Abstract: 1060 aluminium cladding AZ31 magnesium alloy composite ingots were prepared under gas protection to investigate and improve the interfacial combination. The microstructure, phase constituents and microhardness of the matrix and the interface were studied by use of optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is found that the microstructure of the as-cast AZ31 magnesium alloy consists mainly of the α-Mg matrix and the typical divorced eutectic of α-Mg and β-₁₇Al₁₂ phases distributed along grain boundaries. A diffusion fusion layer forms in the interface, leading to a complex metallurgical interface with a multilayer of the α-Mg solid solution zone, the eutectic (α-Mg + β-₁₇Al₁₂) zone and the Mg-Al intermetallic compound zone. The Mg-Al intermetallic compounds are made up of β-₁₇Al₁₂ and AlMg. It is proposed that the formation mechanism of the complex interface layer is due to the emergence of a molten bath on the 1060 Al plate surface at AZ31 melt pouring moment and the rapid solidification subsequently.