Microstructure And Mechanical Properties Of Mg-9Li-1Al/2A12 Composite Plate Based On Accumulative Roll Bonding

Magnesium-lithium（Mg-Li）alloy is currently the lightest metal structural material,which has low density,high specific strength,excellent damping properties and electromagnetic shielding properties.Mg-Li alloy is an ideal lightweight material,but its strength is low,which limits its application in some fields.2XXX series aluminum alloys are another important lightweight materials with low density,high strength and good processability,which are often used in aerospace and other fields.Through the composite rolling and accumulative roll bonding（ARB）process,the ultra-light and high-strength Mg-9Li-1Al/2A12 alloy multilayer composite sheet was prepared by fully combining the respective advantages of the two alloys,which has important significance for the theoretical research and engineering application.In this paper,Mg-9Li-1Al alloy and 2A12 aluminum alloy were used as the component alloys,and the optimal rolling process for preparing the composite plate was investigated by controlling the rolling temperature and rolling reduction,then this process was used to carry out accumulative roll bonding.The evolution of microstructure and mechanical properties during ARB process was analyzed.Finally,on this basis,the effect of aging treatment on the microstructure and mechanical properties was further investigated.The optimal parameters are the rolling temperature of 400℃and the rolling reduction of50%.The alloy plates can achieve synergistic deformation,and the tensile strength of the composite plate is 282 MPa,and the elongation is 22%.Its mechanical properties are between the individual plates（179 MPa～352 MPa,14%～24%）.It maintains a good elongation and provides performance preparation for the subsequent accumulative roll bonding.Accumulative roll bonding of the composite sheets was performed using the optimal process,and the grains in the Mg-Li alloy were gradually refined with the increase of ARB cycles.At ARB5,the grain refinement reached the limit,and the average grain sizes ofα-Mg phase andβ-Li phase were 12.11μm and 2.56μm,respectively,and theβ-Li phase was gradually induced to generateα-Mg phase insideβ-Li phase due to high strain,breaking the the continuity of theβ-Li phase.A gradual decrease in the size of the hard and brittle second phase of the 2A12 aluminum alloy during ARB and a gradual increase in the number of submicron and nanoscale second phases;The gradual formation of diffusion layers of Mg₁₇Al₁₂and Al₃Mg₂ on both sides of the bonding interface of the composite sheet during the ARB process;With the increase of ARB cycles,the interfacial bond strength,specific strength and tensile strength of composite plate gradually increased,the interfacial bond strength at ARB6was 28.7 MPa,the specific strength was 163 N·m/g,the tensile strength reached 359 MPa.The tensile strength increased by 156.4%compared with the pre-rolled magnesium-lithium alloy;The elongation of the composite sheet decreased gradually with ARB,and was 14.3%at ARB6,which was a 16.3%improvement compared to the pre-rolled solid solution state of 2A12aluminum alloy;At the same time,the hardness of the composite sheet was increased under the ARB process,with the hardness of the magnesium-lithium alloy reaching a peak of 72.8 HV at ARB5 and the hardness of the 2A12 aluminum alloy reaching a maximum of 117.4 HV at ARB6,representing an increase of 47.7%and 59.9%in the hardness of the two component alloys,respectively.In order to investigate the effect of aging treatment on the microstructure and mechanical properties of ARB composite plates,ARB5 composite plates were aged at 200℃.The best overall performance of composite plates was obtained when the aging time was 3h.The interfacial bond strength and tensile strength of the composite sheets peaked at 30.4 MPa and375 MPa,respectively,at 3h of aging,which increased by 8.2%and 8.7%,respectively,compared with those before aging.With the extension of aging time,the elongation of the composite plate slowly increased to 20.3%,which was 23%higher compared with that before aging,and the hardness of the magnesium-lithium alloy decreased to 55.2 HV,and the hardness of 2A12 aluminum alloy reached a peak of 127.7 HV at 3h of aging,which was 11.3%higher compared with that before aging.