Effects Of Alloying And Rolling Deformation On Mechanical And Corrosion Behavior Of Binary Mg-Li Alloy

Magnesium-lithium alloy,as the lightest structural metal material at present,has broad application prospects in aerospace,medical and military fields by virtue of its high specific stiffness,strong processing deformation ability and strong anti-electromagnetic interference ability.However,its shortcomings such as low absolute strength,obvious mechanical and corrosion anisotropy and poor corrosion resistance seriously hinder its development.Therefore,it is of great application value and theoretical significance to study the mechanical and corrosion behavior of Mg-Li alloys.In this paper,the effects of icosahedral phase?I-phase?and rolling deformation on the mechanical and corrosion behavior of Mg-8Li base alloys were systematically studied by microstructure characterization,mechanical experiments and corrosion experiments,which provided a basis for subsequent experimental studies and service conditions of Mg-Li alloys.The results show that the yield strength of cast Mg-8Li-6Zn-1.2Y alloy was 91.64%higher than that of Mg-8Li alloy,but the plasticity decreased by 28.78%.During hot rolling,I phase was crushed,?-Mg phase was rolled along the rolling direction and gradually crushed,and?-Li phase was aggregated;the crushed grain of Mg-8Li alloy grew up in the holding process,the great difference in grain size,and the two-phase in rolling Mg-8Li alloys had obvious texture effect.Compared with the Mg-8Li alloy with reduction ratio of33%,the c-axis of Mg-8Li alloy grain with reduction ratio of 90%was in“soft orientation”along the rolling direction?RD?and transverse direction?TD?,the yield strength of the alloy with two orientations is reduced by about 25 MPa,the ductility was increased by 31%and7.5%respectively,and the mechanical anisotropy was obvious.Dispersion distribution of fragmented I phase resulted in second phase strengthening of the alloy;in addition,I phase promoted dynamic recrystallization,resulting in small and uniform grain size and fine grain strengthening of the alloy,and the c-axis was in“hard orientation”,the yield strength and ductility of Mg-8Li-6Zn-1.2Y alloy in RD and TD directions increased by about 20 MPa and 10%respectively,and the mechanical anisotropy of Mg-8Li-6Zn-1.2Y alloy in two orientations was weaker due to the weakening of texture effect by I phase.With the increase of cold reduction ratio from 33%to 90%,the hardening effect of Mg-7Li alloy was more obvious.The hardness of?-Mg phase and?-Li phase increased by 7.35%and 20.75%,respectively.The strength of the alloy increased by 43 MPa and the ductility decreased by a factor of 7%.It was found that owing to grain crushing and texture effect of alloy phase after rolling,the corrosion resistance of Mg-8Li alloy was improved.The corrosion process of rolling Mg-8Li alloys can be divided into two stages:at the first stage,the corrosion resistance of Mg-8Li alloys decreased with the increase of reduction ratio.The main reason is that the higher fragmentation degree of the?-Mg phase was,the more the galvanic corrosion occurred with the?-Li phase,and the corrosion mainly occurred in the?-Li phase with a more negative potential.The second stage,the two phase surface formed different components of the product film,and the Li₂CO₃ surface film on the?-Li phase can tightly bond with substrate and had high stability,which can effectively protect the?-Li phase,while the corrosion of the?-Mg phase intensified and the rate of hydrogen evolution accelerated.In this stage,due to the largest area of?-Li phase proportion?85%?,the corrosion resistance of the alloy with reduction ratio of 90%was greatly improved.The order of corrosion resistance was that the alloy with reduction ratio of 67%was the highest,followed by the alloy with reduction ratio of 90%,and the alloy with reduction ratio of 33%was the lowest.The corrosion resistance of cast Mg-8Li-6Zn-1.2Y alloy was better than that of Mg-8Li alloy because the network distribution of I phase can prevent corrosion from penetrating into the matrix.The crushed I phase after rolling can form more galvanic batteries with the matrix,and the corrosion resistance of the alloy decreased sharply.Rolling alloys,the phase of a-Mg was slender in TD plane,forming a laminated structure with the phase of?-Li;the phase of?-Mg in RD plane was fragmented and smaller in size,I phase was fragmented and distributed in the matrix.The corrosion of Mg-8Li alloy TD surface was serious and directional,but there was no obvious corrosion direction on RD surface,and the alloy showed obvious corrosion anisotropy.The corrosion of Mg-8Li-6Zn-1.2Y alloy on RD and TD surfaces showed weaker directionality,and the corrosion anisotropy was weaker than that of Mg-8Li alloy.