scholarly journals Filling, Feeding and Defect Formation of Thick-Walled AlSi7Mg0.3 Semi-Solid Castings

2016 ◽  
Vol 256 ◽  
pp. 222-227 ◽  
Author(s):  
Jorge Santos ◽  
Anders E.W. Jarfors ◽  
Arne K. Dahle
Keyword(s):  
High Pressure ◽  
Cross Sections ◽  
Surface Segregation ◽  
Defect Formation ◽  
Shear Bands ◽  
Casting Machine ◽  
Shrinkage Porosity ◽  
Cast Material ◽  
Lower Porosity ◽  
Semi Solid

Aluminium semi-solid castings have gained increased attention due to their superior mechanical properties, lower porosity compared to conventional high pressure die cast material. These characteristics suggests that semi-solid casting should be suitable to produce thick-walled structural components, yet most successful applications of semisolid casting have been for thin-walled components. There is a lack of understanding on filling and feeding related defect formation for semi-solid castings with thick-walled cross-sections. In the current study an AlSi7Mg0.3 aluminium alloy was used to produce semi-solid castings with a wall thickness of 10mm using a Vertical High Pressure Die Casting machine. The RheoMetalTM process was used for slurry preparation. The primary solid α-Al fraction in the slurry was varied together with die temperature. The evaluation of the filling related events was made through interrupted shots, stopping the plunger at different positions. Microscopy of full castings and interrupted test samples were performed identifying the presence of surface segregation layer, shear bands, gas entrapment, shrinkage porosity as well as burst feeding.

Reynolds’ Dilatancy and Shear Bands in Semi-Solid Alloys

2008 ◽  
Vol 141-143 ◽  
pp. 337-342 ◽  
Author(s):  
Christopher M. Gourlay ◽  
Somboon Otarawanna ◽  
B. Meylan ◽  
Arne K. Dahle
Keyword(s):  
High Pressure ◽  
Die Casting ◽  
Shear Bands ◽  
Industrial Processes ◽  
Strain Localisation ◽  
Alloy Az91 ◽  
Magnesium Alloy Az91 ◽  
Semi Solid ◽  
Solid Alloys ◽  
Pressure Die Casting

This paper studies the conditions under which strain localisation occurs in partially solid alloys and compares localisation in rheology experiments with features in the industrial processes of Thixomolding® and high pressure die casting (HPDC). To study the fundamentals of localisation, vane rheometry, modified to measure volumetric changes, is used to shear magnesium alloy AZ91 during solidification. Deformation is found to readily localise when the initial microstructure consists of an assembly of crystals in contact. It is shown that such microstructures expand as they are sheared due to Reynolds’ dilatancy, and that localisation takes the form of dilatant shear bands. A study of microstructural features in industrial castings demonstrates that similar dilatant shear bands can form during Thixomoulding® and HPDC.

scholarly journals Influence of Microstructural Inhomogeneity on Fracture Behaviour in SSM-HPDC Al-Si-Cu-Fe Component with Low Si Content

2014 ◽  
Vol 217-218 ◽  
pp. 67-74 ◽  
Author(s):  
Mostafa Payandeh ◽  
Anders E.W. Jarfors ◽  
Magnus Wessen
Keyword(s):  
Surface Segregation ◽  
Fracture Behaviour ◽  
Tensile Specimen ◽  
Cast Material ◽  
Near Surface ◽  
Die Cast ◽  
Microstructural Inhomogeneity ◽  
Trapped Gas ◽  
Semi Solid ◽  
Si Content

In the current paper, a low-Si containing aluminium alloy (1.4-2.2% Si) was used to fabricate a complex shape telecom component using Semi-Solid High-Pressure Die Cast (SSM-HPDC), process. Microstructure and fracture characteristics were investigated. The cast material exhibited microstructural inhomogeneity, in particular macrosegregation in the form of liquid surface segregation bands in addition to sub-surface pore bands and gross centre porosity. Tensile specimen were taken from the cast components. Elongation and microstructural inhomogeneity were investigated and correlated. Fracture surfaces of the tensile specimen were examined under scanning electron microscope (SEM). The study showed that both near surface liquid segregation bands and subsurface porosity strongly affected the fracture behaviour. Dominant for loss of ductility were gross centre porosity. This centre porosity was found to be a combination of trapped gas and insufficient, irregular feeding patterns.

