Morphological evolutions and growth patterns of Zr-containing phases in aluminum alloys

Abstract

Three-dimensional morphologies of Zr-containing phases in Al–(Si–)Zr alloys were studied in detail using field emission scanning electron microscopy. Combining the analysis of crystallographic features with atomic arrangement in the crystal lattices and first-principles quantum mechanics calculations, the growth mechanisms of Zr-containing phases were discussed. As reported in previous work, the increase of Si content in Al–(Si–)Zr alloys leads to the continuous composition evolution and a structure transformation from ZrAl₃ to (Al,Zr,Si) and ZrSi₂. The perfect morphology of ZrAl₃ is compressed cubic, whose lateral surfaces are composed of four groups of symmetric planes. (Al,Zr,Si) has similar crystal shape to ZrAl₃, while the cube is much thicker and the growth process is changed. Further high Si content results in the formation of the ZrSi₂ phase, presenting 18-polyhedral morphology, whose upper and lower surfaces are also covered by (0 0 1) planes, while its lateral surface is composed of eight groups of symmetric {1 1 0} and {1 1 1} planes. Similar growth mechanisms of Ti-containing phases in Al–(Si–)Ti alloys have also been found.