Method Developed for Quantitative Analysis of Inclusions in Solidified Aluminum Ingots
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HE term ‘‘inclusion’’ refers to any type of undissolved foreign material present in cast metal.[1] Inclusions are well known as a common defect in cast structures and normally are obtained during production processes. The types, sizes, and sources of inclusions present in aluminum, as well as their detrimental effects on final products, have been reviewed in detail elsewhere in the literature.[2–6] Investigation of inclusions in aluminum alloys has highlighted the importance of controlling their amount and distribution during the production process. This also has created the need for the ongoing development and use of several melt treatment techniques, such as SNIF,[7,8] as well as inclusion assessment methods. The literature discusses many techniques for counting inclusions in aluminum[3,9–13]; the LiMCA, PoDFA, and LAIS techniques commonly are used, as is the pressure filtration (Prefil) technique commercially known as the Prefil-Footprinter.[14–19] The Prefil apparatus is one of the more recent techniques used to determine the cleanliness of liquid aluminum alloys. It measures the relative cleanliness of a melt by comparison with the benchmark inclusion level for a given alloy, production process, or stage in the process. This technique has the advantage of flexibility, allowing inclusion measurement at any stage of the process chain.[17] It also has the MAJED M. JARADEH, Doctor, and TORBJORN CARLBERG, Professor, are with the Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, FSCN, SE-85170 Sundsvall, Sweden. Contact e-mail: [email protected] Manuscript submitted August 8, 2010. Article published online December 15, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
advantage of providing in situ results in the form of flow-rate charts. These charts minimize the need for the time-consuming metallographic examinations of inclusions demanded by other Prefil techniques, such as PoDFA and LAIS. All aforementioned inclusion assessment techniques are used on the molten aluminum and are expensive or time consuming. Assessment using prefiltration techniques as (PoDFA, LAIS, and Prefil) involves concentrating the inclusions, which means that some information is lost (e.g., as inclusion distribution within the metal). Because concentration also involves some degree of agglomeration, information about inclusion size and shape also might be lost.[10] When it comes to assessing inclusions in the solidified product (i.e., after being cast), only a few inclusion assessment methods are known and supporting literature data are lacking. A typical inclusion assessment method is the light microscopy examination of metallographically prepared samples. Obtaining results by this method, however, is time consuming. As a result of the low inclusion contents and the high tendency of inclusions to segregate into a nonuniform distribution, the direct microscopic analysis of a metal sample surface is impractical because a large area would have to be observed for quantitative assessment.[10] The present work has dev
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