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About the 1996 TMS Annual Meeting: Monday Afternoon Sessions (February 5)

February 4-8 · 1996 TMS ANNUAL MEETING ·  Anaheim, California

CAST SHOP TECHNOLOGY II: Grain Refining and Phase Modification

Proceedings Info

Sponsored by: LMD Aluminum Committee

Program Organizer: Julian V. Copenhaver, Technical/Quality Manager, NSA-A Division of Southwire, P. O. Box 500, Hawesville, KY 42348

Monday, PM Room: A10

February 5, 1996 Location: Anaheim Convention Center

Session Chairperson: Dr. Ray Peterson, Reynolds Metals Company, 3326 East Second Street, Muscle Shoals, AL 35633-1258

2:00 pm

THE RELATIVE IMPORTANCE OF NUCLEATION AND GROWTH MECHANISMS TO CONTROL GRAIN SIZE IN VARIOUS ALUMINUM ALLOYS: Lennart Bäckerud, Dr. Mats Johnsson, Department of Inorganic and Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden

Control of grain size involves control of nucleation as well as growth. A critical review involving criteria for heterogeneous nucleation like particle size, abundance, stability, epitaxy and so forth will be given. Some potential candidates for heterogeneous nucleants are discussed in detail. Being able to supply a sufficient number of potent nuclei constitutes the basis for grain refinement. But the final grain size will be determined by the subsequent growth rate of -Al crystals. This has been found to be controlled by a growth restriction factor [(ki-1)miCo] which, at least for low alloying levels, seems to be additive in nature. Experimental evidence shows a range of composition where optimum grain size can be achieved. This can be related to a change over from cellular to dendritic growth in the equiaxed zone.

2:20 pm

HIGH PERFORMANCE PHOSPHORUS ADDITIVES FOR MODIFICATION OF SILICON IN Al-Si ALLOYS: Dr. Ben Heshmatpour, Shieldalloy Metallurgical Corporation, 12 West Boulevard, P. O. Box 768, Newfield, NJ 08344

A series of FeP, CuP, NiP, FeP+CuP, FeP+NiP, CuP+NiP, and FeP+CuP+NiP based additives were developed as high performance silicon modifiers for application in hyper-eutectic Al-Si alloys. These additives are manufactured by cold compaction of powder constituents with no subsequent high temperature annealing as required in production of competitive products. Primary silicon grain size of below 40 microns is achieved with low phosphorus addition rate (40 ppm) with five minutes contact time. These additives produce high performance at both high (800C) and low (730C) alloy temperatures. The particular sizing of the constituents, as developed and defined in this work, is the key factor in performance of these additives. The broad range of chemistry, form, performance, and low cost offers significant flexibility in application of these additives.

2:40 pm

THERMAL ANALYSIS OF ALUMINIUM ALLOYS AS A TOOL TO EVALUATE THE GRAIN REFINERS EFFICIENCY: Mohamed M. Hariedy, Aluminium Company of Egypt, Nag Hammadi, Egypt; Prof. A. H. Niazy, Assiut University, Faculty of Engineering, Assiut, Egypt; Prof. A. A. Nofal, Central Metallurgical Research & Development Institute (CMRDI), Al Tabin, Cairo, Egypt

Al-5%Ti-1%B and Al-5%Ti-1%C master alloys were used to grain refine some aluminium alloys. The factors that affect the efficiency of the grain refiners (addition rate, holding time, pouring temperature and metal composition) were studied. Thermal analysis was used to evaluate the efficiency of the two grain refiners in parallel with a conventional method (KBI test). The characteristic parameters of the cooling curves have been correlated to the grain size of the castings. It was found that thermal analysis could be used as a tool to evaluate the efficiency of the grain refiners of aluminium alloys prior to casting. Also, it was found that Al-5%Ti-1%C master alloy is more efficient grain refiner than Al-5%Ti-1%B.

