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Korozja stopu AZ91 i kompozytów typu AZ91/SiC w roztworze Ringera


  Magnez, stop AZ91 oraz kompozyty typu AZ91/SiC ulegają aktywnemu roztwarzaniu w roztworze Ringera w temperaturze 36,7°C. Stop magnezu AZ91 dzięki obecności fazy β-Mg17(Al, Zn)12 ma lepszą odporność na korozję niż czysty magnez. Faza β-Mg17(Al, Zn)12 ulega pasywacji, co utrudnia korozję materiału. Obecność węglika krzemu SiC w kompozytach typu AZ91/SiC nie ma istotnego wpływu na odporność korozyjną w roztworze Ringera w porównaniu do stopu AZ91. Słowa kluczowe: magnez, AZ91, kompozyt AZ91/SiC, mikrostruktura, korozja lokalna Corrosion of AZ91 alloy and composite AZ91/SiC in Ringer solution Magnesium, AZ91 alloy and composite materials AZ91/SiC undergo active dissolution in Ringer solution at 36,70C. The corrosion resistance of AZ91 magnesium alloy is determined by β-Mg17(Al, Zn)12 phase. This phase easily undergoes the passivation, hence hinder the corrosion process of AZ91 alloy. However, the presence of SiC in composite AZ91/SiC does not have essential infl uence on its corrosion resistance in Ringer solution compare to corrosion resistance of AZ91 magnesium alloy. Keywords: magnesium, AZ91, AZ91/SiC composite, microstructure, local corrosion ochrona przed korozja 3/2012 1. Wstęp Stopy magnezu ze względu na dobre właściwości mechaniczne oraz małą gęstość (od 1,74-2,0 g/cm³) znalazły zastosowanie głównie w przemyśle samochodowym, lotniczym, a także elektronice. Jednakże w ostatnich latach stopy magnezu przyciągają wielką uwagę jako nowy rodzaj biomateriałów, które ulegają biodegradacji [1-3]. Stanowią nowoczesną propozycję materiałów, które po zakończeniu leczenia są w naturalny sposób usuwane z organizmu. Materiały te są biozgodne, w ludzkim ciele mogą być stopniowo rozpuszczone, [...]

Korozja magnezu i stopu AZ91 w wodnych roztworach jonów chlorkowych i siarczanowych


  Magnez i stop magnezu AZ91 ulegają aktywnemu roztwarzaniu w wodnych roztworach zawierających jony chlorkowe. Stop magnezu AZ91 dzięki obecności fazy β-Mg17Al12 ma lepszą odporność na korozję niż czysty magnez. Faza β-Mg17Al12 ulega pasywacji, co utrudnia korozję materiału. Badania chronoamperometryczne wykazały, że na korozję najbardziej podatna jest osnowa α-Mg. Słowa kluczowe: magnez, AZ91, mikrostruktura, korozja lokalna Corrosion behaviour of magnesium and AZ91 alloy in aqueous solution containing chloride and sulfates ions Magnesium and magnesium alloy AZ91 undergo the active dissolution in the aqueous solution containing the chloride and sulfate ions. The higher corrosion resistance of AZ91 alloy than pure magnesium is related with the presence of β-Mg17Al12 phase. This phase easily undergoes the passivation process and hinder the corrosion of alloy. Chronoaperometry measurements have revealed that the matrix α-Mg is the most susceptible to corrosion 0.1M Na2SO4. Keywords: magnesium, AZ91, microstructure, local corrosion ochrona przed korozja 7/2011 1. Wstęp Stopy magnezu ze względu na stosunkowo dobre właściwości mechaniczne i małą gęstość, znajdują zastosowanie głównie w przemyśle samochodowym, lotniczym, elektronice itp. Pomimo dobrych właściwości mechanicznych, stopy magnezu wykazują wysoką podatność na korozję, co jest przyczyną [...]

