Observation of As-Cast Microstructure Feature of Al Sheet Used for Can Manufacturing with High Forming Properties

Abstract

The as-cast microstructure feature of Al sheet with high forming properties used for pressure can manufacturing pre-treated by different melt-treatment technique was observed and analyzed by SEM, EDAX, TEM and selected area electron diffraction (SAED), etc. It was found that the oxide inclusions in Al sheet were mainly γ-Al2O3, and the Fe-rich impurity phases in the sheet mainly Al3Fe, T1(Al12Fe3Si) or (AlFeSiRE). The crystal structure of (AlFeSiRE) phase was too complicated to be determined. The effect of melt-treatment technique on the as-cast microstructure of the sheet was remarkable. There were a number of oxide inclusions in the Al sheet before or after conventional melt-treatment, which distributed non-uniformly and gathered together in larger block shape with the size of about 10-40μm. The Fe-rich impurity phases in the sheet were mainly Al3Fe and T1, and a few of the meta-stable phase Al6Fe existed in the sheet. These Fe-rich impurity phases appeared in a coarse, long needle/flake or skeletal form, and were easily to gather together with oxide inclusions. When the Al sheet was treated by high-efficient melt-treatment, the amout of oxide inclusions was decreased obviously, and these inclusions distributed more uniformly in the tiny granular form (about or less than 4μm). The Fe-rich impurity phases were mainly (AlFeSiRE), and a small amount of Al3Fe phases also existed in the material. The (AlFeSiRE) phases distributed uniformly along grain boundary in tiny group/sphere or short stick form. No congregation of Fe-rich phases with oxide inclusions was found in the material.