Effect of Nose Radius and Graphite Addition on Turning of AA 7075-ZrB2 in-situ Composites

This paper involves the study of nose radius effect and graphite addition during turning of AA 7075-ZrB2 in-situ metal matrix composite. This in-situ method involves formation of reinforcements within the matrix by the chemical reaction of two or more chemical compounds that produces some changes in the matrix material within the vicinity. To form Zirconium Boride (ZrB2) reinforcement in the matrix, two chemical salts of Potassium Tetrafluoroborate (KBF4) and Potassium Hexafluorozirconate (K2ZrF6) were added. After the fabrication of the test specimen, the specimen is subjected to turning in CNC high speed turning center. Four important parameters of tool nose radius, cutting speed, feed rate and depth of cut were taken for the present investigation. The in-situ composites were fabricated via-stir casting method followed by manually forge it. The fabricated specimen was turned using a 0.4 mm nose radius and 0.8 mm nose radius of PCD CNC inserts. After turning, the metal removal rate and surface roughness were measured and investigated. Based on the results obtained, it was observed that 0.8 mm nose radius inserted tool produced excellent machinability when compared to 0.4 mm nose radius. It was noted here that the higher rate of cutting speed, lower rate of feed rate and lower depth of cut combination process parameter produced excellent machinability. Further, the graphite reinforced in-situ AA 7075-3% ZrB2-1% Gr hybrid composite exhibited improved machinability than others samples of AA 7075 alloy, AA 7075-3%ZrB2 in-situ composite. This was due to self-lubricant property of graphite particles.