Preparation And Properties Of Cu Matrix Composites Reinforced With Aligned Carbon Nanotubes

Based on the excellent performance of carbon nanotubes(CNTs),a new type of copper matrix spot welding electrodes were prepared to improve the lifespan and the joints quality of spot welding electrodes for galvanized steel sheetsThere are four technical difficulties in preparing spot welding electrodes of Cu matrix composites reinforced with carbon nanotubes: interface between carbon nanotubes and Cu,dispersion of CNTs,densification of composites,and alignment of CNTs.To solve these four problems,electroless plating were used to coat Cu bilayers or Ni and Cu bilayers on Single-walled carbon nanotubes(SWCNTs)to improve the wettability between CNTs and copper matrix.Powders were mixed through ultrasonic assisted mechanical agitating to disperse SWCNTs homogeneously in copper matrix.Hot forging and die-stretching were used to density composite samples and align SWCNTs in copper matrix.A three steps refluxing procedure-sensitization-activation-electroless plating were used to get little oxidation,uniform,continuous,compact Cu layer or Ni and Cu bilayers.The layers were still compact and integrated during the next forming processes.SWCNTs were dispersed uniformly and aligned in SWCNTs/Cu powders or composites bulks by using modern testing methods.The mechanical properties of composites increased obviously.The hardness and tensile strength increased 67.3% and 30.4% via the addition of 5vol.% Ni Cu coated SWCNTs,respectively.The tribological properties also increased obviously.The friction coefficient decreased 68% via the addition of 3vol.% Ni Cu coated SWCNTs.The wear rate decreased 91% via the addition of 10 vol.% Ni Cu coated SWCNTs.The composites were anisotropic in conductivity properties.The electrical conductivity of 10 vol.% Ni Cu coated SWCNTs along RD is 11.5% higher than other directions.The thermal conductivity of 10 vol.% Ni Cu coated SWCNTs along RD is 17.7% higher than other directions.Cu matrix composites reinforced with aligned carbon nanotubes were used to manufacture spot welding electrodes of galvanized steel sheet.The Weld nugget diameter tests and Tensile shear tests shows the lifespan of these spot welding electrodes increased obviously.The lifespan increased to around 3700 points via the addition of 3vol.% Ni Cu coated SWCNTs,is 6 times than that of traditional electrodes.This research provides innovative technology for the method of alignment of CNTs.