Raimonda Lukauskaitė

Investigation of Cathodic Cleaning Processes of Aluminum Alloy

On covering aluminum and its alloys with coatings resistant to high-temperature corrosion and attrition, abundant technological problems arise. The key problem is a removal of the film of aluminum oxide Аl2O3 from the aluminum substrate. This permanent, chemically continuous film of oxide reduces adhesion between the substrate and the coating. For improving cohesion of the coating with the substrate, an appropriate pre-treatment of aluminum is required. In the paper, cleaning of aluminum alloy AW 5754 by electric discharge is investigated. This method is considered one of most environmentally friendly methods of surface cleaning. The impact of the parameters of aluminum alloy cathodic cleaning on the surface cleaning width, its roughness and free energy of the surface were examined. In addition, the topography, microstructure and chemical composition of the surface of cleaned aluminum alloy were estimated.

Preparing Al-Mg Substrate for Thermal Spraying: Evaluation of Surface State After Different Pretreatments

The article deals with the pretreatment technique for preparing the surface of aluminum alloy EN AW 5754 before thermal spray. The surface after different pretreatments, including degreasing with acetone, chemical etching with acidic and alkali solutions, grit-blasting, cathodic cleaning, and some combinations of these techniques, has been studied. The investigation of pre-treated surfaces covered the topographical study (using scanning electron microscopy, atomic force microscopy, and 3D profilometry), the chemical analysis by x-ray photoelectron spectroscopy, the evaluation of surface wettability (sessile drop method), and the assessment of surface free energy. Compared with all the techniques used in present work, the cathodic cleaning and its combination with grit-blasting provide the most preferable chemistry of the surface. Due to the absence of hydroxides at the surface and, possible, due to the diffusion of magnesium to the surface of substrate, the surface wettability and the surface free energy have been significantly improved. No direct correlation between the surface topography and the surface wettability has been established.

Research of Properties of Sprayed Coatings on the Aluminium Alloys

In article the cathodic cleaning processes of aluminum alloy AW 5754 and cleaned substrate surface coating by plasma with Ni-Cr-Fe-Si powder were researched. Aluminium substrate roughness after cathodic treatment at different cathodic treatment parameters was established during the experiments. During the investigation a comparison of the calculated medium power 1.6 to 9 kW plasma torch voltage-current characteristics with the experimental results was made. The optimized parameters of aluminium cathode substrate cleaning process were selected; porosity and morphology of plasma sprayed nickel-based coating were determined.

Utilization of sewage sludge-biomass gasification residue in cement-based materials: effect of pozzolant type

ABSTRACT In this study, the viability to utilize the residue, obtained from a sewage sludge (SS) and biomass combustion/gasification plant (GR), in cement-based materials was analysed. Two pozzolanic materials were selected to make GR more recyclable: metakaolin (MK) and spent catalyst waste (Z), received from fluidized-bed catalytic cracking process. Functional and environmental properties of standard cement pastes and mortars as well as binary and ternary combinations of GR with MK and Z were assessed. Results showed that enhanced mechanical strength, reduced water absorption and heavy metals release were obtained for compositions when GR was combined with one of the pozzolanic material MK or Z. Microstructural analysis revealed that due to addition of pozzolan the surface of GR particles was covered by a layer of hydration products. In particular, the use of MK led to the formation of more porous layer whereas application of Z tends to the formation of a dense-layered structure on the surface of GR. N2 sorption results showed that contrary to MK the incorporation of Z into cement composition with GR reduced volume of small capillary pores, and therefore, resulted in lower water absorption and heavy metals release. The obtained results suggest that the application of Z appears to be advantageous pozzolan for the stabilization of SS-biomass gasification residue in cement-based materials.

Thermite welding of Cu–Nb microcomposite wires

Abstract Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

Investigation of the Laser Polishing Influence on the Parts Built by SLS

The use of laser systems in the industrial manufacture of complex geometry details is growing. This phenomenon takes place thanks to laser technologies, such as selective laser sintering (SLS), direct laser metal sintering (DLMS) and selective laser melting (SLM) that make possible, in addition to production of details with complex geometric shapes, also the fast, cheap and effective restoration of damaged elements of the details. However, despite the abundant advantages of the above-mentioned technologies, the details produced on the basis of these innovative methods have typical problems (large value of surface roughness, low wear resistance). In the paper, the influence of changes of the principal technological parameters of the laser polishing on the technological characteristics of the external surface of details built by SLS was studied. Changes of the laser’s technological parameters impact the amount of energy supplied onto the area under processing. Thus, the correct selection of the technological parameters of the laser beam positively affect the microstructure and topography of the top surface layer of the manufactured details, its chemical composition and physical properties as well as diffusive processes in the laser beam impact area.