The Effect Of Al,Si And Y On The Microstrure And Mechanical Properties Of The Mg-4Li Alloys

As the lightest metal structural material in engineering application so far,compared with other metal materials,Magnesium-lithium alloys have many incomparable advantages,such as low density,high specific strength and specific stiffness,good casting performance and mechanical processing and excellent plastic forming ability,etc.which have shown a broad application prospect in the field of aerospace,automotive,communications and so on.It has aroused great interest and wide attention by researchers.However,it is difficult to reach the requirement of the application field because of its low absolute strength,which restricts its further development and application to a great extent.How to improve the comprehensive mechanical properties of Mg-Li alloys has become the focus of researchers.In this paper,the Mg-Li alloys were prepared by high frequency induction heating by magnetic levitation.Firstly,the effects of Al on the microstructure and mechanical properties of as-cast and as-rolled Mg-4Li-xAl alloys were studied by adding different content of Al in Mg-4Li alloy.The experimental results showed that whle the AlLi and ?-Mg17Al12 phase were precipitated in Mg-4Li alloys adding Al element.The hardness and tensile strength of the alloys had a rising trend with the increase of Al element content.Respectively the hardness and tensile strength of as-rolled Mg-4Li-6Al alloys were 75.66 HV,328 MPa.Contrary the plasticity of as-rolled alloys were decreased.When the content of Al element in the alloy reached more than 3wt.%,the performance of the alloys were small.Then considering various factors,Mg-4Li-3Al alloys were chosen as the substrate.It is analyzed the effects of different Si element content on microstructure and mechanical properties of as-cast and as-rolled Mg-4Li-3Al-xSi alloys.The experimental results showed that the herringbone Mg2 Si new phase was precipitated in the Mg-4Li-3Al-xSi alloys adding Si element.The two precipitates were continuously connected to each other and overlapped with each other to form precipitation strengthening.With the increase of Si content(0.5~1~2wt.%),the hardness and tensile strength of the alloy showed a rising trend.Respectively the hardness and tensile strength of as-rolled Mg-4Li-3Al-2Si alloys were 89.21 HV,370 MPa.Contrary the plasticity of as-rolled alloys were decreased.Lastly,it is further investigated and analyzed that the effects of Y content on microstructure and mechanical properties of as-cast and as-rolled Mg-4Li-3Al-2Si-xY alloys on the basis of as-rolled Mg-4Li-3Al-2Si alloys with the best comprehensive properties.The experimental results showed that the Mg24Y5 new phase was precipitated in the Mg-4Li-3Al-2Si-xY alloys with adding Y element.With the increase of the Y element content in the alloys,the refinement effect was more obvious and the more precipitated rare earth phases were generated.The rare earth phases formed in as-rolled alloys were uniformly dispersed in the matrix,and streamline distributed along the rolling direction.Respectively the hardness and tensile strength of as-rolled Mg-4Li-6Al alloys were 91.0 HV,390 MPa.Contrary the plasticity of as-rolled alloys were decreased.When the content of Y element was 2wt.%,the phenomenon of agglomeration and enrichment occured in alloys microstructure.The hardness and tensile strength of the alloys showed a trend of first increase and then decrease with the increase of Y element.