Materials Science Forum Vols. 546-549

Abstract: A high reinforcement content TiB2/2024Al composite with an average particle size of 8μm was fabricated by squeeze casting technology. The dynamic compression behaviors of the composite under varied strain rates were measured using split Hopkinson pressure bar, and its microstructure and fracture characteristic were examined. Resluts revealed that the composite was dense and homogenerous, and the TiB2-Al interface was clean without interfacial reactants. At high strain rate, the TiB2/Al composite showed insensitive to the strain rate, and both the flow stress and the elastic modulus improved little with an increase of the strain rate. The composite failed macroscopically in shear fracture and in split, which were caused by cracking of large reinforcement particles and interface failures under dynamic load.

Abstract: In the present study, MBOw/Al composites were fabricated using squeeze casting method. The interfacial reaction in the composite was investigated using transmission electron microscope (TEM). The tensile properties of the composites with different kinds of matrix were studied. The experimental results showed that the properties of the composite were very good.

Abstract: Two Al-Si alloys (Al-12Si and Al-20Si) and an industrial pure Al were reinforced with 70vol.% dual-sized SiC particles. The composites experienced annealing treatment, to investigate the effect of silicon addition and thermal history on the thermal expansion behavior of high SiC content aluminum matrix composites. The results showed that silicon additions led to a beneficial reduction in the coefficients of thermal expansion (CTEs) of the composites. In the temperature range between 20°C and 400°C, a continuous increase in CTEs with temperature was observed for SiCp/pure Al composite. However, the CTEs of SiCp/Al-12Si and SiCp/Al-20Si showed the maxima at 350°Cand 250°C respectively, then diminished at higher temperatures. This was related to the change of solid solubility of silicon in aluminum at elevated temperatures. The thermal expansion behavior of SiCp/Al composites was also influenced by thermal history. After annealing treatment, the CTEs were reduced when compared with those of as-cast composites. Annealing treatment reduced the original thermal residual stresses, and then altered thermal expansion behavior of the composites.

Abstract: The effects of the interfacial parameters (interface/matrix modulus ratio, interface Poisson ratio and interface volume fraction) and the structural parameters (particulate volume fraction, particulate shape, arrangement pattern and dimensional variance mode) on the elastic modulus of SiCp/6066Al composites were calculated and analyzed. The results showed that component and interface performance significantly influenced the elastic modulus of the composite; but the particulate shape, arrangement pattern and dimensional variance mode were found to have little influence. This means that the effect of the above structural parameters can be negligible. The optimal approach to enhance the elastic modulus and specific elongation of a composite is to improve the interfacial bonding of the particulate. Optimal results are obtained when the interface modulus is 20% ~ 30% of the matrix modulus.

Abstract: The microstructures of sprayed SiCp/Al composite fabricated by thermal spraying technique by optical microscope (OM)
scanning electronic microscope (SEM), transmission electronic microscope (TEM), X-ray (diffractometer) XRD, selected area electron diffraction (SAED), energy dispersive spectrum (EDS) techniques, were investigated. The composite consisted of SiC and Al, along with single crystal Si and amorphorous Si, and tiny Al2O3. The interfaces between SiC particles and Al matrix bonded well, and tiny reactants like Al2O3 were found near the interfaces. The mechanisms of chemical reactions during sprayin were discussed g. The nano-Al grains and particles were observed in the sprayed composite. The formation of nano-Al grains and particles of SiCp/ Al composites were explained. It has been found that Several interface relationships existed in the sprayed composite.

Abstract: The effects of current densities on the morphology and corrosion resistance of anodized coating formed on a SiCp/2024 Al metal matrix composite (MMC) in sulfuric acid solution were investigated by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and polarization curve. The results showed that the surface of the coating was not flat, and cracks existed when the current density increased to 20mA/cm2. The SiC particles could be oxidized during anodizing of the MMC. And the SiC particle anodized at a significantly reduced rate compared with the adjacent Al matrix. This gave rise to alumina film encroachment beneath the particle and occlusion of the partly anodized particle in the coating. As a consequence, the oxide/substrate interface became locally scalloped, and the anodized coating was non-uniform in thickness. Further, oxidation of SiC appeared to be associated with gas-filled cavities in the coating material. The size of cavities above the SiC particles increased obviously and the surface cracks developed when the current density increased. This shows that the anodized coating formed at higher current density has a structural feature with lower corrosion resistance. The polarization results indicated that the corrosion resistance of the coating decreases when the current density increases.

Abstract: Diffusion welding is an advanced bonding process in which similar or dissimilar materials can be bonded in solid state. In this study, aluminium composite (5% and 15% WC) powders were compacted at 450 MPa pressure and sintered at 550 oC for 45 minutes in argon atmosphere.and joined each other by diffusion bonding. The bonding temperatures (585 oC, 600 oC, 615 oC) and dwell time (185 min) were chosen for the welding process at constant 20 MPa. It has been observed that these variations on the welding parameter strongly affected the microstructure and the weldability of the materials.

Abstract: Joining parts by diffusion welding is one of the recent manufacturing techniques, since it allows manufacturing of similar or dissimilar parts, and complex components with high precision. It is difficult to weld Aluminium and its composites by conventional fusion welding techniques. Thus, In this study, diffusion welding technique was applied to weld Al+5-10-15% WCp composites in argon gas. An experimental set up has been designed and series of experiments have been performed, Metallographical examinations have been carried out to determine the welding quality. It was concluded that changes in volume fraction of the reinforcement particles strongly affect the weldability of the materials and their microstructures.

Abstract: Microstructure Sensitive Design (MSD) offers a rigorous mathematical framework for representing the relevant statistical details of the material microstructure for a given design problem, and for developing quantitative invertible relationships between these microstructure representations and the macroscale properties of interest. The methodology makes extensive use of Fourier representations of the distribution functions representing the material internal structure and existing homogenization theories. In this paper, we describe the application of the MSD framework to fcc polycrystals with a specific focus on the crystallographic texture as the microstructure design variable. The advantages of the MSD approach are demonstrated through a number of elastic-plastic property closures for cubic metals.

Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Three different ablative, sacrificial coating were chosen to protect the 6061-T651 alloys from surface melting by laser pulse. This paper analyzes the effect of the paint and foil coatings on the shock wave propagation into the 6061-T651 alloys and the resulting change in mechanical properties. The depths of hardening by laser processing of 6061-T651 alloys up to 1 mm, and the surface hardness reach to 138HV. When the laser pulse energy density increase from 2.8 GW/cm2 to 3.6 GW/cm2, the surface hardness of the black paint, aluminum foil and silica acid black paint samples increase to 19
, 27
, 36
respectively.