Abstract
Gravitational melt-stir casting produced hybrid nano-reinforcements (β-SiCp) and micro-reinforcements (Bi and Sb) of AZ91 composites. SiCp-diffused discontinuous β-Mg17Al12 precipitation with a vital factor of SiC was exhibited at the grain boundary region, formulated Mg3Si throughout the composite and changed the present Mg0.97Zn0.03 phases. The creation of Mg2Si (cubic) and SiC (rhombohedral axes) enhanced the microhardness by 18.60% in a 0.5 wt.% SiCp/AZ91 matrix. The microhardness of 1 wt.% SiCp/AZ91 was slightly reduced after Mg0.97Zn0.03 (hexagonal) reduction. The best ultimate tensile value obtained was about 169.33 MPa (increased by 40.10%) in a 0.5 wt.% SiCp/AZ91 matrix. Microelements Bi and Sb developed Mg3Bi2, Mg3Sb2 and monoclinic C60 phases. The best peak yield strength of 82.75 MPa (increased by 19.85%) was obtained with the addition of 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb. The mismatch of the coefficient of thermal expansion of segregated particles and the AZ91 matrix, the shear transfer effect and the Orowan effect, combined with the quantitative value of phase existence, improved the compressive strengths of the composites with 0.5 wt.% β-SiCp, 1 wt.% β-SiCp and 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb by 2.68%, 6.23% and 8.38%, respectively. Notably, the Charpy impact strengths of 0.5 wt.% and 1 wt.% β-SiCp-added AZ91 composites were enhanced by 236% (2.89 J) and 192% (2.35 J), respectively. The addition of Bi and Sb with SiCp resulted in the formation of a massive phase of brittle Al6Mn. Al–Mn-based phases (developed huge voids and cavities) remarkably reduced impact values by 80% (0.98 J). The discussion covers the quantitative analyses of X-ray diffraction, optical microscopy and scanning electron microscopy results and fracture surfaces.
Highlights
Introduction iationsThe engineering sector has recently shown broad interest in magnesium alloys [1,2,3,4] because of their light weight, which reduces fuel consumption and green gas emission [5]
The present paper investigated the hybrid reinforcements of AZ91 (β-SiCp, Bi and Sb) in the as-cast condition by the gravitational melt-stir casting method
18.60% and 14.66% compared with the as-cast alloy AZ91, respectively, but decreased with alloy added with 1 wt.% β-SiCp was slightly reduced; the addition of β-SiCp limited increasing β-SiCp percentage from 0.5 to 1 wt.%
Summary
The engineering sector (commercial and military aerospace vehicles, automotive industry and shipbuilding industry) has recently shown broad interest in magnesium alloys [1,2,3,4] because of their light weight, which reduces fuel consumption and green gas emission [5]. Magnesium alloys and their composites have low weight (density ρ = 1.74 g/cm3 ), high specific strength (158 KN m/kg) and superior mechanical strength [6]. The FAA removed the prohibition against the use of magnesium alloy in seat frame compartments [9].
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