Reaction-tunable diffusion bonding to multilayered Cu mesh/ZK61 Mg foil composites with thermal conductivity and lightweight synergy

The thermal properties of Mg alloys require further optimization to encounter the increasingly severe heat dissipation demands of high-power densities and highly integrated electronic components.In this study,a novel strategy of reaction-tunable diffusion bonding(RDB)was applied to manipulate the inter-facial reaction in the multilayered Cu mesh/ZK61 Mg foil composites.The displacement of the punch was utilized to quantify the degree of reactive diffusion with adjustable,visible,and high flexibility.The inter-face was artificially manipulated to produce the fluid Mg-Zn eutectic liquid phase filling the interfacial gap at high temperature for a short time,followed by diffusion bonding at low temperature.The thermal conductivity of the composites first increased and then decreased,which was synthetically affected by the amelioration of metallurgical bonding and the moderately reactive consumption of Cu.The reinforcement Cu was converted from the Hasselman-Johnson model to the Rayleigh model,reflecting the optimization of the interfacial bonding quality.The composites with thermal conductivity and lightweight synergy were fabricated successfully.Therefore,RDB is a progressive technique,shedding lights on the innovative lightweight metal matrix composites with high thermal conductivities relevant to the 5G communications and new energy vehicle industries.

Dislocation behavior in Cu single crystal joints under the ultrasonically excited high-strain-rate deformation

The coupling effects of ultrasonic excitation and high-strain-rate deformation are the core factors for weld formation during ultrasonic welding.However,interfacial deformation behavior still shrouds in uncer-tainty because of the contradictory features between mutual dislocation retardation caused by severely frictional deformation and ultrasonic-accelerated dislocation motion.[101]and[111]-oriented Cu single crystals which tended to form geometrically necessary boundaries(GNBs)were selected as the welding substrates to trace the uniquely acoustoplastic effects in the interfacial region under the ultrasonically excited high-strain-rate deformation.It was indicated that for a low energy input,micro-welds localized at the specific interface region,and equiaxed dislocation cells substituting for GNBs dominated in the ini-tial single crystal rotation region.As the welding energy increased,continuous shear deformation drove the dynamic recrystallization region covered by equiaxed grains to spread progressively.Limited discrete dislocations inside the recrystallized grains and nascent dislocation cells at the grain boundaries were ob-served in[101]and[111]joints simultaneously,suggesting that the ultrasonic excitation promoted motion of intragranular dislocation and pile-up along the sub-grain boundaries.The interfacial morphology be-fore and after expansion of recrystallization region all exhibited the weakening of orientation constraint on dislocation motion,which was also confirmed by the similar micro-hardness in joint interface.The first-principle calculation and applied strain-rate analysis further revealed that ultrasonic excitation en-hanced dislocation slipping,and enabled dislocation motion to accommodate severe plastic deformation at a high-strain-rate.

A supersaturated Cu-Ag nanoalloy joint with ultrahigh shear strength and ultrafine nanoprecipitates for power electronic packaging

Ag-Cu bimetallic nanoalloy,integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu,is a prospective bonding material for power electronic packaging.The Ag-coated Cu nanoparticles(Cu@Ag NPs)paste can execute bonding with high quality at 250℃,and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength(152 MPa)dramatically exceeds most nano-paste joints.The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength.Besides,the numerous ultrafine nanograin,high proportion of low angle grain boundaries(7.44%)without deformation,and the Cu nanoprecipitates in the joint would improve subordinately.Furthermore,the high content(16.8%)of∑3 twin boundaries would contribute to the electrical and thermal conductivity.Thus,the multiple strengthening mechanisms with the solid solution,the second precipitated phase,and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.