Strengthening and Toughness of AZ61 Mg with Nano SiO<SUB>2</SUB> Particles

Abstract

The strengthening mechanisms and bending toughness of the AZ61 Mg based composites reinforced by nano SiO 2 particles are examined. The composites were prepared either by spray forming, ingot metallurgy, or powder metallurgy, followed by severe hot extrusion. The spray formed composites exhibit the best nano particle distribution and toughness, but the volume fraction of the nano particles that can be inserted is limited. The nano composites fabricated through the powder metallurgy method possess the highest strength due to the extra strengthening effect from the MgO phase. Strengthening analysis based on the Orowan strengthening mechanism can predict well the composite strength provided that the nano particles are in reasonably uniform dispersion. For composites containing higher nano particle volume fractions greater than 3%, the experimental strength data fall well below the theoretical predictions, suggesting poor dispersion of the reinforcement.

Rapid microwave sintering of carbon nanotube-filled AZ61 magnesium alloy composites

“…Some researchers have reported similar observations in spray formed and extruded AZ61/nano silica (n-SiO 2 ) composites [40] and Mg/CNT composites [25]. Although extrusion was not undertaken on the samples in the present study, the microhardness value of AZ61-3.0CNT (86.9 HV) compared favourably with the 88 HV reported for cast and extruded AZ61/n-SiO 2 in reference [40].…”

“…Although, matrix grain-refinement was reported in [25,[39][40], it could not be solely credited to the nano-reinforcement because the composites were subjected to extrusion.…”

“…The compression test results in Table 5 indicate that the CNTs in the AZ61 matrix Some researchers [3,40,45] have reported similar improvements in the mechanical properties of Mg-based and Al-based composites, which were rationalised based on a number of strengthening factors, including the Orowan strengthening mechanism arisen from the obstruction of dislocation movement by the CNTs [16,40,46], the matrix-reinforcement thermal and elastic moduli mismatch which increases dislocation density and hence, increases strength [16,[45][46] (CTE of Mg = 28.5 X 10 -6 K -1 [21]; CTE of CNTs = 2.7 X 10 -6 K -1 [44]), strong bonding between the matrix and CNTs [48][49], and efficient load transfer from the matrix to the reinforcement [3,16,46]. All the composite samples showed higher failure strains compared to the unfilled matrix, except for the sample AZ61-3.0CNT which had a similar level of failure strain as the monolithic AZ61 alloy.…”

On the strength and strain to failure in particle-reinforced magnesium metal-matrix nanocomposites (Mg MMNCs)

“…3(b). However, the Mg AZ61-SiO 2 data sets [52,53] have several points in the low reinforcement concentration (0.1,0.16, and 0.2 vol%) that are above the expected trendlines (not shown here) indicating that there may be some Orowan strengthening expected from these materials.…”

“…Most of the data exhibits lower ductility than what would be expected for some of the grain sizes achieved. Addition of SiO 2 to AZ61 by Hung et al [53] (green symbols in Fig. 7) exhibits better yield strength and ductility than AZ31 in the spray formed specimens with low concentrations of reinforcement.…”