Rheo-processing of an alloy specifically designed for semi-solid metal processing on the Al-Mg-Si system

Semi-solid metal (SSM) processing is a promising technology for forming alloys and composites to near-net shaped products. Alloys currently used for SSM processing are mainly conventional aluminium cast alloys. This is an obstacle to the realisation of full potential of SSM processing, since these alloys were originally designed for liquid state processing and not for semi-solid state processing. Therefore, there is a significant need for designing new alloys specifically for semi-solid state processing to fulfil its potential. In this study, thermodynamic calculations have been carried out to design alloys based on the Al-Mg-Si system for SSM processing via the ‘Rheo-route’. The suitability of a selected alloy composition has been assessed in terms of the criteria considered by the thermodynamic design process, mechanical properties and heat treatability. The newly designed alloy showed good processability with rheo-processing in terms of good control of solid fraction during processing and a reasonably large processing window. The mechanical property variation was very small and the alloy showed good potential for age hardening by T5 temper heat treatment after rheo-processing

A Multilayer Monte Carlo Model for the Investigation of Optical Path and Penetration Depth at Different Perfusion States of the Colon

There is a great interest in monitoring the oxygen supply delivered to the colon. Insufficient oxygen delivery may lead to hypoxia, sepsis, multiorgan dysfunction and death. For assessing colonic perfusion, more information and understanding is required relating to the light-interaction within the colonic tissue. A multilayer Monte Carlo model of a healthy human colon has been developed to investigate the light-tissue behavior during different perfusion states within the mucosal layer of the colon. Results from a static multilayer model of optical path and reflectance at two wavelengths, 660 nm and 880 nm, through colon tissue, containing different volume fractions of blood with a fixed oxygen saturation are presented. The effect on the optical path and penetration depth with varying blood volumes within the mucosa for each wavelength has been demonstrated. The simulation indicated both wavelengths of photons penetrated similar depths, entering the muscularis layer

Fabrication of metal matrix composites under intensive shearing

Current processing methods for metal matrix composites (MMC) often produces agglomerated reinforced particles in the ductile matrix and also form unwanted brittle secondary phases due to chemical reaction between matrix and the reinforcement. As a result they exhibit extremely low ductility. In addition to the low ductility, the current processing methods are not economical for producing engineering components. In this paper we demonstrate that these problems can be solved to a certain extent by a novel rheo-process. The key step in this process is application of sufficient shear stress on particulate clusters embedded in liquid metal to overcome the average cohesive force of the clusters. Very high shear stress can be achieved by using the specially designed twin-screw machine, developed at Brunel University, in which the liquid undergoes high shear stress and high intensity of turbulence. Experiments with Al alloys and SiC reinforcement reveal that, under high shear stress and turbulence conditions Al liquid penetrates into the clusters and disperse the individual particle within the cluster, thus leading to a uniform microstructure

Solidification and processing of aluminium based immiscible alloys

Copyright @ 2009 TMSThe Al-Sn and Al-Pb based immiscible alloys have significant potential for bearing applications. However, the mixing and understanding of solidification process for immiscible alloys have been long standing challenges for their development. This paper presents solidification and microstructural evolution of the Al-Sn-Cu alloys and also describes the mechanism of effective mixing by the intensive shearing. The experimental work was also focused on analyzing the effects of shear rate, temperature and time on Sn droplets size and their distribution. Results have been compared with earlier study on Al-Si-Pb alloys. Experimental results suggest that the intensive shearing process produces homogeneous and finely dispersed Sn and Pb droplets.This work was funded by the EPSRC and DTI

RNA-Binding Protein CELF1 Controls MARCKS mRA Translation in Oral Cancer Cells

Post-transcriptional gene regulation plays an important role in controlling gene expression patterns in mammalian cells. CUG-binding and Embryonic Lethal vision-type RNA-binding protein 3 (ETR)-like Factor (CELF1), also known as CUGBP1, is a RNA-binding protein involved in post-transcriptional gene regulation through nuclear (alternative splicing) and cytoplasmic (mRNA turnover and translation) mRNA processing events. Primarily, CELF1 is known for its contribution to the development of myotonic dystrophy (DM1). But, published observations from our laboratory and others determined that CELF1 is overexpressed in head and neck squamous cell carcinoma (HNSCC) as well as multiple other cancers. Unpublished proteomic pulsed-stable isotope labeling by amino acids in cell culture (pSILAC) from our laboratory, has identified approximately putative 1350 CELF1 target proteins were controlled at the mRNA translation level in UM74B oral cancer cells. The pSILAC data and subsequent ribosome profiling validation experiments revealed that the protein expression of MARCKS (Myrisoylated alanine-rich kinase C substrate) is significantly reduced upon CELF1 knockdown in comparison to control oral cancer cells. MARCKS is known to play an important role in cell shape, cell motility, secretion, transmembrane transport, and regulation of the cell cycle in cancer cells. We have determined that MARKCS protein is overexpressed in HNSCC cell lines compared to primary normal oral keratinocytes. Moreover, CELF1 directly controls the expression of MARCKS, but its mRNA levels remain unchanged in oral cancer cells. CELF1 ribonucleoprotien immunoprecipitation (RNP-IP) experiments determined that MARCKS mRNA is directly associated with CELF1. The cell migratory role of MARCKS was evaluated by a scratch wound healing assay and transwell migration assay. Depletion of CELF1 and MARCKS independently resulted in reduction of cell migration. Moreover, overexpression of CELF1 in normal non-malignant human oral keratinocyte cells resulted in overexpression of MARCKS and enhanced cell migration. Finally, shRNA-mediated reduction of CELF1 in association with exogenously expressed MARCKS in oral cancer cells, we were able to rescue the CELF1-mediated cell migration phenotype. In conclusion, our results demonstrate that CELF1 controls cell migration through regulating MARCKS protein translation in oral cancer cells

