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Improvements for a cost-effective volume production of advanced aluminum

Periodic Reporting for period 1 - ImpAl (Improvements for a cost-effective volume production of advanced aluminum)

Reporting period: 2015-07-01 to 2016-06-30

Improvements for a cost-effective volume production of advanced aluminum (ImpAl) .The ImpAl project focuses on a group of advanced aluminum materials, PLM-Al, which have been developed by Powder Light Metals GmbH (PLM) since 2000. PLM-Al exhibits significantly better property combinations in terms of strength, weight, thermal conductivity and thermal expansion than alternative materials such as steel, titanium alloys or conventional aluminum. As a consequence, these traditional materials could be replaced by PLM-Al in a wide range of applications, while generating performance gains at the same time. These advantages of PLM-Al are generated through a special nano-crystalline material structure, which is the result of a sophisticated alloying technique and an advanced production technology.

At the start of the project, however, the advantages of PLM-Al could only be realized for a limited number of high performance applications because the production capacity was too low and (in consequence) the production costs were too high for a wider market penetration. Therefore, the ImpAl project aims at expanding the production capacity for PLM-Al while reducing costs by 30-40%.
Development status and technical results after the first project year are as follows:

WP2: Up scaling of melt spinning process means:
to realize a higher metal throughput during processing
to improve material yield during processing and
to shorten or cut-off some of the process steps along the processing chain.

Feedstock manufacturing is done by melt spinning, which is a rapid solidification technology. To guarantee the highest solidification speed the wheel material has to have a very high thermal conductivity. Additionally, melt wettability has to be high and adhesion of the material after solidification has to be as low as possible. These requirements are in some way in conflict with each other so that compromises will be necessary. The up-to-date result are that ceramic are no solution, as wettability is not given and consequently there is no cooling effect at all. Solution is a full metal wheel. However, each alloy under discussion requires its own type of metal for the spinning wheel. So far, tests have been carried out with copper, copper alloys and coated aluminum wheels. There will be some ongoing tests with Ni coatings as well as with steel wheels.

Improving material yield during processing means to trigger the process parameters to the most stable conditions. This is influenced by the nozzle material and the nozzle design. So far different designs have been tested including multi whole systems. Boron nitride performed best of all materials under investigation. However, erosion of the draining wholes during pouring of the metal is still too high. So, there will be some additional tests with even more suitable material combinations.

When running the spinning process long ribbons are generated which have to be chopped into small flakes for downstream processing. By structuring the wheel surface it will be possible to cut off the chopping step during processing. The first results show that short ribbon sections can be generated directly from the spinning process. Final target is to spin off small flakes directly from the wheel. These developments are ongoing.

WP3: A set of binary AlSi alloys has been processed from powder into solid semi-finished products (mostly round bars) for material testing. Si contents are ranging from 20 % by weight up to 60 % by weight. Volumes per batch and processing itself have been done under volume production conditions in order to have realistic material properties and to gain information concerning processing costs.

Property evaluation has been done for all mechanical and physical properties and the alloys show good and consistent properties on a reproducible basis. Next is evaluation of all thermal properties like thermal expansion and thermal conductivity. Furthermore, there will be a fine tuning of the microstructures to design them more favorable for a higher thermal conductivity. First steps have been done successfully into this direction.

Finally, a cleaning system for the wheel surface has to be developed to get the process running in a continuous mode. such a system has been designed but not yet tested.

WP4: In general, AlSi alloys with a significant high Si content are very difficult to machine (saw cutting, milling and turning). However, it is most important for PLM to have detailed know-how and most extensive information available as well as long term experience in machining. Most customers, who want to do machining on their own, need to have machining instructions from PLM to be successful and PLM needs this information to operate machining on the highest quality and the lowest cost level.

First machining trials have been carried out by using cemented carbide inserts and running the cutters on a very high speed with a low feed rate. This is a successful combination, but wear of insert and cutters is tremendous. The quality of the cut surface is acceptable, but not optimal. It has been observed that new inserts and cutters need some time in action to show top perf
State of the art for melt spinning was production of continuous metal ribbons. Achievement during the first reporting period is manufacturing of ribbon sections. The next step will be the manufacturing of short flakes.

Binary aluminum silicon alloys have been developed with improved mechanical and physical properties. The next is dedicated to improving thermal conductivity.

Machining parameters have been evaluated successfully for cutting tools and inserts from cemented carbides. In this way, acceptable surface qualities can be achieved. As a next step, machining trails with PCD (poly-crystalline diamonds) will be executed.

The first level of recycling (re-melting of process scrap) has been carried out successfully. Re-melting of machining chips is in progress. Blending of machining chips with virgin feedstock (powder or flakes) will be subject of the next development step.