Effects of Melt Convection and Solid Transport on Macrosegregation and Grain Structure in Equiaxed Al-Cu Alloys

TITLE AND SUBTITLE:
Effects of Melt Convection and Solid Transport on Macrosegregation and Grain Structure in Equiaxed Al-Cu Alloys

AUTHOR(S):
Rodney S. Rerko, Henry C. de Groh, III, and Christoph Beckermann

REPORT DATE:
May 2000

FUNDING NUMBERS:
WU-101-13-0A-00

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
John H. Glenn Research Center at Lewis Field
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-12217

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-2000-210020

SUPPLEMENTARY NOTES:
Rodney S. Rerko and Christoph Beckermann, The University of Iowa, Department of Mechanical Engineering,
2412 Seawaus Center, Iowa City, Iowa 52242-1000 and Henry C. de Groh, III, NASA Glenn Research Center.
Responsible person, Henry C. de Groh, III, organization code 6712, (216) 433-5025, Mail Stop 105-1,
E-mail: henry.degroh@grc.nasa.gov, and URL: http://cml.grc.nasa.gov/degroh.

ABSTRACT:
Macrosegregation in metal casting can be caused by thermal and solutal melt convection, and the transport of unattached solid crystals resulting from nucleation in the bulk liquid or dendrite fragmentation. To develop a comprehensive numerical model for the casting of alloys, an experimental study has been conducted to generate benchmark data with which such a solidification model could be tested. The objectives were: (1) experimentally study the effects of solid transport and thermosolutal convection on macrosegregation and grain size; and (2) provide a complete set of boundary conditions - temperature data, segregation data, and grain size data - to validate numerical models. Through the control of end cooling and side wall heating, radial temperature gradients in the sample and furnace were minimized. Thus the vertical crucible wall was adiabatic. Samples at room temperature were 24 cm3 and 95 mm long. The alloys used were Al-1 wt. pct. Cu, and Al-10 wt. pct. Cu; the starting point for solidification was isothermal at 710 and 685 °C respectively. To induce an equiaxed structure various amounts of the grain refiner TiB2 were added. Samples were either cooled from the top, or the bottom. Several trends in the data stand out. In attempting to model these experiments, concentrating on these trends or differences may be beneficial.

SUBJECT TERMS:
Grains; Advection; Settling; Segregation; Macrosegregation

NUMBER OF PAGES:
114

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