18.3 Results and Discussion General Microstructure of the composite was given in the Fig. 18.1a only as an example to see well homogeneous distribution of the particle reinforcement in the matrix and also the final arrangement of interface at the matrix/ reinforcements. Figure 18.1b indicates EDS analyses taken from overview microstructure to check the elements participated in the microstructure. Again, general microstructures of the first series of the composites were presented in the Fig. 18.2. As an example, only the first composition of this series (A356-1) was given in this Fig. 18.2a. The distribution of particle reinforcements and the position of the scrap A356 in the matrix were perfectly arranged thanks to the combined method of sintered forging. In the Fig. 18.2b–d, detail information was given about the globular structure and perfect interface at the matrix/ reinforcement. The same evolution was observed on these pictures; eutectic structure is formed always around the globular grains and many others are observed inside of the grains. As for the big size particulate reinforcements, they are at the border of interface and/or to be pushed in the aluminium particles (small size chips). All of these evaluations of the microstructure give a clear idea about the combined process (sintered forging). This process applied for these composites is caused by bonding diffusion at the interface between matrix and reinforcement and some of the particles were forced into the grains during the forging (second) stage of this process. For this reason, very tough, solid and homogeneous structure could be obtained. Porosity and other structural defects were quasi eliminated. The same microstructure was given in the Fig. 18.3 for the second composition (for the sample A356-2). The same microstructural evolution was also observed in this composition with perfect interface and homogenous distribution of the reinforcements. In fact this idea can be applied very well on the industrial parts in an economic way. Even if scrap aluminium particles are used as matrix, the microstructure can be improved by this process very well. Actually, sintered forging process is a novel process mainly called as near-net shape process for the manufacturing of the pieces in the automotive industry [13]. Mainly, this process is used for bulk materials in industrial applications. In fact, low-cost sinter-forging approach to processing of particle-reinforced metal matrix composites gives always high performance (fatigue-creep, etc.) applications of the industrial pieces. In the frame of this present work, only an application was given in the laboratory scales for creating novel composites from scrap aluminium reinforced with particulate reinforcements. This idea should be developed very well on the many other composites. It means that very tough and strong pieces can be obtained with a microstructure similar to the thixoforming but cheaper than the other manufacturing processes. Evolution of the density and micro hardness (HV0.25) evolution of these composites are presented in the Figs. 18.4 and 18.5 for two groups of the compositions. For density values, there are not so much differences between two groups Firstly, the percentage of Mo added in the matrix is not so high (Mo: 2, 3, 4 wt%) and not so much effect of other elements in the density. For micro hardness evaluation, three different zones were evaluated to compare mechanical properties of these composite structures. Not so big differences are observed for both of two groups, but the values measured at the interface and also on the particulate reinforcements can show big differences depending on the type of the particles. As indicated in the former section, the influence of the Mo should be evaluated in detail because high wear resistance is needed for the pieces that should be contact during the function in the mechanical systems. For this reason, we have made a comprehensive study has been carried out on theses composites to compare their wear resistance in case of Mo addition in 001 300.0 250.0 200.0 100.0 50.0 0.0 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 150.0 keV Counts[x1.E+3] Cu Cr FeKescCr Ca Ca Cu Fe Fe Zn Zn S Si S Mo Mo Mo Zn Zn Cu Al Fe Fe Cr CrCu O a b Fig. 18.1 (a) General microstructure of the composite A356-1 and (b) EDS analyses taken from overview microstructure 18 Recycle of Aluminium (A356) for Processing of New Composites Reinforced with Magnetic Nano Iron Oxide and Molybdenum 155
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