Research Background CONCLUSION AND FUTURE WORKS 67

CHAPTER 1 INTRODUCTION

1.1 Research Background

The composite can be defined as a mixture of two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure. This composite is fabricated to improve the properties of conventional or pure material. Composite has been used in almost all areas of industries due to its advantages over the conventional material. Since the development of metal matrix composite MMC for the past three decades, this material has been used in a wide range of application especially in aerospace and automotive application. MMC has advantage of high strength material and can be used in high temperature application. MMC usually been reinforced with ceramic reinforcement such as silicon carbide SiC and Alumina Al 2 O 3 . For light weight application, a light metal group such as aluminium, magnesium and titanium are most considered. Mostly used light metal is aluminium and titanium. But due to increasing fuel price nowadays, magnesium has been considered to replace other light metal due to its light weight which is about 25 and 35 as much as similar volumes of zinc base and aluminium base alloys Khanna O. P., 2004. 1 Besides lightweight, advantages of magnesium are good mechanical damping properties, good castability especially in die casting process and also plentiful of global supply. Despite of its advantages, magnesium when compared with aluminium, it has low strength and ductility, poor wear, creep and corrosion resistance Tjong S. C., 2009. Thus to overcome this problem, magnesium reinforces with ceramic micro and nano particle. In general, MMC been reinforce with micro size reinforcement. Lately, there is extensive interest in the production of metal matrix nanocomposite in which nano particulates are incorporated in base matrix. When compared to composites with micron-sized reinforcements, nanocomposites exhibit comparable or better mechanical properties with the use of lesser amount of nanoparticulate reinforcements. Some nano reinforcement thats been used is nano size alumina particle and carbon nanotube CNT. Alam M. E. et al, 2011 has found that the nanoparticulate alumina has increased the mechanical properties of magnesium alloy AZ31such as hardness, yield strength and ultimate tensile strength. A key challenge in the processing of composites is to evenly distribute the reinforcement phases to attain a defect-free microstructure. Based on the shape, the reinforcing phases in the composite can be either particles or fibers. The reasonably low material cost and suitability for automatic processing has made the particulate- reinforced composite preferable to the fiber-reinforced composite for automotive applications YE H. Z. et al, 2004. One of the main processing of MMC is powder metallurgy. Powder metallurgy is a net shape forming process consisting of producing metal powder, blending them, compacting them indies, and sintering them to impart strength, hardness and toughness. Although the size and the weight of its products are limited, the PM process is capable of producing relatively complex parts economically, in the net shape form and a wide variety of metal and alloy powders. Basically, in the conventional PM production, after the metallic powders have been produced, the sequence consists of three steps. Firstly, blending and mixing the powder, and then compaction, in which the powders are pressed into the desired part shape. The last step of PM method is sintering, which involves heating to a temperature below the melting point to cause solid state bonding of the particles and strengthening the part. 2 Due to the magnesium alloy application are in moving parts or engine parts, wear is a serious problem happened to this material. Although wear only happens at the surface, it can undermine the mechanical function of the parts. It can cause structural failure on the part and make early replacement of the part or component. There were several wear mechanisms such as abrasion, adhesion, delamination, thermal softening and melt. Magnesium and aluminium based metal matrix composites MMCs are prone to suffer wear by delamination, since the discontinuity at the interface between reinforcement and matrix promote crack nucleation and propagation, which are central to the mechanics of delamination. Lim C. Y. H et al, 2005

1.2 Problem Statement