The Formation And Mechanical Properties Of Icosahedral Quasicrystal In Rapidly Solidified Al-Mn-(be) Alloy

In this study, Al-(6,14,18)wt.%Mn and Al-6wt.%Mn-2.5wt.%Be alloy havebeen selected for investigation. The phase composition and morphology of rapidlysolidified Al-Mn-(Be) alloy has been carefully studied to unveil the intrinsic law thatgoverns the growth behavior of icosahedral quasicrystal under varied solidificationcondition. The effect of minor addition of third element on the enhancement ofquasicrystal formation ability has been investigated by adding small amount Be intothe Al-Mn alloy. The mechanical properties of directional solidified Al-(8,10,12)wt.%Mn-2.5wt.Be alloy with varied growth rates have been investigated.This work provides a theoretical foundation for the active control of the phasecomposition and morphology of icosahedral quasicrystalline phase in Al-Mn-(Be)alloy and establishes practical guidance for the development of in-situ quasicrystal-particle reinforced metal matrix composite.The melt-spun binary Al-Mn and ternary Al-6wt.%Mn-2.5wt.%Be alloy hasbeen investigated to reveal the phase composition and morphology under variedcooling rate. Icosahedral quasicrystal exhibits a strong tendency to form under a highcooling rate with large Mn concentration. The addition of Be significantly enhancesthe formation ability of icosahedral quasicrystal in the binary Al-Mn alloy. Theicosahedral phase is present in the melt-spun Al-6wt.%Mn-2.5wt.%Be alloy even thecooling rate is small.The3-D morphologies of icosahedral quasicrystal have been obtained by deep-etching technique. The unique cellular and5-fold petal-like feature of icosahedralphase indicate that this phase is the primary phase homogeneously nucleated fromthe liquid, and α-Al propagates in a planar manner after the solidification oficosahedral phase. The morphology of icosahedral phase varies gradually fromcellular sphere to5-petal flower-like dendrites, and ultimately grows into developeddendrtites. In the rapidly solidified Al-14wt.%Mn alloy, a definite orientationrelationship between crystalline Al57Mn12phase and icosahedral phase has beendiscovered, namely I3//[1-11]Al57Mn12. As the cooling rate increases, the crystallineAl57Mn12will transforms to icosahedral quasicrystal, such transition can be relatedwith the less-ordered atomic stacking.The quasicrystal-reinforced compostite material of Al-(8,10,12)wt.%Mn-2.5wt.%Be alloy has been prepared using Bridgman method. The icosahedral phaseis evenly distributed in the α-Al matrix and has a good interface. In the Al-8wt.%Mn-2.5wt.%Be alloy, the microstructure transforms from approximant H1phase to icosahedral phase as the growth rate increases, and the tensile strength and elongationalso increases with increasing growth rate. When the growth rate is1000μm/s, thetensile strength of Al-8wt.%Mn-2.5wt.%Be alloy reaches238MPa with a elongationrate of6.2%, exhibiting a good mechanical property.