**1. Introduction**

384 Recent Trends in Processing and Degradation of Aluminium Alloys

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aluminium alloy based particulate reinforced metal matrix composites, Acta metal.

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> Metal matrix composite (MMC) is a material which consists of metal alloys reinforced with continuous, discontinuous fibers, whiskers or particulates, the end properties of which are intermediate between the alloy and reinforcement (Schwartz, 1997). These materials have remained the focus of attention of aerospace, automobile and mineral processing industry because of the several advantages they offer which include high strength to weight ratio, elevated temperature toughness, low density, high stiffness and high strength compared to its monolithic counterpart (the original alloy). The particle reinforced metal matrix composites (PRMMC) satisfy many requirements for performance driven applications in aerospace, automobile and electrical industry. The particle reinforced composites can be tailored and engineered with specific required properties for specific application. The commonly used reinforcing materials are silicon carbide, aluminium oxide and graphite in the form of particles and whiskers. Nominal compositions of some well known alloys which are reinforced with whiskers, fibers or particulate is shown table 1. Figure 1 shows that microhardness increases with an increase in filler content of the composites.


Table 1. Nominal composition of some well known alloys reinforced with whiskers and particles

MMC can be continuous or discontinuous. Discontinuous MMC can be isotropic and can be worked with standard metal working techniques such as extrusion, forging or rolling.

Corrosion Behavior of Aluminium Metal Matrix Composite 387

composites. Such dislocations have been observes by TEM. A high dislocation density was

In a TEM experiment, the generation of dislocations started only at 500 K (Vogelsang et al. 1986). It has also been suggested that dislocation were generated in Al – 6061/ 20 SiC MMC

0 1 2 3 4 5 6

ε v (%)

A9

Rule of mixtures Spherical Particles

0 10 20 30 40 50

Si C Si C w p

Volume Percent SiC

Fig. 3. Young's modulus vs volume percent of SiCw, SiCp and reinforcement (Zaki, 2001)

The elongation (%) of the MMC decreased with increased particulate contents as shown by Al 6061 / 20 SiC (p) – The mechanism of fracture toughness is not fully understood. The presences of large clusters of particles promote crack propagation whereas their uniform distribution retards crack propagation. The fracture toughness values of selected alloys are

A9/20% T1 platelets A9/17% T1 platelets

200

v (MPa)

σ

150

100

50

0

Fig. 2. Effect of the size of the platelets (Massardier et al., 1993)

200

180

160

140

Young's Modulus (GPa)

given in Table 3.

120

100

80

observed on Al 6013/SiC (p) interface.

below 573 K.

Continuous reinforcement uses monofilament fibers, wires or fibers such can carbon fibers. The reinforcement materials commonly used are graphite SiO2, SiC, TiC, Al2O3 and glasses.

Fig. 1. Microhardness of Al6061-SiC and Al7075-Al2O3 composites (Vaeeresh et al., 2010)
