Key Engineering Materials Vol. 1031

Abstract: The paper presents the results of the behavior and resistance to the erosion by cavitation of the 2017 A aluminium alloy structure, obtained by the WIG remelted method. The research is in step with the new directions of study and aims to extend the aluminum alloy 2017 A to the manufacture of parts that work in the cavitation regime, such as: pistons and valves of thermal engines, respectively various pump rotors or motor boat propellers. The analysis performed on the basis of the specific curves, constructed according to the indications of the ASTM G32-2016 normas, shows that structure, obtained by the WIG remelting, confers a constant behavior to the cyclic stresses of microjets generated by the hydrodynamics of the vibratory cavitation. The comparison of the results, based on the specific parameters, used in the laboratory and indicated by the ASTM G32-2016 norms shows a resistance to cavitation erosion, clearly superior to the semi-finished structure and those obtained by artificial aging heat treatment at 1800C and 120 0C, with duration of one hour.

Abstract: Aluminum alloy 6082 is known for its use in the manufacture of structures that require welding interventions, high mechanical properties, resistance to pressure and corrosion, such as: boilers, truck structures, bicycles and motor boats. The recent research, regarding the cavitation resistance of the this alloy structure, shows a poor behavior of the semi-finished structure and somewhat improved by artificial aging volumetric heat treatment regimes. On the line of increasing the resistance of the this alloy structure, to the erosive demands of cavitation, they sign up of the rechearch results of the this paper, regarding the behavior and resistance of the vibratory cavitation of the aluminum alloy 6082 structure , obtained by WIG remelting. Comparing with the results obtained on the structures in the semi-finished state and through volume thermal treatments of artificial aging state, using the established parameters, recommended by the ASTM G32-2016 norms, a significant increase in the resistance to cyclic cavitation stresses is found, as a result of the increase in the surface hardness value. The novelty of the work consists in motivating the use of the remelting procedure of the surface structure of aluminum alloy 6082, through WIG remelting in order to increase the surface hardness, with a direct effect on increasing this structure resistance to the cyclical fatigue stresses of shock waves and microjets developed through the hydrodynamic mechanism of cavitation.

Abstract: Nowadays, the application of hydrogen as an energy carrier has become important as a result of decreasing availability of oil and gas fields as well as increasing demands on sustainable energy carriers. Providing an adequate hydrogen transportation infrastructure is a key step. During transportation, many different materials can interact with hydrogen, but in order to transport high quantities of hydrogen at higher pressures, the use of steels is preferred. However, hydrogen has many negative effects on steel, thus extensive research needs to be performed before hydrogen can be transported safely. Solubility of hydrogen in steel depends on the temperature, pressure, and the crystal structure of steel, so welding is also an important subject. Since most of the steel structures are welded, welded joints should also be examined for exposure to hydrogen. In the case of welding, a number of factors can decrease the hydrogen resistance of the welded joint and thus increase the risk of degradation by hydrogen. In this research work, hydrogen damage, and hydrogen traps will be reviewed. Possible ways to reduce the diffusible hydrogen content will also be summarized, as well as aspects of the filler material and shielding gas selection. In addition, an overview will be provided on welding technology aspects of carbon steels related to hydrogen, such as heat input, preheating, t_8/5 cooling time, heat-affected zone size, number of weld runs, effect of discontinuities, etc. In general, filler material with the lowest possible diffusible hydrogen content should be used; for electrode coatings and fluxes, special care should be taken to ensure proper baking; for wire electrodes, care should be taken to ensure surface cleanliness; in case of shielding gas the use of the purest possible shielding gas is recommended, and the use of shielding gas containing hydrogen is prohibited; and strict attention must also be paid to the purity of the base material. In addition, other important considerations for welding technology development will be outlined for carbon steels. Such as pipelines, where the most important technological aspects of welding will also be discussed, e.g. low heat input, multi-pass weld design, etc.