Otpornost na opštu koroziju serije legura cink-aluminijum koje su modifikovane silicijumom i stroncijumom

The resistance to corrosion of the series of zinc-aluminum casting alloys modified with silicon and strontium was studied in a sodium chloride solution. It was shown that general corrosion was the main form of corrosion of Zn25Al-Si-Sr alloys in the test solution. The corrosion process takes place through the anodic dissolution of the alloys, while the cathodic reaction is controlled by diffusion of oxygen in the test solution. Three different electrochemical techniques were applied to determine the corrosion current density, which is the electrochemical indicator of corrosion rate. The value of corrosion current density for each Zn25Al-Si-Sr alloy was calculated using the value of polarization resistance, obtained by electrochemical impedance spectroscopy or by linear polarization resistance technique. The value of corrosion current density was also determined directly from Tafel plots, which were recorded by linear sweep voltammetry. As the content of silicon and strontium in the tested alloys increases, the value of corrosion current density increases gradually. The results obtained by different electrochemical techniques are in good agreementOtpornost na koroziju serije legura cink-aluminijum za livenje, koje su modifikovane silicijumom i stroncijumom, ispitana je u rastvoru natrijum hlorida. Pokazano je da je opšta korozija glavni oblik korozije Zn25Al-Si-Sr legura u navedenom rastvoru. Proces korozije odvija se kao anodno rastvaranje legura, dok je katodna reakcija kontrolisana difuzijom kiseonika u rastvoru. Tri različite elektrohemijske tehnike primenjene su za određivanje gustine struje korozije, koja je elektrohemijski pokazatelj brzine korozije. Vrednost gustine struje korozije za svaku Zn25Al-Si-Sr leguru izračunata je na osnovu vrednosti polarizacione otpornosti, koja je određenai spektroskopijom elektrohemijske impedanse ili tehnikom linearne polarizacije. Vrednost gustine struje korozije je takođe određena direktno iz Tafelovih dijagrama, koji su registrovani pomoću voltametrije sa linearnom promenom potencijala. Sa povećanjem sadržaja silicijuma i stroncijuma u ispitivanim legurama vrednost gustine struje korozije postepeno raste. Rezultati dobijeni različitim elektrohemijskim tehnikama su u dobroj saglasnos

Corrosion behavior of the as-cast and heat-treated ZA27 alloy

Corrosion behaviour of the as-cast and heat-treated ZA27 alloy was examined. The alloy was prepared by conventional melting and casting route and then thermally processed by applying T4 heat treatment regime (solutionizing at 370 °C for 3 hours followed by water quenching and natural aging). Corrosion rate of the as-cast and heat-treated ZA27 alloy was determined in 3.5 wt. % NaCl solution through immersion test using both weight loss method and polarization resistance measurements. It was shown that applied thermal treatment resulted in increased ductility of the heat-treated alloy and had a small beneficial effect on the corrosion resistance of ZA27 alloy

The influence of corrosion on the microstructure of thermally treated ZA27/SiCp composites

The influence of corrosion on the microstructure of ZA27/SiCp composites was examined. The composites were produced by compo casting technique and then subjected to the thermal treatment (T4 regime). Microstructural examinations were performed after 30-day exposure of thermally treated composites in the sodium-chloride solution. Corrosion processes have occurred in the composite matrix. Corrosion did not affect SiC particles in the composites. The local progress of corrosion in depth of the composite matrix was noticed in micro-cracks. Corrosion resistance of ZA27/SiCp composites was evaluated based on the mass loss of composite samples during the immersion test. It was found that corrosion resistance of the composites decreased with increase in content of SiC particles. The applied thermal treatment had a negative influence on the corrosion resistance of ZA27/SiCp composites

Corrosion behavior of compocasted ZA27/SiCp composites in sodium chloride solution

The corrosion behavior of particulate ZA27/SiCp composites in an aerated sodium chloride solution was studied. The composites were synthesized via compocasting with addition of 1, 3 and 5 wt.% SiC particles in the matrix alloy. Composite samples were immersed for 30 days in the 3.5 wt.% NaCl solution open to the atmospheric air. Surface appearance and microstructure of the composites were examined by means of optical microscopy and scanning electron microscopy, while corrosion rates of the composites were determined using the weight loss method. It was revealed that SiC particles were not influenced by corrosion. General uniform corrosion occurred in the composite matrices, mainly in the region of the η phase. Local corrosion was noticed in micro-cracks and near clusters of particulate reinforcements. Results of microstructural examinations and immersion test indicate a slightly lower corrosion resistance of the ZA27/SiCp composites compared to that of the matrix alloy

