Multi Directional Forging Of Zinc Aluminium (Za27) Based Composites Reinforced With Sic and Al2O3 Particles

Abstract

Selection of materials with the expected characteristics is a very important for any industrial application. In the engineering and automotive industries, the current tendency is to use metal matrix composite for production of various components for high performance application. The aim of this study was to investigate the effect of SiC and Al2O3 (5 and 10 wt %) reinforcement in ZA27 matrix alloy. Further to investigate and develop the application of the MDF techniques, which may lead to an improvement in mechanical and tribological properties of these composite for industrial application. To analyse the influence of parameters such as applied load, sliding distance and sliding speed on dry sliding wear behavior of solutionized and MDF processed material using pin on disc test rig was conducted. In this study, the composite were prepared by stir casting technique followed by squeezing process. Multi directional forging (MDF) is one of the severe plastic deformation (SPD) techniques used to develop ultrafine-grained (UFG) materials. Multi directional forging technique was used to process the ZA27/SiC/Al2O3 /SiC + Al2O3 composites to produce refined microstructure in order to study the relationship between the microstructure and mechanical properties. The effects of the MDF processes have been studied on ZA27 based composite at 100 °C and 200 °C of processing temperature with a total equivalent strain of 0.54 and 1.08 respectively. Before MDF process, base alloy and prepared composites were homogenized at 365°C for 5 hours by using muffle furnace and quenched in water to room temperature. The standard metallographic technique was used to analyse the microstructural features of the ZA27 based composite. MDF processed composite were characterized by analyzing the X-Ray diffraction (XRD) profiles and studying microstructures using optical microscopy, scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Density was measured using standard density measurement kit and both theoretical and experimental densities were compared. Mechanical properties such as hardness, tensile strength and ductility from tensile test and fracture surface morphologies of the tensile test samples of both MDF processed and unprocessed composites were studied. Wear behavior of composites before and after MDF process were studied with their wear mechanisms. iv Results revealed that, density of ZA27 alloy decreased by incorporation of SiC and Al2O3 particles. Some Clusters and fair dispersion of SiC and Al2O3 particles in ZA27 matrix were observed in microstructure and confirmed by EDX. SiC reinforced composites performs better when compared with Al2O3 reinforced, mixture of SiC+Al2O3 particles reinforced and ZA27 base matrix material. As the percentage of reinforcement increased from 5 wt% to 10 wt% the properties of the material also increased. Porosity level decreased with an increase in the number of MDF passes when compared with unreinforced materials. Composites reinforced with SiC particles in 5 and 10 wt % were MDF processed at different temperature. The average grain size was reduced from 25-30 µm to 0.2-0.35 µm, 0.45-0.5 µm respectively in the case of samples MDF processed at 100 °C up to three passes and for 200 °C up to six passes it shows 0.8-1.0 µm, 0.9-1.2 µm respectively. The initial lamellar Al-rich and Zn-rich phase was gradually refined to a spherical shape and distributed more uniformly with an increasing number of passes. Ultimate tensile strength of the composite material was increased with that addition of SiC particles and also by MDF process. The highest ductility was obtained when the sample forged at 100 °C 3 passes. Initial ascast condition showed a brittle type of fracture. Brittle mode of fracture was transformed into ductility mode by MDF processing. Wear results showed that samples tested with lower load and sliding distance were showing abrasive type of wear mechanism but as the applied load and sliding distance increased, mechanism changed to adhesion type. This is due to the rise in temperature between the interface of pin and disc, material detached from the pin as debris gets adhered to the surface of pin which influences the mode of mechanism to switch from abrasion to adhesion. MDF processed ZA27/SiCp for 3 passes at 100 °C showed better wear resistance with ultra-fine grains and higher hardness. Composites reinforced with Al2O3 particles in 5 and 10 wt % were MDF processed at 100 °C up to three passes reduced the grain size from 20-30 µm to 0.4-0.45 µm, 0.5- 0.6 µm respectively with the dual type of microstructure having both lamellar to the cellular structure. On further MDF processing at 200 °C upto 6 passes showed the grain size of 1.2-1.4, 1.5 µm with equiaxed grain structure. Small cracks were seen at the edges of the Al2O3 particle because of load applied during MDF process upto 3 v passes at 100 °C and with a higher number of passes the Al2O3 particle broken into several pieces and forms a cluster of Al2O3 particle. Addition of Al2O3 particle increased the UTS and hardness values in both 5 and 10 wt % reinforced composites and further improvement in UTS and hardness value is due to MDF process upto three passes at 100 °C and upto six passes at 200 °C. The ductility of Al2O3 particle reinforced composites was low when compared with other composites. Wear rate of Al2O3 reinforced composite was more when compared with SiC reinforced ones. Results of wear test showed that Al2O3 reinforced composites MDF processed for 3 passes at 100 °C gives higher wear resistance, with abrasion type of wear mechanism. For ZA27/SiC +Al2O3 composites with the average grain size reduced from 15-20 µm to 0.2-0.25 µm, 0.3-0.4 µm when processed at 100 °C upto three passes and 0.8-0.9 µm, 0.9-1.1 µm when processed at 200 °C upto Six passes. Hardness, ultimate tensile strength and ductility of the composites were improved by MDF processing. Substantial improvement in ductility of the present composites after several MDF passes can be attributed to the elimination of as-cast morphology as well as grain refinement, reduction in micro porosity (or micro-voids), redistribution of reinforcing particles, and also the change in the composition of the phases. In an overall, the results of wear test shows, SiC reinforced composite performed better as compared with Al2O3 reinforced and Mixture of SiC+Al2O3 reinforced material. Wear study of composites indicated that the specific wear rate was highly influenced by applied load and sliding distance. As an application, a Cylinder Roller Bearing is fabricated by best performing ZA27/SiC/ Al2O3/SiC+Al2O3 composite material.