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1

The influence of long-term annealing on the microstructure of Elektron 21 magnesium alloy

Kiełbus A.

Inżynieria Materiałowa

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2008

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Vol. 29, nr 4

310-315

EN

Elektron 21 is a new magnesium based casting alloy for used to 200°C. The microstructural changes after long-term annealing at 520°C (2-48 h) and 350°C (500-5000 h) have been presented. For the microstructure observation, a OLYMPUS GX71 metallographic microscope and a HITACHI S-3400N scanning electron microscope were used. Quantitative examination was conducted using the Met-Ilo automatic image analysis program. The Elektron 21 alloy in as-cast condition is characterized by a solid solution structure a with precipitates of Mg12(Nd,Gd) intermetallic phase on grain boundaries. After annealing (solutioning) at 520°C a reduction of the number of Mgi2(Nd,Gd) phase precipitates was observed. Its area fraction falls with the extension of the treatment time from AA=6.55% (as cast state) to AA= 0.5% (24 h of treatment). Also, an increase of the solid solution a grain size was observed from A=649 um2 to J=3000 um2. After annealing at 350°C the precipitation of Mg41Nd5 phase was observed. Its area fraction falls with the extension of the treatment time from AA=3.55% (500 h) to AA=5.55 % (5000 h of treatment). The solid solution a grain size didn't change.

PL

Stop magnezu Elektron 21 jest nowym stopem przeznaczonym do pracy w temperaturze do 200°C. W artykule zaprezentowano zmiany mikrostruktury podczas długotrwałego wyżarzania w temperaturze 500°C (2-48 h) i 350°C (500-5000 h). Do badań mikrostruktury zastosowano mikroskop optyczny OLYMPUS GX71 oraz mikroskop elektronowy skaningowy HITACHI S-3400N. Ilościową ocenę mikrostruktury przeprowadzono z wykorzystaniem programu "Met-Ilo". Stop Elektron 21 w stanie lanym charakteryzuje się strukturą roztworu stałego z wydzieleniami fazy Mg12(Nd,Gd) na granicach ziaren. Po wyżarzaniu (przesycaniu) w temperaturze 520°C obserwowano zmniejszenie udziału objętościowego fazy Mg12(Nd,Gd) z poziomu AA=6,55% (stan lany) do poziomu AA=0,5% (po 24 h obróbki). Natomiast średnie pole powierzchni płaskiego przekroju ziarna roztworu stałego zwiększało się z A=649 um2 do A=3000 um2. Po wyżarzaniu w temperaturze 350°C obserwowano wydzielanie fazy Mg41Nd5. Jej udział objętościowy zwiększa się wraz z wydłużaniem czasu obróbki z AA=3,55% (po 500 h) do AA=5,55% (po 5000 h). Średnie pole powierzchni płaskiego przekroju ziarna roztworu stałego nie zmienia się.

2

Microstructure and mechanical properties of Elektron 21 alloy after heat treatment

Kiełbus A.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

127-130

EN

Purpose: Elektron 21 is new magnesium based casting alloy contains neodymium, gadolinium and zinc for used to at 200 degrees centigrade. It is a Mg-RE-Zn-Zr alloy designed for aerospace and specialty application ns. This alloy has high strength, good corrosion resistance and excellent castability. The aim of the research was to determine the effect of heat treatment parameters on the microstructure and mechanical properties of Electron 21 magnesium alloy. Design/methodology/approach: Solution treatment was performed at 520 degrees centigrade/8h with water cooling. Ageing treatments were performed at 200 degrees centigrade/4-96h and then quenched in air. The microstructure was characterized by JEM 2010 ARP microscope. The examination of the mechanical properties was conducted on an MTS-810 servo hydraulic machine at two temperatures: ambient (ca. 20 degrees centigrade) and 200 degrees centigrade. Hardness measurements by Vickers method were performed on a ZWICK/ZHV50 hardness tester. Findings: The microstructure of the cast alloy consists of alpha-Mg phase matrix with precipitates of intermetallic phase Mg12(Ndx, Gd1-x) at grain boundaries. After solution treatment the Mg12(Ndx, Gd1-x) phase dissolves in the matrix. The ageing treatment applied after solution treatment with air-cooling caused precipitation of a beta'', beta' and beta intermetallic phases. The best mechanical properties (Rm=308MPA, R0.2=170MPa, A5-9.5%) has a alloy with beta' intermetallic phase. Research limitations/implications: The future research will contain microstructural investigations of Elektron 21 alloy after creep tests. Practical implications: Elektron 21 magnesium alloy is used in the aircraft industry for engine casings, gear box casings and rotor heads in helicopters. Results of investigation may be useful for preparing heat treatment technology of the Mg-Nd-Gd alloys. Originality/value: The results of the researches make up a basis for the next investigations of magnesium alloys with addition of Gd and Nd designed to exploitation at temperature to 300 degrees centigrade.

3

Corrosion resistance of Electron 21 magnesium alloy

Kiełbus A.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 1

29-32

EN

Purpose: Elektron 21 magnesium alloy containing neodymium, gadolinium and zinc has high strength, good corrosion resistance and excellent castability. It is designed mainly for aerospace applications. The purpose of the investigation was to study the corrosion resistance of Elektron 21 magnesium alloy in as cast condition and after heat treatment in 3.5% NaCl saturated with Mg(OH)2 solution. Design/methodology/approach: Solution treatment was performed at 525 degrees centigrade/8h/water, while ageing treatments at following conditions 250 degrees centigrade/4-96h/air. Immersion test was performed in 3.5% NaCl saturated with Mg(OH)2 solution at room temperature. Specimens were placed in 3.5% NaCl solution for periods of time between one and 5 days. After immersion test, the microstructure and the appearances of the corroded structure were examind by optical microscopy (Olympus GX-70) and a scanning electron microscopy (Hitachi S3400). Findings: The corrosion rates of Elektron 21 alloy increased with increasing the exposure time and finally (after 5 days) reached maximum value 0.092 mg/cm to the -2 day to the -1. Solution treatment at 520 degrees centigrade for 8 h caused decrease in corrosion rate (0.072 mg cm to the -2 day to the -1) due to dissolving of intermetallic phase precipitates at matrix. Ageing at 200 degrees centigrade for 4 h and 16 h caused next decrease in corrosion rate to value 0.052 and 0.055 mg cm to the -2 day to the -1 respectively, while after ageing for 48h corrosion rate increase to value 0.067 mg cm to the -2 day to the -1 due to increase of volume fraction and size of beta' phase and precipitations of equilibrium beta phase. It was also noticed that the longer time of ageing the higher corrosion rates were observed. Research limitations/implications: Future researches should include investigations of the influence of other environments on the corrosion resistance of Elektron 21 alloy. Practical implications: The improvement of corrosion resistance of Elektron 21 alloy can cause increase in it application in aerospace industry. Originality/value: The relationship between the ageing parameters, microstructure and corrosion resistance in Electron 21 magnesium alloy was specified.