Volume 109, Issue 10

In general, micropore size acts as one of the most significant influencing factors on the fatigue strength of aluminium castings. Hence, an in-depth knowledge of the occurrence of micropore sizes and their local distributions in different locations in complexly-shaped lightweight components is of great interest to the casting industry. In this work, the local properties of AlSi8Cu3 and AlSi7Cu0.5Mg cylinder heads and AlSi8Cu3 crankcases were analyzed. Extensive X-ray computed tomography (CT) scans of three specimen positions revealed significant differences in micropore size and distribution. Two CT scan resolutions were selected, with respect to different micropore size populations in the cast components, to enable accurate detection of the microporosity, in addition to an adequate scanning volume, in order to achieve a statistically approved parameter study. Thereby, specimen positions exhibiting smaller mean micropore sizes were scanned at 3 μm/voxel scanning resolution and ones with larger micropore sizes at 8 μm/voxel. A statistical assessment of all of the alloy specifications and specimen positions indicates that the general extreme value and lognormal distribution appropriately describe the micropore size distributions. Finally, an extensive sensitivity study is presented, aimed at examining micropore size characteristics, such as the porosity, sphericity, maximum and mean values and standard deviation, and to investigate their relationships in the investigated cast specimens.

Spark plasma sintering (SPS) has been recognized, in the recent past, as a very useful method to produce metal matrix composites with enhanced mechanical and wear properties. Obviously, the material's final properties are strongly related to the reinforcement types and percentages as well as to the processing parameters employed during synthesis. The present paper analyses the effect of 0.5 and 1% of carbon nanotubes addition on the mechanical and microstructural behavior of Al-based metal matrix composites produced via SPS. The microstructural and mechanical behavior is analyzed as a function of the SPS parameters: heating rate, sintering temperature and pressure.

We obtained ZnO crystals with different morphologies through a simple hydrothermal method by adjusting the solution pH . We characterized the ZnO crystals by means of scanning electron microscopy and found several different morphologies, including strip-like, flake-like, cone-like, and six-sided prism shaped particles. The reaction mechanism of the ZnO crystal growth was also investigated. The absorption properties of the ZnO samples were studied using ultraviolet–visible spectroscopy. The studies of the optical properties indicated that the absorption peaks of all samples were located at 377.9 nm. However, there was some variation in the absorption spectra of the ZnO particles with different morphologies.

In the present work, the nanocomposite 0.9CaCu 3 Ti 4 O 12 –0.1BaTiO 3 (CC-BT) is synthesized by a solid-state reaction method by sintering at 950°C for 12 h. X-ray diffraction analysis confirms the presence of both BaTiO 3 and CaCu 3 –Ti 4 O 12 phases in the composite ceramic. Transmission electron microscopy analysis of the composite demonstrates the formation of nanoparticles with an average particle size of 40 ± 5 nm. The surface morphology of the composite sintered at 950°C for 12 h obtained by scanning electron microscopy analysis indicates the evolution of large and small grains with a bimodol distribution. The average and root mean square roughness were found to be 1.41 nm and 2.24 nm respectively by atomic force microscopy studies. The dielectric constant of CC-BT ceramic was determined to be 6231 at 100 Hz and 500 K. The presence of the semiconducting grains and the insulating grain boundaries in the composite supports the internal barrier layer capacitance mechanism operative in CC-BT nanocomposite.

Based on a forming temperature-controlled mixed strain-hardening law, a temperature-controlled thermal–microstructure–mechanical model was developed to predict the deformation in ferrite–martensite dual-phase steel before and after complex laser forming. Phase transformation in dual phase steel was predicted by coupling a kinetic transformation model with the developed model during laser forming. The corresponding algorithm of the constitutive model was used in three-dimensional finite element method to simulate the material deformation and mechanical properties during the laser forming. The simulated results agree well with the experimental results. Laser forming influences the mechanical properties of the material significantly, leads to bending deformation of the scanned sample and induces a ferrite-to-martensite transformation. The influence of scanning line number on the tensile strength and bending deformation of the scanned specimen was investigated. The tensile strength and bending angle are related positively to the number of scanning lines on the sample.

The effect of temper rolling and subsequent annealing on texture development and magnetic properties of semi-processed non grain oriented electrical steel has been investigated. The result shows that 5% temper rolling and final annealing at 850°C resulted in strong α-fiber component. The etch-pit technique shows that strain induced boundary migration is responsible for new texture component augmentation. Vibrating sample magnetometery reveals that maximum and minimum magnetic permeability are related to rolling and transverse directions, respectively. Average magnetic permeability is improved to some extent as a result of temper rolling and subsequent annealing.

