Fusion Welding On TA1/Q345 Laminated Structure And Joint Microstructure Evolution

Titanium/steel(TA1/Q345)laminated structure,in which a mild steel plate(Q345)is applied as the base plate and a commercial purity titanium plate(TA1)as the flyer plate,is fabricated via oblique impacting of flyer plate towards base plate driven by detonation wave at extremely high velocity.Due to its excellent corrosion resistance as well as higher mechanical strength,there is considerable demand for TA1/Q345 laminated plate in engineering fields,such as aerospace,petro-chemical engineering and ocean engineering.However,such bimetallic plate is severely restricted because of thermophysical properties mismatching and metallurgical incompatibility between titanium and steel.Subsequently,the present work aimed to fusion joining TA1/Q345 laminated plate.The microstructure evolution as well as the microstructure control was investigated during fusion bonding of TA1/Q345 laminated plate,which is of great theoretical and practical significance.In this investigation,combined experimental and numerical approaches are applied to investigate the explosive welding process of TA1/Q345 laminated plate.The bonding interface is characterized by the periodic wavy morphology.As one of the meshless methods,SPH(Smoothed Particle Hydrodynamic)reproduces the wave morphology and jetting at the interface during explosive welding.The impacting between flyer and base plates leads to severe deformation and considerable amounts of heat generated at the interface,which eventually results in intermetallics formation and microstructure evolution at the interface(recovery,recrystallization and crystal growth).This study reveals the mechanism of microstructure formation based on the experimental and simulation results,which can provide as theoretical guide for the welding of laminated plate.Due to the formation of brittle Fe-Ti phases,the primary objective is the microstructure transition of fusion bonding of TA1/Q345 laminated plates.The microstructure in weld metals is investigated systematically based on the metallurgical reactions of Ti and Fe alloys with Cu,V,Nb and Zr fillers.It shows that a series of Cu-Ti compounds form between Cu and Ti alloys,which inhibit the formation of brittle Fe-Ti intermetallics.Moreover,the microstructure is improved when composite intermediates,such as Cu-V and Cu-Nb are employed.Together with the nanoindentation results,the mechanical properties of individual phase are determined,which demonstrates the possible constitution for TA1/Q345 weld metal.The formation and bonding quality of TA1/Q345 butt welded joint are highly affected by the welding parameters of Cu-based weld metal.The results show that brittle Fe-Ti intermetallics are reduced significantly when TA1/Q345 interface is covered by Cu-based weld metal.Furthermore,the optimization study on Cu-based fillers are carried out.It is proposed that sound joints with homogeneous microstructure distribution as well as limited Fe-Ti intermetallics can be obtained when Cu20V and Cu20Nb filler materials are applied.The corresponding mechanical properties of such welded joints are significantly improved.Based on the optimized welding process and filler materials,nanoindentation and transmission electron microscopy are applied to further identify the microstructure and the corresponding micro-mechanical properties.Cu solid solution which forms between Cu-based weld and Fe matrix has lower hardness.The regions near the TA1/Q345 interface are composed of pTi with FeTi intermetallics dissolved in.Cu-Ti intermetallics are formed between Cu-based weld metal and Ti weld metal.Brittle Fe2Ti intermetallics are dispersed among the Cu solid solution.Furthermore,uniaxial tension and three-point bending tests are performed to determine the macro-mechanical properties and failure mechanisms of microstructure in weld metal.It is interesting to note that Cu solid solution can inhibit the initiation and propagation of cracks in weld metal.Moreover,Cu-Ti intermetallics which are relative softer show higher resistance to cracking than Fe-Ti intermetallics.It is revealed that the mechanical properties of the weld metal are controlled by the distribution and amount of Cu-Ti intermetallics.Based on the above results,the relations among material-microstructure-mechanical property are established.Due to the mismatching of thermo-physical properties among Cu,TA1 and Q345,welding residual stress is concentrated in the TA1/Q345 butt welded joints.Finite element method is used to evaluate the welding residual stress.It is revealed that the residual stress is low after fusion with Cu based filler material.However,the peak residual stress increases significantly after fusion with titanium filler material.The results obtained from finite element simulation are in good accordance with the experimental data.Therefore,simulation results which are considered as theoretical foundation and data support for engineering,can contribute to the residual stress relaxation of TA1/Q345 welded joints.