**5. Materials**

The AZ91 magnesium alloy is the base material. AZ91 magnesium alloy used in the present work was fabricated by stir casting process. This alloy was prepared by commercial magnesium ingots, aluminium ingot and zinc ingot. AZ91 magnesium alloy has main composition of 9% Aluminium, 1% Zinc and 0.3% Manganese. Aluminium of 9% by weight is added to enhance the castability, hardness and as well the freezing range. Zinc is added upto 1% by weight to magnesium as alloy to increase harmful corrosive effects. Zinc when exceed more than 1% will cause hot shots. Manganese (0.3% by weight) was added to increases the resistance against corrosion.

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


### **Table 1.**

*Nominal composition of AZ91 magnesium alloy.*

The remaining was pure magnesium. Chemical composition of AZ91 magnesium alloy is listed in **Table 1**. Titanium, titanium dioxide and graphene were the reinforcements used for the preparation of hybrid composite materials. Titanium (99.9% supplied by Nextgen steel and suppliers, Mumbai) graphene nanoparticles of 99% purity (supplied by AdNano Technologies, Karnataka) and titanium dioxide of 250 nm (99.97% purity supplied by Sisco Research laboratory (SRL) Maharashtra). The AZ91 magnesium alloy and hybrid composites are manufactured by stir casting technique.

## **5.1 Fabrication of base material AZ91 magnesium alloy (matrix)**

Initially the ingots are cut and weighed for right proportion. The proportions are illustrated in **Table 2**.


### **Table 2.**

*Proportion of base material (matrix) AZ91.*

## **5.2 Hybrid composites by stir casting process**

A recent development in stir casting is a two-step process. The effectiveness of the two-step method of processing is mainly attributed to its ability to break the gas layer around the particle surface. Particles have a thin layer of gas being absorbed on their surface, which hinders wetting between the particles and molten metals.

Magnesium alloys has unique feature in solidification. In this process, the metal is heated to above its liquids temperature with inert argon gas atmosphere, because Magnesium is flammable in molten state. Then the metal is fully melted. The melt is then cooled to a temperature between the liquids and solidus points. It is now in a semi-solid state. At this stage, the preheated particles are added and stirred well by mechanical stirrer for certain period of time to ensure proper mixing. The slurry is again heated and mixed thoroughly. This technology is relatively simple, easy adaptable and cost effective.

The test samples were cut into desired size (10 x10x 5) mm and polished with silicon carbide paper up to 1200 grit. Alumina powder polishing was done to ensure mirror image on the specimens. The prepared specimens are washed with acetone and dried. The specimens are then etched with acetic picral (5 mL acetic acid, 6 g picric acid, 10 mL water, 100 mL ethanol (95%) a universal etchant). The test sample was immersed gently until the face turns brown. It was then washed with ethanol and air dried at room temperature.