3:00 pm

METALLURGICAL EFFECTS OF STRONTIUM ON WROUGHT 6061 ALLOYS: F. Paray, J. E. Gruzleski, Department of Mining and Metallurgical Engineering, McGill University, 3450 University Street, Montréal, Québec, Canada, H3A 2A7; Bahadir Kulunk, D. J. Zuliani, Research and Development Center, Timminco Metals, A Division of Timminco Limited, Haley, Ontario, Canada, K0J 1Y0

Aluminum extrusion alloys contain a variety of intermetallics that form during ingot solidification. In the 6061 series of alloys, iron combines with aluminum and silicon to form two types of intermetallics, [[beta]]AlFeSi and [[alpha]]AlFeSi. The type of the intermetallic that is present in these alloys will have an important bearing on the homogenization time, workability and quality of the surface finish of the parts produced from these alloys. It has been demonstrated that the addition of about 150-300 ppm of stronium to 6061 alloy will make the preferred [[alpha]] the dominant intermetallic phase at room temperature which forms during billet solidification. This enables the T4 billet homogenization time to be significantly shortened by eliminating the lengthy time, in excess of 6 hours, needed to transform the as-cast [[beta]] phase to the more desirable [[alpha]] form. It has also been demonstrated that 6061 extrusions produced from strontium-free billets require approximately 6 hours of T4 billet homogenization at 575[[ring]]C to achieve the same surface finish obtained in strontium containing extrusions with billet T4 times of less than 2 hours.

3:20 pm

RECENT ADVANCES IN UNDERSTANDING THE MECHANISM OF ALUMINIUM GRAIN REFINEMENT BY TiBAl MASTER ALLOYS: Dr. M. A. Kearns, S. R. Thistlethwaite, P. S. Cooper, London & Scandinavian Metallurgical Co. Limited, Fullerton Road, Rotherham, South Yorkshire, S60 1DL, England

Experimental data and observations from a number of complementary research programmes on the microstructure and behaviour of TiBAl grain refiners is summarized. These include analysis of the microstructure of nucleant particles within the master alloy and the final product and studies on particle agglomeration phenomena. The studies provide new insight into the nature of potent nuclei and how microstructural features influence grain refiner efficiency. A model is proposed to describe current understanding of how TiBAl grain refiners work. This is in the form of a series of stages from grain refiner addition through to solidification. The model predictions are compared with casthouse experience and lessons are drawn for manufacturers and users of grain refiners.

3:40 pm BREAK

3:50 pm

THE EFFECT OF Sr-MODIFICATION ON THE MELT HYDROGEN CONTENT AND THE HYDROGEN SOLUBILITY IN THE SOLID AND LIQUID Al-Si ALLOYS: Daryoush Emadi, Department of Mining and Metallurgical Engineering, McGill University, Montréal, Québec, Canada, H3A 2A7, and Dépt. des Sciences Appliquées, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada, G7H 2B1; J. E. Gruzleski, Department of Mining and Metallurgical Engineering, McGill University, Montréal, Québec, Canada, H3A 2A7; H. Liu, M. Bouchard, Dépt. des Sciences Appliquées, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada, G7H 2B1

Sr-modification of Al-Si alloys is normally accompanied by an increase in porosity in the casting. In an attempt to understand the nature of this problem, a study was initiated to investigate the effect of Sr on the melt hydrogen content, and the hydrogen solubility in solid and liquid Al-Si alloys. The melt hydrogen content before and after Sr addition remains essentially constant for all ranges of Si content, and Sr treatment does not introduce hydrogen into the melt. In addition, strontium does not affect the rate of hydrogen pick-up by molten Al-Si alloys. Some problems associated with hydrogen measurement in Sr-modified melts are also discussed. Hydrogen measurements in the solid state indicate that Sr does not change the equilibrium hydrogen content in solid A356 alloy. Sr addition decreases the hydrogen solubility in liquid Al-Si alloys. This decrease seems to be more significant at lower temperatures and at higher silicon contents. At lower hydrogen solubilities, the hydrogen level in the liquid reaches the solubility limit at an earlier stage of solidification. As a result, pores can nucleate earlier and grow over a longer period of time resulting in more overall porosity in the solidified alloy.

