Interfacial Microstructure And Joint Strength Of The Cu-Cu And Cu-Al Joints Processed By Low-temperature Ni Electroplating

The welding industry has been committed to finding new joining technologies for decades.So far,several special advanced joining methods,such as laser welding,electron beam welding,friction welding and micro-connection technology have become an important part of modern joining technology.Electroplating has developed relatively mature as a surface modification process.However,its potential and capacity in the joining field have not attracted enough attention from domestic and foreign scholars.The purpose of this study is to investigate the feasibility and reliability of the electroplating process in the joining field.In this study,Cu-Cu and Cu-Al samples were joined by nickel electroplating at a low temperature and the electroplating process was explored.Structure of the interface and the effect of current on the nickel layer were studied by transmission electron microscopy?TEM?etc.Tensile strength of the joint was measured by uniaxial tensile test.In addition,the Cu-Al specimen was subjected to aging treatment,and the effect of aging time on the intermetallic compounds?IMC?as well as interfacial bonding strength of the Al/Ni interface were studied.Electroplating solution formulation was determined with nickel sulfamate as the main salt,nickel chloride as the activator and boric acid as the PH stabilizer.Dense nickel layer was obtained with an uniform morphology and Cu-Cu and Cu-Al samples were successfully joined.A Cu_xNi_1-x unlimited substitutional solid solution was formed at the Cu/Ni interface with a width of approximately 60 nm.The Cu composition showed a linear reduction towards the Ni side and vice versa.The Al/Ni interface was approximately 100 nm wide.A 20 nm-wide layer of the BCC-structured AlNi IMC was observed at the Al/Ni interface near the Ni side.Tensile strength of Cu-Cu joint ranged from 100 MPa to 280 MPa and cracks initiated inside of the nickel layer or Cu.The average ensile strength of Cu-Al joints before aging was 124 MPa,while it was 122 MPa after the 1000 h aging test conducted at 200 °C.The isothermal aging treatment had no effect on the strength of Cu-Al joints.No further IMC growth was observed at the Al/Ni interface during the aging process.Hardness of nickel layer in the direction of growth velocity increased with the increase of the current density,while the hardness in the direction perpendicular to the growth velocity was not affected by the current density.Average grain thicknesses of nickel layer in the normal directions of?111?,?200?,and?220?planes were 188²08 ?,138¹87 ?,and 83¹39 ?,respectively.The grain size of the nickel layer decreased with the increase of the current density.