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to deliver an encore is to add to the cast.


of elasticity (Young’s modulus). Using the universally accepted linear and inverse rule of mixtures, this poten- tial increase can be estimated whereby the well-known border cases apply only to certain geometric alignments of the components in the composite materials. As the percentage of SiCp increases, the modulus moves linearly in the direction of the SiCp modulus and away from the aluminum alloy. This reaction is similar in other proper- ties such as thermal conductivity and expansion. Aluminum alloy/silicon carbide MMC castings can be


produced in 20%, 30% and 40% concentrations of silicon carbide by volume and heat treatable, commonly being furnished to a T77P heat treatment. This enables engineers to design components to their


Aluminum joins copper for WAI’s second Global Continuous Casting Forum


Join a renowned ensemble of continuous casting practitioners, raw material suppliers, and equipment manufacturers on an edu- cational journey from ore to more at WAI’s second Global Continuous Casting Forum.


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desired operating environment. For instance, the property of wear resistance can be understood easily because the aluminum alloys are relatively soft compared to the hard carbide particles, enhancing the wear properties with increased silicon carbide particulate (SiCp). Bonding between the SiCp particles and the aluminum matrix is an important consideration. Purchasing pre-alloyed ingot stock with the percent reinforcement desired and metal- lurgical bond between the parent metal and particles is recommended. The base alloy of currently produced MMC is Aluminum 359, which can be heat treated for specific applications. In addition, the particle size of the SiCp can be varied for more design freedom (Figs. 1-7). Although elongation and fracture toughness decrease with the SiCp in the MMC, the values often are better than other alternative methods to achieve stiffness and thermal properties. This is because as the higher particle contents are cast, the material takes on more of a ceramic character with lower fatigue life and brittle failure with- out plastic deformation. The fluidity of aluminum MMC alloys decreases as


the concentration of SiCp increases; the difficulty of successfully casting higher SiCp concentrations increases. The tendency of aluminum alloy MMC to form shrink- age and gas porosity also becomes a greater concern with higher densities of SiCp. It is essential to minimize turbulence within the melt and during mold filling. Hot isostatic pressing higher percent SiCp MMCs sometimes is necessary to eliminate subsurface gas voids. The reinforcement of metals can have many different


April 27 - 30, 2015 | Atlanta, Georgia, USA With Interwire 2015


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objectives and opens up the possibility for application of these materials in areas where weight reduction is the top priority. The precondition here is the improvement of the component properties. The objectives for light metal composite materials are: • Increase in yield strength and tensile strength at room temperature and above while maintaining the mini- mum ductility or component toughness.


The Wire Association International, Inc. Telephone: (001) 203-453-2777 | www.wirenet.org


• Increase in creep resistance at higher temperatures compared to that of conventional alloys.


• Increase in fatigue strength, especially at higher tem- peratures.


• Improvement of thermal shock resistance. 32 | MODERN CASTING January 2015


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