Interfacial microstructure, mechanical properties and strengthening mechanism of Mg/Al bimetallic composites produced by a novel compound casting with the addition of Gd

To strengthen the bonding properties of Mg/Al bimetallic composites, rare earth Gd was added to the Mg/Al bimetallic composites manufactured by a novel compound casting, and the interfacial microstructure, mechanical properties and strengthening mechanism of the Mg/Al bimetallic composites with Gd addition were studied. Without Gd addition, there was a thin oxide film consisting of an alumina phase in the Mg/Al bimetallic interface, which hindered the diffusion of Mg2Si phase. After adding the Gd, the oxide film in the interface was broken and dissolved, significantly increasing the diffusion distance of the Mg2Si phase. The Al2Gd and Al8Mn4Gd precipitated in the interface. However, with the increase of the Gd content, the distribution of the Gd precipitates gradually became inhomogeneous. The primary Al12Mg17 phase and eutectic structure in the interface were greatly refined due to the heterogeneous nucleation and the inhibition of growth caused by the Mg2Si phase and Gd-rich precipitates. The interface was strengthened under the comprehensive effect of the fine grain strengthening and precipitation strengthening of the Mg2Si and Gd-rich precipitates. When the Gd content increased to 0.6 wt%, the shear strength of the Mg/Al bimetallic composites reached the maximum of 46 MPa, which was 39% higher than that of the bimetallic composite without Gd addition. With the further increase of the Gd content, the aggregation of the Gd-rich precipitates and the excessive thickness of the interface led to the decrease of the shear strength of the Mg/Al bimetallic composites.