Morphological Evolution of Mg-Al-La-Ca Alloy Induced by a Mechanical Stirring Process
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Morphological Evolution of Mg-Al-La-Ca Alloy Induced by a Mechanical Stirring Process Se´rgio Luiz Telles Bartex, Lı´rio Schaeffer, and Vinicius Karlinski de Barcellos (Submitted October 11, 2018; in revised form December 6, 2018) This paper aims to evaluate the morphological evolution of a magnesium-aluminum alloy (Mg-6Al-3La-1Ca) processed by a mechanical stirring process (MSP) with different stirring times. An apparatus for semisolid metal alloy processing was used to melt and obtain rheocast material. Transformation temperatures were determined at a slow cooling rate using computer-aided cooling curve thermal analysis (CA-CCTA) and differential scanning calorimetry (DSC). Isothermal mechanical stirring (605 °C), at 950 rpm, was carried out with a solid fraction of 0.29 and stirring times of 0, 1, 2, 4, 8 and 10 min, followed by fast cooling in water. The results showed that the microstructure after conventional casting (0 min—no stirring) is composed of an a-Mg dendritic matrix, Al11La3, (Al,Mg)2Ca and Mg2Ca compounds. With the 1-min stirring time, it was not possible to obtain globular structures. For stirring times longer than 2 min, a primary a-Mg globular morphology was obtained. Microstructures with 2 min of stirring time showed better globularization than those obtained under the other conditions. Morphological changes were observed for Al11La3 and (Al,Mg)2Ca after the MSP followed by fast cooling. Keywords
magnesium alloys, rheocasting, semisolid, solidification
1. Introduction As the lightest structural metallic materials, magnesium alloys have exceptional characteristics, including low density, good castability, high specific strength and good recyclability. These great characteristics have resulted in a significant application value in industrial fields, such as aerospace, automobile and telecommunications (Ref 1). Ferry et al. (Ref 2) studied the influence of both calcium (1.0% Ca) and lanthanum (3.0% La) addition to a magnesium alloy system (Mg-4.0% Al, 0.5% Zn). They proposed the substitution of misch metal elements by specific amounts of
This article is an invited submission to JMEP selected from presentations at the 73rd World Foundry Congress and has been expanded from the original presentation. 73WFC was held in Krakow, Poland, September 23-27, 2018, and was organized by the World Foundry Organization and Polish FoundrymenÕs Association. Se´rgio Luiz Telles Bartex and Vinicius Karlinski de Barcellos, Post-Graduation Program in Mining, Metallurgical and Materials Engineering – PPGE3M – Foundry Laboratory, Engineering School, Federal University of Rio Grande do Sul, Bento Gonc¸alves Av., 9500, Porto Alegre, RS 91501-970, Brazil; and Lı´rio Schaeffer, PostGraduation Program in Mining, Metallurgical and Materials Engineering – PPGE3M –Metal Forming Laboratory, Engineering School, Federal University of Rio Grande do Sul, Bento Gonc¸alves Av., 9500, Porto Alegre, RS 91501-970, Brazil. Contact e-mail: [email protected].
Journal of Materials Engineering and Performance
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