Computational prediction of the refinement of oxide agglomerates in a physical conditioning process for molten aluminium alloy

Physically conditioning molten scrap aluminium alloys using high shear processing (HSP) was recently found to be a promising technology for purification of contaminated alloys. HSP refines the solid oxide agglomerates in molten alloys, so that they can act as sites for the nucleation of Fe-rich intermetallic phases which can subsequently be removed by the downstream de-drossing process. In this paper, a computational modelling for predicting the evolution of size of oxide clusters during HSP is presented. We used CFD to predict the macroscopic flow features of the melt, and the resultant field predictions of temperature and melt shear rate were transferred to a population balance model (PBM) as its key inputs. The PBM is a macroscopic model that formulates the microscopic agglomeration and breakage of a population of a dispersed phase. Although it has been widely used to study conventional deoxidation of liquid metal, this is the first time that PBM has been used to simulate the melt conditioning process within a rotor/stator HSP device. We employed a method which discretizes the continuous profile of size of the dispersed phase into a collection of discrete bins of size, to solve the governing population balance equation for the size of agglomerates. A finite volume method was used to solve the continuity equation, the energy equation and the momentum equation. The overall computation was implemented mainly using the FLUENT module of ANSYS. The simulations showed that there is a relatively high melt shear rate between the stator and sweeping tips of the rotor blades. This high shear rate leads directly to significant fragmentation of the initially large oxide aggregates. Because the process of agglomeration is significantly slower than the breakage processes at the beginning of HSP, the mean size of oxide clusters decreases very rapidly. As the process of agglomeration gradually balances the process of breakage, the mean size of oxide clusters converges to a steady value. The model enables formulation of the quantitative relationship between the macroscopic flow features of liquid metal and the change of size of dispersed oxide clusters, during HSP. It predicted the variation in size of the dispersed phased with operational parameters (including the geometry and, particularly, the speed of the rotor), which is of direct use to experimentalists optimising the design of the HSP device and its implementation.This research is financially supported by the EC FP7 project “High Shear Processing of Recycled Aluminium Scrap for Manufacturing High Performance Aluminium Alloys” (Grant No. 603577)

Processing of advanced Al/SiC particulate metal matrix composites under intensive shearing – A novel rheo process

Particulate Metal Matrix Composites (PMMCs) have attracted interest for application in numerous fields. The current processing methods often produce agglomerated particles in the ductile matrix and as a result these composites exhibit extremely low ductility. The key idea to solve the current problem is to adopt a novel Rheo-process allowing the application of sufficient shear stress () on particulate clusters embedded in liquid metal to overcome the average cohesive force or the tensile strength of the cluster. In this study, cast A356/SiCp composites were produced using a conventional stir casting technique and a novel Rheo-process. The microstructure and properties were evaluated. The adopted Rheo-process significantly improved the distribution of the reinforcement in the matrix. A good combination of improved Ultimate Tensile Strength (UTS) and tensile elongation (ε) is obtained

Isomer-delayed γ -ray spectroscopy of A=159-164 midshell nuclei and the variation of K -forbidden E1 transition hindrance factors

Excited states have been studied in Sm159, Sm161, Sm162 (Z=62), Eu163 (Z=63), and Gd164 (Z=64), populated by isomeric decay following U238 projectile fission at RIBF, RIKEN. The isomer half-lives range from 50 ns to 2.6μs. In comparison with other published data, revised interpretations are proposed for Sm159 and Eu163. The first data for excited states in Sm161 are presented, where a 2.6-μs isomer is assigned a three-quasiparticle, Kπ=17/2- structure. The interpretation is supported by multi-quasiparticle Nilsson-BCS calculations, including the blocking of pairing correlations. A consistent set of reduced E1 hindrance factors is obtained. Limited evidence is also reported for isomeric decay in Sm163, Eu164, and Eu165

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

MCAST (melt conditioning by advanced shear technology) is a novel processing technology developed recently by BCAST at Brunel University 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 to 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