SYNTHESIS AND FABRICATION OF Al-Zn-TiC in-situ METAL MATRIX COMPOSITES

Abstract

The present study was attempted to highlight a novel direct reaction synthesis in which traditional casting plus rapid solidification techniques were implemented to produce Al7079-TiC in situ composites with homogenous microstructure and improved dispersion strengthening by the reinforcing phases. Casted samples were effectively characterized by scanning electron microscopy followed by energy dispersive spectroscopy and X-ray diffraction. Ingot metallurgy showed a homogenous distribution of TiC particles inside the grain. This particle behavior acted as an excellent nucleation sites for the Al dendrites to grow unvaryingly. TiC reinforcements have semi coherent relationship with α-Al matrix. It was observed that eutectic boundary includes the second phases based on η (MgZn2) and Mg (Zn, Cu, Al)2. Almost 90% of the in situ reinforced TiC were homogenously distributed along the center of the grain. Thermal history conditions have shown an exothermic behavior during casting. Experimental results revealed the evolution of TiC particles in super-heated melt region i.e., dissolution of titanium continued by reaction of titanium with diffused carbon in the Al matrix to form TiC particles. Further they acted as nucleation sites for the α-Al dendrites to grow homogenously. This study presents optimum process temperature for the Al-TiC in situ synthesis. Experimental study has been performed on the abrasive wear analysis of Al-7079/TiC MMCs. The parameters like applied load (9.8N-29.4N), sliding distance (1000m-2000m), sliding velocity (1.5m/s) and SiC-P-600 grit paper (25μm) were used in this study. The influence of sliding distance, applied load and wt.% of (TiC) reinforcement on in-situ Al-7079 under two body abrasion was investigated. Further, the obtained results were compared with the base Al-7079 alloy. It was examined that, the in-situ reinforced composites exhibited significantly greater wear resistance of 20%-60% compared to conventional as cast Al-7079 base matrix. Experimental results confirmed that the wt.% of TiC and sliding distance had higher influence on coefficient of friction and the weight loss was highly affected by the applied load. Further the wear mechanisms involved in the worn surfaces were demonstrated through atomic force microscopy and SEM analysis throughout the surfaces. In the next study, Friction stir welding (FSW) of 6.5 mm thick cast Al-7079-TiC in-situ composite was obtained at 708, 931, 1216 rpm and 40mm/min respectively. Microstructural characterization of FSWed joints revealed a homogeneous distribution of TiC reinforcements iii inside the dynamically recrystallized (DRZ) zone. Heat input required for different rotations were analyzed through a coupled study of thermo-mechanical analysis. Heat input was calculated by considering partial sticking and sliding conditions induced between tool and work piece. Transverse and longitudinal tensile test of the weld sections has been conducted. Grain morphology, heat input and TiC particle reinforcement distribution under different tool rotation has been analyzed and has been further correlated with micromechanics approach to validate the mechanical properties of the FSWed specimen. The predicted results have shown a good agreement with the experimental values. Hardness profile has shown a minimum of HAZ among all weld and an average maximum in the DRZ. The weld joint at 931rpm has exhibited superior mechanical properties as compared to the joints welded at 708 and 1216 rpm respectively. Finally, the thermophysical property analysis pure coconut oil (PC) Al2O3 nano fluids has been analyzed. Further the effectiveness of pure coconut oil- Al2O3 nano MQL lubrication in oblique turning of Al-7079/TiC in-situ metal matrix composites were examined. The experimental evaluation of the thermo physical properties of pure coconut oil/Al2O3 nano fluids with different solid volume fraction of 0.2% to 1.2% at temperature ranging from 303 K to 413 K. The nano particle morphology and composition were analyzed were analyzed using transmission electron microscopy and x-ray diffraction technique. It was observed that the morphology of nano particles were spherical and the average size of particles were 47.5 ± 2 nm. The various thermo physical properties involved for the enhancement in heat transfer of Al2O3/pure coconut oil based nano fluids such as thermal conductivity, specific heat, thermal diffusivity and density were obtained experimentally. The effect of solid volume fraction and temperature on thermo physical properties of nano fluids were examined. Further new correlation was developed for predicting the thermal conductivity of pure coconut oil/Al2O3 nano fluids. Moreover the efficiency of nano fluids for the heat transfer application has been evaluated based on different figure of merit. Finally this environmental friendly nano fluids have been used as a metal cutting fluid under MQL turning of previously procured Al-7079-7wt.%TiC in-situ metal matrix composites. The results obtained were compared with pure coconut oil and dry machining. It has been observed that, the thermal conductivity enhancement of nano fluids provided reduced cutting forces, temperature and surface roughness during machining.