Aluminum - Fly Ash Metal Matrix Composites as Advanced Automobile Material
We've many times documented the value of Coal Ash as a mineral filler, both for plastics, as seen, for one example, in:
West Virginia Coal Association | Texas Makes Plastic Pipe with Coal Ash | Research & Development; concerning, primarily: "United States Patent Application 20020040084 - Fly Ash Filler and Polyvinyl Chloride Compositions and Conduits; 2002; Assignee: Boral Material Technologies, Inc.; Abstract: A composition comprising fly ash particles with an average particle diameter of not greater than 100 micrometers and a moisture content of not greater than 0.25 percent by weight. The compositions are useful as both a filler and a colorant in polymer containing compositions, particularly polyvinyl chloride compositions for extruding pipes and conduits. Desirably, the composition is used at a filler loading level of from about 1 to about 80 parts by weight of the fly ash per hundred parts of the polymer. Fly ash-filled polyvinyl chloride compositions containing the fly ash as described meet commercial requirements and are economically and environmentally beneficial";
and, in Portland Cement-type Concrete, as seen, for only one example, in:
West Virginia Coal Association | Federal Highway Administration Recommends Fly Ash Concrete | Research & Development; concerning the FHWA report: "'Infrastructure Materials Group: Fly Ash'; In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregation, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, and enhances sulfate resistance. FHWA has been encouraging the use of fly ash in concrete";
in which report the FHWA explains that using Coal Ash as a substitute for some or all of the sand and gravel aggregate in concrete mixes, due to both the chemical makeup and the physical structure of Coal Ash, results in concrete that is superior to conventional Portland Cement Concrete in terms of nearly all physical properties, including ultimate compressive strength.
In both those applications, Fly Ash is serving as one component of a "composite" material, that is, something made from two or more separate things that maintain their individual structures and identities in the final product, but combine their physical, and sometimes their chemical, properties together in such a way so as to enhance and improve the overall physical properties of that final product. And, to get a bit of terminology out of the way, in the above "United States Patent Application 20020040084 - Fly Ash Filler and Polyvinyl Chloride Compositions and Conduits", especially, the "Polyvinyl Chloride" plastic to which the Fly Ash is added would be what is known as the "matrix" of the composite material; that is, the stuff that holds it all, the different components of the composite, together.
Things made of what is generically called "fiberglass" are perhaps the best known, or most easily understood, examples, where the glass fibers and the plastic resin that are combined to make the fiberglass object work together to improve properties such as impact resistance and tensile strength. Concrete is much the same, since cured Portland Cement, without gravel or other aggregate in it to make it Concrete, is actually a somewhat weak material with a much lower load-bearing capacity and impact resistance than Concrete.
Although those examples of composites are likely familiar to a certain degree to most of our readers, what is likely less known is the fact that metals, too, can be used to make composites, with properties improved over the primary metal constituent.
In one sense, alloys and amalgams of different metals might be thought of as metal composites. For instance, Gold is a noble metal that resists oxidation and chemical attack, and thus retains it's luster and appearance over time. But, though relatively inert, it is also very ductile and malleable. To hold a shape that it's been formed into, say a wedding ring, Gold has to be blended with a certain amount of another metal, with Copper and Nickel being commonly used. Pure Gold is called "24 Carat" Gold; and, thus, if your wedding ring is "14 Carats", which is the grade perhaps most often used, then 10 out of 24 parts of the metal in that ring, a shade over 40% of it, is a metal other than Gold. And, it's there in honestly-graded jewelry to serve a good purpose: to make it stronger, tougher and more durable; to improve it's utility.
There are, as it happens, other metal composites besides alloys and amalgams; wherein the "matrix" material, as we explained above, is mostly metal, but contains something else besides another metal to impart desired properties; or, just to make the metal better at what it does pretty well in the first place all on it's own; or, to make the finished part less expensive; or, all of the above.
Aluminum, as we all know, is a pretty good metal to make things out of. Relative to iron, it's both lighter in weight and in some ways more resistant to corrosion. It is, however, much weaker, physically, than iron, and much more susceptible to physical abrasion - as anyone who has had to sand out repairs on a car made of both aluminum and steel body parts will know.
That relative physical weakness has limited the use of Aluminum in, especially, high stress and high wear automotive applications, especially in those applications where appreciable heat is generated, where it's lighter weight would otherwise be desired to help achieve performance and/or fuel economy goals.
