Journal of Advanced Materials in Engineering (Esteghlal)

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Aluminum matrix composites reinforced with Al2O3 and SiC particles (5 Vol%) were produced using the hot powder extrusion method. Extrusion temperature and extrusion reduction in area were chosen in the range of 500 to 600°C and 90 to 95%, respectively. The physical and mechanical properties of the extruded composites such as density, tensile strength, elongation and microhardness were evaluated and discussed as a function of extrusion parameters. The microstructure and fracture surface of the products were examined using SEM. The results showed that the composites were fully densified and reinforcement particles were distributed uniformly in the matrix. Presence of Al2O3 and SiC particles increased both strength and microhardness, but decreased the ductility of the composites. Experimental results for hot extrusion of the compacted powder billets also showed that the extrusion pressure was dependent on the ram speed or deformation strain rate.

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In this paper, an analytical method for noncircular shape extrusion is presented. Using this method, non-linear deformation field can be described with Hermit cubic spline which is prescribed by the boundary conditions of the die at its entryand exit. The upper bound method has been used to obtain optimum coefficient of the tangential boundary conditions. The results show that the optimum tangential parameter and the extrusion force determined by this method have good agreement with those obtained from other established methods. Also physical modeling tests show that optimum non-linear die could reduce extrusion force and strain variation compared with those in a linear die.

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Polypropylene (PP) has poor adhesion to metals and other surfaces for its chemical structure. Hence, chemical modification of PP is necessary for metal surface coating application. In this research, grafting of maleic anhydride (MA) onto co(propylene-b-ethylene) in the presence of a dicumyl peroxide (DCP) was accomplished in a single screw extruder. Characteristics of the modified polymer were determined by Infra-red Spectroscopy (IR), Scanning Electron Microscopy (SEM), and adhesion test. Maximum grafting of MA was found to be 1.2832% for 1.5 pph of MA. Adhesion test showed that the samples containing 1 pph of MA (degree of grafting is 0.5816%) had better adhesion to steel surface (17.25 kgf).

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An Al-Mg-Si-Cu alloy was subjected to tensile testing, both under solutionized and ECAE-ed conditions, using strain rates of 10-4 s-1 to 10-1 s-1 at temperatures of 25 ˚C to 325 ˚C to investigate the dynamic strain aging (DSA) phenomenon in the alloy. Negative strain rate sensitivity (m) and increasing ultimate tensile stress were observed in the DSA region with increasing temperature . Regarding the activation energy of the phenomenon, it was suggested that the process is controlled by the interaction of Mg atoms with mobile dislocations at lower temperatures of DSA occurrence while at higher temperatures, the aggregation of Mg atoms and precipitates of a second phase decreases the amount of Mg atoms in the solid solution, resulting in the inverse DSA effect. Moreover, it was shown that at temperatures greater than 250 ˚C, the ratio of post-uniform to uniform elongation increases with increasing temperature or with decreasing strain rate due to the solute drag of Mg atoms in the Al matrix. Processing the alloy by ECAE transferred the negative m values to lower temperatures and decreased the tendency to DSA at higher temperatures. Calculating the mentioned ratio for the ECAE-ed specimens revealed that the post-uniform elongation dominates the uniform elongation at all examined temperatures and strain rates. Also, it was found that for ECAE-ed specimens, the ratio is not so sensitive to variations of temperature and strain rate.

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Investigating the effect of Al₂O₃-TiB₂/Fe complex reinforcement (CCMR) on the mechanical properties of aluminum composites was the goal of this study. For this purpose, the Al₂O₃-TiB₂/Fe reinforcement powders were synthesized during milling and subsequent annealing. Different volume percentages of the produced reinforcement powders (1.25, 2.5 and 5 vol.%) were added to aluminum matrix, milled for 10 h and then hot extruded. The structural phasic and mechanical investigations of the specimens were carried out using X-ray diffraction, scanning electron microscopy and tensile test. The results showed that the metallic component (Fe rich phase) in this new type of reinforcement stuck the ceramic parts (Al₂O₃-TiB2) to aluminium matrix, and has an importance role in the flexibility of the product. The best volume percentage of CCMR in aluminium matrix was about 2.5%. This nanocomposite had a combination of strength and ductility of about 500 MPa and 6%, respectively.
 

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