Enhancing tensile and compressive strengths of magnesium using nanosize (Al₂O₃ + Cu) hybrid reinforcements

Abstract

This study investigates the microstructure and mechanical properties of magnesium (Mg) containing alumina (Al 2 O 3 ) and copper (Cu) nanoparticles as hybrid reinforcements. For composite preparation, the amount of Cu was varied from 0.1 to 0.9 volume percent, whereas the amount of Al 2 O 3 was fixed at 1 volume percent. Mg and its composites were synthesized using powder metallurgy route incorporating energy-efficient microwave sintering followed by hot extrusion. Hybrid reinforcements in Mg matrix led to a grain size reduction, and the grain size decreased with increasing presence of secondary phases (reinforcements and intermetallics). Overall distribution of secondary phases within the matrix was observed to be uniform despite the formation of clusters. A significant improvement in microhardness was exhibited by all composite formulations when compared to pure Mg. The results also showed that yield and ultimate strengths were enhanced in all composite formulations under both tensile and compressive loading while tensile and compressive failure strains were compromised.

Effect of nano-Al2O3 addition and heat treatment on the microstructure and mechanical properties of Mg-(5.6Ti+3Al) composite

“…It corresponds to the presence of Ti (hardness of Ti -0.97 GPa (98 Hv)) and Al 3 Ti intermetallics (hardness of Al 3 Ti -4 GPa (407 Hv)) and their relatively uniform distribution in Mg matrix [15,28]. The presence of nano-Al 2 O 3 particulates added either directly or after ball milling with Ti and Al, has resulted in the reduction in microhardness which is attributed to the larger and widely spaced second phase clusters as observed in the microstructure [29]. Similarly, a marginal reduction in microhardness values is observed in all the composites after heat treatment at 200°C for 5 h. These observations are similar to those reported elsewhere and can be related to the relaxation of internal residual stress which were developed between the matrix and the reinforcements due to the differences in their thermal expansion coefficients [12,30].…”

“…When compared to pure Mg, the composites showed significant improvement in the strength properties, however with a reduction in the compressive ductility. It should be noted in Mg, when there are no second phases present, the formation of twins and its propagation were reported to be favored at relatively lower strength levels resulting in higher fracture strain [29]. On the other hand, in the composites, the presence of secondary phases (intermetallics/reinforcements) obstructs the twin nucleation and propagation and hence delays the yield process contributing to the higher strength properties and also the poor fracture strain due to the restricted twinning process [5,14].…”

“…Thus the overall failure mechanism in all the Mg composites under compression loading is unchanged. Also the developed Mg-composites exhibited rough fracture surfaces with mixed mode of shear and brittle features before and after heat treatment [5, 27,29]. The presence of shear bands generally attributes to the heterogeneous deformation and the work hardening behavior as the work hardening rate is faster in the case of samples failed by shear bands [32,33].…”

“…SEM micrographs showing the distribution of particulate reinforcements and other second phases in the heat treated (a) Mg-(5.6Ti + 3Al) (HT), (b) Mg-(5.6Ti + 3Al)-2.5Al 2 O 3 (HT) and (c) Mg-(5.6Ti + 3Al + 2.5Al 2 O 3 ) composites after heat treatment at 200°C for 5 h.Mg-(5.6Ti + 3Al) composite can be attributed to the fine grain size and the presence of Ti and Al 3 Ti intermetallic phases and their relatively uniform distribution in Mg-matrix [5,27,29]. The direct addition of nano-Al 2 O 3 particulates resulted in an improvement in ductility and work of fracture without significantly affecting the strength properties in the case of Mg-(5.6Ti+ 3Al)-2.5Al 2 O 3…”

“…Graphs showing the distribution of (e) no. of particles vs. particle size and (f) particle aspect ratio vs. particle size.improves the failure strain [5,27,29]. In the case of nano-Al 2 O 3 addition after ball milling, loss in compressive strength values occurred without affecting the compressive ductility taking the statistical deviation into consideration.…”