The use of micro-capillary techniques to study the corrosion resistance of AZ91 magnesium alloy at the micro-scale

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In the present paper, the corrosion behavior of as-cast AZ91 magnesium alloy is investigated in 0.1 M NaClO4 at 25°C. The specimen microstructure was fi rst investigated using FE-SEM/EDS and AFM. It is composed of Mg17Al12 precipitates, eutectic around precipitates and a-Mg matrix. Electrochemical measurements were then carried out after mechanical polishing, on individual phases using the electrochemical microcell technique and extremely small capillaries (diameters between 5 and 10 nm). A large passive domain was observed in the anodic region in sites containing precipitates. Stable pits were detected between -700 and -200 mV vs. Ag/AgCl. By contrast, the passive domain obtained in the matrix was narrow and stable pitting was observed at -1200!200 mV vs. Ag/AgCl. Eutectic was reve[...]

Modelling the effect of SiC particle size on crystallization of magnesium metal matrix composite; AZ91/SiC

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Grain size is one of the most important structural characteristic that determining mechanical properties. Knowing element properties, the proper application regions for it can be chosen to achieve best mechanical properties and performance. Nowadays simulation software can be use to predict the element microstructure. Those programs base on micro-macro model of crystallization. The model consists of partial differential equations (PDEs) that describe the nucleation rate, diffusion in the casting, casting cooling speed and every single grain growth rate. Often it is hard to find the theoretical value of the parameters that appear in those PDEs. It is possible to find them from experiment. The experimental data after applying statistical methods let us find approximated values of the so-called “fitting parameters" in the mentioned models [1÷4]. AZ91 alloy analyzed in this study is hypereutectic alloy. The magnesium primary α-Mg phase is dendritic. During crystallisation there appears eutectic reaction. In this study influence of eutectic is omitted because magnesium primary phase microstructure has most significant influence on mechanical properties of the casting. Model description In the mathematical model it is assumed that heat transfer is governed by Fourier-Kirchhoff (FK) equation: ∂ ∂T = - + c q p cp div gradT τ ρ ρ 1 ( λ ) , (1) where: T, K - is temperature, τ, s - time; cp, J·kg-1·K-1 - specific heat, ρ, kg·m-3 - density, λ, W·m-1·K-1 - thermal conductivity, q = L(dfs/dτ), W·kg-1 - heat of crystallization. During simulation the temperature change speed is calculated. Its value consists of two parts: one, that depends on the temperature gradient and second that is phase change effect. In this article there is an assumption that simulation runs in one element of the melt. With this assumption the gradient depend part of FK can [...]

Modelling the effect of SiC mass fraction on crystallization of magnesium metal matrix composite; AZ91/SiC

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Grain size is one of the most important parameter which determined mechanical properties. Knowing element properties the proper application regions for it can be chosen to achieve best mechanical properties and performance. Nowadays simulation software can be use to predict the element microstructure. Those programs base on micro-macro model of crystallization. The model consists of partial differential equations (PDEs) that described the nucleation rate, diffusion in the casting, casting cooling speed and every single grain growth rate. Often it is hard to find the theoretical value of the parameters that appear in those PDEs. It is possible to find them from experiment. The experimental data that after applying statistical methods let us find approximated values of the so-called “fitting parameters" in the mentioned models [1÷4]. AZ91 alloy analyzed in this study is hypereutectic alloy. The magnesium primary α-Mg phase is dendritic. During crystallisation there appears eutectic reaction. In this study influence of eutectic is omitted because magnesium primary phase has most significant influence on mechanical properties of the casting. Experimental procedure Composite casting The AZ91 alloy was selected as the matrix for the composites. The chemical composition is shown in Table 1. The reinforcement particles are silicon carbide with an average diameter of 45 μm. Composite specimen with 0, 1, 2, 3 and 4 wt. % of SiC particles were prepared using a liquid mixing and casting process. Processing of the magnesium composites consisted of mixing pre-heated SiC particles to 450°C with liquid magnesium melt stirring and mould casting. About 1.4 kg of composite melts was prepared in an electric resistance furnace using a steel crucible under a SF6/CO2 gas atmosphere. The molten AZ91 alloy was held at 700°C for 1 h. After putting SiC particles composite was stirred for 2 min, and then cast at 700°C into mould to produ[...]

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