Effect Of Yttrium And Calcium On Microstructure And Properties Of Intermetallic Compound Mg₁₇Al₁₂

Intermetallic compounds,as its higher temperature resistance,higher hardness,corrosion resistance,anti-oxidation,and the unique physical and chemical properties,have played an important role in the field of materials science.Currently,the study of department of M-Al intermetallic compounds are mainly concentrated on the Ni-Al system intermetallic compounds and Fe-Al system intermetallic compounds at home and abroad,which has been more profound understanding after years of research.Mg₁₇Al₁₂ is important for Mg-Al system intermetallic compounds.At present,the research on Mg₁₇Al₁₂ mostly concentrates on the corrosion coating and hydrogen storage properties.The study of Mg₁₇Al₁₂ single phase of the organizational structure,mechanical properties and corrosion resistance is little and scanty.The two major drawbacks of Mg₁₇Al₁₂,low melting point and poor plasticity,greatly limit its application in the actual production.Intermetallic compound of Ni3Al,Fe3Al also have poor ductility,but we can improve the plasticity by making alloyed.Given that,this paper attempts to enhance the material properties of Mg₁₇Al₁₂ by adding rare earth elements and alkaline earth elements,and also explore the performance of the mechanism of change.In this paper,we select rare earth Y and alkaline earth Ca as adding elements in Mg₁₇Al₁₂.The contents of Y and Ca are 0.5%,1%,2%,4%,5%in the Mg₁₇Al₁₂ alloy respectively.Then its microstructure,structure,hardness,corrosion resistance and mechanical properties were tested.Through these processes,we have derived Mg17Al112 the alloying mechanism of Mg₁₇Al₁₂ identified the reason for the changes of its performance,and determined the optimum amount for improving performance by alloying.The results of this study:?1?A new irregular phase A12Y and a renju shaped phase eutectic structure?-Mg+?-Mgl7Al12 are formed after adding rare earth Y in single phase Mg₁₇Al₁₂.With the increase of Y content,organizations continually be refined,the number of eutectic structure is from little to much,morphology is from the point to the line and from short to long,and the trend of interconnecting into a mesh have appeared.The hardness of the alloy gradually advance with the increase of Y content and this due to grain refinement and the precipitation of the hard phase A12Y.When the rare earth content is 2.0wt%Y,new precipitation A12Y phase and the eutectic Mg₁₇Al₁₂ phase get together can resist corrosion,self-corrosion potential of Mg₁₇Al₁₂+2.0wt%Y is improved by 0.926V compared with Mg₁₇Al₁₂,and self-corrosion current reduce an order of magnitude.It shows excellent corrosion resistance more than Mg₁₇Al₁₂.But with the Y addition,depleted of Al zone is increasing and this may due to the combination of A1 and Y,the uniformity is deteriorated,many eutectic structure promote the corrosion of the alloy so that the corrosion resistance of the alloy has been greatly reduced,even in the addition amount of 5.0 wt%is less than Mg₁₇Al₁₂.The compression performance of Mg₁₇Al₁₂ after adding.Y has been improved significantly.This is the effect of fine grain strengthening and precipitation phase dispersion strengthening.Especially,compression ratio of Mg₁₇Al₁₂+2.0wt%Y increases 6.7 times compared with Mg₁₇Al₁₂.With the increase of Y,excessive eutectics are easier to crack.On the other way,excessive Y leads to the combination of A12Y Phase,increases the stress concentration.These deteriorate the mechanical properties of Mg₁₇Al₁₂.As all things considered,Mg₁₇Al₁₂ has excellent corrosion resistance and mechanical properties after adding 2wt%rare earth Y.?2?Adding Ca in the Mg₁₇Al₁₂is closely related to the amount of addition of Ca on whether it can generate an alkaline earth phase or not.When the added amount of the element Ca is less than 1%,Ca does not combine with other elements to form a new phase,but as the formation of?Mg,Ca?17Al12 solid solution in Mg₁₇Al₁₂.When the added amount of the element Ca is more than 1%,Ca firstly combine with Al generated Al2Ca.The size of Al2Ca is increased larger,and the trend of interconnecting is also more and more clear as the Ca content increasing.The addition of Ca is also contributed to the formation of eutectic structure of ?-Mg + ?-Mg₁₇Al₁₂,which is different form Y addition.The eutectic transition temperature change from 437 ? to 470 ? after adding Ca.This leads to a reduction in eutectic,and poor uniformity.After adding 1%Ca,the hardness of the alloy are proportional to the content of Ca.This is the same reason with adding Y,the difference is that the hardness of Mg₁₇Al₁₂+Ca is lower than the hardness of Mg₁₇Al₁₂+Y.Its attributed to the hardness of Al2Ca is lower than Al2Y.The corrosion resistance of Mg₁₇Al₁₂ is improved after adding Ca,self-corrosion current of Mg₁₇Al₁₂+2%Ca reduce an order of magnitude.Compression performance of Mg₁₇Al₁₂ achieved the best property after adding 1 wt%of Ca.Compression rate improves 1-fold compared with the single-phase Mg17AL12.Overall consideration,lwt%Ca is the best optimum additive amount which have great corrosion resistance and mechanical properties.