Synthesis and characterization of an in-situ magnesium-based cast nano composite via nano-SiO2 additions to the melt

Abstract

In this study, AZ91C magnesium matrix in-situ nano-composites reinforced with oxide particles were produced by the addition of 2 % of mass fractions of silica nanoparticles to the melt using the stir-casting method. For this purpose, nano-silica powder was mixed in molten AZ91C by a special procedure and stirred for 15 min at 750°C and cast in a preheated die at 720°C. Control samples were also cast under the same conditions. Improved microstructure, reduced porosity and increased hardness, tensile strength and yield strength of the composite sample were revealed by microstructural and mechanical investigations. The hardness, yield strength and tensile strength values increased from 65 BHN, 82 MPa and 165 MPa for the monolithic samples to 77 BHN, 97 MPa and 175 MPa for the in-situ formed cast composites. Microstructural and EDS analyses suggested the in-situ formation of Al2O3, MgAl2O4 and MgO oxide particles by in-situ reaction of the Al, Mg and SiO2 in the melt. Keywords: AZ91C alloy, in-situ cast nano-composite, silica nanoparticles, mechanical properties V {tudiji so bili izdelani AZ91C nanokompoziti in situ, na podlagi magnezijeve matrike in oja~ani z oksidnimi delci z dodatkom 2 % nanodelcev silicija za topljenje, z uporabo metode litja z me{anjem. Za ta namen je bil nanosilicijev prah zme{an v raztopljen AZ91C s posebno metodo in nato 15 min me{an na 750°C in lit v predogretem modelu na 720°C. Preizku{anci so bili ravnotako liti v enakih pogojih. Izbolj{ana mikrostruktura, zmanj{ana poroznost in pove~ana trdota, napetostna trdnost in napetost vzorcev kompozita so bili odkriti s preiskavami mikrostrukture in z mehanskimi preiskavami. Vrednosti trdote, napetosti te~enja in natezne napetosti so se pove~ali iz 65 BHN, 82 Mpa in 165 MPa in za monolitne vzorce na 77 BHN, 97 MPa in 175 MPa za in situ formirane lite kompozite. Mikrostrukture in EDS-analize so predlagale in situ formacijo Al2O3, MgAl2O4 in MgO oksidne delce z in situ reakcijo Al, Mg in SiO2 v topljenem. Klju~ne besede: AZ91C zlitina, in situ litje nanokompozitov, nanodelci silicija, mehanske lastnosti

Novel AM60-SiO2 Nanocomposite Produced via Ultrasound-Assisted Casting; Production and Characterization

“…According to the previous reports [33,34], SiO 2 nanoparticles may undergo chemical reactions with the molten Mg as follows:4Mg + SiO 2 = Mg 2 Si + 2MgO…”

“…The Gibbs free energy for the above reaction is calculated to be −84 kJ at the superheat temperature for this research, 700 °C, which shows the reaction is thermodynamically favourable. Boruni et al [33] used amorphous SiO 2 particles and attributed the improvements in the mechanical properties of their samples solely to the secondary phases produced by Mg-SiO 2 and Mg-Al reactions in the melt during the casting process, i.e., Mg 2 Si and MgO. However, the possibility of the contribution by the unreacted SiO 2 particles needs to be taken into account, too, when assessing the mechanical properties of the samples, given the lower melt superheat, and a less severe stirring in this research compared to the work of Brouni et al In the current work, crystalline SiO 2 was used as the reinforcement, which is expected to affect the crystal structure of the matrix by acting as a grain refiner.…”

“…AM60 is an Mg–Al–Mn alloy which, besides good ductility, is featured with suitable strength and thermal stability [30,31,32]. Boruni et al [33] produced an in-situ magnesium-based cast nanocomposite via addition of 2 wt.% nanoparticles of amorphous SiO 2 to the AZ91C melt and reported improvements in the mechanical properties by the introduction of the particles, as a result of the secondary phases produced during the casting process. Huang et al [34] synthesised in situ composite by adding SiO 2 to the Mg melt and addressed the possible thermodynamic reactions of the ceramic particle with the melt.…”