Preparation Of Al/Mg/Al Composite Plate And Study On Its Interface Behavior And Properties

Aluminum/Magnesium laminates which combines the performance advantages of aluminum?Al?alloys and magnesium?Mg?alloys have promising application prospects.Explosive welding?EXW?is an effective way to clad Mg alloys with Al alloys.Up to now,most studies on Al/Mg composite plate fabricated by EXW process have been focused on two-ply composite plate.A few studies on three-ply explosive-welded?EXWed?Al/Mg/Al composite plate with better corrosion resistance were reported.In this paper,the vertical EXW was applied for the fabrication of three-ply Al/Mg/Al composite plate to solve the problem of plate bending in common EXW process.Annealing of EXWed composite plate was carried out to provide technological support for the application of thick Al/Mg/Al composite plate.Al/Mg/Al composite sheet was fabricated by the process of EXW united with hot rolling.Annealing was performed to achieve good combination of interface microstructure and mechanical properties of thin EXWed-Rolled composite sheet.The results will provide useful information for further processing of composite sheet.The systematic research of composites under different states was characterized by using optical microscopy?OM?,energy dispersive spectroscope?EDS?,scanning electron microscopy?SEM?and x-ray diffraction?XRD?and mechanical tests.The results indicated that different morphology with big waveform?BW?and mini waveform?MW?was present in the EXW bonded interfaces.The thickness of diffusion layer was approximately 2.1?m for the BW side and 3.8?m for the MW side indicating that elemental diffusion occurred at both sides.Besides,no any trace of intermetallic compounds?IMC?was observed macroscopically.Optical micrographs of Al/Mg/Al composite plate on AZ31B Mg alloys side showed that the adiabatic shear band?ASB?appears inclined about 45 ° to the interface and numerous twins was produced.A substantial increase in micro-hardness was observed near the interface.As a result,the hardness of interface is significantly higher than that of base metal on both sides.The interface shear strength was 91 MPa for BW side and 92 MPa for MW side,respectively.The shear fracture shows cleavage fracture feature.After annealing,the ASB and twins on Mg alloys side of Al/Mg/Al EXWed composite plate were eliminated.Then the deformed microstructure is gradually replaced by equiaxed grains under the effects of recovery and recrystallization.The thickness of diffusion layer increased significantly with annealing temperature and holding time.BW and MW interfaces of EXWed composite plate annealing at 400°C for 0.5 h presented two distinct diffusion layers and the thickness of two different layers was significantly different.The elemental analysis results indicated that the layer close to the side of Mg alloys was composed of Mg17Al12 phase and the layer close to the side of Al alloys was composed of Al3Mg2 phase.The nano-indentation results of IMC at the interface of EXWed composites annealing 400°C for 2 h showed that the elastic modulus of Al3Mg2 phase and Mg17Al12 phase were about 66.16 GPa and 71.31 GPa,respectively.The hardness of Al3Mg2 phase was about 3.38 GPa and the hardness of Mg17Al12 phase was about 3.02 GPa,indicating that the hardness of Al3Mg2 phase is higher than that of Mg17Al12 phase.By theoretical fitting calculation,the kinetic equations of the growth of BW and MW interface diffusion layers are obtained.The diffusion equation of BW interface is y²=1.11×10^-7exp?-65114/RT?t,and the diffusion equation of MW interface is y²=1.12×10^-7exp?-65085/RT?t.After annealing work hardening and residual stress in the EXWed composite plate were released and the peak value of micro-hardness was significantly decreased.The shear strength of interface at both sides under different annealing conditions was no larger than that of the interface of EXWed composite plate without annealing.With holding time increasing,the shear strength of BW and MW interfaces increased first and then decreased under the condition of annealing at 200?.However,with holding time increasing,the shear strength of both side interfaces decreased gradually when annealing at 300? and 400?.Under the same holding time,the shear strength of both side interfaces decreased dramatically with annealing temperature increasing.Thin three-ply Al/Mg/Al composite sheet with the thickness of 1.78 mm were achieved by six-pass hot rolling.The interfaces of composites bonded linearly and the sound joints were obtained without cracks,tearing,separation,etc.With rolling pass increasing,twins on Mg alloys side gradually disappeared and small recrystallized grains nucleated around large grains and grew up.After six-pass hot rolling,the microstructure of Mg alloys exhibited inhomogeneity in thickness direction of composites.With annealing temperature and holding time increasing,the thickness of diffusion layer increased dramatically after hot rolling.By theoretical fitting calculation,the interface diffusion equation of the Al/Mg/Al composite sheet is y2=2.14×10-7exp?-70878/RT?t.The equiaxed and homogeneous grain morphology of Mg alloys in the thin three-ply Al/Mg/Al composite sheet could be induced by annealing 300? for 1 h.This contributed to the ultimate tensile strength of 235 MPa and considerable increase of elongation by 18.5%.