Preparation Of Carbon Nanotubes Reinforced Copper Matrix Composites By Ultrasonic Welding

Ultrasonic metal welding is a new type of solid state welding method, which isapplicable to all types of metal with good plasticity. Compared to conventionalwelding, the ultrasonic metal welding possesses a large number of advantages, suchas short welding time, small energy consumption, no smoke and dust, etc. This paperstudied the ultrasonic metal welding of the copper/copper, copper/carbon nanotubecomposites. And the effects of the process of parameters, such as the surface state ofthe sample, the welding time, welding pressure, welding head size, etc. then theoptimum welding parameters were got through tensile test and metallurgicalobservation. Moreover, the forming principles of ultrasonic metal welding were alsostudied by optical microscopy, scanning electron microscopy, energy spectrum.For the welding of copper/copper, the best welding pressure and welding timeare about0.7MPa and180ms respectively, the tensile strength of the sample nodecould be up to1143N,66%of the base material; the hardness of the weld could be138HV,30%increased compared with the base material. During the welding process,significant plastic deformation of the weld metal and the formation of a fusion zoneappeared. The welding time could influence the energy input and thus affect thelength of the formed fusion zone, and welding pressure could influence the shearstrain and shear strength of the sample and thus affect the thickness of the fusion zone.Nanoscale grains are observed in fusion zone by the electron microscopy scanning,correspondingly, the hardness and strength increased significantly. However, theinternal strength of the sample after welding exhibits an uneven distribution. Inaddition, when the load is applied, the transition of the solder and the base materialwill break due to the stress concentration indused by the welding head.Carbon nanotubes reinforced copper matrix composites was prepared byultrasonic welding the copper whose surface subjected with alcohol solution whichcontaining carbon nanotubes. In order to increase the wettability of the carbonnanotubes, and make the interfaces stronger connected. In this paper, a layer ofcopper on the surface of carbon nanotubes was successfully formed by electroless plating method, which is also effective to solve the problem of clusters of carbonnanotubes. The main process of electroless plating includes the purification of carbonnanotube, sensitization, activation and electroless deposition. And the pre-treatmentof the carbon nanotubes, pH of the bath, the chemical reaction rate are the mostimportant factors which affect the quality of the coating.On the research of carbon nanotubes reinforced copper matrix composite, wemainly focused on the effects of the surface state and the content of carbon nanotubes.The best joint was found by the observation of mechanical properties and themicrostructure, which was formed by the carbon nanotubes with copper layer. Thecarbon nanotubes without any treatment could reduce the strength of the weldedsample because of the serious clusters. The maximum value of tensile shear strengthand hardness of the best specimens is1310N and150HV, increased by14.6%and15.4%respectively, as compared with those of copper/copper joints. Carbonnanotubes were found uniform dispersed in the joint by EDS, and the best content ofcarbon nanotubes is about0.2-0.5wt%.For the welding of copper/aluminum, the fusion zone was not found because ofthe difference of the hardness and strength of the materials, and the interface of theconnection can be easily observed. The diffusion layer of the two substances is up to10μm, it increases with the increasing of welding time and welding pressure.However, intermetallic compound could be formed when the welding parameters istoo large.