Effect Of Rare Earth Elements On Microstructures And Properties Of AZ80 Alloy

Magnesium alloys possess excellent properties such as high specific strength,high damping ratio,and well casting properties.However,the low strength at room temperature and the poor plasticity severely prevent it from applications.In this paper,the microstructure and properties of AZ80 alloy are optimized by microalloying and adjusting melting process.The influence of rare earth ratio on the microstructure and properties of AZ80 are studied.The effects of melt mixing and melting process parameters on the microstructure of AZ80-RE alloy are investigated.In mix melting,the influence of total content of rare earth on the properties of AZ80-RE alloy is also studied.In AZ80 alloy,when La is separately added for microalloying,the rare earth phase of the acicular Al₁₁La₃ phase and the bulk Al₁₁La₃ phase with a hole in the middle are formed.The size of the RE phase is large,but well distributed.When Gd is separately added,a bulk Al₂Gd phase with a regular edge is obtained,but the bulk phase shows a certain degree of aggregation.When two kinds of rare earth elements are added in combination,the original coarse Al-RE phase is finely dispersed,and at the same time contains a plurality of morphological Al-RE phases.Regardless of the proportion of rare earth elements added to the AZ80 alloy,the number of?-phase which originally network distributed is reduced,and changes into island distribution.When two rare earth elements are added in combination,La and Gd elements grow together to form a structure similar to the replacement solid solution in the formation of Al-RE phase.Bulk Al₂Gd phase,acicular Al₁₁La₃ phase and bulk Al₁₁La₃ with holes in the middle exist reciprocal inhibition phenomenon.Under these inhibitions,AZ80-3La-1Gd alloy possess the best mechanical properties with tensile strength of 223MPa,and the elongation reaches6.61%.Under the condition of total RE content of 3%,4%and 5%,the optimum rare earth element ratio does not change with the total content of rare earth elements.It is found that the bottleneck restriction on the improvement of rare earth magnesium alloy is the size and distribution of Al-RE phase.The stirring effect applied under the ordinary melting process can only well distribute the rare earth phase which is formed originally,but will not refine the phase.Therefore,the body mixing and melting process is adopted.It is found that under the melt mixing and stirring process,the obtained Al-RE phase is remarkably refined.When the mechanical stirring time is 180s,the alloy structure is the smallest and the dispersion.Finally,the microstructure characteristics of the alloys obtained by the total content of different rare earth elements at a ratio of La:Gd of 3:1 under the melt mixing and agitation process were studied.The results show that under the melt mixing and stirring smelting process,the morphology of Al-RE phase changed greatly,and the point shape changed from ordinary smelting process to intermittent needle shape,but the rare earth phase size did not change significantly,so the tensile strength was also.There have been significant changes.The elongation of the alloy obtained under the melt mixing and stirring smelting process is improved,and the elongation is 8.23%at a total rare earth content of 4%,which is 24.5%higher than that in the ordinary smelting process..