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.

The Influence of Intensification Pressure on the Gate Microstructure of AlSi3MgMn High Pressure Die Castings

2009 ◽  
Vol 618-619 ◽  
pp. 607-610 ◽  
Author(s):  
Somboon Otarawanna ◽  
Christopher M. Gourlay ◽  
Hans Ivar Laukli ◽  
Arne K. Dahle
Keyword(s):  
High Pressure ◽  
Die Casting ◽  
Shear Bands ◽  
Strain Localisation ◽  
Solidification Shrinkage ◽  
Intensification Pressure ◽  
Microstructural Characterisation ◽  
Die Castings ◽  
Pressure Die Casting ◽  
Gate Region

This article focuses on the influence of intensification pressure (I.P.) on the feeding through the gate during high pressure die casting (HPDC). Two values of intensification pressure, the lowest and highest possible for the HPDC machine used, were applied to cast AlSi3MgMn tensile-bar specimens. The castings produced with higher I.P. contained a lower total fraction of porosity, as expected. Microstructural characterisation of the gate region showed markedly different features in and adjacent to the gate at the two levels of I.P. used. The microstructures indicate a change in feeding mechanism with increasing I.P. At high I.P. shear band-like features exist through the gate, suggesting that strain localisation in the gate is involved in the feeding of solidification shrinkage during the I.P. stage. At low I.P. such shear bands were not observed in the gates and feeding was less effective, resulting in a higher level of porosity in the HPDC parts.

Addition of Swarf to Produce a Semi-Solid Slurry during High Pressure Die-Casting of AS9U3 Aluminum Alloy

2019 ◽  
Vol 285 ◽  
pp. 271-276
Author(s):  
Hooman Hadian ◽  
M. Haddad-Sabzevar ◽  
Mohammad Mazinani
Keyword(s):  
High Pressure ◽  
Aluminum Alloy ◽  
Solid Fraction ◽  
Die Casting ◽  
Internal Cooling ◽  
High Solid ◽  
Cooling Agent ◽  
High Solid Fraction ◽  
Semi Solid ◽  
Pressure Die Casting

An internal cooling agent is used in rapid slurry forming (RSF) process to produce a high solid fraction slurry for a short period of time. In the process used in this research, the swarf which is known to be a low enthalpy material was added to the melt as the internal cooling agent. During the process, the swarf started to melt and a semi-solid slurry with a relatively high solid fraction was formed. This slurry was formed by exchanging the enthalpies between the low and high enthalpy materials. A commercial Al-Si-Cu alloy, i.e. AS9U3 Aluminum alloy, was used in this investigation. The microscopic examination showed that the Al-Si eutectic colonies start to melt during the melting process of swarf material resulting in the formation of globular Alpha-Al grains due to the multiplication of secondary dendrites arms. The fracture of dendrites arms and the subsequent spheroidization were suggested to be the origin of non-dendritic globular grains in the final microstructure. The amount of primary globular Alpha-phase was measured by the image analysis software. The results showed that during high pressure die-casting of AS9U3 Aluminum alloy using 4 mm thick samples, around 35 percent solid has been formed at the temperature of 580 oC.

scholarly journals Assessment of Mechanisms for Particle Migration in Semi-Solid High Pressure Die Cast Aluminium-Silicon Alloys

2020 ◽  
Vol 4 (2) ◽  
pp. 51
Author(s):  
Madeleine Law ◽  
Christopher Neil Hulme-Smith ◽  
Taishi Matsushita ◽  
Pär G. Jönsson
Keyword(s):  
High Pressure ◽  
Die Casting ◽  
Particle Migration ◽  
Silicon Alloys ◽  
High Pressure Die Casting ◽  
Die Cast ◽  
Semi Solid ◽  
Pressure Die Casting ◽  
Saffman Lift Force ◽  
Externally Solidified Crystals

In semi-solid metal high pressure die casting and in conventional high pressure die casting, it is common to find a defect band just below the surface of the component. The formation of these bands is not fully understood. However, there are several theories as how they occur, and it has been suggested that segregation is caused by the migration of aluminium-rich externally solidified crystals. In the present work the formation of these bands is investigated theoretically by reviewing suitable potential mechanisms for the migration of such crystals. Two mechanisms are identified as the most probable: Saffman lift force and the Mukai-Lin-Laplace effect. However, it was not possible to identify which of these two mechanisms acted in the case studies. Further testing is required to identify the mechanism that is causing the migration of the aluminium globules and suitable tests are proposed.

