Microstructure evolution, mechanical properties and fracture behavior of Al-xSi/AZ91D bimetallic composites prepared by a compound casting

•Microstructure and mechanical behavior of Al-xSi/AZ91D bimetallic composites were studied.•Thickness of interface of Al/Mg bimetallic composites decreased with increasing Si content.•Oxide inclusion defects in interface layer decreased with increasing Si content.•Increasing Si content resulted in an inconsistent preferred orientation of interface layer.•Shear strength of the composites increased with increasing Si content, obtaining a maximum value with 15 wt.% Si.