Types and Properties of Aluminium Alloys and Composites

**3**

**Chapter 1**

*Kavian Omar Cooke*

**1. General background**

to those of the unreinforced alloys [4, 5].

ties, ease of processing, and part fabrication.

the reinforcement and the matrix.

large tensile hydrostatic stresses.

Introductory Chapter: Structural

Aluminum Alloys and Composites

Aluminum is a metal of great importance because of its excellent corrosion resistance, high electrical and thermal conductivity, good reflectivity and very good recycling characteristics. Aluminum atoms are arranged in a face-centered cubic (FCC) structure with a melting point of 660°C. There are nine different series of aluminum, which will be discussed later in this section, four of which are referred to as heat-treatable aluminum alloys, and these alloys are so-called because of the potential to increase the mechanical properties by precipitation strengthening [1, 2]. The properties of heat treatable Al-alloys can be further enhanced by the inclusion of a reinforcing phase that increases the mechanical properties of the overall composite. Metal matrix composites (MMC) are usually manmade materials that consist of two or more distinct phases; a continuous metallic phase (the matrix) and a secondary reinforcing phase. The secondary phase may take the form of continuous or discontinuous reinforcement as particles or fibers. When this phase is introduced into the matrix the overall impact is an improvement of the mechanical properties of the material [3]. The properties of MMCs are comparatively superior

The properties of discontinuously reinforced aluminum MMCs containing particles or short fibers are modest compared to the continuous fiber reinforced MMCs, however, these materials are less expensive to fabricate and have more flexibility in production making them more cost-effective [6–8]. The reinforcements used in fabricating the composites are dependent on the desired material proper-

The stability of the reinforcement/metal matrix interface and the differences in properties such as the coefficient of thermal expansion and thermal conductivity are limiting factors that affect the compatibility of the materials used to make the composite. The quality of the bond is dependent on adequate interaction between

Over the last two decade, the application of nano and micro-sized ceramics such as alumina (Al2O3), MgO nanoparticle [9], boron carbide [10] and silicon carbide (SiC) [11] to aluminum metal matrix composites have become popular reinforcing phases, since these hard phases can lead to an increase in flow stress from the matrix by load transfer across a strong interface from the matrix to the reinforcement [12]. An example of the typical microstructure of a particle reinforced aluminum metal matrix composite is presented in **Figure 1** and shows an Al2O3 particulate reinforced Al-6061 MMC. The properties of these reinforcements include high strength, high modulus of elasticity and high thermal and electrical resistance. The constraint imposed by the ceramic reinforcements on the plastic deformation of the matrix is

## **Chapter 1**
