Orientation Relationships of Precipitates with the Matrix in an Aluminum Quasicrystalline Alloy

Aluminum quasicrystalline alloys present a novel class of high-strength alloys. They possess a high potential for practical applications in many fields. In this study, we used a quasicrystalline Al-alloy with a copper addition to achieving strengthening by heat treatment. The alloys were prepared by melt-spinning and by casting into a copper mold. In both cases, quasicrystals formed during solidification either as a primary phase or as a part of a quasicrystal-containing eutectic. Afterward, the samples were subjected to T5 heat treatment. The hardness of the melt-spun ribbons increased considerably while the hardness of the gravitationally cast samples did not change noticeably. A detailed investigation using transmission electron microscopy (TEM) showed that different types of precipitates can form. At lower temperatures, binary Al-Cu precipitates formed, in the intermediate region prevailed the quasicrystalline precipitates, while at higher temperatures formed T-precipitates (Al20Mn3Cu2). Particular attention was given to determination of their orientation relationships with the Al-rich matrix.