Magnesium matrix composites

Effect of size and surface treatment of carbon fibers on mechanical properties of magnesium matrix composites ... 

D.J. Lloyd Particle reinforced aluminium and magnesium matrix composites. Int. Mater. Rev. 39, 1-23 (1994)... 

Key words magnesium matrix composites, magnesium alloys, creep, short-fibre reinforcement, particle reinforcement... 

Thus, the aim of the present paper is not to review the bulk of the results published to date relating to the creep response of various magnesium-based composites. Instead of such an approach this paper provides a comprehensive report on the extensive experimental results obtained by authors in an investigation of the high temperature creep behavior of the two magnesium alloys, AZ 91 and QE 22, and their discontinuous composites. The objective of the present research is a further attempt to clarify the direct and indirect strengthening effects of short-fiber and particulate reinforcements in creep of magnesium-matrix composites. 

Chen Y, Zhang GD, Wu F, Zhu J, Study of the C/Mg interface in magnesium matrix composites reinforced by carbon (graphite) fiber, Rare Metal Mater Eng, 26(3), 20-25, 1997. 

Divecha AP, Karmarkar SD, Foltz JV, Process for producing graphite fiber j aluminium-magnesium matrix composites, U.S. Pat., 4578287, Mar 1986. 

Hong, Y., Xiaowu, H., Qiao, N., Lei, C., 2011. Aging behaviour of nano-SiC particle reinforced AZ61 magnesium matrix composites. China Foundry 8 (3). 

Zhao-hui, W., Xu-dong, W., Zhaou-xin, W., Wen-bo, D., 2010. SiC nanoparticles reinforced magnesium matrix composites fabricated by ultrasonic method. Transactions of Nonferrous Metals Society of China 20, 1029—1032. 

Reinforcement for metal-matrix composites with such metals as titanium, titanium aluminide, aluminum, magnesium, and copper. Applications are found mostly in advanced aerospace programs and include fan blades, drive shafts, and other components. 

Ceramic matrix composites are produced by one of several methods. Short fibers and whiskers can be mixed with a ceramic powder before the body is sintered. Long fibers and yams can be impregiated with a slurry of ceramic particles and, after drying, be sintered. Metals (e.g., aluminum, magnesium, and titanium) are frequently used as matrixes for ceramic composites as well. Ceramic metal-matrix composites are fabricated by infiltrating arrays of fibers with molten metal so that a chemical reaction between the fiber and the metal can take place in a thin layer surrounding the fiber. 

Often there is a borrowing of terms between metal-intense materials science and polymer-intense materials science where there is actually little relationship between the two. This is not the case with metal-matrix composites (MMCs). Although the materials are often different, there are a number of similarities. For polymer-intense composites, the matrix materials are organic polymers. For MMCs, the matrix materials are typically a metal or less likely an alloy. Popular metals include aluminum, copper, copper-alloys, magnesium, titanium, and superalloys. ... 

At very low surface areas (about 5 m /g) and constant conversion (70%), the contaminant selectivities are dominated by the matrix composition (Table I). Rare earth and magnesium-containing microspheres were prepared to examine the effects of these metal oxides on catalyst selectivities in the presence of nickel and vanadium. These oxides were chosen because the literature (3,5,10-15) has shown them to be effective at reducing the deleterious effects of vanadium in cracking catalysts. 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

N. Wang, Z. Wang, and G. C. Weatherly, Formation of Magnesium Aluminate (Spinel) in Cast SiC Particulate-Reinforced A1 (A356) Metal Matrix Composites, Metall. Trans., 23A[5], 1423-1430 (1992). 

These concepts can be applied to many metallic materials and metal-matrix composites, but they have maximum impact on aluminum and magnesium alloys and components. 

Closer in concept to the DMO process is the infiltration of aluminum alloys in nitrogen to yield Al-AIN composites. Low temperatures (<1000°C) and high magnesium or strontium eontent promote the spontaneous infiltration of liquid metal with a small concurrent nitridation to yield dispersions of AIN [34]. Similar alloys may be infiltrated at higher temperatures, resulting in nitride contents that increase with temperature to yield AlN-matrix composites [35-38]. This process can result in particulate loadings of up to 75%. The mechanical properties of these aluminum nitride composites have been extensively characterized [39]. 

I. P. Tuersley, A. P. Hoult and I. R. Pashby, The Processing of a Magnesium Alumino-Silicate Matrix, SiC Fibre Glass-Ceramic Matrix Composite Using a Pulsed Nd-YAG Laser, J. Mat. Sci. 31, 4111-4119 (1996). 

FIGURE 10. Hybrid barium magnesium aluminosilicate glass-ceramic matrix composite with Nicalon fibre and SiC-whisker reinforcement. The white dots are SiC whiskers distributed in the glass-ceramic matrix. (Micrograph courtesy of Prof. K. Chawla, University of Alabama at Birmingham, USA). 

Magnesium has a density lower than Al, but is more susceptible to corrosion and like Al, requires a protective treatment. Katzman [59] examined suitable treatments for the fabrication of graphite reinforced Mg composites. The tensile properties of coated carbon fiber reinforced Mg composites have been determined by Zhang and co-workers [90]. A study of the compatibility between PAN based carbon fibers and MggLi alloy during the pressure infiltration process was undertaken [91] and Chen and co-workers [92] examined the interface in Mg matrix composites reinforced with carbon fiber. A Ni coated carbon fiber in a Mg matrix will form Mg-Ni compounds and a low melting point eutectic (508°C) [93]. 

The modulus and strength of PNCs reinforced with whiskers compares favorably with composites reinforced with glass and aramid fibers, aluminum, and magnesium aUoy [32, 42]. At a cellulose whisker concentration of 6wl%, high increases in modulus and elongation at break have been obtained for polystyrene-butylacrylate copolymer matrix composites [5j. 

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