Influence of melt pouring temperature and plate inclination on solidification and microstructure of A356 aluminum alloy produced using oblique plate

The preparation of semisolid slurry of A356 aluminum alloy using an oblique plate was investigated. A356 alloy melt undergoes partial solidification when it flows down on an oblique plate cooled from underneath by counter flowing water. It results in continuous formation of columnar dendrites on plate wall. Due to forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously to produce semisolid slurry at plate exit. Melt pouring temperature provides required condition of solidification whereas plate inclination enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained was solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets were heat treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets were analyzed. Effects of melt pouring temperature and plate inclination on solidification and microstructure of billets produced using oblique plate were described. The investigations involved four different melt pouring temperatures (620, 625, 630 and 635 degrees C) associated with four different plate inclinations (30 degrees, 45 degrees, 60 degrees and 75 degrees). Melt pouring temperature of 625 degrees C with plate inclination of 60 degrees shows fine and globular microstructures and it is the optimum.

Influence of plate length and plate cooling rate on solidification and microstructure of A356 alloy produced by oblique plate

A356 alloy melt solidifies partially when it flows down on an oblique plate cooled from bottom by counter flowing water. Columnar dendrites are continuously formed on the plate wall. Because of the forced convection, these dendrites are sheared off into equiaxed/fragmented grains and then washed away continuously by producing semisolid slurry at plate exit. Plate cooling rate provides required extent/amount of solidification whereas plate length enables necessary shear for producing semisolid slurry of desired quality. Slurry obtained is solidified in metal mould to produce semisolid-cast billets of desired microstructure. Furthermore, semisolid-cast billets are also heat-treated to improve surface quality. Microstructures of both semisolid-cast and heat-treated billets are compared. The effects of plate length and plate cooling rate on solidification and microstructure of billets produced by using oblique plate are illustrated. Three different plate lengths (200 mm, 250 mm, 300 mm) associated with three different heat transfer coefficients (1000, 2000 and 2500 W/(m(2).K)) are involved. Plate length of 250 mm with heat transfer coefficient of 2000 W/(m(2).K) gives fine and globular microstructures and is the optimum as there is absolutely no possibility of sticking of slurry to plate wall.

Measurements of thermal radiation in ultralight metal foams with open cells

Highly porous ultralightweight cellular metal foams with open cells have attractive mechanical, thermal, acoustic and other properties and are currently being exploited for high-temperature applications (e.g. acoustic liners for combustion chambers). In such circumstances, thermal radiation in the metal foam becomes a significant mechanism of heat transfer. This paper presents results from experimental measurements on radiative transfer in Fe-Cr-Al-Y (a steel-based high-temperature alloy) foams having high porosity (95 per cent) and different cell sizes, manufactured at low cost from the sintering route. The spectral transmittance and reflectance are measured at different infrared wavelengths ranging from 2.5 to 50 μm, which are subsequently used to determine the extinction coefficient and foam emissivity. The results show that the spectral quantities are strongly dependent on the wavelength, particularly in the short-wavelength regime (less than 25 μm). While the extinction coefficient decreases with increasing cell size, the effect of cell size on foam reflectance is not significant. When the temperature is increased, the total extinction coefficient increases but the total reflectance decreases. The effective radiative conductivity of the metal foam is obtained by using the guarded hot-plate apparatus. With the porosity fixed, the effective radiative conductivity increases with increasing cell size and increasing temperature. © IMechE 2004.

Natural convection in metal foams with open cells

This paper presents a combined experimental and numerical study on natural convection in open-celled metal foams. The effective thermal conductivities of steel alloy (FeCrAlY) samples with different relative densities and cell sizes are measured with the guarded-hot-plate method. To examine the natural convection effect, the measurements are conducted under both vacuum and ambient conditions for a range of temperatures. The experimental results show that natural convection is very significant, accounting for up to 50% of the effective foam conductivity obtained at ambient pressure. This has been attributed to the high porosity (ε > 0.9) and inter-connected open cells of the metal foams studied. Morphological parameters characterizing open-celled FeCrAlY foams are subsequently identified and their cross-relationships are built. The non-equilibrium two-equation energy transfer model is employed, and selected calculations show that the non-equilibrium effect between the solid foam skeleton and air is significant. The study indicates that the combined parameter, i.e., the porous medium Rayleigh number, is no longer appropriate to correlate natural convection by itself when the Darcy number is sufficiently large as in the case of natural convection in open-celled metal foams. Good agreement between model predictions and experimental measurements is obtained. © 2005 Elsevier Ltd. All rights reserved.

Dynamic-response of a laminated plate with friction damping

Invertible dark-center diffraction of the metal film induced by femtosecond laser

We found reversible dark-center diffraction of the transmitted probe beam passing through the chromium film. which is induced by the pump femtosecond laser. The dark-center diffraction of I he transmitted probe beam appears and disappears with and without the pump beam. A view of diffractive optics with binary phase plate is put forward, which explains the reversible dark-center diffractive optical phenomenon. The pre-ablated hole on the metal film can be regarded as a uniform light filed without phase modulation, the Surrounding Circular part around the pre-ablated hole can be regarded as "phase modulated". Therefore, this diffraction optic view might be helpful for us to understand the phase change of the metal film introduced by the femtosecond laser pulse. (C) 2008 Elsevier B.V, All rights reserved.