Corrosion behavior of the as-cast and heat-treated ZA27 alloy

Corrosion behaviour of the as-cast and heat-treated ZA27 alloy was examined. The alloy was prepared by conventional melting and casting route and then thermally processed by applying T4 heat treatment regime (solutionizing at 370 °C for 3 hours followed by water quenching and natural aging). Corrosion rate of the as-cast and heat-treated ZA27 alloy was determined in 3.5 wt. % NaCl solution through immersion test using both weight loss method and polarization resistance measurements. It was shown that applied thermal treatment resulted in increased ductility of the heat-treated alloy and had a small beneficial effect on the corrosion resistance of ZA27 alloy

Corrosion behavior of compocasted ZA27/SiCp composites in sodium chloride solution

The corrosion behavior of particulate ZA27/SiCp composites in an aerated sodium chloride solution was studied. The composites were synthesized via compocasting with addition of 1, 3 and 5 wt.% SiC particles in the matrix alloy. Composite samples were immersed for 30 days in the 3.5 wt.% NaCl solution open to the atmospheric air. Surface appearance and microstructure of the composites were examined by means of optical microscopy and scanning electron microscopy, while corrosion rates of the composites were determined using the weight loss method. It was revealed that SiC particles were not influenced by corrosion. General uniform corrosion occurred in the composite matrices, mainly in the region of the η phase. Local corrosion was noticed in micro-cracks and near clusters of particulate reinforcements. Results of microstructural examinations and immersion test indicate a slightly lower corrosion resistance of the ZA27/SiCp composites compared to that of the matrix alloy

Determination of susceptibility to intergranular corrosion of stainless steels type X5CrNi18-10 in field

In this paper, the DL EPR method (electrochemical potentiokinetic reactivation with double loop) was modified and used to study the susceptibility to intergranular corrosion and stress corrosion cracking of a stainless steel type X5CrNi18-10. The tests were performed in a special electrochemical cell, with the electrolyte in the gel form. Modified DL EPR method is characterized by simple and high accuracy measurements as well as repeatability of the test results. The indicator of susceptibility to intergranular corrosion (Qr/Qp)GBA obtained by modified DL EPR method is in a very good agreement with the same indicator obtained by standard DL EPR method. The modified DL EPR method is quantitative and highly selective method. Small differences in the susceptibility of the stainless steel type CrNi18-10 to intergranular corrosion and stress corrosion cracking can be determined. Test results can be obtained in a short time. The cost of tests performed by modified DL EPR method is much lower than the cost of tests by conventional chemical methods. Modified DL EPR method can be applied in the field on the stainless steels constructions

Examination of the Corrosion Process Impact on the Microstructure and Mechanical Properties of Zn27Al1.5Cu0.02Mg Alloy Castings Reinforced with Silicon Carbide Particles

Na osnovu izvršenih istraživanja ustanovljeno je da postoji međusobna povezanost mikrostrukture, mehaničkih svojstava i korozionog ponašanja čestičnih ZA27/SiC kompozita. Livena ZA27 legura predstavlja metalnu osnovu za dobijanje kompozita. Struktura legure je tipična dendritna. Trajna transformacija dendritne u ne-dendritnu strukturu izvršena je tiksoformiranjem, dok je poluočvrsli rastop legure bio izložen dejstvu sila smicanja. Kompoziti su dobijeni kompokasting postupkom, uz infiltraciju 1, 3 i 5 mas.% SiC čestica u metalnu osnovu. Otpornost prema koroziji matrične legure i ZA27/SiC kompozita određena je na osnovu vrednosti za brzinu korozije u rastvoru NaCl (pH=6,7). Određivanje brzine opšte korozije izvršeno je metodom gubitka mase i elektrohemijskim metodama. Otpornost matrične legure prema koroziji veća je od otpornosti kompozita. Uticaj korozije na mikrostrukturu ispitan je primenom svetlosne i skenirajuće elektronske mikroskopije. Posle izlaganja uzoraka u rastvoru NaCl, promena granice tečenja (pri ispitivanju pritiskivanjem), uzeta je kao pokazatelj uticaja korozije na mehanička svojstva matrične legure i kompozita. U matričnoj leguri procesi korozije zahvataju oblast η faze i oblast smeše faza α+η, a koroziona razaranja su površinskog karaktera. Zapaženo je da je u kompozitima sa većim sadržajem infiltriranih SiC čestica (3 i 5 mas.%) došlo do stvaranja nakupina SiC čestica, što je dovelo do obrazovanja mikroprslina i mikropora. Na ovim mestima proces korozije napreduje u dubinu materijala, što se negativno odrazilo na otpornost prema koroziji i mehanička svojstva čestičnih ZA27/SiC kompozita.On the basis of examination carried out, the mutual dependence of the microstructure, mechanical properties and corrosion behaviour of particulate ZA27/SiC composites was established. As-cast ZA27 alloy was the metal matrix for producing composites. The structure of as-cast ZA27 alloy is typically dendritic. A permanent transformation of the dendritic structure into nondendritic one was achieved through thixoforming during exposure of ZA27 alloy semi-solid melt to the influence of shear forces. Composites were obtained by compocasting process, through infiltration of 1, 3 and 5 wt.% SiC particles into the metal matrix. Corrosion resistance of the metal matrix and ZA27/SiC composites was evaluated on the basis of corrosion rate in NaCl solution (pH=6.7). Mass loss method and electrochemical polarization measurements were used to determine rate of general corrosion. Matrix alloy resistance to corrosion is higher than the resistance of the composites. The influence of corrosion on the microstructure was examined using light and scanning electron microscopy. After exposure of samples in NaCl slution, compressive yield strength was taken as an indicator of corrosion impact on the mechanical properties of the matrix alloy and the composites. Corrosion process in the matrix alloy takes place through η phase (interdendritic phase rich in zinc) and α+η phase mixture, while corrosion damage is limited to the surface of samples. Agglomeration of reinforcing particles was noticed within composites with higher content of SiC particles (3 and 5 mas.% SiC) which resulted in formation of microvoids and microcracks. These were places where progress of corrosion processes in the depth of material was observed, which had a negative impact on the corrosion resistance and mechanical properties of particulate ZA27/SiC composites

