Effect Of Ce Addition On As-cast Microstructure Of AZ31,AZ91 And ZK60 Magnesium Alloys

Magnesium alloys are the lightest structural alloys and have great potential for applications in automotive, aerospace and other industries. However, the mechanical properties and forming performance of commercially available magnesium alloys do not meet the demand of industrial application. Therefore, it is necessary to improve the comprehensive properties of magnesium alloys by alloying and/or microalloying methods. Since Rare earths element Ce is one of the potential alloying and/or microalloying elements, its application in magnesium alloys has received much global attention and many research works have been pursued. However, some different opinions about the effect of Ce addition in magnesium alloys are reported, especially the effect of Ce addition on the grain refinement of magnesium alloy. One opinion is that addition of Ce to magnesium alloys can lead to the grain refinement. Another one is that the addition of Ce to magnesium alloys will result in the grain coarsening rather than the grain refinement. Therefore, further investigation about the effect of Ce addition on the microstructures of magnesium alloys is very important for the improvement of the comprehensive properties of magnesium alloys by alloying and/or microalloying with Ce. In addition, the investigation is beneficial to develop new Ce-containing magnesium alloys with excellent properties.In this paper, the effects of Ce addition on the as-cast microstructures of the three typical magnesium alloys, AZ31, AZ91 and ZK60 alloys, were investigated, and the following research results were obtained:①Adding 0.5~2.0wt%Ce to AZ31 alloy not only can form the Al11Ce3 phase, but also can result in a decrease of the amount ofβ-Mg17Al12 phase and can change the morphology ofβ-Mg17Al12 phase from initial continuous net to discontinuous and/or particle-like shapes. In addition, adding 0.5~2.0wt%Ce to AZ31 alloys does not refine the grains. Oppositely, the grains of the Ce-containing AZ31 alloys are coarsened. Under the experimental conditions of this work, an increase in the Ce added amount, melt holding temperature or holding time can slightly improve the grain coarsening effect resulting from the addition of Ce.②Adding 0.5~2.0wt%Ce to AZ91 alloy not only can form the Al11Ce3 phase, but also can result in a decrease of the amount ofβ-Mg17Al12 phase and can change the morphology ofβ-Mg17Al12 phase from initial continuous net to discontinuous and/or particle-like shapes. In addition, adding 0.5~2.0wt%Ce to AZ91 alloys does not refine the grains generally. Oppositely, the grains of the Ce-containing AZ91 alloys are coarsened, especially the AZ91 alloy added 2.0wt%Ce. Under the experimental conditions of this work, an increase or decrease in the melt holding temperature and holding time can improve the grain coarsening effect resulting from the addition of Ce.③Adding 0.5~1.5wt%Ce to ZK60 alloy not only can form the Mg12Ce phase, but also can change the morphology of the Zn-containing secondary phases from initial discontinuous dot shape to continuous stick and coarse block. In addition, adding 0.5~1.5wt%Ce to ZK60 alloys does not refine the grains. Oppositely, the grains of the Ce-containing ZK60 alloys are coarsened, and the coarsening effect becomes more obvious with the increase of Ce added amount. However, the coarsening effect can be significantly improved by increasing or decreasing melting holding temperature, which even lead to the microstructural refinement of Ce-modified ZK60 alloy.