Electrical Properties of Ag-C Contact Materials Containing Different Allotropes of Carbon
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In-situ synthesized silver-graphene nanocomposite with enhanced electrical and mechanical properties
Silver-graphene composite materials with enhanced electrical and mechanical properties are reported in this work. Ag nanoparticles are in-situ synthesized on the graphene oxide (GO) by chemical reduction of Ag salt mixed with GO in aqueous solution. After hydrogen reduction of GO, powder metallurgy technique and hot-extruding are employed to prepare Ag-rGO composite bulk material. The composite shows improved mechanical properties. The tensile strength of Ag-rGO composite is up to 190 MPa, 5.5% higher than that of pure Ag. The hardness of Ag-rGO is as high as 75 (HV), which is much higher than most carbon-reinforced Ag materials. Moreover, the ductility and conductivity of the Ag-rGO composite material still keep 43% and 1.6 μΩ cm, respectively. The electrical endurance test demonstrates the Ag-rGO composites owns excellent electrical properties. The material has an electrical endurance of 400,000 under current of 20 A and voltage of 220 V. This promising material has great potential application in electric apparatus.
Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder
Abstract In order to obtain high-strength aluminum joints, ultrasonic soldering of 1070 aluminum was conducted under liquidus temperature of Sn–Zn hypereutectic solder. A device for ultrasonic soldering was assembled, which propagated ultrasonic vibrations in a direction perpendicular to joining surfaces. This device joined 1070-Al using quasi-melting Sn–Zn hypereutectic solder without using any artificial spacers. The strength of the solder joints was evaluated by tensile tests. The optimum joining conditions were determined, and the effects of solder compositions and soldering temperature on the joint strength and the solder layer thickness were examined. In this ultrasonic soldering process, the highest tensile strength was obtained for the solder joints fabricated at 220 °C for the Sn–23Zn and Sn–40Zn solder compositions. The joint strength was equivalent to that of 1070-Al heat treated at 220 °C. The sound joints were obtained at 300 °C using Sn–82Zn solder, the liquid phase volume fraction of which was theoretically only 0.24. The present work also revealed that the thickness of retained solder layer in the joint after ultrasonic soldering could be estimated. Accordingly, ultrasonic soldering under the liquidus temperature of Sn–Zn hypereutectic solder could be a spacer-free soldering method to obtain high-strength aluminum joints.