1997 TMS Annual Meeting: Wednesday Session

CAST SHOP TECHNOLOGY: Session VII: Metal Treatment--Inclusion Removal

Session Chairperson: Gregory J. Hildeman, Aluminum Company of America, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069

2:00 pm

MORPHOLOGICAL ASPECTS OF INCLUSIONS IN AA3104 D&I CAN STOCK ALLOY: Xiangwen Wang, Manufacturing Technology Laboratory, Corporate Research & Development, Reynolds Metals Company, 3326 E. 2nd St., Muscle Shoals, AL 335661

Metallic and non-metallic inclusions have long been recognized as one of the most important quality issues for aluminum can body alloys. Existence of the inclusions is often the cause of pinholes and high tear-off rate in the canmaking process. They also impose severe complications for alloy down-gauging. This paper presents the morphological aspects of the major inclusions commonly seen in AA3104 can stock alloy. The potential sources which may introduce inclusions in the alloy are also described. Some case studies are conducted to isolate the inclusions for characterization. The results can be utilized for understanding the mechanism of the inclusion formation and selection of proper materials in dealing with the molten alloy prior to ingot casting in order to minimize or eliminate the potential inclusion sources.

2:20 pm

USE OF MULTIPLE MOLTEN METAL QUALITY INDICATORS TO ASSESS IMPACT OF FILTRATION AND FLUXING MODIFICATIONS ON INTERNAL QUALITY OF PLATE PRODUCTS: Michael M. Niedzinski, Reynolds Metals Company, McCook Sheet & Plate Plant, 1st Avenue & 47th Street, McCook, IL 60525-3294

Feasibility of modifying the molten metal filtration system used on aircraft plate alloys was examined using LiMCA, LAIS, AlSCAN and Ramsley tests with attempts to correlate to final ultrasonic quality of the final product. Simultaneously, impact of alternate fluxing system on an ultrasonic quality was examined using aforementioned tests. Sensitivity of the tests vis-à-vis practice changes is discussed.

2:40 pm

EVALUATION OF THE EFFICIENCY OF CERAMIC FOAM AND PARTICLE BONDED CARTRIDGE FILTRATION SYSTEMS: N.J. Keegan, Foseco International Ltd., 285 Long Acre, Nechells, Birmingham B7 5JR, United Kingdom; W. Schneider, H.-P. Krug, VAW aluminium AG, Georg-von-Boeselager-Str.25, D-53117 Bonn, Germany; V. Dopp, Foseco GmbH, Postfach 1220, D-4280 Borken, Germany

A joint programme was set up between Foseco and VAW aluminium AG in order to establish data on the relevant positions of fine foam ceramic filters and more specifically, to investigate the performance characteristics of bonded particle tube cartridge filter systems. The object of this work was to generate fundamental data on the filtration efficiency of a number of in-line treatment units used singly and in combination. The impact of these treatments on metal quality was determined by LiMCA, PoDFA and LAIS for carefully controlled plant conditions. This paper expands on the result of the first phase of the programme which was presented to TMS in 1996. It goes on to present results of inclusion size distribution removal data for medium and fine pore CFF´s and for the cartridge tube filter. Results of metallographic examination of spent tubes and ceramic foam reported along with PoDFA data of typical metal. After summarizing the relative efficiencies of each of these systems it also includes results of the impact of a degassing unit run alone and in combination with a ceramic foam filter.

3:00 pm

CHARACTERISTICS OF PARTICULATE CAPTURED BY A RIGID TUBE FILTER: Glenn Mabry, W.C. Setzer, KB Alloys Inc., Corporate Technology, 3293 McDonald Road, Robards, KY 42452; John Kaems, Aluminum Company of America, Alcoa South Plant, 300 North Hall Road, Alcoa, TN 37701; Douglas Granger, Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15069

Spent rigid tube filter sections were examined following a number of alloy 3004 casts. Examination revealed the presence of the phases normally found in 3004 which formed during solidification, as well as the capture of salt, oxide and grain refiner particulate. Chemical and SEM analysis revealed that, for the most part, two mechanisms of filter blockage appear to be operative. In addition to filter cake buildup, on a portion of the tube, some of the 1-2 micron grain refiner particulate have reacted within the filter body forming coarser complexes. The blockage mechanisms and their impact on filter life and filter design and usage are discussed.

3:20 pm

INFLUENCE OF Al-Ti GRAIN REFINER ON THE FILTER LIFE: T. Yoshida, K. Kakimoto, Mitsui Mining & Smelting Co. Ltd., TKR Division, 2-26-6 Higashinihonbashi, Chuo-ku Tokyo 103, Japan; A. Hane, T. Nishizaka, K .Hoshino, Mitsui Mining & Smelting Co. Ltd., Corporate R&D Center, 1333-2 Haraichi, Ageo-shi Saitama 362, Japan

It has been known that grain refiner such as Al-Ti and Al-Ti-B would influence on the filter life in molten aluminum filtration. A new experimental technique was conducted to make clear the influence of Al-Ti master alloy on a filter life of Rigid Media Filter (RMF). It is shown that the concentration of titanium in the grain refiner and holding time after adding the grain refiner affect the filter life.

