Study On Structure And Properties Of Hot-Roll Bonded Ti/Al/Mg Laminated Sheets

Ti/Al/Mg laminated sheets have great application prospects in aerospace,automotive and marine industries.The interfacial structure and microstructure of the laminated sheet have great effect on its properties.It is one of the hot issues of research to control the interfacial structure and microstructure of laminated sheet to regulate its mechanical properties.In this paper,the Al/Mg clad sheet,Ti/Al clad sheet and Ti/Al/Mg laminated sheet were fabricated by the hot roll bonding method at 400°C by using commercial Ti6Al4V titanium alloy,AA6061 aluminum alloy and AZ31 magnesium alloy.The interfacial structure and microstructure of the laminated sheets were observed with optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),electron backscatter diffraction(EBSD)and X-ray diffraction(XRD).Tensile and hardness tests were conducted to investigate the mechanical properties of the laminated sheets.The effect of the annealing on the microstructure and mechanical properties of Al/Mg clad sheet,Ti/Al clad sheet and Ti/Al/Mg laminated sheet was studied.The effect of the rolling reduction on the microstructure and mechanical properties of Ti/Al/Mg laminated sheet was explored.The growth laws of the intermetallic compounds(IMCs)in the Al/Mg and Ti/Al interfaces were also discussed.(1)The Al/Mg interface exhibited fine interfacial bonding after hot rolling.The IMCs containing of Al₃Mg₂ and Al₁₂Mg₁₇ phases were observed in the bonding interface after annealing at 250°C or higher.The Al₁₂Mg₁₇ layer showed thick columnar grains and the Al₃Mg₂ layer presented rod-like.The Kirkendall voids and impurities(Mg₂Si and?-Al₈Fe₂Si)formed in the Al₃Mg₂ layer.The thickness of the IMC layers increased linearly with the square root of the annealing time.The activation energies for the growth of Al₃Mg₂ and Al₁₂Mg₁₇ phases were found to be 78.08 and 112.15 k J mol^-1,respectively.The tensile strength decreased with the increasing annealing temperature,but the elongation showed a maximum value at 200°C.The sample anneled at 200°C for 1 h showed the fine mechanical properties with the tensile strength of 238 MPa and elongation of 18.6%.(2)The Ti/Al interface exhibited fine interfacial bonding after hot rolling.The Ti Al₃phase formed in the Ti/Al interface when the annealing temperature was at and above550°C.The Al atoms were the dominant diffusing atoms through the Ti Al₃ layer and reacted with Ti atoms at the Ti/Ti Al₃ interface.A thin layer including Mg Al₂O₄ and unreacted Al was observed in the Ti Al₃ zone near the Al side.The thickness growth of the Ti Al₃ layer was dominated by reaction diffusion and the exponential factor n was 0.82.The tensile strength of the clad sheets initially decreased,the 400°C annealed sample had the smaller tensile strength of 368 MPa,subsequently increased with the increasing annealing temperature,the 550°C anneled sample had the higher tensile strength of 427MPa,and then finally decreased.The tensile strength of the clad sheet was in good agreement with the calculated value from the rule of mixture.The ductility increased with the increasing annealing temperature,reaching its maximum value of 18.7%at 550°C,and then decreased.(3)Ti/Al/Mg laminated sheets exhibited good interfacial bonding.The rolling reduction had a significant effect on the deformation inhomogeneity through the thickness of the Al layer.The shear texture of the Al layer formed near the Ti/Al interface and permeated into the center layer in the sample with the greater rolling reduction.With the increasing rolling reduction,the tensile strength value increased from 355 MPa to 474MPa,and the elongation decreased from 12.4%to 6.7%.The tensile fracture mechanism of the Ti/Al/Mg laminated sheet was connected to the bonding strength of the Al/Mg and Ti/Al interfaces.(4)When the annealing temperature of the Ti/Al/Mg laminated sheet was 200°C or higher,the Al₃Mg₂ and Al₁₂Mg₁₇ were observed at the Al/Mg interfaces,whereas no visible interfacial IMCs appeared at the Ti/Al interfaces even after annealing at 400°C.The Ti layers had the similar microstructures,showing c//TD,<11-20>//ND and<10-10>//RD textures.The annealed Mg layers presented a basal texture and dispersed away from the ND direction.The tensile strength of laminated sheet decreased,while the elongation reached a maximum value at 200°C.The sample annealed at 200°C for 1 h showed the fine mechanical property with the tensile strength of 415 MPa and elongation of 19%.The tensile fracture mechanism of the Ti/Al/Mg laminated sheet was mainly related to the IMC thickness in the Al/Mg interface.