Welding Process And Joint Formation Mechanism Of Dissimilar Metals Based On Electron Beam Welding

This paper studied the process and the joint formation mechanism of dissimilar metals, aluminum / copper and aluminum / steel dissimilar metals were weld by "O" shaped scanning electron beam welding. The joint morphology, microstructure, phase composition, elemental distribution of the joint, and the impact of process parameters on the performance of the joint were studied. And proposed the formation mechanism of electron beam welding of dissimilar metal which can formation intermetallic compound. Due to the poor mechanical performance of electron beam welding, TIG welding with filler wire carried out to obtain the high mechanical performance of aluminum / copper dissimilar metals.The results showed that: the joint shape of aluminum / steel and aluminum / copper dissimilar metal by electron beam welding is acceptable; while this two joint can divided into the interface reaction zone and the metal melting zones; the interface reaction zone is the key role of the joint connection, which mainly consist of intermetallic compounds and eutectic Organization; and both sides of the melting zone is mainly consist of solid solution and eutectic organization. The consist of interface reaction zone of Al / Cu joint include Al2 Cu and eutectic organization which composition by Al2 Cu and α(Al); and the interfacial reaction zone of Al / Fe joints consist of Fe3 Al and Fe Al3 intermetallic compounds and eutectic organization which composition by Fe Al3 and α(Al); and the morphologies of interfacial reaction zone of Al / Fe joints bind with the welding heat input. There is a direct relationship between microhardness distribution with the cross section morphology of the electron beam weld joint. the interface reaction zone have the highest hardness value of the joint, the hardness value and change range of melting zone of both sides are higher than the base metal but lower than interface reaction zone. The parameters of electron beam welding had a great impact on the joints performance; the maximum tensile strength of Al / Cu joint is 71.2MPa, the mechanical properties of the joint is not well; and take TIG welding with the filler wire, when welding current 100 A, welding speed 62 mm / min, shielding gas flow 15 L / min, the tensile strength of the joint can up to 240.32 Mpa. while Al / Fe electron beam welded joints had a good mechanical properties, the tensile strength can achieved 112.6MPa, 87% strength of aluminum base material, which the welding parameters is: steel side electron beam deflection 0.2mm, accelerating voltage is 60 KV, focusing current is 580 m A, scanning amplitude is 0.3mm, the beam current is 40 m A, and welding speed is 1800 mm / min.The mechanism of dissimilar metal weld joint formation which weld by electron beam welding is: with the electron beam effects, both sides of the liquid metal can form a "bilateral pool", when the two liquid metals do not mix with each other, during the formation of the joint, the transfer and diffusion of both sides of the metal elements through mutually flow of welding pool and the elements thermal diffusion. The intermetallic compounds and the eutectic structure which formation by the metallurgical reaction at the interface of two metal pools, and which also is the most important for the connection of the joint.