Cast aluminum-matrix composites for automotive applications

The potential automotive applications of metal-matrix composites, particularly aluminum-matrix composites, are numerous. Although some composite components have reached the demonstrator stage, there is still much work to do and many barriers to conquer before widespread application can be expected. These challenges include such issues as processing for specific properties, compiling property databases and addressing recyclability.     

Aluminum composites for automotive applications: A global perspective

The advancement of metal-matrix composites in the automotive market is still hampered by the low-volume usage of these materials, which is caused by their high cost in comparison with aluminum alloys and, in some cases, by the lack of theoretically predicted properties. Many significant challenges must be met as these materials reach maturity and the technology is scaled-up for automotive-component fabrication. The successful commercialization of metal-matrix composites will ultimately depend on their cost effectiveness for different applications. This requires optimum methods of processing, machining, and recycling, including some very new and advanced forming routes. For more information, contact V.M. Kevorkijan, Stampal SB d.o.o., Partizanska 38, Slovenska Bistrica 2310, Slovenia; telephone 386 62 632 567; fax 386 62 636 660; e-mail kevorkijan.varuzan@amis.net.     

Metal- and intermetallic-matrix composites for aerospace propulsion and power systems

Successful development and deployment of metal-matrix composites and intermetallic- matrix composites are critical to reaching the goals of many advanced aerospace propulsion and power development programs. The material requirements are based on the aerospace propulsion and power system requirements, economics, and other factors. Advanced military and civilian aircraft engines will require higher specific strength materials that operate at higher temperatures, and the civilian engines will also require long lifetimes. The specific space propulsion and power applications require hightemperature, high-thermal-conductivity, and high-strength materials. Metal-matrix composites and intermetallic-matrix composites either fulfill or have the potential of fulfilling these requirements.     

The solidification of metal-matrix particulate composites

The simplicity, economy and flexibility of solidification processes make them attractive methods for the production of particle-reinforced metal-matrix composites. At present, however, there is limited understanding of the phenomena occurring during solidification of these advanced materials. Nucleation and refinement of crystalline phases, physical and chemical interactions between dispersed particles and solidifying interfaces, and buoyancy-driven movement of the particles are areas where a knowledge base is beginning to be formed. Ultimately, the understanding of solidification processes in metal-matrix composites must become complete enough that microstructures can be tailored for specific applications.     

双连通结构铝基复合材料及其应用

双连通结构铝基复合材料由于其特殊的网络交织结构,使它具有传统的单一材料或颗粒增强金属基复合材料所无法比拟的优异性能,在航空航天、汽车工业、电子工业、体育设施以及国防建设等领域具有非常广泛的应用前景,近年来受到世界各国普遍重视。本文总结了这种新型双连通结构铝基复合材料的性能特点、主要的制备工艺以及应用,并指出了所存在的主要问题和今后的发展趋势,为开展相关的研究提供一定的基础。     

Low-cost,fly-ash-containing aluminum-matrix composites

In recent years there has been considerable activity in the development of metal-matrix composites, especially for aerospace, ground transportation, and the leisure industry. Short-fiber-reinforced pistons and cylinder blocks have been marketed by Japanese companies for several years. It is likely that in the near future cast particulate composites like aluminum-graphite, aluminum-silicon carbide, and aluminum-alumina will find widespread applications as brake rotors, drive shafts, cylinder liners, connecting rods, and wrist pins. The cost of metal-matrix composites has been one of the major barriers toward their widespread application. This paper describes the development of cast aluminum-fly ash particle composites (ash alloy). Incorporation of fly-ash particles, which are a waste by-product of coal-based power generation, reduces the cost of aluminum castings by acting as a filler; decreases their density, and increases their hardness, abrasion resistance, and stiffness. Several prototype castings have been made from aluminum-fly ash composites to demonstrate their castability. With sustained research and the support of manufacturing organizations, these alloys can find widespread applications as low-cost aluminum composite components.     

High-strain-rate superplasticity in aluminum-matrix composites

Recent progress in high-strain-rate superplastic forming of aluminum metal-matrix composites has highlighted the potential of these materials for the mass production of complex shapes. This article reviews the current scientific understanding of this subject and identifies the areas where future work is needed to develop the technology to the manufacturing stage.     

Solidification Processing of Metal-Matrix Composites

Both particulate and fiber-reinforced metal-matrix composites feature substantial improvements in stiffness and strength over unreinforced alloys. With decreasing reinforcement prices, these lightweight materials can generate significant improvements in performance and energy consumption in numerous applications.     

