The Mechanisms And Mechanical Properties Of Ultrasoundassisted Transient Liquid Phase Bonding Of SiC Reinforced Magnesium Metal Matrix Composites

Silicon carbon particles reinforced magnesium matrix composites?Si C_p-Mg?have high hardness,strength,elastic modulus,wear resistance and low thermal expansion coefficient,which have been widely used and promoted in the aerospace,electronic chips encapsulation and defense industries.In order to obtain complex and large structure,the joining methods of this material have been unceasingly explored.Therefore,this study used the ultrasonic assisted transition liquid phase diffusion bonding?U-TLPB?method to join SiC_p-AZ91Mg MMCs using pure zinc,aluminum and zinc/Al/zinc composite interlayer.The research deeply analyzed the weld and the fracture microstructure?optical metallography,scanning electron microscopic metallographic?,the weld EDS spectrum data?point,line,face scans?,weld section XRD data,joint shear strength test and weld brazing penetration rate test data,etc.The relationship between bonding temperature/ultrasonic time and the joint microstructure/mechanical properties are investigated.The mechanism of ultrasonic effects and the joining model are established.The maximum shear strength of the joint using Al interlayer is 140MPa of the bonding temperature at 490?and ultrasonic time for 5s.The microstructure of the joint are mainly?-Mg solid solutions and a small quantity of Al₁₂Mg₁₇7 IMCs,and the fracture path is completely located in the bonding seam.The maximum shear strength of the joint using Zn interlayer is also 140MPa of the bonding temperature at 390?and ultrasonic time for 10s.The microstructure of the joint are mainly?-Mg solid solutions and some Mg-Zn IMCs,and the fracture path is completely located in the bonding seam.In order to eliminate intermetallic compounds,this research designed"the first ultrasonic assisted bonding?bonding temperature:400?,and ultrasonic time:5s?+secondary ultrasonic assisted heat preservation?holding temperature:430?,and ultrasonic time:30s?"process,which can be achieved under the condition of the atmosphere without flux.The joint microstructure completely translated into magnesium based solid solution with uniform distribution of SiC particles,the maximum joint strength is 175.5MPa?87.5%of base metal strength?.Ultrasonic assisted mechanism of isothermal solidification is divided into the following two parts:?1?ultrasound produce the acoustic pressure field extruding a large number of liquid out of the bonding seam;?2?the residual liquid phase enclosed in the grain boundary can be further propagated to the base material by the dislocation short-circuit diffusion channel formed by the ultrasonic effects.The SiC particles reinforced phase always preferred to distribute within the eutectic organization,therefore,it is significant to eliminate eutectic organization by ultrasonic effect,which can improve silicon carbide particles distribution and prevent the aggregation.