This Small Business Innovation Research Phase I project involves development of a new class of lightweight aluminum superalloys to replace much heavier cast iron in automobile brake rotors. There is a large market for brake rotors, estimated worldwide at $10 billion. Replacing four cast iron brake rotors in a typical sedan will reduce its weight by about 80 pounds, which translates into significant improvements in gas mileage and reductions in tailpipe emissions. These advantages are anticipated to be compelling to automakers, because of the new U.S. Corporate Average Fuel Economy (CAFE) rules. If successful, the new aluminum superalloys can capture a 2.5% share of the brake-rotor market, equivalent to 25 million brake rotors per year, during the replacement cycle. Other benefits of the switch to aluminum alloy brake rotors include: (a) rapid heat dissipation from the brake surface; (b) faster stopping and acceleration, and better automobile handling; (c) much higher corrosion resistance due to the usage of aluminum; and (d) the elimination of corrosion products (rust which forms on cast iron rotors leads to inhomogeneous heat distribution during braking).
Current commercial lightweight age-hardenable aluminum alloys are not useable above 220 degrees C because the strengthening precipitates dissolve. Thus, there is no widespread commercial usage of aluminum alloys for applications that involve elevated temperatures; e.g., automotive brake rotors. A first alternative is aluminum alloys containing 0.15-0.30% by weight of scandium (which contains heat- and coarsening-resistant Al3Sc precipitates). Another alternative is aluminum-matrix composites with ceramic particles or fibers. The former contain, however, an expensive element (scandium is comparable to gold in price) and the latter involve complicated and expensive processing routes, respectively, severely limiting their usage. The goal of Phase I is to develop successfully and patent new proprietary alloy compositions and heat treatment procedures to produce Sc-free aluminum superalloys able to sustain months of exposure at 400 degrees C and above, without a significant loss of strength. We will also manufacture a prototype brake rotor, in order to further prove out this material.
This Small Business Innovation Research (SBIR) Phase I project was focused on developing a new class of economical aluminum superalloys to be used for a number of different automotive and aerospace components. Our first focus is to replace cast iron with coated aluminum in automotive brake rotor applications. Current commercial aluminum alloys are not useable above ~220 °C (428 °F) because their strengthening agents dissolve and transform to undesirable phases. Automobile manufacturers continue to rely on cast iron for these parts, which are at least 100% heavier than aluminum components with equivalent thermal and mechanical performance. Aluminum alloys containing high concentrations of scandium, aluminum-matrix-composites with ceramic particles or fibers, and steel-clad aluminum alloys are the three main potential alternatives. These materials contain, however, expensive additives such as scandium and often involve complicated and expensive processing routes. In this program, we developed a new class of economical aluminum superalloys, which are completely scandium-free, while displaying the same ambient-temperature and improved high-temperature mechanical properties as compared to scandium-containing alloys, which previously developed and investigated at Northwestern University. The mechanical properties of the developed superalloys were enhanced by the formation of desirable heat-resistant nano-precipitates during heat treatment process. Additionally, we maintain the same properties of pure aluminum, specifically high electrical and thermal conductivities, by microalloying; that is, using alloying elements at hundreds of atomic part per million (at. ppm) concentrations. In a parallel effort, we cast full-size brake rotors (rear rotor of the Ford Fusion model), utilizing 99.5 wt.% pure aluminum. The X-ray inspection scan shows no porosity and shrinkage cavity, which indicates a successful cast and demonstrates the castability of our relatively pure aluminum alloys. This is an important achieved milestone, highly supporting our chance of future success in prototyping and production of brake rotors, utilizing the newly developed aluminum superalloys. The broader impact and commercial potential of this project is the existence of a large market for brake rotors, estimated worldwide at approximately $10 billion market capitalization. The reduction in weight and concomitant reduction in emissions and improvement in performance are anticipated to be of crucial importance to the automotive market due to the new U.S. Corporate Average Fuel Economy (CAFE) rules. Replacing four cast iron brake rotors of a typical US sedan will reduce its weight significantly, which translates into cost-effective improvements in gas mileage and tailpipe emissions. Other potential applications for the developed aluminum superalloys are high-performance wires and cables, cylinder heads, and high-performance aluminum matrices for metal matrix composites and components in aerospace.