一类具强内射的正则环

研究了正则环与强CP-内射环的等价关系,证明了当R为MELT环时,R的正则性与弱正则性是等价的,同时证明了当R为约化环时,R的正则性与强CP-内射性的等价关系,并得出了当R为半本原左拟-duo环时,R的正则性、弱正则性与强CP-内射性是等价的.     

Effect of controlled forced convection on macrosegregation and structure in direct-chill casting of an aluminium alloy

Abstract

Effects of upward or downward forced flow in the centre of the sump of a 195 mm Al-alloy billet on structure and macrosegregation were studied. Introduction of forced flow in the liquid part of the sump resulted in some changes in the structure and dramatic changes in macrosegregation. Upward flow coarsened the structure and increased negative centreline segregation. Downward flow made the structure finer and more uniform across the billet, and suppressed the macrosegregation. Strong downward flow produced positive macrosegregation in the billet. The results are discussed in terms of macrosegregation mechanisms.     

Relative Adhesion Measurement for Thin Film Microelectronics Structures

There is a difference between technologically-important adhesion or practical adhesion, and fundamental or basic adhesion. What is important in the understanding of fundamental adhesion may be of insignificant interest to technology. A manufacturer is interested in how to improve the reliability of the structure being built should an interface problem exist, rather than knowing the precise value of the fundamental adhesion. It is not possible to measure fundamental adhesion for technologically-important structures due to the inability to account for all energy dissipating processes during the test. Adhesion measurements are plagued with the mode of interface loading issue: the resemblance of test interface loading to that of the actual manufactured part. What technology needs is a simple adhesion test method that is practical for product development, giving reliable information about the interface integrity. The present paper compares the value of two adhesion tests for microelectronics applications and emphasizes the importance of locus of failure analyses. A realignment of structure reliability modeling is suggested by the usage of effective fundamental adhesion instead of the standard undeterminable fundamental adhesion.     

Effect of hydrogen content,melt cleanliness and solidification conditions on tensile properties of A356 alloy

Abstract

In this study, the influence of hydrogen content, melt cleanliness and solidification conditions on the porosity distribution and mechanical properties have been investigated in a laboratory scale step mould casting with an A356 alloy. Three hydrogen levels, namely 0·10, 0·20 and 0·40 mL/100 g, were reached by treatment of the melt by Ar degassing, Ar–10H₂ and Ar water vapour mixture respectively. The hydrogen content of the melt was continuously measured. For each hydrogen level, two castings were produced, namely with and without filter. Porosity was increased with increasing hydrogen content but there was no significant effect of filtration. Moreover, similar tensile properties were achieved with different hydrogen levels and different porosity levels.     

Melt conditioning by advanced shear technology (MCAST) for refining solidification microstructures

Abstract

MCAST (melt conditioning by advanced shear technology) is a novel processing technology developed recently for conditioning liquid metal prior to solidification processing. The MCAST process uses a twin screw mechanism to impose a high shear rate and a high intensity of turbulence on the liquid metal, so that the conditioned liquid metal has uniform temperature, uniform chemical composition and well-dispersed and completely wetted oxide particles with a fine size and a narrow size distribution. The microstructural refinement is achieved through an enhanced heterogeneous nucleation rate and an increased nuclei survival rate during the subsequent solidification processing. In this paper we present the MCAST process and its applications for microstructural refinement in both shape casting and continuous casting of light alloys.     

Enhanced melt pool stirring in welding with dynamic polarised laser beam

Abstract

The stirring of the molten material during CO₂ laser welding with a dynamic polarised laser beam (DP) was studied. The key element of the set-up is a high power interference laser beam modulator for CW power rating up to 4 kW. Metallographic cross-sections and EDX analyses of the realised welds in St37 using the contrast material nickel proved the enhancement of melt pool stirring due to DP. Moreover, roughness measurements confirmed a smoothing of the top bead surface as well as a correlation between melt pool stirring and the formation of the top bead ripple structure.     

Optimisation of baffles in six strand round bloom continuous casting tundish: a physical modelling study

Abstract

Physical modelling using water in a one-third scale model was carried out to ascertain the influence of various types of baffles with inclined holes on the liquid flow in a six strand round bloom continuous casting tundish. To characterise the flow in the tundish, residence time distribution (RTD) curves were measured for different types of baffles with inclined holes. Because there is no well known analysis model to characterise the melt flow in multistrand tundishes, a new model was presented to analyse RTD curves and its reasonability was discussed. Furthermore, a new approach for quantifying the similarity among the strands was proposed and the baffle was optimised to improve the inclusion floatation and strand similarity in the tundish.     

Mixed burden softening and melting phenomena in blast furnace operation Part 3 – Mechanism of burden interaction and melt exudation phenomenon

Abstract

This research was focused on expanding the current understanding of the mechanism of softening and melting of ferrous materials including liquid exudation and high temperature material interaction. The bulk softening and melting experiments were interrupted at temperatures of interest and samples were examined for morphological changes. The results of these experiments were complimented with viscosity, surface energy and deformation rate calculations which were helpful in understanding the melt exudation phenomenon. The microstructure of the materials showed a transition from heterogeneous to homogenous state with increasing temperatures. The melt dripping was predominantly observed in olivine fluxed pellets. The exuded slag was primarily composed of an alkali rich phase which was found least viscous of the slags present in this system. The viscosity of the liquid and the structure of metallic shell jointly control the flow of liquid from the ferrous materials. Addition of magnesia in lieu of lime was found to provide beneficial impact, in particular on the rate of liquid evolution at high temperature. Based on the metallographic examination of the samples a mechanism of burden interaction is proposed.     

Evaluation of melt quality of lead free copper alloy castings using cooling curve

Abstract

The melt quality of bronze castings such as JIS CAC406 has successfully checked by observing a fractured surface of specially designed test sample on the melting spot. Lead free copper alloy castings, however, are not successfully applied by this method because the fractured surface does not show a characteristic feature or colour. In this study, the cooling curve method cast into shell cup mould was applied to evaluate and establish melt quality. Melts, under various kind of atmosphere such as over oxidised, hydrogen absorbed, flux covered, adequately deoxidised and so on, were evaluated to check the cooling curve in a cup. Owing to the melting atmosphere, liquidus temperature and solidification behaviour showed a distinct difference. Another application of cooling curve method was carried out to deoxidising process in industrially clean melt. Phosphorus content necessary for and also during deoxidising process was well determined.     

In situ observation of phase selection in undercooled Ni–Al melts

Abstract

Raney-Ni type Ni–68·5 at-% Al alloys are used for catalytic applications in the chemical industry. In this work, melt undercooling experiments were performed by means of the electromagnetic levitation technique. High-energy X-ray diffraction was used to determine the solidification pathway and the origin of microstructure peculiarities in gas atomised powders. The direct observation of the phase selection in Ni–68·5 at-% Al has unambiguously revealed the primary phase formation of β-AlNi to be independent of the level of undercooling up to a maximum of 320 K. On cooling the β-AlNi phase undergoes a fast peritectic transformation L + AlNi → Al₃Ni₂ and is therefore not found in the as-solidified microstructure.