Corrosion Behaviour of the Anodised A356 Aluminium Alloy Produced by the Rheo-High Pressure Die Casting Process

2014 ◽  
Vol 1019 ◽  
pp. 67-73 ◽  
Author(s):  
Levy Chauke ◽  
Kalenda Mutombo ◽  
Gonasagren Govender
Keyword(s):  
High Pressure ◽  
Aluminium Alloy ◽  
Corrosion Behaviour ◽  
Die Casting ◽  
Casting Process ◽  
Optical Microscope ◽  
High Pressure Die Casting ◽  
Semi Solid ◽  
Pressure Die Casting ◽  
A356 Aluminium Alloy

<span><p>Semi-solid metal forming of aluminium alloys has demonstrated the capability to produce near net shaped high integrity components. Anodising of these components for aesthetic and/or improved corrosion resistance is specified by some designers or users of this technology. The corrosion behaviour of fully anodised and partially anodised A356 aluminium alloy plates produced using the CSIR Rheo-High Pressure Die Casting (CSIR-RHPDC) process was investigated using immersion testing in a 3.5% NaCl solution with pH = 7. Optical microscope equipped with image analysis software and scanning electron microscope (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) were used to evaluate the behaviour of the corroded samples. The fully anodised sample showed that the anodised surface displayed some surface degradation. This degradation was more severe on the anodised surface with surface liquid segregation (SLS), but provided sufficient protection to prevent corrosion of the base metal. The partially anodised sample showed severe corrosion of the based metal with the corrosion concentrated in the silicon rich eutectic and SLS regions.</p> <span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3"> </span>

Semi-Solid High Pressure Die Casting of Metal Matrix Composites Produced by Liquid State Processing

2012 ◽  
Vol 192-193 ◽  
pp. 61-65 ◽  
Author(s):  
Lilian Ivanchev ◽  
Sigqibo Templeton Camagu ◽  
Gonasagren Govender
Keyword(s):  
High Pressure ◽  
Solid State ◽  
Metal Matrix Composites ◽  
Liquid State ◽  
Metal Matrix ◽  
Die Casting ◽  
Matrix Composites ◽  
Semi Solid ◽  
Pressure Die Casting ◽  
State Processing

There are two main technologies for manufacturing of particulate reinforced metal matrix composites (MMC), solid state and liquid state processing. The great challenge of producing cast metal matrix composites is to prevent agglomeration of particulates. This tendency is more pronounced with decreasing the particulate size to fine micro- and nano size. A method for producing MMC was successfully implemented for mixing hybrid, nano and low micron sized, reinforcing particles in an aluminium alloy matrix. The hybrid SiC particles were produced by milling 3µm to 5µm SiC particles to a particle size range between 2.5µm and 150 nm. The hybrid particles were mixed with A356 aluminium alloy under combined magneto-hydrodynamic (MHD) and mechanical stirring. The composite was then transferred to a High Pressure Die Casting (HPDC) machine in the semi-solid state. The micron size particles were found to be predominantly in the intergranular eutectic while the nano-particles were predominantly in the primary α-Al grains. Increased ultimate tensile strength, yield strength and hardness were achieved for the new cast metal matrix hybrid component (MMHC) alloy.

Rheology Forming Process of Cast Aluminum Alloys with Electromagnetic Applications

2006 ◽  
Vol 116-117 ◽  
pp. 445-448 ◽  
Author(s):  
T.W Kim ◽  
C.G. Kang ◽  
S.S. Kang
Keyword(s):  
High Pressure ◽  
Die Casting ◽  
Gas Content ◽  
Cast Aluminum ◽  
Forming Process ◽  
Cast Aluminum Alloys ◽  
Low Pressure Die Casting ◽  
Thin Walled ◽  
Semi Solid ◽  
Pressure Die Casting

This paper focuses on a rheo-forming of arm parts fabricated by an electromagnetic stirring system (EMS). This forming process takes place under high pressure of high pressure die casting and thin-walled casting is possible. Also, the productivity is higher than for low pressure die casting because of the shorter cycle time. Rheo-forming is advantageous because forming is performed in the semi-solid state with laminar flow and the gas content is low, which makes welding possible. Therefore, this paper examines arm parts with EMS and has investigated the mechanical properties after T6 and T5 heat-treatment.

Fusion Welding of Rheocast Semi-Solid Metal (SSM) Processed Aluminium Alloy 7017

2012 ◽  
Vol 192-193 ◽  
pp. 161-166 ◽  
Author(s):  
Madeleine du Toit ◽  
Patronica Letsoalo ◽  
Heinrich Möller
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Aluminium Alloy ◽  
Die Casting ◽  
Solid Metal ◽  
Hot Tearing ◽  
High Pressure Die Casting ◽  
Near Net Shape ◽  
Semi Solid ◽  
Pressure Die Casting

Near-net shape casting of wrought aluminium alloys has proven to be difficult due to a tendency towards hot tearing during cooling. Rheocasting, or semi-solid metal (SSM) processing followed by high pressure die casting (HPDC), has recently been shown to be an effective alternative to conventional die casting, yielding near-net shape wrought aluminium alloy castings with less risk of hot tearing. This casting process involves pouring the liquid metal into a processing cup, which is then transferred into a coil for induction stirring and simultaneous forced air cooling. When the metal reaches the semi-solid casting temperature, the resultant slurry is transferred to a high pressure die casting machine and cast to near-net shape. This modifies the as-cast microstructure, yielding a more globular primary phase and results in mechanical properties in the -T6 condition closely approaching those of wrought material in the same condition. Little information is currently available on the response of SSM-HPDC material to welding. This project investigated the influence of autogenous laser and gas tungsten arc welding on the microstructure and mechanical properties of aluminium 7017 after rheocasting. It is possible to successfully weld this material without solidification or liquation cracking. The effect of welding on the rheocast microstructure in the heat-affected zone and weld metal was shown, and the hardness and tensile properties of the resulting joints in the as-welded condition were tested and related to the microstructures achieved.

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