Effect Of Y And Ce On Microstructure And Properties Of Mg-Al-Si Alloy

In the 21st century,the problem of non renewable energy consumption and environmental pollution is becoming more and more serious.Although magnesium alloy has the advantages of high specific stiffness,specific strength and low density,it is an ideal material for car body weight reduction.However,when the working temperature is higher than 120℃,the mechanical properties of the alloy begin to deteriorate,which can not meet the requirements of high temperature work.In order to expand the application scope of magnesium alloy in automobile industry and realize the lightweight of automobile body,so as to achieve the purpose of saving energy and environmental pollution,the first thing is to develop low-cost and good performance heat-resistant magnesium alloy.At present,the alloying elements of most heat-resistant magnesium alloys are rare earth elements,and the addition of rare earth elements is relatively large.This leads to the high price of alloy,it is difficult to achieve large-scale application in the automotive manufacturing industry,and it can not achieve the purpose of lightweight car body.It is worthy of further study to find alloying elements which can replace rare earth elements and are cheap.In this paper,Si and Al are introduced into magnesium alloy by adding Al-26Si intermediate alloy.Firstly,Mg-14Al-5Si is selected as the base alloy for subsequent modification by adjusting the addition of Si elements in the alloy.Then,Mg-14Al-5Si-x Y and Mg-14Al-5Si-y Ce alloys were prepared by adding Y and Ce respectively to Mg-14Al-5Si alloy.According to the structure and properties of Mg-14Al-5Si-x Y and Mg-14Al-5Si-y Ce alloys,the amount of Y and Ce elements with the best modification effect was determined.In this paper,the microstructure and composition of the alloy are analyzed by OM,ICP,XRD,SEM and EDS.The mechanical properties of the alloy are tested by using brinell hardness tester and electronic universal tester.The addition of Si and the content of Al are studied and the effects of the addition of Y and Ce on the mechanical properties of Mg-14Al-5Si-x Y and Mg-14Al-5Si-y Ce alloys are studied in this paper.The results provide the basic data for the research and application of low cost heat resistant magnesium alloys.Al-26Si master alloy was used to introduce Si and Al into magnesium alloy,adding 0.8wt%、2.0wt.%、3.0wt.%、4.0wt.%、5.0wt.%.It is found that the amount of Mg₂Si phase andβ-Mg₁₇Al₁₂ phase in Mg-Al-Si alloy is the most when 5.0wt.%Si is added,and the Brinell hardness of the alloy is the highest,which is 109HB.Therefore,Mg-14Al-5Si alloy is selected to be modified by adding rare earth elements.The Mg-14Al-5Si-x Y alloy was prepared by adding 0wt.%,0.5wt.%,0.8wt.%,1.0wt.%and 1.5wt.%Y to the alloy.It was found that the addition of Y could effectively improve the microstructure of the alloy,and the morphology of Mg₂Si phase andβ-Mg₁₇Al₁₂ phase in Mg-14Al-5Si-x Y alloy was significantly improved.When Y content is 1.0wt.%,the modification effect is the best.At this time,the Mg₂Si phase in Mg-14Al-5Si-1Y alloy changes from coarse dendrite to round,and the average size of Mg₂Si particles decreases to 8.15μm,which is 80.69%less than that in the unmodified Mg-14Al-5Si alloy.The morphology ofβ-Mg₁₇Al₁₂ phase in Mg-14Al-5Si-1Y alloy is also significantly improved,which changes from coarse continuous grid to island when 1.5wt.%Y is added to the alloy,white block Mg-Y-Si compound appears in Mg-14Al-5Si-1.5Y alloy,which consumes more Y element in the melt and weakens the modification effect of Y element,resulting in over modification of Mg-14Al-5Si-x Y alloy.The Brinell hardness,tensile strength,yield strength and elongation of Mg-14Al-5Si-x Y alloy first increase and then decrease with the increase of Y content.The results show that the comprehensive mechanical properties of Mg-14Al-5Si-1Y alloy reach the highest when the Y content is 1.0wt.%,and the Brinell hardness of Mg-14Al-5Si-1Y alloy is 135HB,which is 23.85%higher than that of unmodified Mg-14Al-5Si alloy;the tensile strength,yield strength and elongation of Mg-14Al-5Si-1Y alloy are 147HB,76HB and 5.04%,which are 27.83%,31.03%and 278.95%higher than that of unmodified Mg-14Al-5Si alloy.The Mg-14Al-5Si-y Ce alloy was prepared by adding 0wt%,0.5wt%,1.0wt%,1.5wt%and2.0wt%Ce to the alloy.It was found that the microstructure of Mg-14Al-5Si-y Ce alloy was effectively improved by adding Ce.The morphology of Mg₂Si phase andβ-Mg₁₇Al₁₂ phase in Mg-14Al-5Si-y Ce alloy was also improved.When the content of Ce is 1.5wt.%,the modification effect is the best.At this time,the Mg₂Si phase in Mg-14Al-5Si-1.5Ce alloy changes from coarse dendrite to round dot,and the average size of Mg₂Si particles decreases to6.07μm,which is 85.62%less than that in the unmodified Mg-14Al-5Si alloy;the morphology ofβ-Mg₁₇Al₁₂ phase in Mg-14Al-5Si-1.5Ce alloy also changes from coarse continuous grid to discontinuous and fine.The white rod-shaped Ce Si₂ phase was found in the alloy with 2.0wt.%.On the one hand,the increase of the average size of the compound consumes more Ce in the melt,which weakens the modification effect of Ce on the alloy;on the other hand,the increase of the average size of the compound reduces the number of Ce Si₂ phase which can meet the nucleation core size of Mg₂Si crystal,resulting in the over modification of Mg-14Al-5Si-2Ce alloy.The Brinell hardness,tensile strength,yield strength and elongation of Mg-14Al-5Si-y Ce alloy first increase and then decrease with the increase of Ce content.The comprehensive mechanical properties of Mg-14Al-5Si-1.5Ce alloy reach the highest when Ce content is1.5wt.%,and the Brinell hardness of Mg-14Al-5Si-1.5Ce alloy is 145HB,which is 23.85%higher than that of unmodified Mg-14Al-5Si alloy;the tensile strength,yield strength and elongation of Mg-14Al-5Si-1.5Ce alloy are 149 MPa and 92 MPa respectively Compared with the unmodified Mg-14Al-5Si alloy,it increases by 22.82%,58.62%and 193.98%respectively.When Y and Ce are added to Mg-14Al-5Si alloy,the modification effect of Y onβ-Mg₁₇Al₁₂ phase is better than that of Ce,and the modification effect of Ce on Mg₂Si phase is better than that of Y.The effect of Y element on the elongation of the alloy is more significant,while Ce element on the strength and hardness of the alloy is more significant.