The manufacture of aluminium matrix composites with B4C reinforcing element and addition of graphite and the analysis of mechanical features and their machinability on milling

In this study, metal matrix composite materials with B4C particle-reinforced and Gr addition were produced via powder metallurgy technique. In the production of composites, as a matrix material under 200 ?m-sized master alloy Alumix 123 powder and as a reinforcing member, 22~32 ?m B4C and average 150 ?m-sized nickel-covered graphite powders were used. Seven different samples (in weight, 5% B4C, 10% B4C and 15% B4C particle-reinforced, 1% Gr, 3% Gr, reinforced 5% Gr added 10% B4C and Alumix 123) were produced with hot pressing technique. By applying precipitation hardening to all composites, some of the mechanic features (hardness, density and cross-breaking strengths) and microstructures were analyzed. After microstructure analysis, homogeneous distribution was identified. Heat treatment has a great effect on the hardness of the composites and 15% B4C reached the highest hardness. The highest cross-breaking strength was measured on matrix alloy composites and the cross breaking strengths was measured on the 5% Gr added sample.The samples were tested for their machinability with milling technique by using coated and uncoated cementite carbide and cubic boron nitrides cutting tools. Machinability tests were carried out under dry cutting conditions. The tests were carried out with four different cutting speeds between 50-110 m/min, 0,5 cutting depth and 0,11 fixed feed rate. All the samples were analyzed for cutting force and surface roughness in the aspect of machinability. Tool wear tests were carried out in the samples reinforced with B4C+Gr. Depending on the ratio of B4C in the samples, increase in the cutting force was identified and the highest value was determined in the samples reinforced with 15% B4C. However, the cutting force for B4C+Gr added composites decreased. In the aspect of surface roughness, the lowest value was determined in 15% B4C. Active wear mechanism was identified to be the abrasive wear mechanism and depending on the increasing Gr rate, decrease in flank wear was identified. Under all conditions cubic boron nitrides had the highest performance among cutting tools.Key words : Metal matrix composite (MMC), composite, powder metallurgy, hot pressing, machinability, cutting forces, surface roughness