Molecular Dynamics Simulation And Experimental Research On Ni/Al Explosive Welding

Compared with single metal,metal composites are widely used because of their excellent properties,such as light weight,oxidation resistance,friction resistance and good mechanical properties.Explosive welding technology can directly connect a variety of the same and different materials,and the composites prepared by explosive welding have exceptional mechanical properties.Ni/Al composites prepared by explosive welding have excellent mechanical properties,oxidation resistance and corrosion resistance,and are widely used in military and aerospace fields.At present,there is little research on the bonding mechanism of explosive welding interface,and the research results are not ideal;the bonding mechanism of Ni and Al explosive welding has not been discussed.The study of the bonding mechanism of Ni/Al explosive welding interface is helpful to obtain high quality Ni/Al welding parts.In this paper,the explosive welding process of Ni and Al is simulated.The morphology of Ni/Al bonding interface,atomic structure of Ni and Al,microstructure,cutting characteristics and tensile properties of welding parts are studied in each stage of explosive welding.Under different charge height,thin Ni/Al composite plates are prepared by parallel explosive welding.The interface morphology,element distribution,diffusion layer thickness,Vickers microhardness test and quasi-static tensile test of Ni/Al composites were studied.The results show that:1.Diffusion fusion between dissimilar atoms is realized at the welded joint under the action of temperature and pressure.The bonding mechanism of Ni/Al bonding interface: the loading stage for the pressure bonding,the unloading stage for diffusion bonding or melting-diffusion bonding,and the cooling stage for diffusion bonding.With the increase of impact speed or charge height: the interface waveform of the composite plate becomes more and more obvious;the number of waveforms increases gradually;the wave amplitude decreases gradually;the interface bonding strength is getting better and better.The diffusion of Al atoms to the Ni side is more obvious in the unloading stage and cooling stage.The thicker the atomic diffusion layer is,the more dislocations are produced.2.Disordered atoms on the Ni side and the Al side are mainly grain boundaries,and there is a melting zone at the grain boundaries,indicating that the explosive welding mechanism includes the melting welding mechanism.Due to the extremely high strain rate and thermal effect,the cellular dislocation structure in Ni plate,the polygonal dislocation structure in Al plate and the typical solidification structure in mixed zone are formed,and the fcc structure and bcc structure can be reversed in explosive welding.In the cooling stage,the higher the initial temperature of loading,the higher the reverse conversion rate of fcc structure.When impact speed is 1500 m/s,1750 m/s and 2000 m/s,respectively,it increases by 7.0%,15.6% and 28.0%respectively.The hcp structure is the medium to promote the transformation of fcc and bcc structures,which provide a reference for explaining some problems encountered in explosive welding.3.The atoms near the Al region produce microcracks first,and the microcracks will not propagate along the bonding interface of the composites.When the cooling rate is high and the equilibrium temperature of the system is higher than the melting point of Ni,there are nanoparticles in the weldment after explosive weldment.Compared with the weldment whose equilibrium temperature of the system does not reach the melting point of Ni,the weldment with nanoparticles can obtain the highest tensile strength and the best plastic deformation,and the tensile strength of the composite plate is higher than that of the initial target Al 1060.The forming process of welding parts results in a disordered nucleation and dislocation arrangement of atoms near the interface.When the cutting tool is in contact with the interface of the workpiece,part of the dislocations are triggered,and the work hardening effect occurs at the bonding surface.Materials with higher hardness than the substrate can be obtained by changing the thickness of the explosive.In the case of no thermal action,the welded parts after cutting can strengthen the contact and diffusion of heterogeneous atoms,and strengthen the mechanical properties.In the case of the same explosive thickness,the interface with Al as the composite plate can obtain higher hardness and tensile strength than the interface with Ni as the composite plate.