In this study, double-layer structured 316L stainless steel foam is fabricated through a layer by layer space holder method. The fabricated foams contain uniform pore distribution and can be categorized as body centered cubic crystal structures. Each sample is made of two layers in the axial direction. To induce 51 vol.% and 62 vol.% porosity in the first and the second layers, 1.7 to 2.0 mm and 2.0 to 2.4 mm spherical carbamide particles are used, respectively. In this study, the effect of the height of each layer on the compressive behavior of the fabricated foams is investigated in detail. The results indicate that compressive deformation of the double-layered foams starts from the high porosity (62 vol.%) layer and then shifts to the low porosity (51 vol.%) layer. Deformation of the double-layered 316L foams demonstrates two plateau regions, whose lengths depend on the heights of the low and high porosity layers.

Mg–Y–Zn alloys with different contents of alloying elements were prepared. The microstructure and mechanical properties of these Mg–Y–Zn alloys were investigated by using scanning electron microscopy, X-ray diffraction and tensile testing. The results show that the as-cast Mg–Y–Zn alloy is mainly composed of α-Mg, Mg 12 YZn and Mg 3 Y 2 Zn 3 phases. After Mn addition, a small quantity of Mn phase arises in the as-cast Mg–Y–Zn–Mn alloy. After extrusion, the microstructure of the alloys is of an inhomogeneous character showing fine grains produced due to dynamic recrystallization. Tensile strength of as-extruded Mg-9Y-1Zn, Mg-9Y-3Zn and Mg-9Y-3Zn-1Mn reached 249.86 MPa, 303.19 MPa and 322.15 MPa, respectively. The gradually increasing strength can be attributed to fine grain strengthening, second phase strengthening and LPSO structure. Additionally, the tensile fracture surfaces were examined under scanning electron microscopy, and all of their fracture morphologies exhibit dimple facture character.

Semi-solid billets of A356 alloy were fabricated using a sloping-plate device. This study investigated the effects of reheating on the microstructural evolution of the alloy. Prolonged holding times and higher reheating temperatures caused the primary α-aluminum particles to gradually grow and spheroidize, resulting in increased liquid fraction. The optimal reheating condition was 580°C for 25 min, during which the average grain size increased to 89.3 μm and the shape factor reached 1.18. The secondary phases were also refined by the reheating process.

In this work, we present the synthesis of SBA-15 materials modified with 6 and 9 mol.% of Zr and P, respectively. Silanol SBA-15 groups were detected by Fourier transform infrared spectroscopy. X-ray diffractograms revealed that the typical hexagonal arrangement of SBA-15 was preserved after Zr and P introduction, and the structure was confirmed by transmission electron microscopy. After the Zr introduction, the morphology of SBA-15 changed from fibrous particles to a semi-spherical shape according to scanning electron microscopy, while nitrogen physisorption revealed the stability of the textural materials after the P introduction. The infrared spectra of pyridine adsorption indicated that the Zr and P incorporation into SBA-15 generated adequate Lewis and Br⊘nsted acidities to carry out methanol dehydration and direct the selectivity towards dimethyl ether, with medium-strong acid sites being responsible for obtaining up to 99% selectivity towards dimethyl ether.

Two T6 (500°C × 3 h, water quenching and 210°C × 6 h, air cooling) samples of Al-13Si-5Cu-2Ni-1Mg alloy were furture heated to 350°C and 420°C, respectively for various times. The tensile strength of the alloy, measured at both room temperature and 350°C is observed to abnormally increase, especially for the samples that were heated to 420°C. Al 11 Cu 5 Mn 3 nanoparticles that form stably during these heating processes exhibit a higher volume fraction after the exposure to 420°C than that obtained by the exposure to 350°C. These nanoparticles were responsible for enhancing the alloy's tensile properties because of the precipitation strengthening effect of the second nano-phase.

The influence of minor Nd substitution on the microstructure and corrosion resistance of Mg–Zn–Y alloy were investigated. Results indicate that the partial substitution of Nd for Y can effectively refine grains but deteriorate the corrosion resistance of extruded Mg–Zn–Y alloy. The corrosion rates, measured by immersion tests in 3.5% NaCl solution at 25°C, are 12 and 19 mm · y −1 for the Mg-5.6Zn-1.4Y and Mg-5.6Zn-1.0Y-0.4Nd alloys, respectively. The negative effect of Nd is associated with enhanced microgalvanic corrosion resulting from grain refinement and higher area of second phase, as well as to a degraded protectiveness of the corrosion product layer.