But, one way to overcome the deficits of Aluminum and still take advantage of most of it's benefits is to use it as the base metal, the matrix, of a metal composite, wherein an added component can improve certain needed physical properties and help to make such a "metal matrix composite" suitable for use in higher performance applications.
And, such metal composites are known and utilized, as explained in:
Metal matrix composite - Wikipedia, the free encyclopedia; "A metal matrix composite (MMC) is a composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. MMCs are made by dispersing a reinforcing material into a metal matrix. ... For example, carbon fibers are commonly used in aluminum matrix to synthesize composites showing low density and high strength. The matrix is the monolithic material into which the reinforcement is embedded, and is completely continuous. This means that there is a path through the matrix to any point in the material, unlike two materials sandwiched together. In structural applications, the matrix is usually a lighter metal such as aluminum, magnesium, or titanium, and provides a compliant support for the reinforcement. In high temperature applications, cobalt and cobalt-nickel alloy matrices are common. The reinforcement material is embedded into the matrix. The reinforcement does not always serve a purely structural task (reinforcing the compound), but is also used to change physical properties such as wear resistance, friction coefficient, or thermal conductivity. The reinforcement can be either continuous, or discontinuous. Discontinuous MMCs can (in some cases) be worked with standard metalworking techniques, such as extrusion, forging or rolling. In addition, they may be machined using conventional techniques, but commonly would need the use of polycrystaline diamond tooling (PCD). Discontinuous reinforcement uses ... short fibers, or particles. The most common reinforcing materials in this category are alumina and silicon carbide".
And, as it happens, another of the "reinforcing materials in this category", i.e., "particles", which can be used in Aluminum "metal matrix composite"s is Coal power plant Fly Ash. As seen in excerpts from the initial link in this dispatch to:
"Aluminum - Fly Ash Metal Matrix Composites as Advanced Automobile Material
Final Report; September, 2001
Cosponsors: United States Department of Energy; Wisconsin Electric Power Company; Electric Power Research Institute (EPRI)
(This) report is a corporate document that should be cited in the literature in the following manner:
Aluminum-Fly Ash Metal Matrix Composites As Advanced Automobile Material, EPRI, Palo Alto, CA; 2001.
(We remind you of just one of our earlier reports concerning the above Wisconsin Electric Power Company, aka "We Energies", as accessible via:
West Virginia Coal Association | Wisconsin Coal Ash Utilization Guidebook Available | Research & Development; concerning: "Coal Combustion Products Utilization Handbook (2nd Edition); By Bruce Ramme & Mathew Tharaniyil (We Energies); 2004";
and, note that one complete chapter in the Handbook is:
"8. Fly Ash Metal Matrix Composites; 'Metal matrix composites (MMCs) are engineered materials formed by the combination of two or more materials, at least one of which is a metal, to obtain enhanced properties. MMCs tend to have higher strength/density and stiffness density ratios, compared to monolithic metals. They also tend to perform better at higher temperatures, compared to polymer matrix composites. Though MMCs have been in existence since the 1960s, their commercial applications have been limited due to their higher cost and lack of proper understanding. More recently developed MMCs, especially cast aluminum-fly ash composites, have the potential of being cost effective, ultra light composites, with significant applications. Such composites, if properly developed, can be applied for use in automotive components, machine parts and related industries'".
The above book was published subsequent to the study reported herein, but still notes some difficulties in achieving a consistent particle distribution in Aluminum-Fly Ash MMC's that are simply cast from molten metal with the Coal Ash blended in, with subsequent limitations on the amount of Ash that can be utilized in MMC's, expressed as a weight percentage of the casting.
There has been subsequent work on improving casting techniques for MMC's containing Fly Ash, including some in other countries, as we will document in at least a few future reports. The upshot being that higher percentages of Ash can be used in castings; and, different casting techniques have been developed that enable such higher loadings of Ash, with the potentials for such high Ash composites actually noted in places in this earlier work. - JtM)
Report Summary: Metal matrix composites such as silicon carbide-aluminum, alumina-aluminum and graphite-aluminum represent a class of emerging materials with significant potential for commercial use
in the auto and aerospace industries. In industrial foundry trials, a joint industry and Department of Energy project demonstrated a promising new process for producing a low cost aluminum metal matrix composite containing fly ash particles.
