Method Developed for Quantitative Analysis of Inclusions in Solidified Aluminum Ingots

Abstract

A deep-etching method was used to determine inclusions in solidified direct chill cast aluminum ingots. The technique was developed to allow easy quantification of the amount and size distribution of inclusions over billet lengths and cross sections. A pressure filtration (Prefil) test also was used to verify molten alloy cleanliness during casting, and the results of these measurements then were compared. The amount and distribution of nonmetallic inclusions were analyzed, as determined using a NaOH deep-etching method over billet lengths and cross sections. A higher inclusion count was observed at both billet ends, with more inclusions located nearer the billet section centerline. Furthermore, the inclusion density in the radial direction at every distance along the billet length was distributed inhomogeneously. Differences were observed between Prefil samples taken at different casting stages. The Prefil curves and metallographic analysis of Prefil residue obtained from melt samples, at an early casting stage or before degassing, indicate more oxides than in a melt sample taken under steady-state casting conditions. A reasonable correlation was established between the number of inclusions in the molten alloy (measured using Prefil and LiMCA) and the etch pits on deep-etched surfaces of billet cross sections.

Analysis of Distribution of Nonmetallic Inclusions in Aluminum DC-Cast Billets and Slabs

“…Furthermore, it can be observed in Figure 3(b) that most of the large, nonmetallic inclusions are near the billet bottom. It is also important to mention in this article that there is a relation between the size of etchpits and the size of inclusions, [3] where it was shown that the pits are about 10 times as large as the originating inclusion. Figure 4(a) shows the radial distribution of nonmetallic inclusions through a B 228-mm billet crosssection, in three selected zones (Figure 1(a)) of equal cross-sectional area.…”

“…The work also examines the impact of metal treatment on final slab quality when using 30-ppi and 50-ppi ceramic foam filters (CFFs). This paper is a continuation of the author's previous work, [3] in which a deep etching method was developed for the investigation and analysis of inclusions.…”

“…[2] A detailed description, analysis, and validation of the technique is presented in Jaradeh and Carlberg. [3] From the studied etched slices, selected 5 9 10-mm samples were cut for microscopic observation. The inclusion types in the studied alloys were examined under a light optical microscope and using scanning electron microscopy with energy-dispersive X-ray spectroscopy.…”

“…Using a newly developed deep-etching test [2,3] that allows quick determination of the inclusions in large specimens, such information is now available. Knowledge of the inclusion content and size distribution in solidified Al castings is particularly important for subsequent processing, extrusion, and rolling.…”

Mechanism to remove oxide inclusions from molten aluminum by solid fluxes refining method

“…Without proper refining treatments of molten aluminum, such oxide inclusions will be retained in the aluminum ingots after casting, which invariably causes many problems such as a diminishing of mechanical properties, poor machinability and surface quality [1][2][3] . To date, the most widely accepted and frequently adopted method to remove oxide inclusions such as oxide films from molten aluminum is solid flux refining (also known as refining agents, treatment agents or fused agents) [4][5][6] .…”