ABSTRACT
Gas-atomized powders are frequently used in metal additive manufacturing (MAM) processes. During consolidation, certain properties and microstructural features of the feedstock can be retained. Such features include porosity, secondary phases, and oxides. Of particular importance to alloys such as Al 6061, secondary phases found in the feedstock powder can be directly related to those of the final consolidated form, especially for solid-state additive manufacturing. Al 6061 is a heat-treatable alloy that is commonly available in powder form. While heat treatments of 6061 have been widely studied in wrought form, little work has been performed to study the process in powders. This work investigates the evolution of the Fe-containing precipitates in gas-atomized Al 6061 powder through the use of scanning and transmission electron microscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS). The use of coupled EDS and thermodynamic modeling suggests that the as-atomized powders contain Al13Fe4 at the microstructure boundaries in addition to Mg2Si. After one hour of thermal treatment at 530 °C, it appears that the dissolution of Mg2Si and Al13Fe4 occurs concurrently with the formation of Al15Si2M4, as suggested by thermodynamic models.
ABSTRACT
Aluminum 5056 is a work-hardenable alloy known for its corrosion resistance with new applications in additive manufacturing. A good understanding of the secondary phases in Al 5056 powders is important for understanding the properties of the final parts. In this study, the effects of different thermal treatments on the microstructure of Al 5056 powder were studied. Thermodynamic models were used to guide the interpretation of the microstructure as a function of thermal treatment, providing insight into the stability of different possible phases present in the alloy. Through the use of transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), combined with thermodynamic modeling, a greater understanding of the internal microstructure of Al 5056 powder has been achieved in both the as-atomized and thermally treated conditions. Evidence of natural aging within these powders was observed, which speaks to the shelf-life of these powders and the importance of proper treatment and storage to maintain consistent results.
ABSTRACT
Metallic powders are commonly used in additive manufacturing processes. While their post-process consolidated properties are widely studied, there is little research on the properties of the powders prior to consolidation. Understanding the powder characteristics before use in additive manufacturing processes could lead to fine-tuning properties of additively manufactured materials. The three-dimensional grain structure of metals can be useful in predicting their properties and microstructure. Powder particles are much smaller and more difficult to fixture and polish than their bulk counterparts, hence typical protocols are difficult to use when serially sectioning them. This method describes a recommendation as to how to fixture, mill, and image metallic powder particles using a Xe P-FIB to mill and take EBSD measurements. It is based on milling and imaging techniques used for bulk materials, but with the specific advantage of how to fixture the powder sample. Our modifications include: â¢the method of fixturing the specimen to the holder.â¢the method of protecting the sample during milling.
