Microstructure of 7N01 Aluminum Alloy Microalloyed with Er and Zr in the Homogenization Process

The microstructure and segregation of 7N01 aluminum alloy microalloyed with Er and Zr before and after homogenization process at 470 °C for 24 h have been investigated using transmission electron microscope (TEM), and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscope (EDS) and transmission electron detecter (STEM). SEM images and EDS line scan results showed that there were dendritic segregation of Mg and Zn and micron-sized primary phases along dendrites in the as-cast alloy. The primary phases were mainly Al2Mg3Zn3 containing Al, Zn, Mg and Mn. And a small amount of primary phases were the particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr. After homogenization at 470°C for 24 h, dendritic segregation of Mg and Zn was eliminated, Al2Mg3Zn3 and the particles containing Al, Zn, Mg and Mn were basically dissolved. The particles containing Al, Zn, Mg, Mn, Cr and Er and the particles containing Al, Zn, Mg, Er, Mn, Fe and Cr remained. Meanwhile, TEM and STEM images showed that a large number of secondary phases appeared after the homogenization, which were mainly distributed in the inter-dendrite area. EDS results showed that the block-shaped and rod-shaped phases with the width of 10-70 nm and length of 100-500 nm were the particles containing Al, Cr and Mn or Al, Mg, Cr and Mn, and the ellipsoid secondary phase with the size of 50-100 nm was MgZn2.