The Influence of Rare Earth Lanthanum on the Microstructure and Mechanical Properties of As-Cast 6082 Aluminum Alloy

Abstract: The microstructure refinement mechanism and mechanical properties of 6082 aluminum alloy with different content of rare earth La element were investigated. The results showed that the addition of La can refine the α-Al grains, change the volume fraction of the Mg2Si particles and modify the morphology of AlFeSi intermetallic phase. The grain size of α-Al was significantly refined compared with the La-free alloy. With the increase of La content from 0.1wt.% to 0.8wt.%, the volume fraction of the Mg2Si particles with a La-rich surface layer increased first and then decreased. Besides, the long strip-like phase β-AlFeSi was transformed to be script-like π phase α-AlFeSi. Moreover, the rare earth La element was not distributed in the intermetallic compound AlFeSiMn and AlFeSi, but mainly distributed in the areas where Si element is enriched. During solidification, the rare earth La rapidly diffused around Mg2Si particles to form a rare earth layer, and almost no La can be observed in the α-Al matrix. An excellent combination of strength and ductility was obtained when the rare earth La content is 0.2 wt.%. The proper addition of 0.2 wt.% La in 6082 aluminum alloy can modify the long strip β-AlFeSi phase to be the script-like π phase α-AlFeSi and increase the volume fraction of spherical Mg2Si phase simultaneously, which contributed to improvement of the mechanical properties