Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys

Abstract

Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton's like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration.     

Ionic Polymer–Metal Composite of Thermo-Responsive Selemion AMV Coated with Gold Foils

Highly dehydrated gold foil-coated Selemion AMV exhibited large bending under electrical stimulation. It bore a relatively well-controllable bending characteristic by the control of electrical stimulation. Conventional ionic polymer–metal composite bending mechanisms could not explain its bending behavior. We speculated that Joule heat played a central role in the bending induction. Employing the classical lamination theory, the influence of Joule heat on its bending behavior was theoretically investigated. The results calculated roughly agreed with the experimental results. Hence, we concluded that the Joule heat was the primary cause of bending induction.     

14—REVERSIBLE AND IRREVERSIBLE DIMENSIONAL CHANGES IN WOOL FABRICS

An account is given of experiments made with an apparatus constructed for recording, simultaneously and continuously, weight and length changes during the drying and steaming of fabrics. Hot air at a temperature of 100 or 115°C was used in the drying experiments. Steaming was done under the same conditions. The maximum level to which the moisture regain could be increased with steam varied with the fabric construction. Below this maximum level, absorption and desorption experiments with relaxed fabrics gave reproducible and identical hygral-expansion curves. Moisture-regain changes below saturation caused by steaming and drying did not completely release the strain in fabrics cohesively set. The difference resulting from the use of saturated and superheated steam was negligible. The lower the temperature during cohesive setting, the less resistant was the set towards moisture-regain changes.     

Evaluation of through thickness residual stress in multipass butt welded joint by using inherent strain

Abstract

The through thickness residual stress of an eight pass butt welded plate joint is evaluated using inherent strain analysis. The residual stress distribution is obtained in detail along the thickness direction from measurements using multiple strain gauges. The residual stresses agree with the results of the thermal elastic–plastic analysis as well as the values obtained by direct measurement of the specimen surface, which is not used in inherent strain analysis. These results indicate that both inherent strain analysis and thermal elastic–plastic analysis are effective in evaluating through thickness residual stress. Therefore, each analysis method should be chosen after considering the object to be evaluated and the characteristics to be analysed.     

Estimation of air gap and heat transfer coefficient at different faces of Al and Al–Si castings solidifying in permanent mould

Abstract

In the casting processes, the heat transfer coefficient at the metal/mould interface is an important controlling factor for the solidification rate and the resulting structure and mechanical properties. Several factors interact to determine its value, among which are the type of metal/alloy, the mould material and surface conditions, the mould and pouring temperatures, casting configuration, and the type of gases at the interfacial air gap formed. It is also time dependent. In this work, the air gap formation was computed using a numerical model of solidification, taking into consideration the shrinkage and expansion of the metal and mould, gas film formation, and the metallostatic pressure. The variation of the air gap formation and heat transfer coefficient at the metal mould interface are studied at the top, bottom, and side surfaces of Al and Al–Si castings in a permanent mould in the form of a simple rectangular parallelepiped. The results show that the air gap formation and the heat transfer coefficient are different for the different casting surfaces. The bottom surface where the metallostatic pressure makes for good contact between the metal and the mould exhibits the highest heat transfer coefficient. For the sidewalls, the air gap was found to depend on the casting thickness as the larger the thickness the larger the air gap. The air gap and heat transfer coefficient also depend on the surface roughness of the mould, the alloy type, and the melt superheat. The air gap is relatively large for low values of melt superheat. The better the surface finish, the higher the heat transfer coefficient in the first few seconds after pouring. For Al–Si alloys, the heat transfer coefficient increases with increasing Si content.     

Investigation of thermal properties of Al–Si matrix reinforced fine SiCp composites

Abstract

The characterisation of thermal expansion coefficient and thermal conductivity of Al–Si matrix alloy and Al–Si alloy reinforced with fine SiC_p (5 and 20 wt-%) composites fabricated by stir casting process are investigated. The results show that with increasing temperature up to 350°C, thermal expansion of composites increases and slowly reduces when the temperature reaches to 500°C. The values of both thermal expansion and conductivity of composites are less than those for Al–Si matrix. Microstructure and particles/matrix interface properties play an important role in the thermal properties of composites. Thermal properties of composites are strongly dependent on the weight percentage of SiC_p.     

