Papers by Keyword: Magnesium Matrix Composite

Abstract: In elastic deformation range, this paper reports a finite element study of effect of length and diameter of the fiber on intrfacial stress of AZ91D metal matrix composites reinorced by short fiber. The nuit cell model is developde in ansys. It was found no infuence the fiber length has on the interfacial regions. There is considerable increase in intefacial von-Mises stress near the fiber end with increase in fiber diameter, and the region of stress transfer become wider. So, the risk of crack and debonding increase.

Abstract: Constant stress tensile creep tests were conducted on an AZ 91–25 vol.% Al₂O₃-SiO₂ short fiber composite and on an unreinforced AZ 91 matrix alloy. The creep resistance of the reinforced material is shown to be considerably improved compared with the matrix alloy. The creep strengthening arises mainly from the effective load transfer between plastic flow in the matrix and the fibers. Microstructural investigations by SEM revealed good fiber–matrix interface bonding during creep exposure. Short fibers have a great function in load bearing and load transfer, and greatly hinder the dislocation movement, thus enhancing the creep resistance of the composite. Damage and multiple rupture of aluminum silicate short fiber, quality of the interface combination between aluminum silicate short fiber reinforcement and the matrix, are two important factors of the creep deformation microstructure process control of Al₂O₃-SiO_2(sf)/AZ91 composite. The creep mechanism of the composite is dislocation and grain boundary sliding control.

Abstract: A TiN nanocoating was deposited on carbon fibres before their consolidation with AZ91E magnesium alloy, provided as a matrix of the composite. The main interest was the interface microstructure. Structural investigations were performed with a FE-SEM Hitachi 3200S scanning electron microscope and a Tecnai G2 FEG high resolution electron microscope equipped with energy dispersive X-ray spectrometer (EDS) and high angle annular dark field (HAADF) detectors. The observations of the fibre-matrix interface revealed the presence of a multilayered zone around the fibres. It consisted of a regular oxide layer with a thickness of approx. 100 nm around the fibre, followed by a titanium-rich layer and a region of longitudinal sharp shaped crystals directed toward the magnesium alloy matrix. This type of interface microstructure suggests that deposition of TiN as a technological nanolayer ensures the proper wettability of fibres by the metal matrix, but does not prevent diffusion processes. It was revealed that both, i.e. diffusion of elements contained in the matrix through the TiN nanolayer and diffusion of oxygen and carbon toward the surface took place.

Abstract: Constant stress tensile creep tests were conducted on AZ91D–20 vol.%, 25 vol.%, and 30 vol.% Al₂O₃-SiO₂ short fiber composites and on an unreinforced AZ91D matrix alloy. The creep resistance of the reinforced materials is shown to be considerably improved compared with the matrix alloy. With the increasing volume fraction of short fibers, the creep resistance of AZ91D composites is improved, and their creep threshold stresses are also increased accordingly. Because of the increasing volume fraction of short fibers, loads of bearing and transmission of short fibers will increase, and thus the creep resistance of AZ91D composites further improves, but the precipitation of β-Mg₁₇Al₁₂ precipitate increases in the number, it is easy to soften coarse, so that threshold stress of AZ91D composite does not increase greatly.

Abstract: The TiB2/AZ31 magnesium matrix composite was fabricated via self-propagating hightemperature synthesis (SHS) and then hot extruded. The influence of hot extrusion on the microstructure and property of TiB2/AZ31 composites was investigated. The results show that hot extrusion and synthesized TiB2 particles could refine the grain size obviously. The synthesized TiB2 particles are micro- and nano-sized, dispersing homogenously in the matrix. The interface between the matrix and the particles are good bonding. Meanwhile, slip and twinning are the main deformation modes during the hot extrusion. The fracture surface of hot-extruded TiB2/AZ31 magnesium matrix composite has more dimples than the as-cast AZ31 magnesium alloy. The improvement of microstructure seems to be beneficial for the fracture ductility of TiB2/AZ31 magnesium matrix composite.

Abstract: SiCp/AZ61 composites reinforced with SiC particles were fabricated by semi-solid stirring-melt casting technique. The creep properties of the composites have been studied by dynamic mechanical thermal analysis, micro-structural and XRD observation. The results show that the matrix grains were refined obviously at high temperature with SiC particles introducing and the creep properties of SiCp/AZ61 composites were improved comparing with AZ61 alloy. SiC particles were substituted for Mg₁₇Al₁₂ phase that was easily intenerated at high temperature on grain boundaries. The pinning of SiC particles prevents dislocation and slip of grain boundary at high temperature.

Abstract: The thixo-forging of magnesium matrix composite was analyzed with computer numerical simulation based on rigid viscoplastic finite element method. The constitutive model of SiCp/AZ61 composite was established in our prior literature. Behavior of metal flow and temperature field were obtained. The differences between traditional forging and thixo-forging processes were analyzed. Results indicated that thixo-forging was better in filling cavity than forging. Simulation results were good agreement with experimental ones.

Abstract: Mg2Si/AZ91D magnesium matrix composites are fabricated from AZ91D-Al2(SiO3)3 system by direct melt reaction method. The effects of the variation Al2(SiO3)3 addition contents to the microstructures and mechanical properties of the composites are investigated. The results show that the amounts of Mg2Si particles are increased and the structures of AZ91D magnesium alloy are refined with the Al2(SiO3)3 content increasing. When the additional content of Al2(SiO3)3 is 3wt.%, the tensile strength of the composite reaches 178.6MPa, which is increased by nearly 14.5% than that of AZ91D matrix alloy.

Abstract: AZ91 magnesium matrix composite was fabricated by squeeze infiltration process. The aluminum silicate short fibers were used as reinforcement, and aluminum phosphate was adopted as binder, fabricating process was improved as well as reducing fabricating cost effectively. The optimum technique of squeeze casting, that was, preform-body temperature of 6600C, mould temperature of 5600C, pouring temperature of 7600C and pressure of 30~50MPa. The reaction products were investigated by optical microscopic, XRD and SEM. The results show that an ideal stronger interface is formed by the chemical reaction between magnesium alloy matrix and aluminum phosphate binder due to the produce of MgO particles and a little MgAl2O4 particles in the interface. AZ91 magnesium matrix composite is well-organized, and its grain size is significantly smaller than that of the matrix. The structure of AZ91 magnesium matrix composite is uniform without casting defects such as shrinkages and inclusions.

Abstract: Magnesium matrix composites SiCp/ AZ61 reinforced with SiC particulates was fabricated by stirring-melt casting technique. The damping properties of the composites have been studied with dynamic mechanical thermal analysis and micro-structural observation. The results show that matrix grains introduced SiC particulates were refined obviously at room temperature and the properties of SiCp/ AZ61 composites were improved comparison to AZ61 alloy. Meanwhile, the improvement of damping properties can be explained by G-L dislocation pinning theory. The damping characterization is explained with the increasing of quantities of the grain-boundaries for the introducing of SiC particles and the ease of interface slipping in temperature.