Toughening mechanisms in Mg/Al macrocomposites: Texture and interfacial mechanical interlocking

In this study, two types of new bimetal magnesium/aluminium (Mg/Al) macrocomposites with millimetre-scale Al core reinforcement were fabricated using casting coupled with hot coextrusion. The first macrocomposite was fabricated with an unthreaded Al core while the second one had a threaded Al core. Microstructural characterization revealed Mg texture change and interdiffusion of Mg and Al into each other across the interface in an unbalanced manner. Stress at the bimetal interface was attributed to solid solution formation, thermal expansion mismatch, unbalanced Kirkendall strain, lattice misfit strain and strain localization effects. Results revealed that the presence of the Al core leads to a decrease in strength but an increase in failure strain and toughness (work of fracture) of Mg. The threaded Al core reduced 0.2%YS and UTS of Mg by 17% and 15%, respectively, and enhanced the failure strain and toughness of Mg by 102% and 73%, respectively. This was 1.4 and 1.6 times less the reduction, and about 6 and 7 times more the increment, when compared with the corresponding changes of 0.2%YS, UTS, failure strain and toughness of the unthreaded macrocomposite, respectively. The toughening mechanisms in bimetal Mg/Al macrocomposites are investigated in this paper.