MICROSTRUCTURE OF AS-MELT SPUN Al-Cu-Mg-Fe-Ni ALLOY AND ITS VARIATION IN CONTINUOUS HEAT TREATMENT

A commercial AA2618 alloy was treated through melt spinning at rotating speeds of 20 and 40m*s-1. The as-melt spun ribbons were characterized by a combination of optical microscopy (OPM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The microstructural evolution of the ribbons in a continuous heating process was investigated, and the microhardness was also measured under different conditions. It was found that AlxFeNi is prone to precipitate in AA2618 alloy due to the minimal solubility of iron and nickel. Fine AlxFeNi particles appeared along the grain boundaries at the chilling sides of as-melt spun ribbons, and at both the grain boundaries and in the interior of grains at the free sides. On continuous heating AlxFeNi precipitated steadily and uniformly throughout the matrix until melting. The microhardness of as-melt spun ribbons decreased significantly from the chilling surfaces to free surfaces. Precipitation of AlxFeNi lowered the hardness of the alloy.