Structure and properties of Al-Mg alloy sheets produced by accumulative roll bonding.

Ispitivan je uticaj akumulativnog spajanja valjanjem (ARB postupak) i konvencionalnog hladnog valjanja (CR postupak) na mehanička i koroziona svojstva standardne AA5083 legure sa 4.2 mas. % Mg i modifikovane legure, sa sadržajem Mg od 5.1 mas.% i dodatkom 0.5 mas.% Zn. Rezultati ispitivanja jednoosnim zatezanjem pokazali su da dolazi do značajnog povećanja parametara čvrstoće i smanjenja izduženja nakon svakog ARB provlaka i sa porastom stepena deformacije CR postupkom. Pokazana je prednost ARB postupka nad klasičnim postupkom hladnog valjanja obzirom da se mogu postići veći stepeni deformacije i veća rafinacija strukture. Pokazano je da povišen sadržaj Mg doprinosi porastu čvrstoće, dok se potencijal za ojačavanje i koroziona otpornost smanjuju. Viši nivo čvrstoće CR traka rezultat je veće gustine dislokacija i izraženijeg deformacionog ojačavanja zbog intenzivnije interakcije dislokacija kod konvencionalnog valjanja u odnosu na ARB postupak. Rezultati testa gubitka mase (NAMLT) pokazali su otpornost jednoslojnih CR i višeslojnih ARB traka ispitivanih legura prema intergranularnoj koroziji (IGC) u deformisanom stanju. Međutim, nakon 7 dana senzitizacije na 100 i 150 °C, CR uzorci AA5083 legure postaju osetljivi, dok ARB uzorci ostaju otporni prema IGC. Za razliku od standardne legure, CR i ARB trake modifikovane legure pokazale su veliku osetljivost prema IGC nakon tretmana senzitizacije. Osetljivost prema IGC u korelaciji je sa različitom morfologijom i raspodelom β-faze (Mg2Al3) istaložene tokom senzitizacije. Otkriveno je da postojanje smicajnih traka usled intenzivne plastične deformacije u višeslojnoj ARB strukturi, i pasivnog filma između slojeva doprinosi povoljnoj raspodeli β-faze u strukturi otpornih ARB uzoraka što su potvrdili i rezultati elektrohemijskih ispitivanja. U slučaju IGC osetljivih CR uzoraka, velika količina β-faze istaložena je duž granica zrna. Elektrohemijski parametri su u dobroj korelaciji sa rezultatima NAML testa, koji su potvrdili prednost ARB višeslojne strukture u odnosu na konvencionalno hladno valjanu, i ustanovljeno je da ARB postupak ima realnu mogućnost praktične industrijske primene za izradu višeslojnih traka jer omogućava transformaciju Al-Mg legura u materijale novih, pobolјšanih svojstava.Influence of accumulative roll bonding (ARB) and conventional cold rolling (CR) on the mechanical and corrosion properties of an AA5083 type alloy with 4.2 wt% Mg and a modified alloy with 5.1 wt% Mg and addition of 0.5 wt% Zn was studied. Tensile tests showed significant increase in strength and a decrease in elongation after each ARB deformation and cold rolling reductions. The advantage of ARB processing over conventional cold rolling was due to the possibility to achieve high degree of deformation and a grain structure refinement. Higher Mg content in a modified AA5083 alloy contributed significantly to the increase in strength, while strain hardening potential and corrosion resistance were reduced. The higher strength level of cold rolled material was attributed to higher dislocation density and the hardening effect due to more intensive dislocation interactions compared to ARB processed material. Results of nitric acid mass loss test (NAMLT) revealed that cold rolled (CR) monometal and ARB processed multilayered specimens were resistant toward intergranular corrosion (IGC) in as-deformed state. However, after 7 days of sensitization at 100 and 150 °C, CR material of AA5083 alloy became IGC sensitive, while ARB specimens stayed resistant. On the other hand, both cold rolled and ARB processed specimens of a modified alloy became IGC susceptible after sensitization. IGC susceptibility of the tested alloys can be correlated with different morphology and distribution of β-phase (Mg2Al3) precipitated during sensitization. It was found that an extensive shear banding within ARB multilayered structure and the existence of passive film between the layers contributed a favorable distribution of β-phase in the structure of IGC resistant ARB specimens. In case of IGC susceptible cold rolled specimens, large amount of β-phase precipitated preferentially along the elongated grain boundaries. Electrochemical parameters were in a good correlation with the results of NAML tests, which in turn, confirmed the superiority of ARB multilayered structure over conventional cold rolled structure in terms of IGC susceptibility and corrosion stability