Corrosion performance and mechanical properties of joined automotive materials

The automotive industry envisions that an optimized vehicle in terms of performance and cost can be achieved only by using different materials at different vehicle locations in order to utilize the functionality of the different materials to a full extent. Currently, steel and aluminum are the most important construction materials for the mass production of automotive structure. However, other materials such as magnesium alloys and stainless steel are also used. The use of dissymmetric assemblies of materials in the automotive industry has also led to the development of joining technologies other than spot welding and arc welding such as clinching, adhesive bonding, laser welding, and MIG brazing. However, and despite the development of these new joining technologies, there are still important gaps of knowledge with regards to the corrosion performance of different joint populations using dissymmetric and symmetric materials. Materials commonly used in the automotive industry including steel and aluminum‐based susbtrates were assembled with different combinations using various joining techniques in order to evaluate their corrosion performance as well their mechanical properties after cyclic accelerated corrosion tests. The results indicated a relationship between the corrosion inside the confined joint and the decrease of the mechanical properties of the assemblies.     

Emerging technologies for the in-situ production of MMCs

Among the numerous methods of producing discontinuously reinforced metal-matrix composites, technologies allowing insitu production of the reinforcing phase offer significant advantages from a technical and economic standpoint. The in-situ formation of a ceramic second phase provides greater control of the size and level of reinforcement, yielding better tailorability of the composite properties. As an example, significantly finer ceramic particulates are possible, which minimizes toughness degradation that is traditionally associated with composites containing relatively large particles. Several emerging, innovative technologies in this area are under development. As with any new technology there are technical challenges, but it is believed that these processes have unique capabilities and, thus, they present cost-effective production processes for metal-matrix composites.     

Titanium composite materials for transportation applications

Discontinuously reinforced titanium alloys containing in-situ formed TiB needles are emerging as candidate materials for advanced applications. This new family of titanium composites presents technical advantages, and it can be less expensive and easily amenable for net-shape manufacturing relative to titanium metal-matrix composites developed to date. The production of a master compound by a novel and cost-effective process called self-propagating high-temperature synthesis (SHS) has been studied. This master compound could be subsequently used in an investment casting process to obtain TiB-reinforced net-shape titanium-matrix composites. The SHS technique and its features were investigated in depth before a suitable master compound was defined and produced. Cast samples obtained from the addition of the master compound have been produced and the most important issues concerning the processing, microstructure, and mechanical properties are highlighted in this paper.     

Using Amorphous Phases in the Design of Structural Alloys

The recent discovery that amorphous alloy powders can be prepared by mechanically alloying a mixture of pure crystalline intermetallics is opening new windows to the synthesis of engineering materials. Amorphous powders synthesized by mechanical alloying may find application in the design of structural alloys, high thermal conductivity alloys, and metal-matrix composites.     

Spray Casting Aluminum and Al/SiC Composites

The gas metal arc welding process has been modified to deposit aluminum, aluminum alloys and Al/SiC composites on a substrate or in a mold. Density is close to theoretical and mechanical properties are comparable to those of wrought or cast materials. The thermal characteristics of the deposit vary with controllable parameters. This new process can be adapted to produce a variety of pure metals or metal-matrix composite materials.     

Metal- matrix composite processing technologies for aircraft engine applications

Titanium metal-matrix composites (MMC) are prime candidate materials for aerospace applications be-cause of their excellent high-temperature longitudinal strength and stiffness and low density compared with nickel- and steel-base materials. This article examines the steps GE Aircraft Engines (GEAE) has taken to develop an induction plasma deposition (IPD) processing method for the fabrication of Ti6242/SiC MMC material. Information regarding process methodology, microstructures, and mechani-cal properties of consolidated MMC structures will be presented. The work presented was funded under the GE-Aircraft Engine IR & D program.     

Metal- and Polymer-Matrix Composites: Functional Lightweight Materials for High-Performance Structures

The special topic “Metal- and Polymer-Matrix Composites” is intended to capture the state of the art in the research and practice of functional composites. The current set of articles related to metal-matrix composites includes reviews on functionalities such as self-healing, self-lubricating, and self-cleaning capabilities; research results on a variety of aluminum-matrix composites; and investigations on advanced composites manufacturing methods. In addition, the processing and properties of carbon nanotube-reinforced polymer-matrix composites and adhesive bonding of laminated composites are discussed. The literature on functional metal-matrix composites is relatively scarce compared to functional polymer-matrix composites. The demand for lightweight composites in the transportation sector is fueling the rapid development in this field, which is captured in the current set of articles. The possibility of simultaneously tailoring several desired properties is attractive but very challenging, and it requires significant advancements in the science and technology of composite materials. The progress captured in the current set of articles shows promise for developing materials that seem capable of moving this field from laboratory-scale prototypes to actual industrial applications.     

