Thixoforming A356 Aluminum Bipolar Plates at High Solid Fractions

Thixoforming investigations have been developed primarily for the manufacturing of bulk components, and the current knowledge is very limited with respect to the fabrication of thin cross sections of alloys. We studied the effectiveness of thixoforming process for the fabrication of A356 aluminum alloy bipolar plates with microchannels on both sides. Feedstock semisolid slurries, with different solid contents of ~55, 50, and 45 pct, were prepared at 858 K, 863 K, and 868 K (585 °C, 590 °C, and 595 °C), respectively, and were used to thixoform 1.20-mm-thick bipolar thin plates. The microstructures of the thixoformed thin plates consisted of (i) large primary α-Al globular grains, (ii) a quenched liquid phase, and (iii) fine secondary α-Al particles. The fraction and size of the primary α-Al globular grains decreased, and the primary α-Al globular grains became more spherical with the increasing thixoforming temperature. It seemed that these changes in the microstructural features led to the reduction in the agglomeration and interaction among the primary α-Al globular grains surrounded by the liquid matrix during thixoforming. This enabled the semisolid slurry to effectively flow and fill in the sharp corners (such as the microchannels) of the die cavity at higher thixoforming temperatures. The thin plates thixoformed at 868 K (595 °C), consequently, exhibited the highest dimensional stability and the fewest internal defects. The liquid matrix surrounding the primary α-Al grains solidified inside the die cavity after thixoforming. Either the liquid phase was instantly quenched or fine secondary α-Al particles were formed inside the die cavity. The fraction and size of the latter increased with increasing thixoforming temperature. The surface hardness of the thixoformed plates was measured, and the hardness values were correlated with the microstructural features of the thixoformed plates.     

Optimized formulation of an oxidative curing system for liquid polysulfide sealants used in fuel tanks by D‐optimal design method

In this work, the effective parameters in liquid polysulfide curing system were optimized by D ‐optimal design method. Five main components in the formulation, carbon black, vulcanizing agents (MnO₂, Na₂Cr₂O₇, and PbO₂), CaCO₃, fumed silica, and chlorinated paraffin, were selected. Mechanical and chemical properties of the samples were investigated. The results showed that tensile strength, hardness, viscosity, and optimum cure time (t₉₀) presented a suitable coordination with reduced quadratic model. For elongation at break and swelling tests, reduced two‐factor interaction (2FI), and for peel strength, a linear model showed the best correlation. To achieve the desirable properties for liquid polysulfide sealants used in fuel tanks, an optimized amount of the above components in the formulation were used. Finally, MnO₂ curing system, compared with Na₂Cr₂O₇ and PbO₂, was selected as the best choice. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental investigation on mechanical properties of extruded foamed PVC‐wood composites reinforced with continuous glass fibers

In this study, mechanical performances of extruded foamed and unfoamed PVC‐wood composites, reinforced with continuous glass fibers, were investigated. A specially designed die was used to incorporate the continuous glass rovings into the extruded rectangular shaped profiles. The experimental variables were the number of continuous glass rovings (0–2‐4) and the presence or absence of the chemical foaming agent. Three point bending tests as well as density measurements were conducted to evaluate the mechanical properties and density reduction upon foaming. The results showed that the flexural strength of the reinforced profiles was significantly increased, as 58% increase in flexural strength was noticed for wood plastic composites (WPCs) reinforced with four glass rovings. The highest density reduction (14%) was observed upon foaming for profiles reinforced with four glass rovings, while resulting in strength deterioration. Moreover, results revealed the remarkable effect of reinforcement on preserving mechanical performance of the foamed samples, as 88% increase in flexural strength of the foamed samples reinforced with four glass rovings was observed compared with the unreinforced foamed ones. For the foamed WPCs reinforced with even two glass rovings, the higher specific strength values were also noticed compared to the unreinforced and unfoamed samples. POLYM. COMPOS., 37:1674–1680, 2016. © 2014 Society of Plastics Engineers     

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

This paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved.     

Magneto Optical Properties of FeB<Subscript>x</Subscript>Fe<Subscript>2−x</Subscript>O<Subscript>4</Subscript> Nanoparticles

In this study, FeB_xFe_2?xO₄ nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µ_B and almost half or less with respect to 4 µ_B of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K _eff ) are between 43.3 × 10⁴ and 19.4 × 10⁴ emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeB_xFe_2?xO₄ NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe₃O₄ NPs in the literature. The bigger E _g values are mainly attributed to B concentration and partly to quantum confinement effect.     

Physical properties of normal grade biodiesel and winter grade biodiesel

In this study, optical and thermal properties of normal grade and winter grade palm oil biodiesel were investigated. Surface Plasmon Resonance and Photopyroelectric technique were used to evaluate the samples. The dispersion curve and thermal diffusivity were obtained. Consequently, the variation of refractive index, as a function of wavelength in normal grade biodiesel is faster than winter grade palm oil biodiesel, and the thermal diffusivity of winter grade biodiesel is higher than the thermal diffusivity of normal grade biodiesel. This is attributed to the higher palmitic acid C(16:0) content in normal grade than in winter grade palm oil biodiesel.