| Explosive welding technique is one of the most promising solid-state welding methods for producing laminated composite materials,which achieve a metallurgical bond by high-speed oblique collision accompanied with a jet and small-scale melting at the interface,aided by detonation energy of an explosive.Compared to other welding technologies,the advantages of explosive welding mainly lie in the high bonding strength,small heat-affected zone,and the ability to directly join wide varieties of similar and dissimilar metals.Thus,explosive welding technique has been playing an irreplaceable role in many industrial fields,such as petrochemical industry,marine engineering,aerospace and so on.However,shortcomings such as low energy utilization and severe environmental damage always exist.In recent years,with the acceleration of urbanization process and growing concern about environmental protection,the contradiction between explosive welding and ecological environment is daily outstanding,which hinders the further development of this technique.The main reason for this problem is the backward charging method.In the traditional explosive welding technique,the upper surface of the explosive is exposed to air,so amounts of energy are released in the air in the form of shock wave.As a result,not only the energy utilization rate of explosives is low,but also the pollution of noise and dust is serious.In order to solve the above problems,this paper puts forward using colloid water as a covering for explosives.Titanium/steel were chosen as a model system,and several experiments were carried out to investigate the effects of the covering thickness on the impact velocity,noise,and dust produced by this explosive welding technique.The results showed that,the covering could significantly reduce the explosive dust and noise pollution,while improving the ability of the explosive to drive the flyer plate.Compared to the explosive with no covering,when the covering thickness was 30 mm,60 mm,100 mm,and 150 mm,respectively,the impact velocity was increased by 32.2%,37.0%,39.5%,and 40.8%,the explosion noise was reduced by 4.0%,6.3%,7.4%and 8.2%,and the explosion dust was reduced by 30.1%,46.1%,62.0%and 70.9%.Due to the careful control of welding parameters,high quality wave bonding was achieved in all tests,indicating the ability to obtain high quality welding for this technology.In addition,the thickness of the covering had a great influence on the microstructure of the bonding interface,and the wavelength and amplitude of the wave tended to increase first and then decrease with increasing the covering thickness.For the interface with a covering,a vortex structure with local melting region was found at the crest of the wave,while no vortex region was detected at the interface without covering.In order to further improve the energy utilization rate of the technology using colloid water as a covering for explosive and solve the problem of high-speed uncontrollable motion for the welding plate in double-sided explosive welding,a self-restrained explosive welding technology(SREW)was proposed,where the motion of the welded plates was constrained by impacting with each other.Taking steel/steel,stainless steel/steel explosive welding as examples,the restraint effect of the welding plate,dynamic parameters and bonding quality of this technology were systematically studied.The results showed that,compared to the conventional method,the explosive consumption for SREW with a five-layer setup was reduced by 63%,when getting the same bonding interfaces and the same numbers of welded plate.The SREW technology also enabled to clad three or more composite plates simultaneously,which is helpful to improve the work efficiency and save explosion place.Compared to the double-sided explosive compound technology,although the explosive consumption increased by 20%,the SREW technology showed an excellent restraint effect.After the explosion,all the composite plates were kept in the initial position,making it’s application possible.In addition,a measuring system for dynamic parameters of explosive welding was built using PVDF and plasma probe,and the measured values were in good agreement with the theoretical calculation results,providing a simple and high-precision measuring method for obtaining dynamic parameters of explosive welding.To solve the problem of energy waste and damage of foil caused by excess energy in conventional technology,it was proposed to reduce the excess energy output of the explosive by reducing the amount of explosive used,with the help of colloidal water.The effect of colloidal water thickness on the critical thickness of explosive was studied systematically.Taking the explosive welding of 1060 aluminum foil and Q235 steel plate as an example,the feasibility test of the new technology was carried out,and the bonding properties of the clad plate were investigated through mechanical performance tests and microstructure observations.The results showed that,with increasing thickness of colloid water,the critical thickness decreased significantly,and the detonation velocity at the critical thickness also reduced.This is helpful to reduce the consumption of explosives and the excess energy in foil weld.Compared to the conventional method,the consumption of explosive was reduced by 25.4%due to the colloid water covering effect,and the kinetic energy of the aluminum foil was also reduced,making the macroscopic integrity better for the aluminum foil after the explosion.This indicates that the new technology can improve the welding quality and reduce the production cost.The microstructure observations showed that the 1060/Q235 interface is characterized by asymmetric wavy metallurgical bonding,with a large number of local melting zones containing micropores and cracks,indicating that the collision energy was still high,and further measures may be taken to reduce the kinetic energy of the flyer plate so as to improve the bonding quality.Nevertheless,the 1060/Q235 sample showed excellent bending resistance.After bending to 90°,the aluminum foil surface was flawless,and no macroscopic delamination,fracture and other defects were found in the bonding interface.Achieving high quality tantalum coatings on common metals is still a challenging task,due to potential technical problems such as high differences in melting points and formation of intermetal lic compounds.In order to provide a new idea for the preparation of high quality tantalum coating,an improved explosive welding technique was successfully employed to prepare tantalum coatings on a steel substrate.The microstructure evolution and element distribution of the bonding interface were analyzed by SEM and EDS,and the microstructure characteristics(grain shape,size distribution,texture and grain boundary)were further studied by EBSD.The mechanical properties of the bonding interface were revealed by nano-indentation,tensile and bending tests,and the relationship between microstructure and mechanical properties was discussed.Finally,the corrosion resistance of tantalum coating was evaluated by electrochemical test.The results showed that the improved explosive welding technique was a suitable method to produce a Ta coating on steel substrate.At the macro scale,there were no defects on the surface of tantalum foil except the boundary region.At the micro scale,the tantalum/steel interface presented a high quality wave metallurgy bonding,and there were no micron scale defects.Importantly,a new vortex structure was observed at the tantalum/steel interface,where the local melting area was completely surrounded by tantalum matrix,and the microscopic analysis of the bended samples showed that this vortex structure could effectively prevent the crack growth outwards in the melting area.EDS analysis results showed that there were two types of melting zones at the tantalum/steel interface,namely vortex melting zone and interface melting zone.The difference of the element content in the two regions revealed their different forming mechanisms,namely,the vortex melted zones were formed by strong intermixing of participant metals,while the interfacial melted zones were dominant by atomic diffusion.EBSD results showed that equiaxed fine grains were dominant in Ta foil adjacent to the bonding interface,while the grains were elongated and strongly curved in Q235 plate.Meanwhile,a strong texture was identified near the bonding interface,due to some grains deflecting under the stress waves.In addition,the formation of intermetallic compounds in melted zone was confirmed by EBSD point analysis.Due to the hardening effect caused by the explosion,the strength value of the tantalum/steel composite was increased and the ductility was reduced when compared to the base metal.However,after the tensile tests,no separation happened at the Ta/Fe interface,and the surface of Ta foil still showed a crackfree condtion,indicating that the bonding interface has a high strength.Under bending load,no delamination,cracks or fractures were found at the bonding interface and the surface of Ta foil,indicating a reliable bending property.Nanoindentation test results revealed inhomogenous micro mechanical properties near the bonding interface due to the combined action of work hardening and the existence of fine grains and intermetallic compounds,and the width of the hardened zone was determined to be～140μm on both sides of the interface.Finally,the corrosion test indicated that the corrosion resistance of Q235 plate was highly improved after being coated by Ta foil using explosive welding. |
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