▎ 摘　　要

NOVELTY - The method for ultrasonically brazing nickel-plated graphene-reinforced tin-based lead-free composite solder, involves rolling nickel-plated graphene-reinforced tin-based lead-free composite, polishing surface with sandpaper, ultrasonically cleaning with acetone, removing oil and oxide impurities, brazing, overlapping the two copper substrates, uniformly migrating into brazing seam, and naturally cooling the brazing seam structure. The composite solder comprises silver, copper, rare earth element, graphene, nickel and tin. USE - Method for ultrasonically brazing nickel-plated graphene-reinforced tin-based lead-free composite solder (claimed). ADVANTAGE - The method enables ultrasonically brazing nickel-plated graphene-reinforced tin-based lead-free composite solder with excellent mechanical properties and high strength, and effectively inhibits the brazing nickel-plated graphene aggregation and floating. DETAILED DESCRIPTION - Method for ultrasonically brazing nickel-plated graphene-reinforced tin-based lead-free composite solder, involves (1) rolling nickel-plated graphene-reinforced tin-based lead-free composite, cutting into 15 mm x 20 mm x 0.1 mm ribbon, polishing surface of to-be-welded copper substrate with sandpaper, ultrasonically cleaning with acetone, removing oil and oxide impurities after drying, (2) placing the solder ribbon on overlapping structure of two copper substrates, (3) brazing the copper substrate in vacuum furnace, ultrasonically applying load to upper and lower overlapping surfaces of copper substrate through vibration pressure head fixedly connected on the ultrasonic transmission rod, solder melting, overlapping the two copper substrates such that nickel-plated graphene in the solder does not float under the action of ultrasonic wave, uniformly migrating into the brazing seam, and naturally cooling the brazing seam structure. The nickel-plated graphene-reinforced tin-based lead-free composite solder comprises 1.0-3.5 wt.% silver, 0.4-0.8 wt.% copper, 0.08-0.11 wt.% rare earth element, 0.01-0.11 wt.% graphene, 0.01-0.11 wt.% nickel and remaining tin. An INDEPENDENT CLAIM is included for preparation of nickel-plated graphene-reinforced tin-based lead-free composite solder, which involves (A) preparing nickel-plated graphene reinforced phase by (a) placing the graphene oxide nanosheets in concentrated solution of nitric acid and concentrated sulfuric acid mixed solution, ultrasonically dispersing after centrifuging, repeatedly washing the filter cake with deionized water until neutral, drying to obtain roughened graphene oxide nanosheets, (b) carrying out reflux treatment of hydrazine hydrate as reducing agent and graphene oxide nanosheets, repeatedly washing with deionized water until neutral, placing in a vacuum oven at 75-80 degrees C for 20-24 hours to obtain reduced graphene oxide nanosheets, (c) drying, reducing the graphene oxide nanosheets in planetary ball mill at 150-180 rpm for 2-3 hours, then adding nickel acetate, continuously milling for 1-3 hours, (d) placing the mixed reduced graphene oxide nanosheets and nickel acetate in nitrogen muffle furnace, heating at 350-400 degrees C, heat-preserving for 2-3 hours, reducing the surface of graphene oxide nanosheets to obtain nickel-plated graphene reinforced phase, (B) preparing nickel-plated graphene-reinforced tin lead-free composite solder by (a) ball milling nickel-plated graphene-reinforced phase, tin-silver-copper and absolute ethanol using zirconium dioxide ball at 150-180 rpm for 8-10 hours, (b) molding the mixed powder using 20 mm steel mold, holding pressure at 160-170 MPa for 25-30 minutes, (c) placing the compact in a vacuum oven, sintering at 180 degrees C for 2 hours, and (d) extruding the sample at room temperature to obtain final product.