| With the rapid development of modern industry,the performance of welding structure between the same metal can't meet the needs of industrial production anymore.Therefore,exploring the weldability between dissimilar materials and manufacturing composite structure of dissimilar materials have considerable demand.For example,the composite structures between copper and stainless steel are employed in the aerospace,electronics and petro-chemical engineering to fully utilize the high strength and corrosion resistance of steel and high electrical conductivity and high thermal conductivity of copper.However,the thermophysical properties mismatching between copper and stainless steel makes cracks easily formed in the weld and the heat affected zone of steel,which severely limit the application of dissimilar composite weldment between copper and stainless steel.Subsequently,the present work aimed to joining the copper and stainless steel by welding technology The microstructure and properties of joint were investigated and the mechanical properties of the joint were improved by developing matching welding materials to control microstructure,which is great of practical significance.In this paper,the constitution of T2 copper and 304 stainless steel were conducted by gas metal arc welding using filler material of pure copper.The influence of process parameters on the comprehensive performance of welded joints were revealed by analyzing the microstructure and mechanical properties of welded joints obtained by different parameters.With the increase of welding heat input,the transition zone between the stainless steel and the weld metal(iron-rich layer)tends to increase first and then decrease,and the dendritic and spherical iron-rich phases distributed in the weld are increase.The micro-hardness of the weld zone significantly improved,but the tensile strength of the welded joint has not changed,and its average value can reach more than 90%of the copper base metal.In addition,the toughness of the weld metal is generally low,and the highest value(Ak=35J)is only 54%of the copper base metal.Therefore,when the process parameters are suitable,the strength of the welded joint can meet the requirements of engineering,but the low toughness is still a negative factor restricting its application in engineering.On this basis,in order to improve the toughness of the weld metal,the Cu based composite intermediate(Cu-Si and Cu-Ni)were designed and employed to connect stainless steel and copper in this study.The welding results show that the welds obtained with the composite intermediate are well,and there are no obvious macro defects in the cross section of the welded joint.For the Cu-Si weld,the size of the iron-rich phase in the weld is significantly reduced,and the impact toughness of the weld metal(Ak=41J)is slightly improved;For the Cu-Ni weld,due to the infinite mutual solubility between Ni and Fe,the content of the iron-rich phase in the weld is increased,and it mostly exists in the form of dendrite.At the same time,the impact toughness of the weld metal(Ak=54J)is significantly improved.It can reach 83%of copper base metal.In contrast,the performance of welded joints welded by using Cu-Ni welding wire is superior.In addition,combined with the Fe-Cu binary phase diagram as well as the solidification characteristics of Cu-Fe alloy,the formation process of welded joints and the microstructure formation mechanism of the weld metal were analyzed in this paper,which can provide an effective theoretical guide for the subsequent research on the welding between copper and stainless steel. |
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