Background: During the last decade, under EPRI sponsorship, the utilization of waste by-products such as fly ash as a filler material in light metals and alloys like aluminum has been explored at the University of Wisconsin – Milwaukee (UWM) for potential applications in engineering components. This research has examined various aspects of making aluminum - fly ash composites by an inexpensive stir mixing and casting technique and has evaluated the properties of the resulting composites. Fly ash represents a unique, inexpensive resource of solid and partly hollow microspheres that are otherwise quite expensive to produce. Under the previous work, UWM had fabricated parts in the laboratory using standard casting techniques, including stir, squeeze, sand, pressure die, gravity, and permanent mold methods, as well as forging and
extrusion techniques.
(We'll also have more to separately report on the above work at the University of Wisconsin – Milwaukee (UWM); especially in the form of several patents concerning such uses of Fly Ash.)
Objectives: To demonstrate inclusion of fly ash in a standard ASTM test bar utilizing different casting
techniques and manufacture of different fly ash-enhanced parts with dissimilar property-performance goals. Parts selection as well as subsequent evaluation was based on a multi-dimensional matrix of life cycle considerations, property-performance requirements, material content (aluminum and fly ash), and casting techniques. Project tasks were structured to enable observation of manufacturability, durability, and recyclability of the fly ash – aluminum composites.
Approach: The two participating foundries used production floor expertise to establish a baseline for
process-material relationships and material microstructure optimization. Such skill and knowledge is critical, since software models are not yet available for fly ash-enriched material flow processes governed by fluid flow or by plastic deformation. The foundries established the correct relationships between processing temperature, processing parameters, and solidification structures, modifying mold filling to address low turbulence filling of the mold and prevent the formation of oxides and gas entrapment. Ultimately this approach led to the optimum manufacturing steps and mold filling parameters for candidate parts.
Results: This commercialization project demonstrated the ability to successfully mix 400-lb (182-kg)
melts of aluminum-flyash composites and produce selected prototype castings of aluminum - fly ash composites. The use of these castings have the potential to reduce the cost and weight of automotive parts, in addition to providing a high value use of ASTM Class F type fly ash.
(We remind you that "Class F type fly ash" is what we get from the combustion of our eastern US bituminous Coal. Similar techniques have been developed which utilize "Class C" fly ash from lignite coal, typically mined in western states, again as we will document in separate reports.)
Several parts were successfully produced, including a differential housing carrier. The differential housing exhibited a weight reduction of 65% over the current iron part and passed the MIL 2175 Grade ‘C’ Casting Standard. As a precursor to industry qualification, Visteon accepted the component for further testing of sound dampening and thermal expansion.
EPRI Perspective: Ashalloy (TM), a metal matrix fly ash particle composite, presents an opportunity for a number of potential industrial applications.
(We find it interesting that a Coal Ash and Aluminum composite was found so promising that a commercial trade name was devised and officially registered for it.)
In particular, Ashalloy (TM) could help enhance the competitiveness of foundries, where the melting of ingots consumes considerable electricity. The substitution of fly ash as a filler in aluminum produces a composite with improved engineering characteristics at a lower cost.
(The above point about helping to "enhance the competitiveness of foundries" by reducing the amount of Aluminum ingots that need to be melted, a process that "consumes considerable electricity" is a particularly apt one, we think. The byproduct of electricity generation from Coal, the Ash, can be used in a way that conserves the electricity.)
Abstract: Aluminum alloy (A356)-fly ash composite ingots of up to 182 kg and selected parts were successfully cast in sand and permanent molds using conventional foundry techniques. The sand and permanent mold castings including differential carriers, intake manifolds, motor mounts, electric covers, and brake drums show adequate castability of the melts containing fly ash particles. Aluminum-fly ash melts were also pressure die cast into mounting brackets and squeeze cast successfully into mounting brackets. The squeeze cast samples exhibited the best microstructure and properties. The overall project work demonstrates the feasibility of making a variety of prototype components from industrial-size melts of aluminum-flyash composite alloys, using sand, permanent mold, pressure die casting, and squeeze casting techniques.
The results of microstructure analysis and property examination indicate that the strength of casting is
significantly influenced by the amount and distribution of fly ash particle in the castings. The room temperature tensile strength of composite castings containing less than 8% fly ash by volume is similar to that of the base alloy and then decreases with further increase in fly ash contents. This decrease in properties may be related to clusters of fly ash observed in the microstructures of castings. Additional work is needed to improve the distribution of fly ash in the matrix in sand and permanent metal castings to enhance its bonding with the matrix. The tensile strength measured at 600 °F is about 7 to 10 ksi (48 to 69 MPa) for the composite castings containing 2 to 12 % fly ash by volume, which is higher than the base alloy’s 4 ksi (28 MPa).
