Effect of Y and Ce addition on microstructures and mechanical properties of LZ91 alloys

Abstract

As a duplex Mg–Li alloy, Mg–9Li–1Zn (LZ91) has attracted increasing attention, but its strength needs to be further improved. This paper aims to explore the effect of Y and Ce in different proportions on microstructures and mechanical properties of LZ91. The microstructures and mechanical properties of as-cast and cold-rolled LZ91 alloys with Y and Ce addition were investigated. The grain size of the LZ91 was refined due to the addition of Y and Ce. Y significantly strengthened LZ91 while Ce weakened the strengthening effect of Y. The mechanical properties increased first and then decreased with the content of Y and Ce, however, it still showed a strengthening effect compared to LZ91 alloys. The addition of Y caused the formation of Mg24Y5 and Mg12ZnY. With the addition of Ce, Mg12Ce and CeZn5 formed with a continuous-network distribution. Mg–9Li–1Zn-1.5Y exhibited the most excellent microstructure and mechanical properties in as-cast state (UTS, YS, and elongation are162MPa, 130 MPa and 49.6%, respectively) and cold-rolled state (UTS, YS, and elongation are 255 MPa, 231 MPa and 31.9%, respectively) states because of the prominent refinement effect of Y on α phase and the dispersion strengthening by Mg24Y5. Meanwhile, the elongation of Mg–9Li–1Zn-1.5Ce after cold rolling was abnormally enhanced. This was explained that the coarse Mg12Ce in the as-cast state was broken into fine dispersed particles after cold rolling. This paper provides a reference for the selection and quantification of rare earth elements in duplex Mg–Li alloys. It also provides a reference way to refine large-size second phases in duplex Mg–Li alloys.