Corrosion of archaeological artefact made of forged iron

One artefact of the archaeological cultural heritage from Roman period (IV century) that was found near Å abac in Serbia, was analysed. In corrosion products of the artefact (knife), dominant phases were goethite (α-FeOOH) and magnetite (Fe3O4). Presence of these types of corrosion products explains a good preservation of the base metal (iron) over the centuries and stability after excavation. Also, the less stable lepidocrocite (γ-FeOOH) and the phases that come from rocks and land surrounding environment (like SiO2) were identified in the corrosion products. Phases containing chloride ions (i.e. akaganéite) have not been detected in the corrosion products. This indirectly indicates that the amount chloride ions were rather low in underground exploitation conditions

Influence of an accumulative roll bonding (ARB) process on the properties of AA5083 Al-Mg alloy sheets

In this study, fully annealed AA5083 type alloy sheets with 1 mm in thickness were processed by accumulative roll bonding (ARB) at room temperature, up to 6 ARB cycles. It was found that microstructure was refined and mechanical properties were significantly improved with ARB processing. The maximum achieved values of hardness and tensile strength were two and three times greater than that of the initial material, respectively. This was attributed to the intensive strain hardening and grain size refinement which occurred during ARB deformation. However, the uniform elongation values were decreased by increasing the number of ARB cycles, and early fracture was registered. SEM fractography of fractured surfaces after tensile tests revealed a typical ductile fracture of ARB processed specimens, which was changed with ARB deformation. It was observed that ductile area on the fractured surfaces and the amount of necking, which occured before fracture, were decreased with increasing the number of ARB cycles.  http://dx.doi.org/10.5937/metmateng1404285

Naponska korozija metala i legura i njihovih zavarenih spojeva, Deo II: metode ispitivanja

U radu su razmotrene metode ispitivanja naponske korozije metala i legura i njihovih zavarenih spojeva. Opisani su principi tih metoda, postupci izvođenja, oblasti primene, kao i prednosti i nedostaci pojedinih metoda. Shematski su prikazani tipični rezultati koji se dobijaju njihovom primenom. Posebna pažnja je posvećena metodama ispitivanja naponske korozije zavarenih spojeva. Opisane su klasične metode ispitivanja statički opterećenih glatkih uzoraka (Cprstenovi, uzorci na savijanje itd.), kao i savremene metode kao što je metoda male brzine deformacije (SSRT) i metode zasnovane na principima mehanike loma. Navedeni su odgovarajući standardi (ISO i ASTM) za njihovo izvođenje, kao i preporuke za sprečavanje naponske korozije zavarenih spojeva različitih metala i legura

Korozija topa 75/27, model 1911. deport iz kolekcije Vojnog muzeja u Beogradu

This paper analyzes the state of the French Cannon 75/27 model 1911. Déport made of steel. The amount of non-corroded materials, the presence of cracks and other defects in the cannon were determined by the radiographic method. The composition of corrosion products were analyzed using diffraction of X-rays (XRD method). In addition to goethite α-FeO(OH), lepidocrocite γ-FeO(OH) and magnetite Fe3O4, the presence of akaganeite was observed in the corrosion products, β-Fe8O8(OH)8Cl1.35 which indicates the accelerated corrosion of the base metal. With the ion chromatography method, the content of chloride, sulphate and other ions in corrosion products were examined. On the basis of conducted experiments, it can be concluded that it is necessary to treat the cannon in appropriate solutions, as quickly as possible, to remove chloride and sulphate ions.U ovom radu analizirano je stanje francuskog topa 75/27 model 1911 Déport izrađenog od čelika. Za određivanje količine nekorodiralog materijala, prisustva prslina i drugih defekata u eksponatu korišćena je radiografska metoda. Sastav korozionih produkata je analiziran metodom difrakcije rendgenskih zraka (XRD). Pored getita, α-FeO(OH), lepidokrokita, γ-FeO(OH) i magnetita, Fe3O4, na eksponatima je uočeno prisustvo akaganita koje ukazuje na aktivnu koroziju osnovnog metala. Metodom jonske hromatografije je određen sadržaj hloridnih i drugih anjona u korozionim produktima. Na osnovu izvedenih eksperimenata nameće se zaključak o neophodnosti tretmana topa u odgovarajućim rastvorima što je moguće pre u cilju uklanjanja hloridnih i drugih koroziono aktivnih jona

