Applied Mechanics and Materials Vols. 217-219

Abstract: The tensile creep behaviors of two NiAl-based alloys (HIPed NiAl-33.5Cr-0.5Zr and DS NiAl-28Cr-5.8Mo-0.2Hf) have been investigated. The creep results indicated that the creep curves of both alloys have similar shapes, which are composed of primary creep stage, steady-state creep stage, longer accelerated creep stage, and about 25-45% creep strain. The apparent stress exponents are in the range of 4.8-7.5 and the apparent activation energies of 520-584 kJ/mol were also analyzed. The creep deformations were controlled by the sub-grain boundary formation for the HIPed NiAl-Cr(Zr) and dislocation climb for the DS NiAl-Cr(Mo,Hf). The creep rupture data of both alloys obey the Monkman-Grant relationship.

Abstract: Hot ductility testing is used to evaluate the liquation cracking susceptibility of high Strength aluminum alloy 2219, the fracture surface of hot ductility samples are inspected by SEM, the results showed that the melting point of α(Al)-CuAl2 divorced eutectic is higher than that of α(Al)- CuAl2 eutectic. The α(Al)- CuAl2 divorced eutectic is prior to melting during heating process and solidification during cooling process, so the BTR of Al-Cu alloy 2219 is narrow. The low liquation cracking susceptible and good weldability of Al-Cu alloy 2219 due to the rapidly recover the strength and ductility in elevated temperature which caused by the α(Al)-CuAl2 divorced eutectic solidification during cooling process.

Abstract: Grain-refined TiB₂-TiC_x composites were designed and fabricated by reaction hot pressing under 30 MPa at 1800 °C choosing 4.8 Ti-B₄C material system with Al, C and Si₃N₄ as additives. The microstructure of the resultant was homogeneously grain-refined TiB₂-TiC_x matrix reinforced by AlN-SiC solid solution particles that were embedding tiny TiB₂-TiC_x crystals. The obtained specimen showed relative high flexural strength of 860±30 MPa and fracture toughness of 13.6±0.3 MPa·m1/2, which can be explained by several toughening mechanisms.

Abstract: Heterogeneity of composition and microstructure in cast large sized 3104 aluminium alloy slab were studied using AES-ICP, OM, SEM, etc. The results show that the cooling rate on the cross section of 3104 slab is different, macro-segregation is found in the different section in the slab .The content of Ti decreases gradually from the surface to about 1/4 thickness of the slab, then increases rapidly to the center of slab; other elements content increases gradually from the surface to the about 1/4 thickness and then decreases rapidly to the center; the grain size on the surface area is fine, and the grain size at the center is coarse , segregation of Mg is found within the grains; great amount compound is found to be of presence on the grain boundary, with chemical compositions of Al 87（FeMn）13 and Al83（FeMn）12Si5; The compound size at the surface area is comparatively smaller, and coarser at the centre of slab.

Abstract: Mg alloys are drawing a lot of attention and have been extensively studied. The major obstacle to the practical application of the alloys is the poor formability at room temperature, originating basically from the insufficient number of slip system. Development of a proper microstructure and/or texture is one promising solution to improve the formability. In the present work, after extrusion and full annealing, rolling at 300°C with different starting textures, the microstructures, texture developments and tensile properties of AZ31 Mg alloys are studied. After full annealing strong ∥ED fiber texture and weak + ∥ED fiber texture (c-axes in the radial direction) were developed. After rolling at 300°C many twins were formed, and the strong ∥ED fiber texture changed to ∥ND texture. Yield strength, tensile strength and elongation changed obviously depending on the microstructure and textures.

Abstract: Numerical simulations of different PELE jacket and filling materials are carried out to research the influence of the materials characteristics on PELE effects. The results indicate that the materials characteristics have obvious influence on PELE effects. For jacket materials, the elastic modulus and density are the key factors that influence PELE effects, the maximum radial speed and scattering angle of fragments, and the penetration hole size of 4340 steel are larger than these of tungsten alloy, thus the PELE effects of 4340 steel are better. For filling materials, the elastic modulus is the key factor influencing PELE effects, the maximum radial speed and scattering angle of fragments, and the penetration hole size of PE, nylon and aluminum increase successively, the aluminum filling material has better PELE effects.

Abstract: In order to improve the stabilities of A95-aluminum-silicon sols, the influences of various ultrasonic field, ultrasonic time and ultrasonic frequency on the property of aluminum-silicon sols were researched. The physical-chemical performances of sols, such as the sol viscosity, rheological properties and microstructure, and so on, were measured. The results show that the influence of sonochemical actions on the stability of the Al₂O₃-SiO₂ sol is remarkable. Standing wave fields accelerate the molecules agglomeration of the sol. In the diffusion wave fields, the stability of the sol increases with ultrasonic frequency enhances, but the stability first increases and then reduces with the extension of ultrasonic time. When ultrasonic frequency and ultrasonic time is 100 Hz and 60 minutes respectively, the stability of the Al₂O₃-SiO₂ sol is the best.

Abstract: In the present work, basing on the rheological model of Chen and Fan [1], the rheological behavior of AlSi6Mg2 alloy at transient state is investigated. It has been shown that the deagglomeration of particles is about two orders of magnitude faster than the agglomeration of them. The inequality of agglomeration rate and deagglomeration rate is thought as the origin of the thixotropy of SSMS. Subsequently, the similar trend of the variation of the viscosity and the average agglomerate size with shearing time and resting time shows that the microstructure of SSMS determines its rheological behavior, while the external flow conditions (such as shear rate, shearing time, etc) influence the viscosity by changing its microstructure. The present study predicts that the CF model can describe reliably the transient rheological behavior of AlSi6Mg2 alloy.

Abstract: In this study, the variation of workability of semi-continuously casted and extruded ZK60A magnesium alloy was investigated. To determine the deformation capability of two different billets, uniaxial compression tests were conducted at elevated temperatures and two different strain rates. In addition, the microstructural evolution was investigated using electron backscatter diffraction (EBSD) to compare the microstructure before and after the extrusion. The formability of ZK60A depending on the microstructure is discussed based on the experimental results obtained in this study, and is compared with earlier research in the literature.

Abstract: The microstructural characters and refining property of Al-Ti-C grain refinement alloy prepared by ultrasound coupling method were studied by analytical means such as SEM, and the reaction synthesis mechanism of Al-Ti-C grain refinement was discussed. Experimental results show that the Al-Ti-C alloy refiner using “thermite reduction method” under high-energy ultrasound was prepared experimentally. Its microstructure character is that master alloy has smaller size of TiC, its quantities are larger and are dispersed. Melt reaction is generally that the source of titanium releases Ti atoms under high temperature of ultrasonic. Ti atoms react with aluminum to generate TiAl3, and react with carbon to generate TiC.