No 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

Internal defects are among the problems in gravity casting of aluminum parts. The main internal volumetric defects are gas and shrinkage defects which form during solidification of the melt and drastically reduce the quality of the produced parts. These defects adversely affect the mechanical properties of thin walled castings parts. In this study, ceramic nanoparticles coatings were applied on the sand mold and the effect of mold coatings on the reduction of defects were investigated. X-ray radiography was used to detect defects in sand molds with ceramic nanoparticles coatings. For comparison, this test was performed on molds with micro-ceramic and graffiti coatings and uncoated sand mold. The results showed that the maximum amount of gas and shrinkage defects was observed in casting parts from AL4-1 alloy in uncoated molds. On the other hand, the minimum defects were found in molds coated with ceramic nanoparticles. It seems that the reduced defects in casting parts in molds coated with ceramic nanoparticles may be due to high thermal and chemical stability and higher heat transfer rate of the coating. These results can facilitate the production of high quality aluminum alloys parts using nanotechnology.

In this study, TIG welding was used to clad and repair the surface of cast AZ91C magnesium alloy. Then, friction stir processing and T6 heat treatment wrer applied on the welded region. Microhardness results showed an improvement in the mean hardness of welded zone and also FSPed zone. Increase in the mean microhardness of the welded zone after T6 heat treatment to the maximum value was also concluded. The results of wear test showed that the wear resistance of the welded area was improved. Further improvement in wear properties was obtained after friction stir processing and T6 heat treatment.