Effect Of Rare Earth Elements And Solidification Rate On The Microstructure And Phase Composition Of AZ31-RE-Sb

Rare earth alloying is a an effective way to improve the microstructure and mechanical property. However, the large needle-like rare earth phase disappears in the Mg alloys containing Al, which has a very strong breaking effect on the base of alloy and hence likely to cause stress concentration. As a result, this would produce unfavorable effects on the mechanical property of alloy.Based on the AZ31, this paper researches the different effect of MM and pure Ce on the microstructure by OM,XRD,SEM&EDS,DTA and so on. Especially, the different behavior of MM-Sb and Ce-Sb on the AZ31 is studied based on the research of our lab; Furthermore, as cast,sub-rapid solidification and extrusion processing are used for these alloys to study the effect of solidification rate on the microstructure of alloys. The solidification process is studied by DTA, and the operating mechanism of spheroidizing of rare earth is analyzed. At last, extraction process of AZ31+1%Ce+1%Sb alloy is studied, and extracts is further analyzed, which provides a valuable reference for improving and controlling the microstructure and of mechanical property AZ31.The results show that:compared with MM, pure Ce has different effect on the microstructure of AZ31 alloy. The phases of AZ31-Ce isα-Mg,β-Mg17Al12和Al11Ce3. Compared with AZ31-MM, the grain of AZ31-Ce refined stronger and the second phase dispersed in the matrix Mg, meanwhile, the large needle-like rare earth phase is less. By DTA, the precipitation order of the second phase for every alloy is defined. That is, for AZ31 alloy:α-Mg→β-Mg17Al12; for AZ31-Ce alloy:Al11Ce3→α-Mg→β-Mg17Al12; for AZ31+Ce+Sb alloy:CeSb→Al11Ce3→α-Mg→β-Mg17Al12. The combined effect of both MM-Sb and Ce-Sb can get dispersed phases, and MM-Sb refine the grain more strongly.The solidification rate has a great influence on the microstructure,the phase and solidification process of alloys. The results show that:In the range of sub-rapid solidification, along with the increasing of solidification rate, the second phases become more refinement, spheroidizing and diffusion.Φ2mm bar has the best microstructure, which contains Al-Ce-Sb ternary phase; In the range of rapid solidification, along with the increasing of solidification rate, the worm-like second phases are discovered. This is different with the globular phases of as sub-rapid solidification alloy which contain more Sb and less Al. According the DTA, compared with the as cast alloy, as sub-rapid solidification alloy has higher eutectic temperature. The globular Al-Ce-Sb ternary phases separate out at 630.03℃, while the worm-like phases of rapid solidification alloy separate out at 628.61℃.According the research on extraction of AZ31+1%Ce+1%Sb alloy, the best extraction solution is setted:VHCl=VH2O=1:1. By XRD analysis, the extracted phases are defined:Mg17Al12,Sb,AlSb,CeSb and Al4Ce; By SEM&EDS, the morphology of the extracted phases is defined:Sb is polyhedron, AlSb is irregularity polyhedron, and globular CeSb is a variation of irregularity polyhedron.