Investigation On The Electron Beam Welding Of Al/cu Bilayer Laminated Composite

Al/Cu bilayer laminated composite has gained growing attention due to the advantages with low density and price competitiveness of Al and superior electrical conductivity of Cu over some Cu alloys.For these reasons,Al/Cu bilayer laminated composite has been widely used in many industries,such as marine,automobiles and aerospace at present.Welding technology,as an important forming technology,plays an important role in promoting the application of Al/Cu bilayer laminated composite.In this study,hot-rolled Al/Cu bilayer laminated composite(also called Al/Cu bimetallic sheet)with 6.5 mm thick was butt welded via the electron beam welding(EBW).The EBW process was optimized,and the relationship among the welding process parameters,formation and properties of the joints was established.Moreover,the microstructure evolution mechanisms of Al/Cu bilayer laminated composite during the EBW were revealed.Firstly,for the single-sided EBW,one-side welding with back formation of Al/Cu bilayer laminated composite could be realized in Modes ?(Cu cladding layer is placed upon the Al base layer)and ?(Al base layer is placed upon the Cu cladding layer)under the welding voltage of 60 kV,welding speed of 300 mm·min-1,welding current of 55 mA and the focusing current of 427 mA.Moreover,in Mode ?,the microstructure was composed of Al2Cu IMC at the interface,whereas the fusion zone consisted of(Al2Cu+?-Al)eutectic structure and Al2Cu intermetallic compound.In Mode ?,the Al2Cu intermetallic compound and(Al2Cu+?-Al)eutectic structure were formed at the interface,whereas the fusion zone consisted of(Al2Cu+?-Al)eutectic structure and a-Al grains.However,due to the adverse effects of the brittle intermetallic compounds,the average tensile strengths of these joints were only 47.9%(Mode ?)and 67.4%(Mode ?)of the base material,respectively.In addition,the fracture locations of these two joints were both at the edge of the weld zone,and the fracture characteristics of the joints were mainly brittle fracture.Furthermore,the dilution of the Cu cladding layer during the welding process would also seriously affect the overall performance of the bilayer laminated composite.In order to improve the mechanical properties of the joints and reduce the dilution of Cu cladding layer,the double-sided EBW welding technology was proposed to weld Al/Cu bilayer laminated composite.The result shows that the sound butt joints were obtained via the double-sided EBW.Furthermore,in the double-sided EBW process of Al/Cu bilayer laminated composite,according to the different degrees of internal penetration,six different welding modes including the both incomplete penetrations of Al side and Cu side(Mode ?),full penetration of Al side and incomplete penetration of Cu side(Mode ?),excessive penetration of Al side and incomplete penetration of Cu side(Mode ?),both full penetration of Al side and Cu side(Mode ?),full penetration of Al side and excessive penetration of Cu side(Mode ?),incomplete penetration of Al side and excessive penetration of Cu side(Mode?)in the double-sided EBW butt joints were obtained.With the increasing of heat input,the degree of internal penetration increased significantly.When the welding voltage is 60 kV,welding speed is 300 mm·min-1,welding current of Cu side is 39 mA,welding current of Al side is 45 mA,and the focusing current is 427 mA,the joint obtained in mode ? presents the full penetration of Al side and Cu side and the most excellent weld formation.Moreover,the joint obtained in Mode IV presented the highest tensile strength(117 MPa),reaching approximately 92.9%of the base material strength.Whereas the fracture location of the joint was at the center of the weld.Furthermore,the fracture characteristic of the joint was mainly cleavage fracture.In addition,the Cu cladding layer was barely diluted,and the conductivity of the joint could reach 99.3%of the base material.The microstructure of double-sided EBW joint was examined by scanning electron microscope,transmission electron microscope and X-ray diffractometer.Moreover,the microstructure of the weld on the Al and Cu sides of the joint was similar.In the weld edge,it consisted of well-developed columnar structures.In the weld center,the fine equiaxed structures formed,whereas the microstructures of the interface zone were Al2Cu intermetallic compound and(?-Al+Al2Cu)eutectic structure.Compared with single-sided EBW,the Cu cladding layer was barely diluted during the double-sided EBW,reducing the formation of brittle intermetallic compounds in the joint,which is an effective way to solve the welding of Al/Cu bilayer laminated composite.