Microstructure And Mechanical Properties Of Mg-Li/Al Composite Plate Fabricated By Roll Bonding And ARB

With the advantages of low-density, good machining property, excellent castability,damping ability, electromagnetic shielding, weaken anisotropy, high specific stiffness and specific strength, etc, Mg-Li alloy is becoming one of more and more attractive materials. It has widespread applications in the fields of aerospace, military industry, machinery, vehicles,3C products, medical and microelectronics. However, its corrosion resistance is so poor that the broad application of Mg-Li alloy in the actual life may be limited. Therefore, it is important to improve its corrosion resistance. It is known that aluminum and aluminum alloys have better corrosion resistance and they are extensively used as lightweight materials. In this paper, Al/Mg-Li alloy/A1 composite plates were fabricated by hot rolling with 50% thickness reduction at 400℃, and Mg-Li/Al clad metal sheets were fabricated by accumulative roll bonding(ARB). The microstructure and mechanical properties of Al/Mg-Li alloy/Al composite plates were investigated after they were annealed, and the evolution of microstructure and mechanical properties of Mg-Li/Al clad metal sheets during accumulative roll bonding was researched.The composite plates fabricated by hot rolling have a good bonding strength. The composite plates were annealed at 200℃-400℃ for 1h. When the temperature is lower than 300℃, no obvious diffusion layer is formed at the interface. The diffusion layer consisting of Al3Mg2 and Mg17Al12 is formed at the interface after annealing at and above 350℃,meanwhile the recrystallization occurs in the Mg-Li alloy. The diffusion layer becomes thicker with the increase of the annealing temperature, causing the decrease of ultimate tensile strength. Because of the diffusion layer, the bonding strength and the hardness of the clad plate at the joint interface increase sharply, the tensile strength decreases sharply. When annealed at 400℃, the bonding strength is 22.64MPa, the hardness at the joint interface is 95.8HV, the tensile strength is 155.23MPa and the elongation is 25.69%.Composite plates were annealed for different time at 300℃ ,the recrystallization occurs in the β(Li) phase holding 0.5h. The nodularization occurs in the a(Mg) phase for 1h, and there is no diffusion layer occurs at the interface. The microstructure of Mg-Li alloy remains unchanged and a thin diffusion layer is formed at the interface for 1.5h. When annealing time was prolonged, the microstructure of Mg-Li alloy remains unchanged,intermetallic compounds consisting of Al3Mg2 and Mg17Al12 is formed discontinuously at the interface. The intermetallic compounds links up gradually holding 2.5h. The diffusion layer remains unchanged holding 3h.With the prolonged annealing time, the hardness of Mg-Li alloy keeps in a stable scope at the beginning, and then decreases gradually, the hardness of pure A1 decreases slowly at the beginning, then decreases sharply for 1h, finally decreases slowly again, the hardness of the interface decreases gradually at the beginning, increases sharply for 1.5h, then increases slowly. With the annealed time prolonged, the bonding strength increases gradually, reaches the maximum value of 19.12MPa for 3h. The tensile strength increases then decreases, finally decreases sharply. The elongation increases, and then remains constant. The tensile strength of the composite plates is 204.51MPa and the elongation is 16.39%.Al/Mg-Li clad metal sheets were fabricated by accumulative roll bonding, its bonding strength reaches 10.45MPa. With the increase of ARB passes,the α-Mg and β-Li phases are gradually elongated. The average grain size of the α-Mg phase in the fifth passes is approximate 20μm, the average grain size of the P-Li phase ranges between 5μm and 10μm.The α-Mg and β-Li phases break into small pieces and cause a uniform distribution, and the average grain size of the β-Li phase is less than 5μm. With the increase of ARB passes, the ultimate tensile strength of the composite plates, hardness of Mg-Li alloy and pure Al are enhanced. In the sixth passes, the ultimate tensile strength is 290.54MPa, and the microhardness values of Mg-Li alloy and pure A1 reaches 75.1 HV and 79.4HV,respectively.