scholarly journals Effects of thermal gradients on defect formation during the consolidation of partially impregnated prepregs

2017 ◽  
Vol 51 (28) ◽  
pp. 3987-4003 ◽  
Author(s):  
T Centea ◽  
G Peters ◽  
K Hendrie ◽  
SR Nutt
Keyword(s):  
Cross Sections ◽  
Process Design ◽  
Defect Formation ◽  
Formation Mechanisms ◽  
Thermal Gradients ◽  
X Ray ◽  
Gradient Magnitude ◽  
Lower Porosity ◽  
X Ray Computed ◽  
Nonisothermal Conditions

We describe the effects of thermal gradients on the consolidation of partially impregnated prepregs. Laminates were cured on a heated tool in isothermal and nonisothermal conditions. Key process parameters were varied, including thermal gradient magnitude, air evacuation direction, and vacuum quality. Laminate quality was assessed using microscopy of polished cross-sections and X-ray computed tomography, and interpreted relative to the evolution of resin and prepreg properties during cure. The results show that thermal gradients influenced the rate of impregnation of the prepreg and the rate of gas transport, and affected the amount and distribution of porosity when air was not fully evacuated. Temperature distributions that led to cold regions at the ply boundaries were advantageous, typically exhibiting lower porosity than isothermal baselines. Conversely, gradients resulting in hotter-than-average part perimeters effectively sealed air within the laminate, degrading quality. The results clarify fundamental defect formation mechanisms for partially impregnated prepregs and other processes reliant on air evacuation through an unsaturated preform and provide guidelines for part, tool, and process design.

Scattering of Electrons at High - Pressure and Restoration of Image Contrast in High Pressure Scanning Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 384-385
Author(s):  
J. S. Shah ◽  
R. Durkin ◽  
A. N. Farley
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Pressure ◽  
Cross Sections ◽  
Single Scattering ◽  
Image Contrast ◽  
Experimental Scheme ◽  
Medium Resolution ◽  
Scattering Approximation ◽  
Scanning Electron

It is now possible to perform High Pressure Scanning Electron Microscopy (HPSEM) in the range 10 to 2000 Pa. Here the effect of scattering on resolution has been evaluated by calculating the profile of the beam in high pressure and assessing its effect on the image contrast . An experimental scheme is presented to show that the effect of the primary beam ionization is to reduce image contrast but this effect can be eliminated by a novel use of specimen current detection in the presence of an electric field. The mechanism of image enhancement is discussed in terms of collection of additional carriers generated by the emissive components.High Pressure SEM (HPSEM) instrumentation is establishing itself as commercially viable. There are now a number of manufacturers, such as JEOL, ABT, ESCAN, DEBEN RESEARCH, selling microscopes and accessories for HPSEM. This is because high pressure techniques have begun to yield high quality micrographs at medium resolution.To study the effect of scattering on the incident electron beam, its profile - in a high pressure environment - was evaluated by calculating the elastic and inelastic scattering cross sections for nitrogen in the energy range 5-25 keV. To assess the effect of the scattered beam on the image contrast, the modification of a sharp step contrast function due to scattering was calculated by single scattering approximation and experimentally confirmed for a 20kV accelerated beam.

scholarly journals High density of shear bands in the Vitreloy bulk metallic glass subjected to high-pressure torsion

2021 ◽  
Vol 1008 ◽  
pp. 012031
Author(s):  
Vasily Astanin ◽  
Dmitry Gunderov ◽  
Zhi Qiang Ren ◽  
Ruslan Valiev ◽  
Jing Tao Wang
Keyword(s):  
High Pressure ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
High Pressure Torsion ◽  
Shear Bands ◽  
High Density

scholarly journals EVOLUTION OF THE CARBON NANOTUBE BUNDLE STRUCTURE UNDER BIAXIAL AND SHEAR STRAINS

2020 ◽  
pp. 525
Author(s):  
Leysan Kh. Rysaeva ◽  
Dmitry V. Bachurin ◽  
Ramil T. Murzaev ◽  
Dina U. Abdullina ◽  
Elena A. Korznikova ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Shear Strain ◽  
Cross Sections ◽  
Degrees Of Freedom ◽  
Shear Bands ◽  
Volumetric Strain ◽  
Structural Evolution ◽  
Biaxial Compression ◽  
Chain Model ◽  
Nanotube Bundle