Evaluation of woven fabric composites for automotive applications

This paper summarizes the results of a recent study [1] funded by the National Science Foundation to investigate the feasibility of woven fabric composite materials for automotive applications. By identifying the advantages and limitations associated with woven fabric composites and by comparison with current automotive materials, the potential for successful application of these materials is investigated. In particular, strength, fatigue, moldability, and cost effectiveness have been identified as critical indicators of the potential for these materials in automotive applications. The results of an experimental evaluation of the static and fatigue properties of woven composites and comparable unidirectional tape composite laminates are discussed. An analytic model designed to quantify the effect of fabric weave configuration on relative conformability to complex geometries is also presented. Preliminary component designs utilizing woven fabric composites are considered in terms of potential weight savings, potential fabrication methods, and projected cost effectiveness. Finally, the key factors impeding the successful implementation of these materials in particular automotive structural applications are identified and reviewed.     

Sustainable end-of-life vehicle recycling: R&;D collaboration between industry and the U.S. DOE

Approximately 15 million cars and trucks reach the end of their useful life in the United States each year. More than 75% of the materials from end-of-life vehicles are profitably recovered and recycled by the private sector; automotive materials recycling is a success story. To achieve greater fuel efficiency and safety, today’s cars incorporate an increasing share of innovative light-weight materials. While these materials greatly enhance efficiency during vehicle use, they can present special challenges for recycling. These challenges will persist as automotive designs and the mix of materials used in vehicles continue evolving to further improve safety and performance. To meet the challenges of automotive materials recycling, the U.S. Department of Energy has recently expanded its collaborative research with industry in this area. This article discusses this collaborative government/industry approach to sustainable end-of-life vehicle recycling. For more information, contact Edward J. Daniels, Argonne National Laboratory, 9700 S. Cass Avenue, Building 362, Room C393, Argonne, IL 60439-4815; (630) 252-5279; fax (630) 252-1342; e-mail edaniels@anl.gov.     

The CVD coating of fibers for composite materials

Among the new composite materials, fiber-reinforced metal-matrix composites and ceramic-matrix composites have been given special attention for their potential uses in a variety of fields. A successful fabrication process for a fiber-reinforced composite requires that the fiber be protected, usually by a coating, during fabrication and service. The chemical vapor deposition process is a key technology for fiber coating. A survey of the current fiber coating programs seems to show that current process design in the industry is based on trial-and-error methods. New coating processes are, therefore, developed primarily by experimentation and prior experience. Ultimately, it is hoped that analytical and numerical process simulation will be used to reduce the need for costly trial-and-error process development.     

Cast Metal-Matrix Composites

The metal casting route offers considerable potential for the production of metal-matrix composites (MMC's) because of its near-net shaping capability which minimises machining requirements. The authors consider the metal-casting route in context with other shaping methods for MMC manufacture. Factors of importance, such as melt preparation and solidification processing, are reviewed before experimental details are described. The properties of MMC's based on the Al-Cu, Al-Mg and ZA alloy systems, and produced by squeeze casting, are discussed.     

Reducing Vehicle Weight and Improving U.S. Energy Efficiency Using Integrated Computational Materials Engineering

Transportation accounts for approximately 28% of U.S. energy consumption with the majority of transportation energy derived from petroleum sources. Many technologies such as vehicle electrification, advanced combustion, and advanced fuels can reduce transportation energy consumption by improving the efficiency of cars and trucks. Lightweight materials are another important technology that can improve passenger vehicle fuel efficiency by 6?C8% for each 10% reduction in weight while also making electric and alternative vehicles more competitive. Despite the opportunities for improved efficiency, widespread deployment of lightweight materials for automotive structures is hampered by technology gaps most often associated with performance, manufacturability, and cost. In this report, the impact of reduced vehicle weight on energy efficiency is discussed with a particular emphasis on quantitative relationships determined by several researchers. The most promising lightweight materials systems are described along with a brief review of the most significant technical barriers to their implementation. For each material system, the development of accurate material models is critical to support simulation-intensive processing and structural design for vehicles; improved models also contribute to an integrated computational materials engineering (ICME) approach for addressing technical barriers and accelerating deployment. The value of computational techniques is described by considering recent ICME and computational materials science success stories with an emphasis on applying problem-specific methods.