4:10 pm

DEVELOPMENT AND EVALUATION OF Al-Ti-C MASTER ALLOYS AS GRAIN REFINERS FOR ALUMINIUM: Eng. M. A. Hadia, Aluminium Company of Egypt, Nag Hammadi, Egypt; Dr. A. A. Ghaneya, Assiut University, Faculty of Engineering, Assiut, Egypt; Prof. A. H. Niazy, Assiut University, Faculty of Engineering, Assiut, Egypt

A series of Al-Ti-C master alloys with different amounts of titanium and carbon (Al-3.5%Ti-0.5%C, Al-3.5%Ti-0.7%C, and Al-5%Ti-1%C) has been developed by adding activated graphite to molten Al-Ti binary alloys. The microstructures of the developed alloys were investigated. The efficiency of the produced alloys as aluminium grain refiner was evaluated. The effects of the following factors were investigated: addition rate of each master alloy, the pouring temperature of the refined metal and the holding time before pouring. Also, the contact time for each refiner was studied. The results were significant and the refiner Al-5%Ti-1%C was the most effective.

4:30 pm

MICROSTRUCTURES AND PROPERTIES OF STRONTIUM TREATED ALUMINIUM ELECTRICAL CONDUCTOR ALLOYS: Dr. B. Closset, Timminco S.A., 44, ch. Petite-Boissière, 1208 Geneva, Switzerland; F. Paray, J. Gruzleski, McGill University, 3450 University Street, Montréal, Québec, Canada H3A 2A7; Dr. H. Mulazimoglu, American Racing, 19200 South Reyes Avenue, Rancho Dominguez, CA 90221

Aluminium electrical conductor wires must meet specified strength and electrical resistivity. In this study the composition of a typical 6201 electrical conductor alloy was altered by varying respectively the Mg, Si, and Fe levels. After a standard T4 treatment and quenching, various T6 artificial aging cycles were applied to Sr modified and unmodified conductor wires. Electrical resistivity and machanical properties were investigated. For a given chemical composition and T6 heat treatment cycle, it was shown that the tensile strength of strontium-treated alloys can be improved by 10%. The microstructure of the as-cast samples were evaluated by optical microscopy and the morphology of intermetallic compounds related to the properties.

4:50 pm

HIGH-RESOLUTION TRANSMISSION ELECTRON MICROSCOPY OF GRAIN-REFINING PARTICLES IN AMORPHOUS ALUMINIUM ALLOYS: Peter Schumacher, University of Oxford, Department of Materials, Parks Road, Oxford, OX1 3PH, United Kingdom; A. L. Greer, University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ, United Kingdom

Crystallization from aluminium melts and crystallization from amorphous aluminium alloys occur by a similar nucleation mechanism on heterogeneous nucleation sites. The low atomic mobility in the amorphous aluminium alloy permits the observation of nucleation events in high resolution electron microscopy. TiB2 particles exhibit on their basal facets a thin layer of Al3Ti which nucleates [[alpha]]-Al. All three phases reveal an epitaxial orientation relationship between their close-packed directions and planes. The underlying TiB2 substrate stretches the aluminide layer on the basal facets of the boride closer to the lattice of the aluminium. The Al3Ti thereby becomes a better nucleation substrate by better lattice matching. However, the thinly stretched layer is not only a good nucleation substrate for aluminium, but also can act as an adhesive between borides once these make physical contact.

5:10 pm

THE FLEXIBLE AlSr10/15: P. C. van Wiggen, KBM Master Alloys B.V., Kloosterlaan 2, 9936 TE Delfzijl, The Netherlands

In this paper, three different perspectives are presented to outline the success of Aluminium Strontium 10/15% rod (AlSr10/15). This rod is commercially applied for the modification of aluminium alloys. An illustration is given of the improved ductility of this super-fine microstructured alloy, thus offering the required flexibility and reliability for in-line additions made from coils. It is explained how the in-line addition method itself proves to yield multiple improvements in today's aluminium casting operations. Last minute (in-line) addition is synonymous to flexibility in production. Finally, the paper will describe the successful use of AlSr10/15 rod in the production of aluminium wires with improved flexibility (springs, for example).

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