Thermal characterization of SOI CMOS micro hot-plate gas sensors

This work reports on thermal characterization of SOI (silicon on insulator) CMOS (complementary metal oxide semiconductor) MEMS (micro electro mechanical system) gas sensors using a thermoreflectance (TR) thermography system. The sensors were fabricated in a CMOS foundry and the micro hot-plate structures were created by back-etching the CMOS processed wafers in a MEMS foundry using DRIE (deep reactive ion etch) process. The calibration and experimental details of the thermoreflectance based thermal imaging setup, used for these micro hot-plate gas sensor structures, are presented. Experimentally determined temperature of a micro hot-plate sensor, using TR thermography and built-in silicon resistive temperature sensor, is compared with that estimated using numerical simulations. The results confirm that TR based thermal imaging technique can be used to determine surface temperature of CMOS MEMS devices with a high accuracy. © 2010 EDA Publishing/THERMINIC.

The practical feasibility of using RFID in a metal environment

Passive Radio Frequency Identification (RFID) has revolutionized the way in which products are identified. This paper considers the effect of metals on the performance of RFID at ultra high frequency (UHF). The paper establishes read patterns in space, highlighting the interference of RF waves due to three different metals, one ferrous and the other two non ferrous, when placed behind a transponder. The effect of thickness of the metal plate is also examined. Different metals have been found to have different interference effects although there are some similarities in their read patterns related to their material properties. Also experiments have been carried out to identify and establish various methods of improving this performance. Finally, differences between performance-measuring parameters, namely attenuating transmitted power and calculating read rate at a fixed attenuation are established and possible reasons of these observations are presented. © 2007 IEEE.

Bulk forming of sheet metal

Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation. © 2012 CIRP.

Multi-hit armour characterisation of metal-composite bi-layers

The ballistic performance of equi-mass plates made from (i) stainless steel (SS); (ii) carbon fibre/epoxy (CF) laminate and (iii) a hybrid plate of both materials has been characterised for a spherical steel projectile. The hybrid plate was orientated with steel on the impact face (SSCF) and on the distal face (CFSS). The penetration velocity (V 50) was highest for the SS plate and lowest for the CF plate. A series of double impact tests were performed, with an initial velocity V I and a subsequent velocity V II at the same impact site. An interaction diagram in (V I,V II) space was constructed to delineate penetration from survival under both impacts. The degree of interaction between the two impact events was greater for the CFSS plate than for the SSCF plate, implying that the distal face has the major effect upon the degree of interaction.

Mode I fracture of sheet metal

The perceived wisdom about thin sheet fracture is that (i) the crack propagates under mixed mode I & III giving rise to a slant through-thickness fracture profile and (ii) the fracture toughness remains constant at low thickness and eventually decreases with increasing thickness. In the present study, fracture tests performed on thin DENT plates of various thicknesses made of stainless steel, mild steel, 6082-O and NS4 aluminium alloys, brass, bronze, lead, and zinc systematically exhibit (i) mode I “bath-tub”, i.e. “cup & cup”, fracture profiles with limited shear lips and significant localized necking (more than 50% thickness reduction), (ii) a fracture toughness that linearly increases with increasing thickness (in the range of 0.5–5 mm). The different contributions to the work expended during fracture of these materials are separated based on dimensional considerations. The paper emphasises the two parts of the work spent in the fracture process zone: the necking work and the “fracture” work. Experiments show that, as expected, the work of necking per unit area linearly increases with thickness. For a typical thickness of 1 mm, both fracture and necking contributions have the same order of magnitude in most of the metals investigated. A model is developed in order to independently evaluate the work of necking, which successfully predicts the experimental values. Furthermore, it enables the fracture energy to be derived from tests performed with only one specimen thickness. In a second modelling step, the work of fracture is computed using an enhanced void growth model valid in the quasi plane stress regime. The fracture energy varies linearly with the yield stress and void spacing and is a strong function of the hardening exponent and initial void volume fraction. The coupling of the two models allows the relative contributions of necking versus fracture to be quantified with respect to (i) the two length scales involved in this problem, i.e. the void spacing and the plate thickness, and (ii) the flow properties of the material. Each term can dominate depending on the properties of the material which explains the different behaviours reported in the literature about thin plate fracture toughness and its dependence with thickness.

