The evolution of microstructure in the MB8/2024 dissimilar alloy joints by using Al/Zn/Cu/Zn multi- interlayers via ultrasonic-assisted brazing was investigated. The results show that the addition of aluminum foil on the MB8 side realized the transformation of Al₃Mg₂ binary intermetallic compounds (IMCs) to AlMg₄Zn₁₁ ternary IMCs along the interface between copper foil and MB8 magnesium alloys. This transformation reinforced the joints and then the shear strength reached a maximum at 22 s (85.26 MPa). Thermodynamic analysis shows that ？G_Mg,Al,Zn of AlMg₄Zn₁₁ (-38.65 kJ/mol) was smaller than that of Al₃Mg₂ (-31.94 kJ/mol), which provided a basis for the IMC transformation. Mg₃₂(Al,Zn)₄₉ quasicrystal was found for the first time using ultrasonic-assisted brazing due to the cavitation effect.