A. V. Kazantzis, Z. Chen, University of Groningen and the Netherlands Institute for Metals Reseach, Groningen, Netherlands; J. T. M. De Hosson, The University of Groningen, Netherlands Institute for Metals Reseach, Groningen, Netherlands
Two coarse-grained Al alloys AA5182 with as-received grain sizes 19 and 34 μm have been evaluated with respect to their superplastic properties. They exhibited moderate elongation to failure reaching maxima, in excess of 300%, at temperatures between 425 and 450oC and at strain rates 10-2 s-1.Extreme grain refinement by recovery, reconstruction and recrystallization produced microstructures consisting of grains as small as 2 μm at the tip region, suggesting that the precipitates are quite effective in pinning the subgrain boundaries, which in turn are readily converted into low and high angle grain boundaries.
This grain refinement, however, occurred also randomly in other locations in the specimens, wherever large strain was localized, resulting in multiple necking in specimens exhibiting maximum elongations prior to failure.This behavior renders coarse grained AA5182 Al-alloys quite unstable, as superplastic materials and, despite their low fabrication cost, their precipitate size needs to be regulated further, so that their superplastic elongation to retain the uniformity that is required in practical applications in the automotive and aerospace industry.
Summary: This paper outlines our results from tensile test experiments on specimens of AA5182 Aluminium Alloys provided by Aleris Corus.
The tests were carried out using specimens made by EDM having gauge size 16 mm and deformed in extension at temperatures between 350 and 500 degrees C and at strain rates between 10-3 and 10-1 s-1.
The specimens were heated in a 3-zone split furnace and the testing temperature was reached within 15 to 18 minutes. When failure occurred the furnace was quickly opened and the specimens were quenched in water.
The paper outlines data on maximum elongation to failure, mechanical properties and microstructure characterisation using SEM, EDX and EBSD orientation imaging microscopy. Necking instabilites are catergorized with respect to their distance from the point of failure as a function of temperature and strain rate. The microstructure at the region where necking instabilities were observed is compared with the microstructure in the as-recieved specimens, in the heat treated region of the specimen near the grip, in the uniformly deformed gauge as well as that adjacent to the broken tip (where final failure of the specimen occurred).
