Positive effect of Sc and Zr on globular microstructure formation in AA7075 thixoforming feedstock

Journal Article · Wed May 04 00:00:00 EDT 2011 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3589653· OSTI ID:21516696

Rogal, L; Dutkiewicz, J; Litynska-Dobrzanska, L ^[1]; Olszowska-Sobieraj, B ^[2]; Modigell, M ^[3]

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1. Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, 30-059 Krakow 25 Reymonta St. Poland (Poland)
2. University of Science and Technology, Faculty of Foundry Engineering, 30-059 Krakow, 23 Reymonta St. Poland (Poland)
3. RWTH Aachen-Dept. of Mechanical Process Engineering (Germany)

One of methods of obtaining a fine globular microstructure in a semi-solid range, necessary for thixoforming process, is modifiers additions. For this purpose 0.5 weight percent of modifying elements-scandium and zirconium-was added to 7075 alloy. The microstructure of such alloy consisted of homogeneously distributed globular grains of solid solution with the following chemical composition: Mg - 1.9%, Al - 91.6%, Cu - 1.0%, Zn - 5.5%(all in wt.%). Quantitative metallographic analysis showed that the average grain size was 23.5 {mu}m, much smaller than in the alloy without additions and 3.08% volume fraction of precipitates in the form of a layer between spherical {alpha}(Al) grains. X-ray phase analysis of the 7075 alloy with Sc and Zr additions confirmed the dominant presence of aluminum solid solution and the intermetallic hexagonal phase MgZn{sub 2}. Electron diffraction pattern confirmed location of {eta}MgZn{sub 2} phase at the grain boundaries. EDS chemical analysis of the {eta}MgZn{sub 2} phase showed following content of elements: Mg - 17.2%, Al - 20.4%, Cu - 27.8%, Zn - 34.6%. The larger amount of Cu and Al indicated non-stoichiometry of the {eta} phase, which can be presented with a formula [Mg(Zn,Al,Cu){sub 2}]. Additionally, inside the aluminum solution, small, square-shaped precipitations enriched with Sc and Zr were observed. Electron diffraction pattern allowed identification of the precipitates as cubic Al{sub 3}(Sc,Zr) phase. The average hardness of feedstock was 105 HV5. DSC analysis during heating of the alloy enabled the estimation of a solidus line, at temperature of 548 deg. C and a liquidus line at temperature: 656 deg. C. For cooling, the temperatures for solidus and liquidus were 545 deg. C and 636 deg. C respectively. Additionally, the relation of liquid phase as a function of temperature was determined. Measurements of rheological properties in the semi-solid range, using the Searl system indicated that an increase of a particle size leads to an observable decrease of viscosity during isothermal shearing.

• OSTI ID: 21516696
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1353; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
ALUMINIUM COMPOUNDS
CALORIMETRY
CHEMICAL ANALYSIS
COHERENT SCATTERING
CONFIGURATION
COPPER COMPOUNDS
DIFFRACTION
DISPERSIONS
ELECTROMAGNETIC RADIATION
ELECTRON DIFFRACTION
GRAIN SIZE
HARDNESS
HOMOGENEOUS MIXTURES
IONIZING RADIATIONS
MAGNESIUM COMPOUNDS
MECHANICAL PROPERTIES
METALLOGRAPHY
MICROSTRUCTURE
MIXTURES
PARTICLE SIZE
PRECIPITATION
RADIATIONS
SCANDIUM ADDITIONS
SCANDIUM ALLOYS
SCATTERING
SEPARATION PROCESSES
SIZE
SOLID SOLUTIONS
SOLUTIONS
SPHERICAL CONFIGURATION
STOICHIOMETRY
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT ALLOYS
TRANSITION ELEMENT COMPOUNDS
VISCOSITY
X RADIATION
ZINC COMPOUNDS
ZIRCONIUM ADDITIONS
ZIRCONIUM ALLOYS