volume application," said Mark Bennett, Advanced Technology Manager for Blackhawk.
 Steve Hubbard, Blackhawk Automotive Plastics' Process Technician, examines an injection-molded nanocomposite step-assist for the 2002 GMC Safari and Chevrolet Astro. |
When compared to a conventional TPO, the new nanocomposite can provide up to a 20% weight savings (between 7.5 and 8% on the step-assist), a similar stiffness—1000-1200 MPa (145,000-174,000 lbf/in2)—and more ductile strength at low temperature. The new nanocomposite is also TPO cost-equivalent, has a class A surface, is more recyclable (because of less additive material), and does not require new tooling.
Filler content for the nanocomposite is based on a class of clays known as smectites and represents 2.5-3% of the part (the figure for TPO filler content is typically 15-20%). In addition to improved throughput, the new nanocomposite provides improved paint adhesion and quality when compared to a talc-filled TPO, according to Bennett.
Other exterior parts being looked at for a TPO-based nanocomposite include body claddings and sail panels. "We're studying interiors, and we see no roadblocks to getting there," Taub said.
- Kami Buchholz
Carpenter's soft magnetic alloy
 Hiperco Alloy 15 has high magnetic saturation and low coercivity. |
Carpenter Technology Corp.'s Hiperco Alloy 15 is a soft magnetic alloy with reduced cobalt content offering high saturation magnetization (flux density) and relatively high electrical resistivity. An addition to Carpenter's Hiperco family of soft magnetic alloys, the new grade can be considered for many new and high-performance applications for which cost considerations have restricted the use of higher-cobalt soft magnetic materials.
The 15Co-2.7Mn-Fe alloy can be used for applications such as actuators, relays, fuel injectors, switched reluctance motors, magnetic bearings, flywheels, sensors, high-performance electromagnets, and linear motors. For solenoid applications, it is particularly suitable for those that have to be turned on and off with great force.
Hiperco Alloy 15 has a high magnetic saturation (22.3-22.8 kilogauss) and possesses a degree of flux density greater than that of iron and silicon-irons at high fields. Electrical resistivity for AC applications is 38-42 µohm•cm (125-138 µohm•in), compared with Hiperco Alloy 27, which is 19 µohm•cm (62 µohm•in). The new grade's coercivity is relatively low at 1.9 to 2.4 oersteds. Its magnetic properties can be optimized by a two-step annealing process—heating first at 2156°F (1180°C), then holding at 1292°F (700°C).
Hiperco Alloy 15 can be used as a substitute for materials such as nickel-irons, ferritic stainless steels, silicon irons, as well as irons that do not provide adequate flux density. Unlike the higher-cobalt alloys, Hiperco Alloy 15 is ductile at room temperature. It can be forged to produce bulk parts, cold-compacted in powder forms, and made into strip products. While it can be processed via stamping and machining, it also can be easily bent and formed.
The product is available in strip, bar, and plate.
- Patrick Ponticel
