Nanocomposites and nanomaterials

The formation of metastable phase Al3Mg in the Al-Mg-C system during mechanical alloying 

Rud A.D., Lakhnik A.M., Kirian I.M.

G.V. Kurdyumov Institute for Metal Physics N.A.S. of Ukraine
36 Academician Vernadsky Boulevard, Kyiv 03142, Ukraine
E-mail: kiryan.inna@gmail.com

Al-Mg based alloys are the light metallic materials, and they have widespread applying in aerospace, automotive and materials handling due to a set of unique properties. At now many categories of Al-Mg alloys were developed for industrial applications. However, the mechanical properties of aluminum alloys are sharply reduced at elevated temperatures. So, in order to enhance their industrial applications, many efforts have been applied to improve the mechanical strength and heat resistance of Al-Mg alloys in recent years. Among the non-equilibrium processing methods, the mechanical alloying (MA) has been widely used for the production of metastable materials. In this work we have focused on the metastable phase formation in Al-Mg powders during MA. 
The samples were prepared from a commercially available magnesium, spectroscopic graphite and aluminum powders. The ternary elemental powder mixture (75at% Al-25at% Mg) + 5wt% C has been prepared. The sample was milled in argon gas atmosphere in the laboratory planetary ball mill Fritsch Pulverisette P-6 at the room temperature for 1, 3, 5, 7, 9 and 12 hours, respectively. The rotation speed was 400 rpm for all experiments. From XRD analysis it was found that the reaction between the elemental Al and Mg powders is started after ~5 h milling. Increasing the milling time up to 7 h drastically changes phase composition of the sample. The best Rietveld refinement for XRD pattern after MA 7 h was obtained for two phases: metastable intermetallic Al3Mg [1] and Al. The lattice parameters for these phases are 0.4119 nm and 0.4048 nm, respectively. The further MA during 12 h leads to the unessential changes in the positions of the peaks for the Al3Mg and Al phases and increasing the content of the phase Al3Mg. From the Rietveld refinement has been found that the obtained sample contains ~ 79.2 wt% of Al3Mg phase and ~ 20.8 wt% Al. The lattice parameters are 0.4057 nm and 0.4122 nm, respectively. The transmission electron microscopia also confirmed the presence of a metastable phase Al3Mg in the synthesized material.
 
1.	Fu L., Ke J.-L., Zhang Q., Tang B.-Y., Peng  L.-M., Ding W.-J. Mechanical properties of L12 type Al3X (X =Mg, Sc, Zr) from first-principles study // Phys. Status Solidi B. -2012.-P. 1–7.