**3. Scenario of composite materials and magnesium alloys**

Light weight material still plays a significant role in structural application in the field of automotive and aerospace sectors. Demand for newer materials increases every year which is evident in various scientific researches carried all over world by researchers. It has been possible because of growing technologies, processing techniques, advent of newer phase in materials and its applications in this customer's demand driven world. Composite materials have brought a revolution in the world of material. These materials are unique and different from the monolithic or heterogeneous materials. Composite materials constitute two or more distinct type of material which is not the by-product of chemical reaction between the constituents. It has two phases (constituent material), one of the constituent is reinforcing phase which are discontinuous and are embedded in continuous phase called matrix.

*Experimental Investigation of Mechanical and Wear Behaviour of AZ91 Magnesium Hybrid… DOI: http://dx.doi.org/10.5772/intechopen.104703*

Matrix is continuous phase whose work is to retain the shape of the composite, share the stress to other phase. They provide better finish to the product.

Reinforcement phase is strong and may not be less dense. Reinforcing phase may be in the form of fibres, particles or flakes. They contribute the desired properties and also transfer the strength to the matrix.

## **3.1 Types of composites**

The composites materials are classified into three major types. Polymer matrix composites. Ceramic matrix composites. Metal matrix composites.

## **3.2 Polymer matrix composites**

Polymer Matrix Composites (PMCs) has organic polymer as matrix and reinforcing phase are a variety of short or continuous fibres. Organic polymers are long chain of carbon. Fibres are used to enhance the mechanical properties and to carry loads. Matrix's purpose is to bond the fibres and protect reinforcing phase. Polymer matrix composites are categorised into two types based on mechanical properties (strength and stiffness): reinforced plastics and advanced composites. Reinforced plastics are polymer matrix composites that impart additional strength by adding embedded fibrous material into plastics. These type of composites are usually cheap and consist of polyester resins reinforced with glass fibres (low stiffness). Advanced composites consist of matrix and fibres which facilitates superior stiffness and strength. Fibres in advanced composite type are mostly high performance like graphite, aramid. Advanced composites are relatively expensive but possesses high strength and superior stiffness.

## **3.3 Ceramic matrix composites**

Ceramics are solid materials which exhibit very strong ionic bonding and in few cases covalent bonding. Ceramic matrices such as silicon nitride, silicon carbide surround the fibres. They are the good choice for high temperature applications. Ceramic matrix composites possess principal characteristics like resilience to oxidation and high compressive strength. Production errors or scratches may lead to cracks in conventional ceramics. However in ceramic matrix composite, by embedding the fibres, fracture toughness values is enhanced. Even crack propagation was hindered by the presence of fibres (reinforcement) in matrix of ceramic composites.
