Microstructures and Properties of Rapidly Solidified Aluminum Alloys
Zindel, Jacob Wesley
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https://hdl.handle.net/2142/71836
Description
Title
Microstructures and Properties of Rapidly Solidified Aluminum Alloys
Author(s)
Zindel, Jacob Wesley
Issue Date
1986
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Abstract
This investigation studied the origin, thermal stability, and mechanical properties of microstructures produced in aluminum alloys that had been rapidly solidified by laser surface melting (LSM) or chill block melt spinning (CBMS). The alloys, all of which had the same solute content, had the composition Al-4.1Fe-0.6X (at.%), where X was Mo, Ce, Cr, V, or Zr. A binary Al-4.7Fe (at.%) was used for comparison.
Microstructures of rapidly solidified alloys were affected by the degree of undercooling achieved in the liquid. Large undercoolings caused the alloys to nucleate as (alpha)-Al cells with intercellular dispersions of fine, randomly oriented T' particles. This microstructure, which was unaffected by etching, appearing featureless in optical micrographs, would make up the entire sample providing the rate of heat extraction is sufficient to inhibit recalescence effects. Lesser undercoolings produced darkly etching microstructures such as eutectics or structures with primary intermetallic particles.
The microhardness of the light etching material was high in the rapidly solidified state, but it softened considerably during annealing as the fine cells transformed into coarse Al(,6)Fe and Al(,3)Fe particles. Ternary additions were made in an attempt to improve the thermal stability of the cellular microstructure, with Mo proving to be the most effective.
In order to evaluate the mechanical properties of a representative alloy, melt spun Al-4.1Fe-0.6Mo ribbon containing a large volume fraction of the cellular microstructure was produced in sufficient quantity to be consolidated by extrusion. The original ribbon microstructure decomposed during extrusion, resulting in microstructures similar to those observed in extruded powders. Tensile strengths of the extruded ribbon were comparable to those of extruded powder of the same composition. Extruded ribbon had a higher fracture toughness than the extruded powder, probably due to the fact that it had a more homogeneous original microstructure.
Subscale tensile specimens were fabricated from Al-4.1Fe-0.6Mo (at.%) and Al-4.1Fe-0.6Ce (at.%) LSM material and tested at 20 and 315(DEGREES)C. While no improvement in room-temperature strength was seen, the elevated-temperature strengths were clearly superior to those of extruded materials.
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