Thermal properties of new copper matrix composite reinforced by β-eucryptite particulates

Abstract

Cu matrix composites with different volume fraction of Ag coated β-eucryptite particulates were successfully fabricated by powder metallurgy method. Low thermal expansion coefficient and high thermal conductivity were attained simultaneously in the new Cu matrix composite. The microstructure of β-eucryptite–Cu composite was studied by scanning electron microscope and transmission electron microscope. The thermophysical properties of β-eucryptite–Cu composites were analysed by means of thermal dilatometer and diathermometer. No interfacial reaction products between β-eucryptite and Cu were found in the composite. The research indicates that β-eucryptite, which has a negative coefficient of thermal expansion, is a useful reinforcement, which can remarkably reduce the coefficient of thermal expansion of Cu matrix composite. The effects of volume fraction of β-eucryptite particulates on the thermal expansion coefficient and thermal conductivity of the composite were investigated.     

Microstructure and physical properties of Al/diamond composite fabricated by pressureless infiltration

Abstract

The Al/diamond composite was fabricated using a pressureless infiltration method. The microstructure and physical properties of the composite were investigated. The composite has a very low coefficient of thermal expansion (CTE) of 3·9 × 10^?6 K^?1. The thermal conductivity (TC) of the composite is 12% higher than that of the Al alloy matrix. The lower TC of the composite than the expected value was attributed to the existence of interfacial low conducting phases and the porocity of the composite.     

Diffusion annealing and laser surface alloying with aluminium to enhance oxidation resistance of carbon steels

Abstract

The oxidation behaviour of a carbon steel was investigated after modifying the surface in three different ways, namely: (a) physical vapour deposition of aluminium by a resistance heating evaporation technique; (b) diffusion annealing of predeposited aluminium; and (c) laser surface alloying with predeposited aluminium. While diffusion annealing at a temperature of 1023 K was found to result in the formation of Al₁₃Fe₄ and Al₅Fe₂ phases, laser surface alloying resulted in a case containing Al₁₃Fe₄ and Al₂Fe phases. The oxidation behaviour of all the above specimens was studied at 873 K for a total duration of up to 200 h. The mass change and morphological modifications to the surface were monitored at regular intervals of 25 h. It was observed that aluminising results in a substantial enhancement of the high temperature oxidation resistance in comparison with the untreated base material, by virtue of the superior oxidation resistance of the intermetallic phases formed on the surface. Furthermore, laser surface alloying was found to result in better oxidation resistance, in comparison with diffusion annealed and as deposited specimens.     

Plans for the future for the Packaging,Transport, Storage and Security of Radioactive Material Journal

Abstract

The regulatory driven design of radioactive material transportation packages leads package vendors to perform analyses that demonstrate the ability of packages to meet the regulatory requirements. For risk assessment and communication, the analysis of package response to thermal environments that are more severe than those described in the regulations is required. In general, experimental and analytical assessments of casks exposed to thermal insults other than the regulatory environment are performed in the USA by the Department of Energy national laboratories. This paper provides a brief summary of some recent thermal analyses of spent fuel transportation packages exposed to thermal environments different from regulatory standards. The analyses were performed by Sandia National Laboratories under several different projects for multiple customers. These analyses examined the response of spent fuel packages exposed to severe thermal environments different from the regulatory hypothetical accident condition. One assessment determined the response of four generic casks to very long duration engulfing fires. The results from these analyses included fire durations necessary to reach critical temperatures of the fuel and seals. In another assessment, two certified spent fuel casks were analysed for exposure to 1 h pool fires. The height of the cask above the pool was varied to study the effect of the vapour dome on the heating of the casks. Another assessment investigated the effect of offset long duration fires on rail cask performance, which showed that casks can withstand offset fires of much longer duration than the regulatory fire. Other assessments examined the response of packages to thermal environments resulting from propane fires and realistic liquid hydrocarbon fires that included various positions of the transportation rail car in the simulation.