Allosteric modulation of pyrophosphatase activity of rat osseous plate alkaline phosphatase by magnesium ions

Pyrophosphatase activity of rat osseous plate alkaline phosphatase was studied at different concentrations of calcium and magnesium ions. with the aim of characterizing the modulation of enzyme activity by these metals. In the absence of metal ions, the enzyme hydrolysed pyrophosphate following Michaelian kinetics with a specific activity of 36.7 U/mg and K-0.5 = 88 mu M. In the presence of low concentrations (0.1 mM) of magnesium (or calcium) ions, the enzyme also exhibited Michaclian kinetics for the hydrolysis of pyrophosphate, but a significant increase in specific activity (123 U/mg) was observed. K-m values remained almost unchanged. Quite different behavior occurred in the presence of 2 mM magnesium (or calcium) ions. In addition to low-affinity sites (K-0.5 = 40 and 90 mu M, for magnesium and calcium, respectively), high-affinity sites were also observed with K-0.5 values 100-fold lower. The high-affinity sites observed in the presence of calcium ions represented about 10% of those observed for magnesium ions. This was correlated with the fact that only magnesium ions triggered conformational changes yielding a fully active enzyme. These results suggested that the enzyme could hydrolyse pyrophosphate, even at physiological concentrations (4 mu M), since magnesium concentrations are high enough to trigger conformational changes increasing the enzyme activity. A model, suggesting the involvement of magnesium ions in the hydrolysis of pyrophosphate by rat osseous plate alkaline phosphatase is proposed. (C) 1998 Published by Elsevier B.V. Ltd. All rights reserved.

A Comparison of Deep Drawing and Ironing of Metal Alloy Strip Produced conventionally and Non-conventionally via Semi Solid Material Processing

A semi solid thin strip continuous casting process was used to obtain 50%wt Pb/50%wtSn strip by single and twin roll processing at speed of 15 m/min. A 50%wt Pb/50%wtSn plate ingot was also cast for rolling conventionally into strips of 1.4 mm thickness and 45 mm width for comparison with those achieved non-conventionally. This hypoeutectic alloy has a solidification interval and fusion temperature of approximately 31 degrees C and 215 degrees C respectively. The casting alloy temperature was around 280 degrees C as measured by a type K immersion thermocouple prior to pouring into a tundish designed to maintain a constant melt flow on the cooling slope during semi solid material production. A nozzle with a weir ensures that the semi solid material is dragged smoothly by the lower roll, producing strip with minimum contamination of slag/oxide. The temperatures of the cooling slope and the lower roll were also monitored using K type thermocouples. The coiled semi solid strip, which has a thickness of 1.5 mm and 45 mm width, was rolled conventionally in order to obtain 1.2 mm thick strip. The coiled thixorolled strip had a thickness of 1.2 mm and achieved practically the same width as the conventional strips. Blanks of 40 mm diameter were cut from the strips in a mechanical press, ready for deep drawing and ironing for mechanical characterization. All the strips achieved from non-conventional processing had the same mechanical performance as those achieved conventionally. The limiting drawing ratio (LDR) achieved was approximately 2.0 for all strips. Microscopy examination was made in order to observe phase segregation during processing.

The effect of thermal cycles on the mechanical properties of fiber-metal laminates

The effect of thermal-shock cycles on the mechanical properties of fiber-metal laminates (FMLs) has been evaluated. FML plates were composed by two AA2024 Al sheets (1.6 mm thick) and one composite ply formed by two layers of unidirectional glass fiber epoxy prepreg and two layers of epoxy adhesive tape of glass fiber reinforced epoxy adhesive. The set was manufactured by hand layup and typical vacuum bag technique. The curing cycle was in autoclave at 125 +/- 5 degrees C for 90 min and an autoclave pressure of 400 kPa. FML coupons taken from the manufactured plate were submitted to temperature variations between -50 and +80 degrees C, with a fast transition between these temperatures. Tensile and interlaminar shear strength were evaluated on samples after 1000 and 2000 cycles, and compared to nonexposed samples. 2000 Cycles corresponds to typical C Check interval for commercial aircraft maintenance programs. It was observed that the thermal-shock cycles did not result in significant microstructural changes on the FML, particularly on the composite ply. Similarly, no appreciable effect on the mechanical properties of FML was observed by the thermal-shock cycles. (c) 2012 Elsevier Ltd. All rights reserved.

ALLOSTERIC MODULATION BY ATP, CALCIUM AND MAGNESIUM-IONS OF RAT OSSEOUS PLATE ALKALINE-PHOSPHATASE

Alkaline phosphatase from rat osseous plate is allosterically modulated by ATP, calcium and magnesium at pH 7.5. At pH 9.4, the hydrolysis of ATP and PNPP follows Michaelis-Menten kinetics with K0.5 values of 154 muM and 42 muM, respectively. However, at pH 7.5 both substrates exhibit more complex saturation curves, while only ATP exhibited site-site interactions. Ca2+-ATP and Mg2+-ATP were effective substrates for the enzyme, while the specific activity of the enzyme for the hydrolysis of ATP at pH 7.5 was 800-900 U/mg and was independent of the ion species. ATP, but not PNPP, was hydrolyzed slowly in the absence of metal ions with a specific activity of 140 U/mg. These data demonstrate that in vitro and at pH 7.5 rat osseous plate alkaline phosphatase is an active calcium or magnesium-activated ATPase.