Subgrain strengthening of aluminum conductor wires
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T H E R E is a significant economic incentive to develop an aluminum electrical conductor as an a l t e r native to copper for selected applications as communications, building and magnet wire. Fully annealed electrical conductor (EC) grade aluminum (minimum 99.45 Al) has a much lower strength than annealed electrolytic tough pitch (ETP) copper and therefore is inadequate for certain applications. Consequently, considerable effort has been devoted to developing higher strength aluminum conductors through alloying and wire processing. Both approaches are constrained by the need to maintain high electrical conductivity. The alloys which have evolved are limited to about 1 pct of alloying additions, p r i m a r i l y elements which are highly insoluble in aluminum. F u r thermore, the degree of strain hardening of the wire product is r e s t r i c t e d by the need for ductility and notch insensitivity. The manufacturing of aluminum conductor wire is characterized by large plastic deformations at room temperature, with some intermediate or final annealing, in going from supply rod to the wire product. As a consequence, the wire materials develop well-defined subgrain structures.* It is well established that *We will not make a strict distinction between dislocation cells and subgrains since there is no consistent use of these terms in the literature. One working definition which seems appropriate is to use the term dislocation cells if the dislocation character of the boundaries is evident in electron microscopy while the term subgrains if the boundaries are sharp instead of diffuse, Clearly, subgrains imply more extensive recovery.
in relatively pure metals, which have undergone static or dynamic recovery, the strength is p r i m a r i l y controlled by the size and character of the subgrains. 1 This paper describes the influence of wire processing variables, in aluminum conductor wire manufacturing, on the formation of subgrain s t r u c t u r e s in three conductor materials and in turn, relates the structure to the strength.
D A V I D K A L I S H is S u p e r v i s o r , M e t a l l u r g i c a l E n g i n e e r i n g G r o u p ,
Bell Laboratories, Norcross, GA 30071. B.G. LeFEVREis Associate Professor of Metallurgy, GeorgiaInstitute of Technology,Atlanta, GA 30332. Manuscript submitted May 14, 1974. METALLURGICAL
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A
EXPERIMENTAL Materials The materials examined were electrical conductor (EC) grade aluminum (99.45 A1)*, an alloy nominally *All compositions in weight percent.
A1-0.55Fe-0.55Co and an alloy nominally Al-0.75Fe0.15 Mg. The principal impurity in EC-AI is ~0.25 Fe. The m i c r o s t r u c t u r e s of the three alloys contain dilute nonuniform dispersions of incoherent intermetallic particles that were identified by both selected area electron diffraction and X - r a y diffraction to be the stable FeAI 3 phase, the metastable FeA16 phase and the stable (Co, Fe)2AI9 phase; Fe and Co are highly insoluble in AI. There is a greater density of these particles in the Al-Fe-Mg and A1-Fe-Co a
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