Shape memory alloys: Properties, demands and opportunities in engineering applications

Shape memory alloys (SMAs) are a subclass of shape memory materials (SMMs), which are materials that, in response to a specific impact like thermal, mechanical, or magnetic changes, can "memorize" or hold into their prior form. This review addresses the properties, demands, and application prospects of SMAs, and provides a synopsis of recent advancements, as well as a historical background. Due to their special and exceptional qualities, SMAs have attracted a lot of interest and attention recently in a wide range of commercial applications; basic and applied research investigations have supported this commercial development. In order to shed light on design, issues faced by SMA developers, this paper explains the characteristics of these materials that make them perfectly suited for variety of applications, addressing also the accompanying constraints. This paper offers a pertinent overview of current SMA research

Repair of steel construction on truck-mounted crane TADAHO TL 200 II/K

Prilikom sanacije težilo se optimalnoj primeni postupaka u cilju svođenja uticaja dodatnih napona i deformacija na minimum koji su neminovni pratilac sanacije. Primenom opisane tehnologija zavarivanja uspešno je izvršena sanacija čelične konstrukcije strele samohodne autodizalice TADAHO TL 200 II/K nosivosti 95t. Nakon sanacije (Slika 5) urađena je kontrola zavarenih spojeva (vizuelno, penetrantsko i radiografsko ispitivanje). Posle završenih kontrolnih ispitivanja, izvršena je montaža svih pet segmenata strele autodizalice na noseće vozilo, urađena je proba nosivosti autodizalice, nakon čega je ona puštena u eksploataciju

Non-destructive evaluation of cavitation erosion behavior of alumina-based ceramic materials

Numerous industrial parts, devices, and processes are designed to withstand the conditions that lead to cavitation erosion. Metallic, ceramic, and composite materials used for these conditions must achieve specific mechanical characteristics required to resist cavitation erosion. When molten metal or alloy flows and comes into contact with refractory material or coated furnace linings, cavitation erosion can occur. This phenomenon is particularly expected in metallurgy, especially in casting operations. Alumina-based refractories, specifically low cement castable (ALCC), are often used in furnace lining applications due to their superior properties, such as high refractoriness, thermal stability, and mechanical characteristics. Mullite is another refractory material frequently used in foundry lining applications. It can be utilized as a coating in casting processes, such as the Lost Foam process, which is a novel method for producing high-quality, cost-effective castings. These two refractory materials were chosen to study their behavior under cavitation conditions. An ultrasonic vibratory test with a stationary specimen (ASTM G-32) was used for experimental cavitation determination. The results of mass loss and surface morphological parameters of degradation revealed that ALCC samples eroded predominantly at the surface, while the mullite samples exhibited more significant degradation by depth

Cavitation resistance of explosively welded aluminium/steel joint

Explosion welding is an unconventional method of joining two dissimilar metal materials, mostly used to clad dissimilar materials or when some unusual geometries need to be joined. Some of the bimetal joints obtained this way have applications in special cutting tools, transition joints, propellers and turbine blades, and therefore it is important to know the wear resistance of welded joints. In this research, explosive Demex, based on ammonium nitrate and trinitrotoluene, was used to weld plates of aluminium alloy AW-2024 and steel 1.0216. The welding procedure was carried out in the configuration of parallel plates. The quality of the welded joint was inspected on samples cut out from the welded plate by the method of microscopic analysis on the cross-section and by an ultrasonic cavitation test. Materials erosion in the zone of the welded joint after each of 4 cavitation cycles was observed using an optical microscope and by monitoring the mass loss. The wear resistance of the created bimetal was analysed from the aspects of further exploitation