(Again, up to a point, Fly Ash can improve the properties of Aluminum castings. The "decrease in properties" at higher loadings is due to segregation of the Ash, i.e. "clusters of fly ash", in the cast article. Later work also describes it as a settling phenomenon; and, again, techniques have been devised to prevent it. - JtM)
(This) project demonstrated that cast Ashalloy(TM) automotive parts can be fabricated using standard foundry techniques. Early adoption of this technology was advanced by:
(1) identifying machine components for prototype production;
(2) establishing alliances with metal fabricators and foundries to fabricate prototype products for in-service testing; and:
(3), preparing preliminary engineering specifications for raw material blends, product designs, and manufacturing techniques.
Fly Ash–Enhanced Aluminum Alloy Metal Matrix Composite: AshalloyTM; Ashalloy contains the additive, fly ash, to reduce weight and cost, improve selected material properties, reduce energy consumption and pollution, and overcome the cost hurdle that has kept other metal matrix composites from wider use.
Ashalloy represents a series of ash-derived metal matrix composites that are combinations of two or more materials engineered to achieve tailored properties. In some cases, fly ash serves as a low cost filler to replace expensive aluminum or its alloys. In other cases, its purpose is to improve component properties such as the reduced Coefficient of Thermal Expansion (CTE) lighter weight, increased hardness and improved abrasion resistance.
Ashalloy can possess unique combinations of properties not achievable in monolithic materials. Depending on the materials and their relative proportions, these properties may include high specific strength, specific stiffness, damping properties, abrasion resistance, and low coefficient of thermal expansion.
Development of Ashalloy castings containing electric utility coal fly ash will conserve energy, materials, and protect the environment.
Continued research will result in the commercialization of a new material that will make American foundries more competitive, and provide the automotive industry with new low-cost, lightweight materials, to achieve the U.S. Environmental Protection Agency’s CAFE fuel efficiency standards in the future.
An inexpensive casting technique has been developed to produce aluminum-fly (Ashalloy) composites containing various percentages of both as-received and classified fly ash powders. The technique involves suspension of suitably pre-treated fly ash particles in molten aluminum alloys by special procedures. The molten metal-fly ash slurries are then cast into molds where the metal solidifies to give composites. Large ingots of Ashalloy measuring three inches in diameter and up to fifteen inches in length, containing up to twenty percent by volume of fly ash, have been produced in research laboratories using this technique.
Using pressure infiltration techniques it is possible to obtain metal matrix composites containing up to 65% coal fly ash filler.
(As we noted earlier, it is possible through special casting techniques to achieve quite high loadings of Coal Ash; and, it might even be feasible, with those more advanced casting techniques, to think about making automobile structural parts, perhaps like "differential carriers, intake manifolds, motor mounts, electric covers, and brake drums", out of, mostly, "65%", Coal Ash.)
UWM research found that coal fly ash particles dispersed in common commercial alloys can improve engineering characteristics such as hardness and abrasion resistance. And even in composites where materials properties are not improved, the fly ash acts as an effective filler to reduce base-metal requirements, thereby decreasing the density and the cost of the aluminum components.
The research (has) demonstrated the ability to successfully produce 400 pound (182 kg) melts and selected prototype castings of aluminum – fly ash composites. Attempts were also made to make 3,000 lb (1364 kg) melts of aluminum – fly ash composites to produce a large number of ingots and castings from a single melt. The use of these castings have the potential to reduce the cost and weight of automotive parts, in addition to providing a high value use of F type fly ash.
The cost of aluminum-fly ash castings are expected to be lower than aluminum-silicon carbide alloys, and possibly even monolithic aluminum alloys. Fly ash is a by-product and it will cost at the most 5 to 10 cents per pound ($0.11 to 0.22/kg) after beneficiation compared to 75 cents per pound ($1.65/kg) of aluminum and $2 to $5 per lb ($4.40 to $11/kg) for silicon carbide. However there will be some incremental cost of mixing fly ash in terms of equipment and consumables, pretreatments of the melt and the fly ash, and possibly higher machining costs. The manufacturing process to make aluminum-fly ash castings on industrial scale is still evolving and it is not possible to offer a quantitative cost figure, other than to state that Aluminum-fly ash castings are likely to be very attractive due to the lower cost of fly ash.
