| Particulate reinforced aluminum-based metal matrix composite (MMC) hasnot only high specific strength, high specific modulus, low thermal expansioncoefficient, good wear resistance and isotropic properties, but also simplemanufacturing method and low cost. Thus, it has been applied in aerospace,military, automotive and electronic industries. With commercial application of itsproducts, the application fields will expand further. However, its application hasbeen severely restricted by the lack of a suitable joining method. The recent studiesshowed that the transient liquid phase diffusion bonding (TLP bonding) is one ofeffective methods. In this paper, TLP bonding of 6061 aluminum-based MMCcontaining 19.4vol-% alumina (Al2O3P/6061Al) was investigated systemically,including formation process of TLP bonded joint and effects of interlayer materials(pure Cu, pure Ag, pure Ni, Al-Si alloy, Al-Cu alloy and Al and Cu multi-layer) andbonding parameters on microstructure, mechanical properties and fracture featureof the joint. Formation process of TLP bonded joint was studied mainly by detecting thechanges of microstructures of TLP bonded joints in different stages and dissolutiontemperatures of interlayer were determined by differential scanning calorimetry(DSC) technique. Copper interlayer with 25μm thickness and initial assemblytorque with 1.96N?m were employed in the work. The experimental results showedthat the formation process of TLP bonded joint comprises four stages: plasticdeformation and solid diffusion (stage 1), dissolution of interlayer and base metal(stage 2), isothermal solidification (stage 3) and homogenization (stage 4). In stage1, the thickness of the interlayer decreased, the interlayer and the base metalscontacted more closely and the interdiffusion of atoms occurred, which wouldfavour the formation of liquid. In stage 2, dissolution of the interlayer occured in545℃～550℃ (heating rate 5℃/min). With dissolution of the base metal, liquidlayer widened and average copper concentration of liquid layer decreased. ivAbstractConsequently, the completion of stage 2 could be determined by width andchemical composition of liquid layer. In this stage, reinforcement phase particulatewas well-distributed. The reason was that the density of liquid is close to that ofAl2O3 particulate and Al2O3 particulate redistribution in liquid needs time. In stage3, the liquid layer width decreased and Al2O3 particulate segregated in the center ofthe joint. In stage 4, average copper concentration of the joint decreased andhomogenization of the joint occurred. With increasing initial assembly torque from1.96N?m to 4.9N?m, stage 2 and stage 3 were changed. At this condition, the liquidlayer width decreased after dissolution of interlayer and unchanged with furtherincreasing temperature, but with increasing holding time the liquid layer widthdecreased till the completion of isothermal solidification. Therefore, it was difficultto distinguish the two stages. At the same time, since liquid layer width reduced atthe beginning of the isothermal solidification, completion time of isothermalsolidification decreased greatly and composition of the joint was morehomogeneous. Further studies for the joint with high initial assembly torquerevealed that there was a solute concentration transition zone in solid/liquidinterfaces during stage 2, which might be induced by concentration gradient ofsolute in solid and liquid. When interlayer was pure metal (Cu,Ag,Ni), under the condition that thebonding temperature was higher than their eutectic temperatures, the joints hadsimilar microstructure, close shear strength, and same failure site. Microstructure ofthe joints mainly consisted of the particulate segregation region (P), the denudedparticulate region (D) and the base material region. The P region and D regionconsisted of α-Al and Al2O3 particulate. However, in the P region volume fra... |
PDF Full Text Request