Interaction Between Eutectic Intermetallic Particles and Dispersoids in the 3003 Aluminum Alloy During Homogenization Tr
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ALUMINUM alloys in which manganese is the main alloying element are among the most commonly produced alloys in the world today, due to their relatively low cost, high strength to weight ratio, workability, and excellent corrosion resistance. Manganese is used as an alloying element, to improve the mechanical properties of the alloys through solution hardening, without markedly decreasing the corrosion resistance. Among the 3xxx series of alloys, 3003 aluminum is widely used for the manufacturing of automobile radiators and air conditioners. This alloy is usually direct chill cast (DC) into rolling ingots. After solidification, the microstructure consists in a chemically inhomogeneous supersaturated matrix, with Al6(Mn,Fe) eutectic intermetallics and a very small quantity of a-Al(Mn,Fe)Si particles formed at the solidification cell boundaries or in the interdendritic areas. Such a microstructure strongly affects the alloy’s M. DEHMAS, Associate Professor, E. AEBY-GAUTIER and P. ARCHAMBAULT, Research Directors, and M. SERRIE´RE, Scientist, are with the Institut Jean Lamour-SI2M UMR 7198 CNRS, Universite´ de Lorraine, CS 50840, 54011 Nancy Cedex, France. Contact e-mail: [email protected] Manuscript submitted July 15, 2011. Article published online October 18, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
mechanical properties, and hence its potential engineering applications.[1–5] Before further thermomechanical processing, homogenization treatment must be carried out to limit microsegregation in the matrix. Extensive research was carried out on the composition of the supersaturated solid solution. Many studies have identified the eutectoid transformation of primary Al6(Mn,Fe) eutectic intermetallics into a-Al(Mn,Fe)Si particles: (3Al6(Mn,Fe) + Si fi a-Al12(Mn,Fe)3Si + 6Al), which nucleate at the interface of the Al6(Mn,Fe),[5–9] and a simultaneous intra-granular precipitation of dispersoids, also identified as a-Al(Mn,Fe)Si, which often nucleates on dislocations.[10,11] The dispersoids’ morphology was characterized as spherical and rodlike in shape.[12] The quantitative aspects of the relationship between these phase transformations were poorly documented. Li and Amberg quantified the evolution of eutectic intermetallics[10] as well as dispersoid precipitation[12] in DC AA3003 aluminum alloy, during continuous heating and homogenization treatment. These authors characterized variations in the quantity and size of the phases. However, they did not establish any link between the chemical composition of the phases and did not provide any analysis of the interdependence of changes in eutectic intermetallics and dispersoid formation. VOLUME 44A, FEBRUARY 2013—1059
In the present article, following an initial illustration of the microstructural and chemical changes associated with homogenization, when applied under conditions of industrial heat treatment, a quantitative analysis is made of the simultaneous evolution of eutectic intermetallics and dispersoids during isothermal holding between 673
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