Research On Interface Control And Transition Materials Of Copper/Steel Composite Structure Additive Manufacturing

With the rapid updating of equipment,technology and materials,higher requirements are put forward for the accuracy,performance and service environment of mechanical parts,so that single material can't satisfy engineering requirements.Copper alloy and alloy steel composite structure play an important role in ship vehicles,pressure vessels and weapon equipment due to their excellent low temperature toughness,corrosion resistance and high strength toughness.However,the linear expansion coefficient and thermal conductivity between copper and steel are quite different,which virtually increases the difficulty of connecting the two.When the copper/steel composite structure is prepared by welding,the coarsening of heat affected zone and macro/micro cracks in the welded joint will reduce its mechanical properties.Additive manufacturing technology is widely used in the field of metal manufacturing due to its high precision and flexible forming.Therefore,it is of great practical significance to prepare copper/steel composites by arc additive manufacturing technology.In this paper,arc additive manufacturing of ER50-6 low alloy steel and HS211 silicon bronze bimetal composite structure was carried out based on arc additive manufacturing equipment of gas metal arc welding.By studying the forming quality of single-pass single-layer weld and single-pass multi-layer weld of two materials,the influence of welding parameters on weld width and weld height was revealed,and the optimum process window of weld forming was clarified.Based on the optimized process parameters,this paper also focused on the influence of the surfacing sequence of the two groups of materials on the microstructure and mechanical properties of the copper/steel composite structure.There was a melting unmixed zone at the interface of the two groups of samples,which was mainly composed of rich-Fe phase(?-Fe)and rich-Cu phase(?-Cu).Due to the difference of melting point between copper and steel,the melting unmixed zone of HS211/ER50-6 thin-walled specimen was the largest,and the penetration crack in the melting unmixed zone will greatly reduce the mechanical properties of the specimen.Therefore,the tensile strength of ER50-6/HS211 thin-walled specimen was the highest,about 207.5 MPa,and the impact absorption energy of the specimen can also reached about 20%-25%of the silicon bronze matrix.Permeable cracks easily leaded to direct cracking of copper/steel interface,and then the formation mechanism of permeable cracks was studied.This phenomenon was mainly related to the grain boundary wettability of liquid copper and low alloy steel.If the temperature in the molten pool was higher than 1025?(the melting point of silicon bronze),the liquid copper will wet and penetrate the grain boundary of low alloy steel,and finally form osmotic cracks.Based on the above research,in order to eliminate the penetration crack and improve the mechanical properties of the interface position of copper/steel thin-walled composite structure,four groups of transition welding materials for copper/steel gradient connection(Cu-Ni,Fe-Ni,Cu-Al and Ni-Cr)were prepared.When the transition welding material was added between low alloy steel and silicon bronze,there was no melting unmixed zone on the side of low alloy steel,which also reduced the tendency of copper penetration to a certain extent.Among them,Cu-Ni,Fe-Ni and Cu-Al transition welding materials had good metallurgical bonding with silicon bronze.By characterizing the mechanical properties of the specimens,four groups of tensile specimens were broken in the silicon bronze matrix.Among them,the tensile strength of the specimen added with Cu-Ni transition wire was the highest,about 345.2 MPa,which was 137.7 MPa higher than that of the original specimen.The interfacial impact absorbed energy of the specimen with Ni-Cr transition wire was the highest,about 40 J,which was 20 J higher than that of the original specimen.The microhardness of Cu-Ni and Cu-Al specimens also showed a continuous gradient change.Therefore,the bimetallic composite structure of silicon bronze and low alloy steel can be rapidly and efficiently formed by using the arc additive manufacturing technology of gas metal arc welding and adding transition materials.