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Aluminium Casthouse Products
| Through improved process design, solidification
technology and alloy development, assist aluminium casthouses
to reliably produce aluminium alloy products of specified quality
which meet the application needs of CAST's partners and their
customers. |
Casthouse products are cast from primary aluminium
alloys and include billet, block, and ingot used for manufacturing.
Billet for manufacturing extrusions is used in many applications
ranging from window frames to automotive space frames. Aluminium
block is subsequently rolled to form sheet and foil, while ingot
is used for remelting and cast to form metal components such as
cylinder heads and engine blocks.
R&D activities in the Aluminium
Casthouse Sector range from fundamental research into the behaviour
of aluminium alloys to the development of innovations to improve
aluminium manufacturing processes. These activities lead not only
to a deepening of our understanding of the metallurgy of aluminium
wrought, foundry and master alloys but also leads to ways to provide
step-change improvements to existing casting technologies. There
has been an emerging demand for the provision of educational training
packages for metallurgists, engineers and production staff in the
Aluminium Casthouse Sector and this need is being addressed with
the preparation of world-class training materials.
This year CAST has focussed
on structuring Aluminium Casthouse projects
to address the various needs of the industries that influence Aluminium
Casthouse activities and to service this Sector's value chain. Two
projects within the Sector now have multiple industry partners,
reflecting the complexity of the aluminium casthouse business.
In
addition to current partnerships involved in medium- to long-term
research projects within CAST, the team in the Aluminium Casthouse
Products Sector has provided short term technical services to the
industry in general. This activity has been extended and consolidated
this year with the formation of CASTconsult,
a team that coordinates all our short term, rapid response, consulting
and metallurgical testing services.
Projects
Improved Quality of DC
Cast Billet
To develop an understanding of the effects of
alloy chemistry and billet diameter on the formation of the steady-state
as-cast billet microstructure of 6000 series alloy, and the susceptibility
of those microstructures to hot cracking.
One of the achievements of
this project has been the compilation of a comprehensive microstructural
atlas of several VDC as-cast aluminium extrusion alloys for use
by CAST's stakeholder in its production and marketing activities.
The atlas provides information on grain structure, solute and intermetallic
particle constitution and distribution within the microstructure
at locations across the diameter of a billet.
Extensive characterisation
of hot cracking susceptibility versus alloy composition, grain refinement
condition and solidification rate has been carried out using the
CAST hot cracking test rig and significant new understanding has
now emerged.
The team is developing a microstructure-based
solidification and hot tearing model that is to be validated by
VDC casting experiments. If proven, this
will be extended to optimise both alloy composition and casting
practice to improve casting pit recoveries.
Case
Study
DC Casting
- Helping casthouses to improve DC casting recovery
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Development of 6000 Series
Alloy Automotive Sheet
To develop knowledge and skills relating to automotive
sheet applications of 6000 series alloys, with the view to optimisation
of alloy composition and/or thermo-mechanical processing in order
to better meet sheet product forming and end-use requirements.
Selected 6000 series alloys
that were VDC cast during the project compared favourably to the
benchmark materials obtained from international suppliers, in terms
of key mechanical properties when exposed to an extensive range
of thermo-mechanical treatments.
Methods to minimise natural
ageing and maximise bake hardening potential without compromising
alloy formability have been investigated. Studies into the effect
of solution treatment conditions and alloying element additions
have indicated future research directions that may be pursued.
The existing project concluded
at the end of 2001. The industry partner is currently exploring
marketing options, before moving to the next stage of R&D activity.
Any future work is likely to include a sheet manufacturer as a second
industry partner.
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Fundamentals of Ingot Casting
Solidification
To build a versatile ingot casting test rig and
establish analysis techniques for investigating the ingot casting
process. Compile important heat flow data that characterises ingot
solidification, e.g. formation of air gap and changes in heat transfer
coefficients.
CAST's fully-instrumented ingot
casting test rig has been successfully developed to simulate plant
conditions and employed in studies to ascertain the manner in which
remelt ingots solidify in terms of ingot and mould temperature profiles,
heat flows and air gap formation over time. Key operating parameters
have been identified and the respective gains or losses in solidification
time measured. One of the industry partners in this project is currently
assessing these under full-scale production conditions with a view
to incrementally improving their casting machine productivity.
This project concluded in late
2001, and a new project, with the same two industry partners, was
established at the start of 2002 to build on the in-depth knowledge
and expertise gained and to develop practical step-change productivity
improvement solutions.
Case
Study
Ingot Casting - stretching the boundaries
of established casting technology
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Productivity Improvement
Ingot Casting
To develop a suitable method of increasing ingot
casting machine productivity by reducing ingot solidification time
by at least 20%.
Based on the success of the
earlier ingot casting project (reported on previous page), the partnership
between Comalco (aluminium ingot producer), o.d.t. (casting machine
manufacturer) and CAST has continued with work aimed at significantly
increasing casting machine productivity.
Several ideas and concepts
for decreasing ingot solidification time by significant levels have
been fast-fail tested on the casting rig. This process has identified
several options for further in-depth testing. Potential to reduce
ingot solidification times and increase productivity has emerged.
If successful the partnership
plans to engineer and implement the design options that yield greatest
productivity gains based on test rig data for full-scale testing
on conveyor chain ingot casters. It is hoped that application of
the findings will spin-off in new casting machine design and retrofitting
of existing machines.
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Investigation of the Wear
of Aluminium Extrusion Dies
To develop an understanding of the mechanisms
underlying the wear of extrusion dies used for aluminium alloys
and to apply this knowledge to improve die life and extrusion quality.
Techniques have been developed
to enable detailed microstructural studies of used extrusion dies
using transmission electron microscopy. The areas of focus were
the worn die land and build-up regions associated with extrusion
pickup defects. The intermetallic phases present in the worn and
build-up areas have been characterised and some unexpected observations
have been made. The work has indicated a possible avenue for developing
a new method of enhancing the wear resistance of extrusion dies.
Further work is needed to validate this approach.
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Modification of AI-Si Alloys
To develop improved modifiers for the aluminium
alloy foundry industry based on an enhanced understanding of the
nucleation and growth mechanisms of Al-Si eutectic and how these
interact with porosity formation.
This year, Comalco (a primary
aluminium and alloy producer) joined the project as the second industry
partner with the original partner, London & Scandinavian Metallurgical
(LSM) (a master alloy manufacturer). Building on CAST expertise
related to eutectic solidification, further studies have been carried
out to ascertain the possibility of physically controlling the nucleation
and growth of Al-Si eutectic cells. In conjunction with metallographic
studies of the eutectic structure and porosity distribution, electron
back scattered diffraction (EBSD) techniques have been used to characterise
the orientation relationships between eutectic aluminium and other
phases present.
Once suitable eutectic control mechanisms are
identified, prototype master alloys will be produced by one partner,
and incorporated into foundry alloys by the other. Later alignment
with a third downstream foundry user will complete the value chain
and allow full product testing.
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