This paper investigates the corrosion of shot peened AA7075 aluminium alloys aged at different temperatures. The surface integrity of the hardened layer was evaluated with SEM, EDS, differential ...scanning calorimetry, hardness, and roughness measurements, and in the end also with corrosion resistance tests. The research results indicated that there were significant differences in precipitates distribution between aluminium alloys artificially aged at different temperatures. As the ageing temperature increases, the microhardness decreases, which influences the final roughness condition of the surface layer after shot peening. The results of potentiodynamic polarisation tests indicate that shot peening enables shifting the pitting potential to positive values, which ensures slightly higher corrosion resistance. SEM images confirmed the dissolution of the aluminium matrix near the separated iron-rich phases of the Al
form (Fe, Mn) by the action of galvanic cells.
The breakdown of the drill bit or rapid decrease of the rate of penetration during the drilling process results in a delay in the progress of drilling. Scientists and engineers are increasingly ...focusing on research to extend the bit life and improve the drilling rate. In our work, “in situ” drilling parameters were monitored during the drilling process with the roller cone drill bit IADC 136, diameter 155.57 mm (6 1/8"). After drilling, the bit was thoroughly examined to determine the damage and wear that occurred during drilling. The following modern and standardized investigative methods were used: an analysis of rock materials and an analysis of micro and macrostructure materials of the roller cone bit. Analyses were carried out using optical and electron microscopy, a simultaneous thermal analysis of materials of drill bit, analysis of the chemical composition of materials of drill bit, and a determination of the geomechanical parameters of rock materials. The resulting wear, local bursts, and cracks were quantitatively and qualitatively defined and linked to the drilling regime and the rock material. The results of our investigation of the material of the roller cone bit can serve as a good base for the development of new steel alloys, which can resist higher temperatures and enable effective drilling, without structural changes of steel material.
Recycling is now, more than ever, an important part of any foundry process due to the high cost of energy. The basis of the work presented here is a study of the addition of foundry scrap returns to ...the melt in order to reduce material and energy costs. The most important issue in such a process is the quality of both the prepared melt and final product. In this work, scrap returns were added to the AlSi9Cu3 base alloy in different proportions. Chemical composition was monitored, the solidification path was predicted by CALPHAD calculations and monitored by thermal analysis, and the formed microstructure was studied. The mechanical properties were also determined. The results showed that as the amount of scrap returns increased, elements such as Fe, Ni, Pb, Sr, etc. were more built up and elements such as Mg, Mn, Cr, etc. were decreased due to oxidation. The different chemical composition led to a reduced Mn:Fe ratio, resulting in the formation of needle-like Fe-rich phases and a decrease in mechanical properties.
The interaction between a molten magnesium alloy AE44 and a SiC–Al2O3–SiO2 ceramics and the resulting reaction products were studied. The samples were investigated using optical and electron ...microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. SiO2 was predominantly reduced by Mg during the contact of the magnesium-rich melt with the ceramics. The main reaction product was MgO, whilst Si dissolved in the melt. Two novel tetragonal phases formed at the interface: AlSiRE and AlMgSiRE, having a specific mutual crystallographic orientation relationship. The interactions resulted in strongly connected interfaces between the metal and ceramics after short interaction time; however, interactions lead to disintegration of the ceramics after longer contact time.
A developed methodology for determining the physical properties of mineral fibers prepared from different input mixtures under the same spinning wheel conditions is described and discussed. Energy ...dispersive X-ray fluorescence spectroscopy was combined with simultaneous thermal analysis and thermogravimetry to study the mineralogical composition and typical melting and crystallization temperatures. The mechanical properties measured with nanoindentation were related to the mineralogical properties and the results obtained are in agreement with the literature. The developed methodology shows reliable performance and demonstrates the ability to study the mechanical properties of mineral fibers, their mineralogical composition, and thermal properties. The presented experimental methodology opens up the possibility of researching the mechanical properties of mineral fibers for the purpose of defining production recipes in the field of mineral thermal insulation materials.
The aim of this study was to determine the correlation between the size and the distribution of microstructural constituents and their cooling rate, as well as the correlation between the mechanical ...properties and the cooling rate of AlSi9Cu3 aluminum alloy when cast in high-pressure die casting (HPDC) conditions. In other words, the ultimate goal of the research was to determine the mechanical properties for a casting at different cooling rates. Castings with different wall thicknesses were chosen, and different cooling rates were assumed for each one. Castings from industrial technological practice were systematically chosen, and probes were extracted from those castings for the characterization of their mechanical properties. Special non-standard cylinders were created on which compressive tests were carried out. The uniqueness of this research lies in the fact that the diameters of the designed cylinders were in direct correlation to the actual wall thickness of the castings. This is important because the solidification of metal in the die cavity is complex, in that the cooling rates are higher on the surface of the casting than in the center. Local in-casting cooling rates were determined using numerical simulations. It was discovered that with increasing cooling rates from 60 K/s to 125 K/s the values for strength at 5% deformation increased on average from 261 MPa to 335 MPa.
Deactivated (detoxified) asbestos-cement (DAC), i.e. asbestos-cement slates thermally treated at 1100 °C in order to convert the harmful asbestos fibers into non harmful mineral phases, has been ...successfully mixed with 74.6 wt% quartz sand and up to 63.2 wt% basalt sand, to produce stone wool with mechanical properties and composition competitive with commercial stone wool. The sample with 50 % DAC and 50 % basalt provided the best comparison with commercial stone wool in terms of liquidus temperature (lower than for the other mixtures) and Young’s modulus (higher). Through further composition optimization and utilization of multiple components, we estimate that future batches could utilize 70–75 % of DAC. These promising results and expectations highlight a feasible reuse of DAC as secondary raw material for stone wool production and a possible route to the elimination of a toxic waste from the environment and the preservation of primary raw materials.
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•Asbestos-containing materials still represent a serious health problem.•Thermally deactivated asbestos-cement can be successfully reused.•Rock-wool can be produced using deactivated asbestos-cement.•A rapid conclusion of the “asbestos problem” is envisaged.
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