SEARCH RESULT

Aluminum is widely used as a matrix material in metal matrix composites, thanks to its lightweight and adequate mechanical properties. Utilization of aluminium is limited, due to its low hardness and low wear resistance. In order to improve these properties, reinforcements are introduced into aluminum generally in particulate form, forming metal matrix composites. Ceramic particles are mostly utilized as reinforcements, due to their high hardness [1,2]. In the present study, Al2O3 particles were used as reinforcement in aluminum matrix. As a result, aluminum matrix composites having 0-20 vol.% Al2O3 particles were obtained. Matrix alloy was aluminum having 4 wt.% Cu. This matrix was selected since it provides liquid phase sintering, in addition to precipitation hardening. Powder metallurgy was chosen for the preparation of Al2O3 reinforced aluminum matrix composites. Powder metallurgy has the advantage of obtaining a homogenous distribution of the reinforcement particles in the metal matrix. In addition, metal matrix composites with a high range of reinforcement particle amount can be obtained by this method. Also, near net shapes can be obtained by powder metallurgy. Liquid phase techniques such as stir casting were also employed in the literature for forming Al2O3 reinforced aluminum matrix composites. Casting techniques have the disadvantages of resulting in inhomogeneous structure of the formed composite and insufficient wetting of the reinforcement particles [3]. Preparation of the composites via powder metallurgical routes consisted of mixing, pressing and sintering. After mixing Al2O3, aluminum and copper in powder form, pressing was performed in steel die set with 600 MPa pressure. Sintering of the pressed samples was conducted at 600 oC for 30 min in flowing nitrogen. Heating and cooling rates were about 6 oC/min. Samples were cut, polished and were subjected to metallographic examinations with an optical microscope. Hardness tests were performed with a Brinell hardness tester. Three point bending tests were conducted with a universal mechanical tester having 50 kN capacity. It was found by optical microscopy examinations that the Al2O3 particles were homogenously distributed in the aluminum matrix (Figure 1). Prepared composites had almost full density. Al2O3 addition was seen to increase hardness of the obtained composites. Unreinforced Al4Cu alloy had a hardness of about 45 HB10 and the composite having 10 vol.% Al2O3 presented a hardness value of 51 HB10. Three point bending strength of the unreinforced alloy was about 390 MPa. Three point bending strength was 335 MPa in the composite containing 20 vol.% Al2O3. Therefore, obtained composites provided an increase in the hardness values, whereas there was a reduction in the three point bending strength of the composite structures.

International Symposium on Light Alloys and Composite Materials
UHAKS

H. Erdem Çamurlu Zeynep Tekyurt