Investıgatıon Of The Mechanıcal And Machınabılıty Propertıes Reınforced Wıth B4c And Sic Partıcıpate Of Aa6061 Matrıx Composıte Materıals


Thesis Type: Postgraduate

Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2019

Thesis Language: Turkish

Student: Sibel TİNGA

Supervisor: RAMAZAN ÇITAK

Abstract:

This study investigates the production of various reinforced and non-reinforced composite materials (AA6061), (3 % B4C + 9 % SiC), (6 % B4C + 6 % SiC), (9 % B4C + 3 % SiC), (12 % B4C), (12 % SiC), (3 % B4C), (6 % B4C) and (9 % B4C) using powder metallurgy (PM). AA6061 powders with grain sizes below 100 μm are used as the matrix material and B4C powders with sizes below 10 μm and SiC powders with sizes below 8 μm are used as the reinforcement material. The powders are weighed on a micro-balance and their mixture proportions in terms of weight are determined. Next, they are mixed for 30 min in a three-dimensional mixer. The mixtures are then subjected to cold pressing under a pressure of 200 MPa to form metal block samples. These are subjected to hot extrusion in an extrusion mold heated at 500 °C after being subjected to a sintering process for 60 min at 550 °C. This produces samples with a cross-sectional area of 25×30 mm and Ø30 mm. These age-hardened are next subjected to a dissolution process for 1 h, immediately followed by a rapid cooling process with water in a furnace heated at 530 °C with a heating speed of 10 °C/min. The cooled samples are then artificially aged for 8 h by heating them at 175 °C with a heating speed of 10 °C/min. The composite materials produced are examined in terms of density changes, hardness, tensile strength, and machinability. Furthermore, optical microscopy and scanning electron microscopy are performed to examine the microstructure and surface fractures. Average density of composite materials are 99 % and above. The best hardness and tensile strength were measured 12 % SiC reinforced composite materials. Machining tests have been applied using four different cutting speeds (200, 224, 230 and 250 m/min) and three different feeding rate (0,15, 0,1875 and 0,27). Cutting forces were decreased with increasing cutting speeds of materials. Cutting speeds was decreased caused by time to time fluctuations of cutting forces. Average surface roughness was decreased with increasing cutting speeds and surface roughness was increased with increasing feed rates. Increasing reinforced ratio was effected as positive on surface quality