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In this paper was proposed to design new casting alloys on the base of the Al-Mg-Si system using Li addition to achieve precipitation strengthening effect and alloying by Ti+Zr to achieve saturation of solid solution and grain refinement effect. The as-cast and heat treated structure of permanent mould casting of AlMg5Si2Mn containing 1.0 wt.% Li and 0.1 wt.% Ti+0.1 wt.% Zr alloys was investigated by differential scanning calorimetry, microhardness measurements, scanning and transmission electron microscopy and energy dispersive X-ray analysis. Mechanical properties of these alloys were investigated with modern automated ball indentation method. This method showed good convergence with standard tensile tests and allows to determine hardness, yield stress and elastic modulus of tested alloys. It was observed that addition of Li causes modification of (Al)+(Mg2Si) eutectic lamellas making them thinner and interlamella distance becomes larger. Ti+Zr addition does not change eutectic morphology but strongly reduces the size of -Al dendrites, also, it produces the nucleation particles for primary Mg2Si crystals. Homogenization of studied alloys at 570 C results in disintegration of Mg2Si lamellas and this process takes 30 min to transform plate like lamellas to fine spheres. It was established that hardness and microhardness both of Li and Ti+Zr containing alloys decrease at the same time. Further heating does not produce remarkable changes of hardness. Artificial aging leads to the increasing of hardness and microhardness. Obtained results showed that heat treatment of AlMg5Si2Mn improves its mechanical properties with Li and Ti+Zr assist precipitation hardening and solid solution strengthening effects.
Keywords: aluminum, casting alloys, eutectic, microstructure, automated ball indentation, elastic modulus© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.