An　Mg-Al-Zn-Er　filler　metal　is　developed.　During　the　melting　of　filler　metal,　ultrasonic　vibration　is　applied　to　the　liquid　metal.　The　power　of　ultrasonic　is　600　W,　the　frequency　of　ultrasonic　is　20　kHz,　and　the　ultrasonic　vibration　time　is　0-240　seconds.　The　liquid　filler　metal　is　casting　under　600°C.　The　experiment　results　show　that　the　melting　points　of　developed　filler　metal　do　not　exceed　355°C　and　the　melting　range　is　not　beyond　10°C,　which　benefit　for　the　soldering.　The　ultrasonic　vibration　acting　on　the　melting　filler　metal　has　the　effect　of　purifying　microstructure,　refining　the　grain　and　accelerating　the　precipitation　of　α-Mg　and　Al3Er.　During　the　soldering　of　AZ31　magnesium　alloy,　the　Al3Er　precipitation　phase　act　as　nucleation　site,　preventing　the　coarsening　of　crystal　grain.　When　the　ultrasonic　vibration　time　of　solder　is　approaching　180　s,　the　shear　strength　of　lapping　joint　is　59.7　MPa,　which　is　almost　one　point　two　times　that　of　the　filler　metal　which　has　not　undergo　ultrasonic　treatment.　©　2014　Journal　of　Mechanical　Engineering.