Effect Of Rolling Process On Microstructure And Mechanical Properties Of Mg-Gd-Ni Alloys

Magnesium alloys,as structural and functional materials,are increasingly used in the electronics industry,aviation development,automobile industry,medical treatment and other areas due to their high specific strength and stiffness.However,one of the key factors restricting the further application and development of magnesium alloys is their low mechanical properties and poor corrosion resistance.In recent years,some scholars have found a kind of magnesium alloy with Long-period Stacking ordered phase,which exhibits excellent mechanical properties at room temperature and high temperature,and attracts much attention.It is found that Mg-Gd-Ni alloys containing LPSO phase have high strength,good plasticity and high temperature stability.However,as-cast magnesium alloys are prone to defects such as shrinkage and voids,and the structure is relatively thick.Researchers are still committed to optimizing the structure of magnesium alloys by adding alloying elements and deformation processing to further improve the mechanical properties of the alloys.However,the effect of deformation processing on the mechanical properties of LPSO-Mg-Gd-Ni alloys has not been systematically studied.Therefore,it is necessary to systematically analyze the effect of deformation processing technology on the microstructure and mechanical properties of Mg-Gd-Ni alloy containing LPSO phase.In this paper,Mg-Gd-Ni alloys containing LPSO phase(Mg₉₈Gd_1.5Ni_0.5,Mg₉₇Gd₂Ni₁ and Mg₉₆Gd₃Ni₁)were prepared by conventional casting method.The deformation of Mg-Gd-Ni alloys was investigated by different rolling processes.The effects of rolling process on the microhardness of Mg-Gd-Ni alloys containing LPSO phases were analyzed by means of scanning electron microscopy（SEM）,X-ray diffraction（XRD）,tensile test and hardness test.The effect of rolling deformation on the microstructure and mechanical properties of Mg-Gd-Ni alloy and the effect of volume fraction of LPSO phase on the microstructure and mechanical properties of the alloy were studied.The strengthening mechanism of rolling process on Mg-Gd-Ni alloy containing LPSO phase was systematically explored,and a more efficient and convenient rolling process was explored.The results show that with the increase of rolling deformation,the precipitated LPSO phases in Mg₉₇Gd₂Ni₁ alloy are crushed from as-cast lamellar lattice structure to form fibrous structure orderly arranged along the rolling direction,and the matrix structure is refined.The tensile strength and hardness of Mg₉₇Gd₂Ni₁ alloy increased by about 50% and 40%respectively,but the plasticity decreased and the elongation decreased by about 50% when the rolling deformation increased from 40% to 80% under the dual mechanism of fiber strengthening and fine grain strengthening.However,the plasticity of the alloy increases greatly with the increase of deformation at high temperature,and the alloy has a strong high temperature stability.The volume fraction of LPSO phase in the alloy is affected by adjusting the content of Gd and Ni.With the increase of volume fraction of LPSO phase,the distribution of LPSO phase in the alloy changes from discontinuous to continuous,and the size increases.Meanwhile,the matrix of a-Mg is refined.Because the hardness and strength of LPSO phase are higher than that of matrix,the mechanical properties of the alloy are improved obviously when the volume fraction of LPSO phase increases.The analysis of alloy composition shows that all Ni elements exist in LPSO phase,that is,Ni promotes the growth of LPSO phase.It was found that the comprehensive mechanical properties of Mg₉₆Gd₃Ni₁ alloy with 80%rolling deformation were better.However,due to the numerous rolling passes and complex processes of alloy sheets with 80% deformation obtained by conventional rolling process,the inter-pass heat treatment lengthens the process time,thus increasing the production cost,which is not suitable for large-scale industrial production.In this paper,60% deformed alloy sheet was prepared by large plastic deformation cumulative overlapping rolling process.It was found that the comprehensive mechanical properties of the sample were not significantly different from those of 80% deformed alloy by conventional hot rolling.The cumulative overlapping rolling process can greatly improve the mechanical properties of the alloy,reduce rolling passes and time-consuming.It can achieve the target performance with higher efficiency and energy saving,and is suitable for industrial mass production.