Study On Process And Properties Of Joining Al/cu Dissimilar Metals

The welding-brazing process joining two kinds of dissimilar metals with different melting points,can take into account the characteristics of the melting welding and brazing process,with high efficiency,unlimited workpiece size and other advantages.In recent years,Welding-brazing processes of different heat sources have been developed for the joining of Al/Cu dissimilar me tals.In this paper,Al/Cu dissimilar metals were joined with lap and butt joints by pulsed double electrode gas metal arc welding-brazing,and the microstructure,mechanical properties and electrical conductivity of the joints were investigated.In this study,the appropriate welding process parameters of Al/Cu dissimilar metals were obtained by plate surfacing process,and the welding parameters were optimized.ER1100,ER5356,ER4043 and ER4047 were used as filler materials to obtain the sound lap and butt joints of Al/Cu dissimilar metals.The results showed that the Al/Cu welding-brazing joint was mainly composed of fusion zone between Al base metal and weld metal,weld zone,and Cu-weld metal brazed interface zone,and Cu-weld metal brazed interface zon e could be further divided into intermetallic compound layer and Al-Cu eutectic region.The IMC layer was mainly composed of stripe and block Al2 Cu,and weld zone was mainly composed of ?(Al)solid solution and ?(Al)+?(Al2Cu)or ?(Al)+S(Al2Cu Mg)/?(Al2Cu)eutectic structure precipitated from grain boundary.When the composition of filler wire was different,the eutectic microstructure was also different.The thickness of the IMC layer increased with the increase of the welding heat input,and it was found that addition of Si element in filler wire could inhibit it.Then,the micro-hardness,tensile strength and fracture mode of welding-brazing joints of Al/Cu dissimilar metals were studied.The micro-hardness of the Cu base metal was higher than that of the A l base metal,lower than hardness of weld zone,and the highest hardness was observed in the IMC layer.Meanwhile,the micro-hardness of the weld zone increased with the Si element content of filler wire,especially the ER4047.The tensile strength of joints firstly increased and then decreased with the increase of heat input,and increased with the increase of Si element content.The welding heat input had a great influence on the fracture position of the joints.The lap joints were ruptured at the fusion line of the Al base metal,the weld/Cu interface,and the heat-affected zone,respectively.The first two were brittle fracture,and the latter was ductile fracture.However,the butt joints were generally ruptured at the IMC layer of the brazing zone or the heat affected zone of the Al base metal,and fracture mode of the former was caused by a variety of reasons.Finally,the influence of welding heat input and filler wires on the electrical conductivity of welding-brazing butt joints of Al/Cu dissimilar metals was studied.When the same kind of wire was used,the conductivity of the joints increased first and then decreased with the increase of the welding current,which is related to the wettability and spreadability of weld metal on base metal,weld defects and the thickness of the IMC layer.In addition,the electrical conductivity of the butt joint from large to small followed by ER4043,ER4047,ER5356 and ER1100 under the same welding parameters,which indicated that the conductivity of the joint was increased due to IMC suppressed when the content of Si was low,and the conductivity of the joint was reduced due to the presence of precipitate Si phase when the content of Si was higher.