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DEVELOPMENT OF A NEW ALUMINIUM GRAIN REFINER FOR FOIL LITHOGRAPHIC SHEET AND AIRCRAFT PLATE APPLICATIONS

Objective


A process for the production of AlTiC grain refiners was developed and an alloy, which nearly met set specification of the microstructure apart from the maximum size of the TiC particles was produced as to be seen in Table 1. This newly developed AlTiC master alloy has a composition of 5 % Ti und 0,25 % (LSM).
D.C. casting tests on pilot and industrial scale with this alloy showed a grain refinement performance comparable to boron based commercial master alloys at same addition rates. Produced litho sheets revealed no difference in quality in comparison to commercially produced litho sheets (VAW). The work undertaken to improve the microstructure quality of the AlTiC master alloy regarding maximum TiC particle size was not successful up to date (LSM, KBM). Therefore the full scale testing campaigns could not be carried out (VAW, Hoogovens).
The formation of TiC in a master alloy takes place by reaction of Ti with carbon particles in the melt, forming a compact Ti shell surrounding the carbon. Nucleant of the (-aluminium is TiC. The agglomeration tendency of TiC is less than the tendency of TiB2 of commercial AlTiB master alloys. In Zr containing high strength Al alloys TiC shows no poisoning effect of the grain refinement (TUB).
The established standard test method for the evaluation of the grain refining efficiency bases on the so called Alcoa Cold Finger Test (ACF-T). For the preparation of the microstructure of the master alloy and for test of the TiC agglomeration behaviour new methods have been developed. The basis of the agglomeration test is a melt spinning process. Standard test procedure descriptions were prepared (TUB).
This project intends to develop a new grain refiner, essentially composed of A1, Ti and C, methods of quality control for elimination of casting defects and for property improvements of wrought and cast products of aluminium ant its alloys, ant to verify the improvements in foil, lithographic sheet and aircraft plate applications through large scale industrial tests. Presently available commercial grain refiners are master alloys of A1, Ti and B containing coarse TiB2 particles, which cause porosities in foils, surface defects in sheets and high cracking rates in continuously cast ingots of high strength aluminium alloys containing Cr and/or Zr. Moreover, the scrap value is progressively depreciated due to repeated grain refining treatments with the conventional methods, which also involve use of fluoride salts for the production of grain refiners causing evolution of poisonous gases.

The objective is to develop new grain refiners initially on laboratory and pilot plant scales, followed by large scale production with consistent quality. Small and full scale casting campaigns using the new grain refiners will be carried out, supported by laboratory evaluation, followed by production and evaluation of foils, litho, and high strength aluminium semis for aerospace structural applications.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Vereinigte Aluminium Werke AG
Address
Georg-von-boeselager-straße 25
53117 Bonn
Germany

Participants (4)

HOOGOVENS ALUMINIUM BV
Netherlands
Address
Uilenstede 475
1183 AG Amstelveen
KAWECKI-BILLITON METAALINDUSTRIE BV
Netherlands
Address
Kloosterlaan 2 P.o. Box 156
9930 AD Delfzijl
London & Scandinavian Metallurgical Co Ltd
United Kingdom
Address
Fullerton Road
S60 IDL Rotherham
TECHNISCHE UNIVERSITÄT BERLIN
Germany
Address
Straße Des 17 Juni 135
1000 Berlin