Interfacial Microstructure And Properties Of Mg Alloy Laminated Composites

In recent years,the demand and development of high performance light-weight structural materials have become particularly urgent due to the increasingly serious energy crisis and environmental pollution.As the lightest metallic structural material,Mg and its alloys have shown a growing interest for weight critical applications,including aerospace,automotive,communication electronics and other structural engineering parts.Furthermore,Mg and its alloys are commonly used for vibration and noise control as well as energy absorption devices because of their high damping capacity.However,some obvious disadvantages,such as relatively low absolute strength,limited ductility and insufficient stiffness restrict their extensive applications.In the last few decades,the compositing method has been successfully employed to enhance the properties of Mg and its alloys via introducing various reinforcements into the matrix.In this paper,the continuous NiTi fiber reinforced Mg3Al Zn composite(SMAFR-AZ31)was fabricated via vacuum hot pressing sintering based on the design philosophies of fiber reinforcing.Meanwhile,based on the laminate reinforcing and transient liquid phase(TLP)bonding mechanisms,the Mg3Al Zn-Ti6Al4V laminate metal composite(AZ31-TC4 LMC)and NiTi fiber reinforced AZ31-TC4 LMC((NiTi_f/AZ31)-TC4 LMC)were successfully fabricated.Moreover,the preparation parameters,interfacial bonding mechanism,mechanical and damping properties of the composites were systematically studied,and the mechanical strengthening mechanism,failure modes and damping mechanisms of each composite were analyzed.In order to reveal the interface formation,damping and toughening mechanisms of SMAFR-AZ31 composite,the microstructure characterization,damping,tensile,compression,bending and fracture toughness tests were carried out,and the damage mechanism was studied.The results show that the interfacial bond between NiTi fibers and AZ31 matrix is excellent without visible voids,and the boundaries of the original AZ31 foils disappear completely after 560?/360min sintering.A nanocrystalline-amorphous reaction layer with a width of 0.1?m?2?m was formed along the NiTi_f/AZ31 interface in SMAFR-AZ31composite.The damping factor of the composite is 184%higher than that of AZ31 alloy at66?,which is attributed to the phase transformation in the NiTi reinforcement.The normal tensile strength of SMAFR-AZ31 composite is 57.6MPa,which is 178.3%higher than that of AZ31 laminate sheet.The quasi-static compressive yield strengths of the composite are increased by 33.3%and 249.0%when loading perpendicular and parallel to the fiber direction,respectively.The tensile strength,yield strength and failure strain of SMAFR-AZ31composite are 23%,54%and 15.4%higher than those of AZ31 alloy,respectively.The bending yield strength and bending strength of the composite are increased by 21.7%and36.6%compared with AZ31 alloy,respectively.The fracture toughness of the composite is15.3%higher than that of AZ31 alloy.The oxide amorphous phase formed at the NiTi_f/AZ31interface improves the interfacial bonding strength,so that the load can be transferred to the high-strength NiTi reinforcement from AZ31 matrix.In addition,the passivation of crack tip as well as the deformation,pull-out,fracture and debonding of the fiber play an effective role in strengthening the composite.To clarify the microstructure evolution,damping and toughening mechanisms in AZ31-TC4 LMC,the staged sintered and fine characterization of the interface were carried out.In addition,the damping,tensile,compression,bending and fracture toughness of the composite were also tested.After keeping temperature at 560?for 300 min,it can be observed that the eutectic layer disappeare completely at TC4/AZ31 interface in AZ31-TC4LMC.The TC4/AZ31 interface consists of an intermetallics layer with a width of 20?108nm and a Mg-O reaction layer with a thickness of 300nm.The continuous intermetallics layer is Al_192.40Fe_46.22phase with hcp structure.Besides,the Al_192.40Fe_46.22phase has a specific orientation relationship with the?-Ti matrix:[1210]Al_192.40Fe_46.22//[1101]?-Ti,(2024)Al_192.40Fe_46.22//(0111)?-Ti.For the adjacent AZ31 foils interface in AZ31-TC4 LMC,the secondary recrystallization causes the formation of a secondary recrystallization texture,{0001}//HPD,<0001>//PLD.The damping factor of AZ31-TC4 LMC is?0.0111 under ambient condition,which is better than that of AZ31 alloy(?0.0081).The improvement of damping property is attributed to the interfacial damping mechanism of TC4/AZ31 interface.The quasi-static compressive yield strengths of the composite are increased by 71.6%and242.1%when loading perpendicular and parallel to the laminate direction,respectively.The tensile strength and yield strength of AZ31-TC4 LMC are about twice than that of the as-received AZ31 foil,and the specific strength is 38.8%higher than that of AZ31 alloy.Furthermore,the bending strength and fracture toughness of AZ31-TC4 LMC are increased by 33%and 129.9%,respectively.The extremely narrow intermetallics layer around the TC4/AZ31 interface has not undergone severe delamination during the mechanical tests.Therefore,the mechanical properties of the composite are significantly improved through the load transfer effect.In order to elucidate the hybrid-reinforced and damping mechanisms of the(NiTi_f/AZ31)-TC4 LMC,the interfacial microstructure,damping,tensile,compression,bending and fracture toughness tests were carried out.SEM observation shows that the microstructure of(NiTi_f/AZ31)-TC4 LMC is compact without obvious macroscopic defect,and the fiber arrangement is uniform.(NiTi_f/AZ31)-TC4 LMC shows an internal friction peak when the test temperature rises to 65?.Compared with the AZ31 alloy and AZ31-TC4 LMC at the same temperature,the damping factors are increased by 221.9%and 96.2%,respectively.The enhancement of damping property is attributed to the phase transformation in NiTi alloy.The quasi-static and dynamic compressive properties of(NiTi_f/AZ31)-TC4LMC are almost the same as those of AZ31-TC4 LMC.The tensile strength of(NiTi_f/AZ31)-TC4 LMC is increased by 112.7%and 4.4%compared with the as-received AZ31 foil and AZ31-TC4 LMC,respectively.For the failure strain,these values are 4.2%and44.7%.In addition,compared with the as-received AZ31 foil,the specific strength of the(NiTi_f/AZ31)-TC4 LMC is increased by 33.3%.The bending strength of(NiTi_f/AZ31)-TC4LMC is 36.4%and 81.2%higher than that of AZ31-TC4 LMC and AZ31 alloy,respectively.Among the various as-fabricated composites,the(NiTi_f/AZ31)-TC4 LMC obtains the best fracture toughness,which is 165.7%,130.4%and 15.6%higher than that of AZ31 alloy,SMAFR-AZ31 composite and AZ31-TC4 LMC,respectively.Based on the hybrid-reinforced mechanism,the high-performance fiber and foil reinforcements can effectively improve the comprehensive properties of the composite through load transfer effect of the interface.