Erosive wear properties of ZA-27 alloy-based nanocomposites: Influence of type, amount, and size of nanoparticle reinforcements

Metal matrix nanocomposites (MMnCs) comprise a metal matrix filled with nanosized reinforcements with physical and mechanical properties that are very different from those of the matrix. In ZA-27 alloy-based nanocomposites, the metal matrix provides ductility and toughness, while usually used ceramic reinforcements give high strength and hardness. Tested ZA-27 alloy-based nanocomposites, reinforced with different types (SiC and Al2O3), amounts (0.2 wt.%, 0.3 wt.%, and 0.5 wt.%) and sizes (25 nm, 50 nm, and 100 nm) of nanoparticles were produced through the compocasting process with mechanical alloying pre-processing (ball milling). It was previously shown that the presence of nanoparticles in ZA-27 alloy-based nanocomposites led to the formation of a finer structure in the nanocomposites matrix and an improvement in the basic mechanical properties (hardness and compressive yield strength) through the enhanced dislocation density strengthening mechanism. Solid particle erosive wear testing demonstrated that these improvements were followed with an increase in the erosive wear resistance of tested nanocomposites, as well. Additionally, by analyzing the influences of type, amount, and size of nanoparticles on the erosive wear resistance of nanocomposites, it was demonstrated that there is an optimal amount of nanoparticles, which in our case is 0.3 wt.%, and that the presence of SiC nanoparticles and smaller nanoparticles in nanocomposites had more beneficial influence on erosive wear resistance

Ispitivanje piting korozije nerđajućeg čelika AISI 304 u rastvorima hlorida

Stainless steels and their welded joints are often susceptible to pitting corrosion in solutions containing chloride ions. Testing of pitting corrosion of stainless steels is performed using chemical and electrochemical methods. In this work pitting corrosion of the stainless steel AISI 304 was tested in chloride solutions, without the presence and in the presence of sulphate or nitrate ions. The tests were performed in order to determine the efficiency of these ions to prevent pitting corrosion, as well as to present the capabilities of the methods applied. Electrochemical methods were used to determine the value of pitting potential (Epit) and the critical pitting temperature (Tpit). The values of these parameters represent a measure of the resistance of stainless steels and their welded joints to pitting corrosion.Nerđajući čelici i njihovi zavareni spojevi često podležu piting koroziji u rastvorima koji sadrže hloridne jone. Ispitivanje piting korozije nerđajućih čelika se vrši primenom hemijskih i elektrohemijskih metoda. U ovom radu vršeno je ispitivanje piting korozije nerđajućeg čelika AISI 304 u rastvoru hlorida, bez prisustva i u prisustvu sulfatnih, odnosno nitratnih jona. Ispitivanja su izvedena u cilju određivanje efikasnosti navedenih jona u sprečavanju piting korozije, kao i prezentacije mogućnosti primenjenih metoda. Korišćene su elektrohemijske metode za određivanje piting potencijala (Epit) i određivanje kritične temperature pitinga (Tpit). Vrednosti navedenih parametara predstavljaju merilo otpornosti nerđajućih čelika i njihovih zavarenih spojeva prema piting koroziji