The Influence of Strontium on Microstructural and Rheological Behavior of the Semi-solid A380 Aluminum Alloy
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an aluminum alloy widely used in the die casting processes. Recent works have also sought to understand the behavior of this material in thixoforming and rheocasting processes.[1–4] This alloy is mainly composed of Al, Si, Cu, Fe and Zn, which ensures this material has a complex microstructure, composed mainly by dendritic a-Al structures, eutectic structures as well as intermetallic ones such as b-iron, a-iron and h-Cu phases.[3]
JOA˜O PAULO GABRE FERREIRA and LUCIANO AUGUSTO LOURENC¸CATO are with the Department of Mechanical Engineering, Federal Technological University of Parana, Rua Doutor Washington Subtil Chueire, 330 - Jardim Carvalho, Ponta Grossa, PR CEP 84017-220, Brazil. Contact e-mail: [email protected] ANGEL SA´NCHEZ ROCA is with the Faculty of Mechanical and Industrial Engineering, Orient University, 90400 Santiago de Cuba, Cuba. HIPOLITO DOMINGO CARVAJAL FALS is with the Department of Mechanical Engineering, Federal Technological University of Parana and also with the Orient University, Santiago de Cuba, Cuba. Manuscript submitted March 2, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Currently, there are several ways to obtain microstructures suitable for thixoforming in aluminum alloys.[5] Among these techniques, chemical grain refinement by the addition of elements such as Ti and B is advantageous compared with the traditional routes as it does not require any specific equipment to obtain an equiaxial microstructure, resulting in a simple and cheap technique for obtaining a good-quality semi-solid material.[6] One of the issues related to the grain refinement technique in aluminum alloys is the poisoning effect of Si, where Si levels > 3 pct decrease the effect of the refining elements.[7] Several studies have been conducted trying to overcome this effect.[8,9] The results show that different ratios of Ti and B in the master alloys or an even greater amount of the conventional TiBAl 5/1 alloy are some of the alternatives to refine the a-Al phase grain in aluminum alloys with high Si contents. Another mechanism used to modify the microstructure of Al-Si alloys is the addition of elements such as Sr, La, Na and Sb.[10–13] The addition of small quantities of Sr can change the faceted Si structures to a fibrous morphology,[14,15] providing a better mechanical behavior to Al-Si alloys.[10,14] In addition, previous studies have described other effects when adding Sr to Al-Si alloys, such as the reduction of the eutectic
temperature,16 increase of a-Al phase solidification rate,[16] reduction of the surface tension of liquid[17] and reduction of the viscosity of the liquid metal.[18] Due to the different effects caused by the Sr modification in Al-Si alloys, it becomes pertinent to evaluate the effect of Sr in the behavior of these materials in the semi-solid state. Therefore, this article aims to understand the influence of Sr modification on the microstructural evolution of A380 alloy in the semi-solid state as well as the effect of this change on the rheological behavior of this alloy.
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MATERIALS AND ME
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