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Benchmarking


Aluminum Melt Treatment


Recent surveys developed and distributed by the AFS Aluminum Division sheds light on trends and methods of grain refinement and eutectic modification in practice at aluminum casting facilities. AFS ALUMINUM DIVISION; BENJAMIN GROTH, VESUVIUS USA (FOSECO), PITTSBURGH; BRIAN BEGAN, FOSECO, CLEVELAND


A


luminum casting personnel often ask about best practices for grain refinement and eutectic modification in aluminum alloys. A wide vari- ety of practices are utilized in the aluminum


casting industry and many technical papers have been pub- lished, as well as multiple discussions conducted on the issue. Yet, debate continues regarding best practices for refinement and modification, particularly when it comes to strontium additions. And there have been few documented statistics on what practices are being followed in metalcasting facilities. Two separate surveys, one 10-question survey on grain


refinement and one 15-question survey on eutectic modifi- cation, were distributed electronically to AFS membership, specifically those categorized as casting aluminum. Forty-six members responded to the grain refinement survey, while 50 responded to the eutectic modification survey, with some overlap between responding members. Respondent demo- graphics were similar between each survey (Figure 1). It would be helpful to at least define the intended goal of


each melt treatment. • Grain-ref ining: Generally speaking, a grain refiner will act on the size and structure of the grains within an aluminum casting, resulting in a finer grain size. This leads typically to reduced porosity and a reduction in the size of pores, as well as improved feeding and a reduced tendency for shrinkage formation. This is typically accomplished with the addition of titanium and boron in an aluminum master alloy.


• Eutectic modif ication: Modification of the silicon is typi- cally achieved through a strontium or sodium addition. The additive acts on the silicon in the alloy system, trans- forming the morphology of the silicon from long strands to small particles. The result of this transformation is


an improvement in mechanical properties, specifically tensile strength and elongation. Given below are the compiled results from each sur-


vey, with brief discussion for most questions. Some of the responses have been combined for brevity. Tis study can help aluminum melting personnel benchmark their opera- tion to see how it compares to other in the aluminum cast- ing facilities.


AFS Grain Refinement Survey Results


What kind of alloy does your metalcasting facility use? Perhaps unsurprisingly, nearly 95% of the responding


metalcasters are consistently casting A356 aluminum alloy. Te 300 series alloys, in general, were the most cast by those surveyed (66%), with 500 series and 700 series alloys being cast as well. Some higher copper and zinc content alloys were mentioned as having been previously run within cer- tain plants. Of those surveyed, almost half (47%) have steady jobs running four or more different alloys. Tis trend was across all plant sizes.


Which grain refinement techniques do you use? Which do you use most often?


Te dominant technique for refining used today is


controlled additions of cut “TiBor” rod (titanium plus boron master alloy). Seventy percent of the survey respondents said they use chopped rod on a daily basis as their most prevalent refinement method, with 10% saying they utilize purchased ingots with grain refining elements added to them. Te lat- ter was exclusive to metalcasting facilities smaller than 100


November 2016 MODERN CASTING | 43


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