Effect of erbium on microstructure and properties of AA6061 twin-roll casting sheet

Abstract

In this study, the effect of adding trace Er element on the microstructure and mechanical properties of AA6061 twin-roll casting sheet was evaluated. An NF6–300 vertical twin-roll cast-rolling mill was used to prepare AA6061 twin-roll casting sheet with different Er contents, and the main phase morphology and formation mechanism of Er in the alloy were analyzed using microstructure observation, scanning electron microscopy, transmission electron microscopy, and other microstructure analysis techniques. The results show that the addition of a small amount of Er can form the primary Al3Er phase in the alloy. This phase structure becomes an excellent heterogeneous nucleation core of α-Al. This significantly affects the grain size of AA6061 TRC sheets. In addition, Er interacts with the Fe in the TRC sheet. Therefore, the iron-rich phase in the structure changes from coarse needle-like and skeletal shapes to smaller short rods and blocks, and micron-sized spheroids or lumps appear in the structure. Spheroid-like iron-rich phase contains Er. When the amount of Er addition exceeds 0.4 wt%, the number of rare-earth compounds and impurity phases in the structure increases significantly, and they mainly precipitate along the grain boundaries. This increases the strengthening effect of second phase and greatly reduces the plasticity of the material. When the amount of Er addition reaches 0.4 wt%, the comprehensive mechanical properties of TRC sheet are the best. At this time, the tensile strength, yield strength, and elongation are 160.14 MPa, 124.77 MPa, and 10.68%, respectively.