Processing and Mechanical Properties of Quasicrystal-Reinforced Al-Alloys
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Processing and Mechanical Properties of Quasicrystal-Reinforced Al-Alloys F. Schurack, J. Eckert and L. Schultz IFW Dresden, Institute of Metallic Materials, P.O. Box 27 00 16, D-01171 Dresden, Germany ABSTRACT We investigated the suitability of powder metallurgy as well as die casting for the fabrication of light-weight Al-based composites with quasicrystalline particles embedded in an aluminum matrix. Al-Mn-Ce and Al-Cu-Fe quasicrystalline powders were synthesized by milling of elemental powder mixtures or arc-melted prealloys using a planetary ball mill. The mixture of the quasicrystalline phase and the Al-matrix phase with an appropriate ratio was realized by an initial aluminum excess or by blending of quasicrystalline powder with pure aluminum. The powders were consolidated by hot extrusion. Bulk samples of ∅3mm diameter and 50mm length were also directly prepared by squeezing the melt into a copper mold. CCRTcompression tests revealed a yield strength of about 400 MPa, an ultimate strength of 565 MPa and a ductility of up to 19 % fracture strain as optimum mechanical properties. INTRODUCTION The combination of different properties of quasicrystals offers numerous possibilities for their technological application. A limiting factor, however, is the extreme room temperature brittleness. Although this is in general considered as detrimental it can be used in combination with other materials in a very beneficial way. A first impetus to the commercial use of quasicrystals as a strengthening phase was given in 1995 by the finding of the precipitation of quasicrystalline (qc) particles in a maraging steel matrix upon tempering treatment [1]. High strength light-weight materials were developed making use of quasicrystals as the strength-bearing component in dual-phase Al-matrix composites. Since the qc-phase in most of the reported alloys is metastable and in order to achieve a rather fine mixture of the components on a micrometer or even a nanometer scale, nonequilibrium processing techniques like melt spinning [2,3], gas atomization [4,5] or mechanical alloying [6,7] were applied. The latter method has been repeatedly proven to be well suited for the processing of quasicrystalline materials which are difficult to obtain by solidification techniques [7-11]. The objective of this paper is to compare the suitability of this solid state powder metallurgy route and of a die casting technique for the processing of bulk composite materials. EXPERIMENTAL DETAILS Milling experiments starting from Al-Mn-Ce and Al-Cu-Fe powders (purity >99.95 wt.%) were performed using a RETSCH PM400 planetary ball mill (400 rpm) and hardened steel balls and vials. All powder handling was carried out in argon atmosphere (O2, H2O < 1 ppm). The wear debris from the milling tools was less than 0.1 at.%. The oxygen content of the powders after milling was between 0.02 and 0.4 at.%. Bulk samples were prepared by uniaxial hot pressing and hot extrusion of the powders. Cylindrical rods of ∅3×50 mm were prepared by K9.11.1
squeezing the melt into a
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