Close packed carbon nanotube bundles are materials with highly deformable elements, for which unusual deformation mechanisms are expected. Structural evolution of the zigzag carbon nanotube bundle subjected to biaxial lateral compression with the subsequent shear straining is studied under plane strain conditions using the chain model with a reduced number of degrees of freedom. Biaxial compression results in bending of carbon nanotubes walls and formation of the characteristic pattern, when nanotube cross-sections are inclined in the opposite directions alternatively in the parallel close-packed rows. Subsequent shearing up to a certain shear strain leads to an appearance of shear bands and vortex-like displacements. Stress components and potential energy as the functions of shear strain for different values of the biaxial volumetric strain are analyzed in detail. A new mechanism of carbon nanotube bundle shear deformation through cooperative, vortex-like displacements of nanotube cross sections is reported.

Microstructure Control and Structure Analysis in the Semi-Solid State of Different Feedstock Materials for the Bearing Steel 100Cr6

2006 ◽  
Vol 116-117 ◽  
pp. 177-180 ◽  
Author(s):  
Wolfgang Püttgen ◽  
Wolfgang Bleck ◽  
B. Hallstedt ◽  
Peter J. Uggowitzer
Keyword(s):  
Solid State ◽  
Grain Growth ◽  
Dynamic Mechanical Properties ◽  
Negative Influence ◽  
Bearing Steel ◽  
Cast Material ◽  
Fine Grained ◽  
Semi Solid ◽  
Hot Rolled ◽  
Feedstock Material

The bearing steel 100Cr6 in the forged and hardened condition is of great importance in industrial use. Escaping the geometry restrictions of conventional forging, the application of semi-solid metalworking (SSM) offers significantly increased design freedom. Using conventionally available rolled feedstock material with carbide banding, however, results in a higher segregation tendency during thixoforging, and thus special attention was paid to the feedstock’s “quality”. To achieve a fine-grained, globular microstructure in the semi-solid state, castings with and without the addition of 100 ppm titanium were compared with the hot rolled material. With its inherent nitrogen Ti forms TiN particles, which reduce grain-growth in austenite. The results indicate that TiN precipitates strongly affect grain growth during solid state processing, but the grain size in the semi-solid state can only be influenced for short process times. Generally the cast feedstock materials possess smaller globulites in the semi-solid state compared to forgings, so that a reduction of the sponge effect and a minimization of the segregation in produced components are expected. Since the cast material already showed a fine-grained, globulitic microstructure, the use of TiN is not recommended because of the possible negative influence of TiN on the dynamic mechanical properties.

Study on Rheo-Diecasting for In Situ Synthesized Mg2Si/AM60 Composites

2011 ◽  
Vol 383-390 ◽  
pp. 707-711
Author(s):  
Hong Yan ◽  
Yong Hu ◽  
Xiao Quan Wu
Keyword(s):  
Die Casting ◽  
Casting Machine ◽  
Chinese Script ◽  
Matrix Composites ◽  
Forming Process ◽  
Magnesium Matrix ◽  
Magnesium Matrix Composites ◽  
Mechanical Stirring ◽  
Semi Solid

Magnesium alloys have high specific strength, specific stiffness, excellent thermal conductivity and casting properties, which have a great prospects development in the industry, However, its low plasticity and ductility limited its application. Magnesium matrix composites can effectively improve its performance. Magnesium alloy die-casting is the main forming process, the conventional high-pressure die-casting (HPDC) defects in multi-cavity type, easy to volume gas, non-heat-treated. Compared with HPDC, the rheo-diecasting (RDC) process has been greatly developed for near-net shape components. In this paper, Mg2Si /AM60 composites is fabricated by in-situ synthesis and semi-solid magnesium matrix composites which are rheoformed in the die-casting machine are prepared by mechanical stirring. The results indicate that the microstructure of composites is non-dendritic and Chinese script type Mg2Si are fine distributed. The fundamental morphology of microstructure by HPDC is dendrite and liquid-phase distributed between dendrite irregularly. The RDC samples have close-to-zero porosity, less segregation, the most of semi-solid of microstructure in rheo-diecasting is spherical or as-spherical structure.

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