3:40 pm BREAK

3:50 pm

DEPOSITION OF PARTICLES TO A BUBBLE: Elin Haugland, Thorvald A. Engh, Norwegian University of Science and Technology, Department of Metallurgy, Alfred Getz Vei 2b, N-7034 Trondheim, Norway

Experiments have been performed to study turbulent deposition of particles to a bubble. Water, containing particles, flowed down through a column. Bubbles were let into the column through a glass capillary tube in the lower part of the column, and then held at the capillary tube. The experiments were carried out with quartz particles in both clean distilled water and in water which amine was added. The bubble was allowed to rise into a collector tube. To determine the amount of particles collected by the bubble, the water/particle dispersion was filtered and the remaining mass was weighted. Velocities and turbulence were measured by laser doppler velocimetry. Particle-bubble collisions were studied with a high-speed videocamera. The results indicate that particle collection on the bubbles reaches saturation. The particles seem to have a certain residence time at the bubble surface, before they leave the bubble.

4:10 pm

ENHANCED FLOTATION OF INCLUSIONS TO BUBBLES DUE TO TURBULENCE: Rune Gammelsæter, Stein Tore Johansen, SINTEF Materials Technology, N-7034 Trondheim, Norway; Knut Bech, The Norwegian University of Science and Technology, N-7034 Trondheim, Norway

Experimental results indicate that turbulence may enhance the flotation rate of non-metallic inclusions to bubbles significantly. In this paper possible flow phenomena responsible for such effects are investigated. We recognize that the turbulent flow consists of a spectrum of eddy sizes. The eddies larger than the bubble diameter can only displace the bubble. Only the smaller eddies contribute to an enhanced turbulent deposition of inclusions. The turbulent flow over single bubbles are computed and the turbulent trajectories of inclusions approaching the bubbles are calculated. The resulting collection efficiencies are discussed and compared to available experimental results.

4:30 pm

KINETICS OF INCLUSION REMOVAL FROM MOLTEN ALUMINUM UNDER AN APPLIED ALTERNATING MAGNETIC FIELD: Ashish D.Patel, Nagy El-Kaddah, Department of Metallurgical & Materials Engineering, The University of Alabama, P.O. Box 870202, Tuscaloosa, AL 35487-0202

Electromagnetic filtration is an emerging technology for purification of molten metals. This particle separation method relies on the huge difference in the electrical conductivity of the metal and non-metallic inclusions to drive the motion of the under an applied force field. The principle of electromagnetic separation will be briefly reviewed together with methods of generating a force field in molten metals. Also described is an induced current separator for the removal of non-metallic inclusions from molten aluminum. The key feature of this system is that the force field has no stirring component, which is necessary to prevent particle entrapment within flow eddies. The system was used to investigate the kinetics of inclusion removal from molten aluminum using 100 and 200µ size particles at low applied magnetic field of 0.015 T. The results show complete removal of these inclusion particles under these conditions and particle migration in the melt occurs in a direction opposite to the force field, as predicted by the theory. Analytical expression was developed to predict the rate of inclusion removal in induced current systems. The experimentally determined rate was found to be in good agreement with theoretical predictions. The scale-up of the system for industrial applications will be discussed.

4:50 pm

CONSISTENCY OF INCLUSIONS IN PURE MAGNESIUM: Per Bakke, Dag Ove Karlsen, Norsk Hydro a.s., P.O. Box 2560, N-3901 Porsgrunn, Norway; Jean-Alain Laurin, André Provost, Norsk Hydro Canada Inc., 7000 boul. Raoul-Duchesne, Bécancour, Québec, Canada G0X 1B0

In order to examine the consistency of metal quality with respect to oxide inclusions, salts and intermetallic particles, filter samples were taken randomly from the casting chamber during normal production of pure magnesium at Norsk Hydro Canada in 1995. The contents of oxide particles, oxide films, salts and intermetallic particles were measured by optical microscopy and image analysis of the sliced and polished filter samples. The results indicate that the contents of oxide particles, oxide films, salts and intermetallic particles are low and consistent; normally well below 1 mm3/kg for all types of inclusions. Oxide inclusions and intermetallic particles are usually smaller than 50 µm and 20 µm, respectively. The filter sampling method and analysis technique used in the quantitative microscopy are discussed in some detail, emphasising advantages and drawbacks. The impact of the most common inclusions in pure magnesium on aluminium alloy quality is discussed from a thermodynamic point of view.

5:10 pm

THE EFFECTS OF MAGNESIUM, ATMOSPHERE COMPOSITION, AGITATION AND TEMPERATURE ON THE SURFACE OXIDE FILM FORMATION AND MELT INCLUSION CONTENT IN Al-Mg ALLOYS: Daryoush Emadi, Mihriban Pekguleryuz, Alcan-UQAC Chair in Solidification and Metallurgy of Aluminum, University of Quebec at Chicoutimi, Local 4-333 Chicoutimi, Quebec, Canada G7H 2B1

To obtain high quality ingots, the generation of inclusions must be prevented during the various stages of liquid metal manipulation. In an attempt to understand the nature of oxide film generation, the oxidation behaviour of Al-Mg melts with different Mg contents of 1 wt%, 3 wt% and 5 wt% were studied in air, argon and carbon dioxide. Moreover, the effects of agitation and temperature on the nature of melt surface oxide films were investigated. For each condition, the growth process and the morphology of the surface oxide films behaved differently. In addition, this study used the Liquid Metal Cleanliness Analyzer (LiMCA) and Porous Disk Filtration Apparatus (PoDFA) to investigate the effect of melt agitation and Mg content on the melt inclusion content. The results indicate that agitation and magnesium increase both the melt inclusion content and the average inclusion size. In addition, the oxide film removal from the surface of the melt affects the melt oxidation behaviour significantly.