Resistance to electrochemical corrosion of the extruded magnesium alloy AZ80 in NaCl solutions

Abstract

The purpose of this study was to evaluate the electrochemical corrosion resistance of the extruded magnesium alloy AZ80 in NaCl solutions. The resistance to electrochemical corrosion was evaluated on the grounds of registered anodic polarisation curves. Potentiodynamic tests were performed in solution with a concentration of 0.01-2.00 M NaCl. In addition, immersion tests were performed, and they allowed us to determine the corrosion rate. Scanning electron microscopy was applied to observe the microstructure after the immersion tests (after removing the corrosion products). Phenomena that happen on the surface of the alloy were evaluated with the application of electrochemical impedance spectroscopy. The tests enabled us to determine the impedance spectra of the system and the data obtained during the measurement was matched to the equivalent system. An optical profilometer was used for the measurement of the geometrical features of the surface of the alloy. The results of the performed tests prove explicitly the deterioration of the corrosion characteristics of the alloy with an increase in the molar concentration of the NaCl solution. A decrease of the corrosion potential and the polarisation resistance was observed, as well as an increase of the corrosion current density. It was proved that irrespective of the concentration, pitting corrosion can be found on the surface of the alloy. The potential to use the extruded magnesium alloy AZ80 in the aircraft and automotive industries is connected with the necessity to apply protective layers on elements made from the tested alloy. Keywords: extruded magnesium alloy AZ80, electrochemical corrosion, potentiodynamic and immersion tests, SEM, EIS Namen te {tudije je bil oceniti odpornost ekstrudirane magnezijeve zlitine AZ80 proti elektrokemijski koroziji v raztopini NaCl. Odpornost proti elektrokemijski koroziji je bila ugotovljena na podlagi anodnih polarizacijskih krivulj. Izvr{eni so bili potenciodinamski preizkusi v raztopini s koncentracijo od 0,01-2 M NaCl. Dodatno so bili izvr{eni tudi preizkusi s potapljanjem, ki so omogo~ili dolo~itev hitrosti korozije. Vrsti~na elektronska mikroskopija je bila uporabljena za slikanje mikrostrukture po potapljanju (po odstranitvi korozijskih produktov). Pojavi na povr{ini zlitine so bili ocenjeni z elektrokemijsko impedan~no spektroskopijo. Preizkusi so omogo~ili dolo~itev impedan~nega spektra sistema in z meritvami dobljeni podatki so se ujemali z ekvivalentnim sistemom. Opti~ni profilometer je bil uporabljen za merjenje geometrijskih pojavov na povr{ini zlitine. Rezultati izvr{enih preizkusov so potrdili poslab{anje korozijskih lastnosti zlitine pri pove~anju molske koncentracije raztopine NaCl. Opa`eno je bilo zmanj{anje korozijskega potenciala in polarizacijske odpornosti, kot tudi pove~anje gostote korozijskega toka. Dokazano je, da se ne glede na koncentracijo jami~asta korozija pojavi na povr{ini zlitine. Mo`nosti uporabe ekstrudirane magnezijeve zlitine AZ80 v letalstvu in avtomobilski industriji je povezana z nujnos...

Evaluation of the Quality of Coatings Deposited on AZ31 Magnesium Alloy Using the Anodising Method / Ocena Jakości Powłok Wykonanych Na Stopie Magnezu Az31 Metodą Anodowania

“…During each test, 2 grams of an erodent agent were applied to the specimen at 45° for 1 minute. An image of the test device is presented in Figure 9 [7,10,15]. Fig.…”

“…It is estimated that in the nearest future, magnesium alloy applications will increase yearly by about 15-20%, mainly as complementary for advanced composite materials used in aviation industry [11][12][13][14]. At present, the AZ31 alloy is of a very high practical importance among magnesium casting alloys due to its good strength and plastic properties as well as high corrosion resistance and wear resistance [15][16][17]. It is used for production of rolled articles (i.e.…”

“…It is used for production of rolled articles (i.e. strips, sheets) and extruded products [4,9,15]. Basic strength properties of the AZ31 alloy are presented in Table 1 [1,4,13,18,20].…”

“…Types of coating that is based on the conventional Dow 17 and HAE processes as well as meets current requirements regarding the aerospace and automotive industries are the Tagnite ® and Eltron's coatings [1]. Electrolytes that are used in these processes contain less harmful substances such as chromic acid, permanganates, fluorides or other heavy metals [15,[18][19][20]. At present, a lot of research on compositions of alkaline baths with additions of phosphates, silicates, borates and organic substances is conducted [15][16].…”

“…Electrolytes that are used in these processes contain less harmful substances such as chromic acid, permanganates, fluorides or other heavy metals [15,[18][19][20]. At present, a lot of research on compositions of alkaline baths with additions of phosphates, silicates, borates and organic substances is conducted [15][16]. However, to obtain an effective anodic coating, proper electrical parameters must be selected.…”