Environmental Benefits: The use of Ashalloys decreases aluminum requirements and hence can reduce emissions of greenhouse gases and criteria pollutants associated with aluminum production. Both forms of environmental degradation occur during the process of refining bauxite ore, reducing alumina to aluminum, and melting aluminum into ingot for casting at foundries. The emissions include CO2, perfluorocarbons, SO2, NOx, and particulates.
Economic Benefits: At less than half the cost of aluminum composites and 10 to 30% less than the cost of all-aluminum alloys, Ashalloy provides significant savings to foundries and U.S. parts makers relative to foreign producers. Further, savings can be passed on to consumers, thereby boosting the competitiveness of U.S. automakers and other industries that adopt Ashalloy parts. Utilities also benefit by avoiding ash disposal and monitoring costs. The savings from the use of fly ash in aluminum castings arise from several factors:
Reduced Energy Consumption for Aluminum Production: The annual displacement of 225,000 tons of aluminum with ash can reduce the energy purchased for primary aluminum production by about US$156 million annually (based on specified assumptions).
Lower Material and Energy Costs for Parts Manufacture: Savings in parts manufacturing costs will be roughly proportional to the ash content. ... Moreover, by requiring fewer aluminum ingots per casting, Ashalloy reduces the energy required to produce the raw material, and melt the aluminum.
Availability of Low-Cost, Lightweight Material: An overriding goal of the U.S. auto industry is vehicle weight reduction. Demonstration of net-shape components produced from magnesium and fly ash provides an engineering rationale for replacing iron ... with magnesium ... resulting in a ..weight savings of 74%.
Additionally, secondary weight savings are realized by the conversion of iron, aluminum, and magnesium structural and chassis components to fly ash-enhanced metal matrix composites.
The US Dept of Energy Lightweight Materials Program has projected that a 25% weight reduction of current vehicles would result in a gasoline savings of 750,000 barrels/day or a 13% reduction in U.S. gasoline consumption.
The CO2 emissions would also be reduced by 101 million tons per year.
Lower End-Use Energy Consumption through Improved Gas Mileage: The annual avoided purchase of 70.2 million gallons of gasoline saves $105.3 million (1996 dollars), assuming an average cost of US$1.50/gallon.
Avoided Ash Disposal Costs: Electric utilities generate about 60 million tons of coal fly ash per year, most of which is landfilled at a cost approaching $1 billion. These disposal costs are rising rapidly as landfill sites grow scarce. By selling ash as a metal matrix filler, utilities would not only avoid disposal costs, but bring in revenue. Utilities can collect and process ash within the anticipated market value of US$100/ton. The potential U.S. market for fly ash in Ashalloy (all industries) is estimated at more than 1 million tons of ash annually."
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We'll close there, although the full report is much more detailed, with some physical testing data and photos of various molded "Ashalloy"(TM) parts.
We wanted to point out that the projected market, "estimated at more than 1 million tons of ash annually", is relatively puny compared to the potential demand for Fly Ash in the making of cement and concrete, which applications could consume, at current rates of production, as we've elsewhere documented, virtually all of our annual Coal Ash output, and then some.
The plastic filler and, as herein, Ashalloy(TM)-type applications are, though, with an "anticipated market value of US$100/ton", perhaps a higher-value end use, with the potential for greater profit for Coal Country marketers of Coal Ash.
However, we do note that such a market value is likely far too optimistic.
The Cement and Concrete markets, which are by far the largest potential consumers of Coal Ash, wouldn't bear such a price; and, the real goal is likely the productive and profitable consumption of as much Ash as possible, relative to incurring costs for disposal. So, the basic price for Coal Ash would most probably be set by what price would be required to achieve maximum penetration into the Cement and Concrete markets, with a certain amount of that price discounted by accounting for otherwise mandatory costs of disposal.
Still, herein is explained another incremental, profitable market for Coal Ash, in an application where, like it's employment in plastic and concrete composites, the Ash, with all of it's potentially-objectionable components and compounds, would be "encapsulated", as the technical terminology has it, and safely locked up - - and securely shielded from the complaints of environmentalists - - virtually forever.
That, in addition to, as explained herein by the "United States Department of Energy; Wisconsin Electric Power Company"; and, the "Electric Power Research Institute", the potential for Coal Ash to contribute significantly, through it's use in "Aluminum - Fly Ash Metal Matrix Composites", to the overall goals of "gasoline savings of 750,000 barrels/day" and a potential, coincident reduction in "CO2 emissions" of "101 million tons per year".
