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The aim of the present study was to determine the evolution of resistance to pitting corrosion and changes in the mechanical properties of ultrafine-grained aluminium during annealing. In contrast to the numerous papers devoted to the topic of the corrosion resistance of severely deformed aluminium alloys, a unique approach has been taken in this study. The size and distribution of the primary intermetallic particles, which are crucial in terms of corrosion resistance, remain constant during annealing. Therefore, the influence of other microstructural features could be investigated and compare with the results of mechanical properties. It was shown that the ultrafine-grained structure of commercially pure aluminium was stable up to 200 °C. Higher annealing temperatures caused significant grain growth and a reduction in dislocation density, which resulted in a drop in mechanical strength. Also, the corrosion resistance slightly decreased, since with an increase in annealing temperature a decrease in the corrosion potential, pit size, and the area damaged by corrosion attack were noted. The best combination of mechanical strength and resistance to pitting corrosion has been achieved for as-deformed state.

This study describes the role of bimodal grain size distribution on the corrosion resistance of Mg–4Li–3Al–1Zn (LAZ431). The coarse-grained microstructure formed in the alloy after extrusion was compared with the bimodal grain size distribution observed in the alloy after additional annealing. The microstructure observations show that the extruded alloy, as well as the one after subsequent annealing, were composed of α(Mg), MgZn2, coarse AlMn-rich precipitations, and nanosized AlLi, Mg17Al12 and Li2MgAl. The annealing caused microstructure transformation and triggered anomalous and inhomogeneous grain growth of the alloy, which increased the ratio of cathodic grain interiors to anodic high-angle grain boundaries. This decreased the corrosion resistance of the annealed alloy in chloride-containing solution.The results of this work also show that the precipitations play only minor role in corrosion behavior of both alloys, and the major corrosion mechanism occurred between high-angle grain boundaries and grain interiors.

In this study, the microstructure and corrosion resistance of the as-extruded and as-extruded with subsequent heat treatment Mg-3Al-1Zn-15Li (LAZ1531) alloys have been investigated. The alloys’ microstructures consisted of α(Mg), β(Li), Θ-MgLi2Al and Mg17Al12. As a result of annealing, the β(Li) to α(Mg) transformation occurred, and the recrystallization supported the reformation of the Mg17Al12. The electrochemical tests showed that the increased amount of α(Mg) and higher amount of Mg17Al12 in the heat-treated alloy favored reactions and determined it as having better corrosion resistance in 3.5 wt.% NaCl.

The effect of nitriding on the surface structure, mechanical properties and corrosion resistance of hydrostatically extruded 316 LVM stainless steel was evaluated and compared with coarse grained counterpart. Hydrostatic extrusion was performed at either room or elevated temperature and resulted in microstructure refinement. Nitrided layers of a similar thickness were formed on the samples irrespective of their microstructure. The nitriding process was performed at 430 °C for 5 h. The processing conditions did not affect the bulk mechanical properties of the micro and HE processed samples and their mechanical strength remained unchanged after nitriding. The electrochemical measurements revealed that the nitrided hydrostatically extruded 316 LVM steels had better corrosion resistance than their microcrystalline counterpart.

Thermally sprayed coatings are one of the potential ways to increase corrosion performance of Mg alloys dedicated for aircraft applications. In our research, a novel thermal spray process called Warm Spraying (WS) was used to deposit Ti coatings onto AZ91E magnesium alloy. WS gives us the possibility to control the temperature of the sprayed particles by changing the nitrogen flow rate (NFR) what as a result determine the porosity of WS coatings. The microstructure, porosity and oxygen content of coatings deposited under three different NFR was determined. A relation between porosity, oxygen content and NFR was revealed. The corrosion testing in 3.5% NaCl solution of as-sprayed coatings revealed their poor corrosion resistance that led to fast degradation of the substrate. The following post-treatment with epoxy-based polymer resulted in a significant improvement of the corrosion performance of Ti warm sprayed coatings.

Present study investigates the effect of microstructure on electrochemical response of commercially pure aluminium. Electrochemical testing included OCP measurements and potentiodynamic polarization. Results reveal insignificant differences for samples with different grain size, shape and fraction of HAGBs. These parameters are assumed as only slightly affecting electrochemical response. Fe-containing intermetallics have the highest impact, as pits nucleate in their vicinity. In examined materials intermetallic particles retained a consistent size and distribution for all samples. Therefore, no difference in electrochemical parameters or number of pits is observed. The only difference is in the shape of the pits, because dissolution occurred along HAGBs.

The effect of temperature and humidity on the heat effect of disposable warmers based on exothermic powder was investigated. A chemical analysis and microscopic observations were performed on exothermic powder consisting of iron powder, sodium chloride, vermiculite, diatomite and active carbon. The heat effect of warmers was investigated at temperatures of 15, 20, 25, 30 °C and humidities of 60, 70 and 80%. The microscopic observations revealed the morphology of the exothermic powder and the oxidation mechanism of the iron particles. The results indicate that temperature significantly affects the heat effect of the warmers investigated, whereas humidity has only a minor impact.

The material studied is a commercially available 316LVM stainless steel with an initial grain size of 30 μm. To refine the microstructure down to the nanoscale, hot (at 1000 °C) and room temperature hydrostatic extrusion were applied with a total true strain of 1.4. An annealed sample with coarse grains of 35 μm in diameter was used as a reference sample. The results indicate that after hot hydrostatic extrusion, the microstructure consisted mainly of cells with tangled dislocation walls, while after room temperature hydrostatic extrusion, twins of various width and shear bands could be distinguished. Hydrostatic extrusion is also an efficient way to tailor the corrosion resistance and mechanical properties of 316LVM stainless steel. Performed at room temperature, hydrostatic extrusion resulted in an ultra-high-strength material with limited but sufficient ductility. Performed at high temperature, hydrostatic extrusion resulted in a material with a very good combination of strength (approximately 900 MPa) and ductility (elongation to failure higher than 20%). Both hydrostatically extruded steels maintained good passivation behavior in 0.1 M H2SO4. In the presence of chloride ions, susceptibility to localized attack increased for the steel extruded at room temperature, but did not change for the hot-extruded steel. Keywords: Austenitic stainless steel, Hydrostatic extrusion, Severe plastic deformation, Dynamic recrystallization, Corrosion resistance

Corrosion tests were carried out to study the corrosive behaviour of medium carbon steels with a ferrite–pearlite microstructure during exposure to a synthetic flowback facturing fluid saturated with carbon dioxide. Metallographic investigations, screening tests, surface morphology investigations and identification of surface products were used for this purpose. The results obtained indicate that the corrosion of N80-1 carbon steel was significantly lower than that of K55 carbon steel. The layer of corrosion products consisted of an outer layer of carbonates and an inner layer with cementite lamellas. Higher grain refinement of N80-1 steel compared to that of K55 steel caused the formation of a denser, more homogenous layer of corrosion products, which significantly reduced the corrosion of the base material.

Joints made from ultrafine grained aluminium alloy 1050 are investigated in order to examine the corrosion behavior and microstructural changes between base materials and stir zones. Samples in the initial state, after four and eight passes of Incremental ECAP (I-ECAP) process were joined with similar plates using Friction Stir Welding. Initially refined microstructure after I-ECAP transformed to homogenous few micron sized grains structure in stir zones. AlFeSi particles present in the microstructure became fragmented during plastic deformation and welding process. The observed minor differences in corrosion resistance include slightly higher values of corrosion potentials but more complex pits' morphology for I-ECAP processed samples comparing to the stir zones.