The Mechanical Behavior of Rapidly Solidified Al-Al2Cu and Al-Al3Ni Eutectics at Elevated Temperatures

Abstract

The mechanical behavior of semi-continuously cast Al-Al2Cu and Al-Al3Ni eutectics has been studied in tension at temperatures between 350–500 deg C (Al-Al2Cu) and 500–625 deg C (Al-Al3Ni). The microstructures of both eutectics were found to be relatively unstable at elevated temperatures, even in the absence of deformation, as a result of their fine, imperfect microstructures in the as-cast condition. During deformation spheroidization occurred rapidly, so that the fibrous/lamellar reinforcement was largely eliminated. During hot deformation of the Al-Al2Cu eutectic, the “degenerate” lamellar structure was gradually replaced by an equiaxed microduplex structure via polygonization of both phases. This structure subsequently demonstrated superplastic flow, with an increase in the strain-rate sensitivity index from about 0.3 to about 0.5. Final failure resulted from nucleation of cavities at Al2Cu - Al2Cu - Al triple junctions with cavity growth along Al2Cu-Al2Cu grain boundaries. The Al-Al3Ni eutectic did not exhibit superplastic flow probably due to the lower volume fraction of the Al3Ni phase, which “spheroidized” during deformation. A process for fabricating wire by a continuous process from the melt is outlined.