Nanocomposites and nanomaterials
Nanostructured complex ligatures for aluminum alloys
A.L. Berezina1, O.A. Molebnyi1, T.O. Monastyrska1, S.L. Polyvoda2
1 G.V. Kurdyumov Institute for Metal Physics of the NAS of Ukraine. 
Vernadsky Blvd. 36, Kyiv-142, 03680, Ukraine. 
E-mail: moleb@imp.kiev.ua
2 Physico-Technical Institute of Metals and Alloys of the NAS of Ukraine. 
Vernadsky Blvd. 34/1, Kyiv-142, 03680, Ukraine.
It is known that alloying of aluminum alloys with transition metals (TM) can significantly reduce the temperature range of crystallization. It increases the resistance to the hot cracks formation and reduces the rate of concentration liquations as-cast. At the same time, the ingot structure modification and the grain structure refinement are observed depending on size and degree of structural fit of the TM intermetallides with the matrix. TM are refractory and exhibit low solid-solubility in α-Al. Therefore, to introduce them into the melt, intermediate alloys (ligatures) are used which can significantly reduce the melting point. In standard ligatures TM is introduced in the form of dispersed intermetallides. The using of Al-Sc ligatures has shown the possibility of complex ligatures creation that provides not only grain refinement due to the primary highly dispersed Al3Sc intermetallides but also form an abnormally supersaturated solid solution of Sc in Al, the decomposition of which leads to formation of nanodispersed refractory hardening particles to improve the strength and thermal stability of the alloys.
In this paper, the task was to find out of a nanostructured complex Al-Zr ligature to replace an expensive and less thermally stable Al-Sc. The binary Al-Zr alloys were chosen to determine the base composition of the alloy. Studies of the structural state of the alloys were carried out as a function of: a) the Zr content (1%-9%); b) melting and casting temperatures of alloys (800,900,1000,11000C); c) the time of magneto-hydrodynamic (MHD) melt mixing (0.5-4 hours); d) crystallization rates (100, 103, 106 deg/sec). It is shown that the most acceptable parameters for the nanostructured complex ligature preparation are the following: composition of the Al-3%Zr alloy, casting temperature of the alloy 10000С, crystallization rate of 103 deg/sec. It should be noted that overheating of the melt without providing the appropriate rate of crystallization is ineffective.
The obtained ligatures efficiency was tested on Al-Zn-Mg and Al-Mg alloys. It is shown that the new type of ligatures can be obtained on an Al-Zr basis, which not only modifies the grain structure of the ingot, but also provides an increase in the volume fraction of nanosized reinforcing nanoparticles of the refractory Al3Zr phase that results in growth of thermostability and strength of the alloys.