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2 2008

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Microstructure and tensile properties of sand cast and die cast AE44 magnesium alloy

Rzychoń T., Kiełbus A.

Archives of Metallurgy and Materials

2008

Vol. 53, iss. 3

901-907

The AE44 magnesium alloy was prepared by gravity and die casting methods. The microstructure and mechanical properties were investigated. The results demonstrated that microstructure of sand casting consist of Iarge grains of a solid solution and needle-shaped Al11RE3 phase, globular particles of Al10RE2Mn7 and smali volume fraction of Al2RE. Die casting process caused significant refinement of structure and change of phase composition. Die cast AE44 alloy consists of Al11RE3 phase and precipitates of Al2RE and Al2.12RE0.88 compounds. The mechanical properties at room and elevated temperaturę of the sand cast alloy are relatively Iow due to coarse-grain structure. Die-casting process increases the ultimate tensile strength, yield strength and elongation of AE44 magnesium alloy.

W pracy przedstawiono wyniki badań mikrostruktury i właściwości mechanicznych stopu magnezu AE44 po odlewaniu do formy piaskowej i ciśnieniowym. Mikrostrukturę odlewu piaskowego charakteryzuje znaczna gruboziarnistość i obecność faz międzymetalicznych AI11RE3, Al10RE2Mn7 i Al2RE, której udział objętościowy jest nieznaczny. Zastosowanie odlewania ciśnieniowego powoduje silne rozdrobnienie mikrostruktury i zmiany składu fazowego. W odlewie ciśnieniowym obserwuje się iglastą fazę AI11RE3 oraz wydzielenia faz A12RE i Al2.12RE0.88- Właściwości mechaniczne odlewu piaskowego w temperaturze otoczenia i podwyższonej są stosunkowo niskie. Po odlewaniu ciśnieniowym obserwuje się podwyższenie wytrzymałości na rozciąganie, granicy plastyczności oraz wydłużenia.

The influence of Nd and Ho addition on the microstructure of Mg-7Al alloy

Bryła K., Dutkiewicz J., Faryna M., Dobatkina T., Rokhlin L.

Archives of Materials Science and Engineering

2008

Vol. 29, nr 1

40-44

Purpose: of this paper was to examine effect of Nd and Ho on the microstructure of as-cast and solid-treated Mg-7Al alloy, and to study the response to ageing by hardness changes measurements of investigated alloys during aging at 200oC. Design/methodology/approach: The microstructure of Mg-7Al-3Nd and Mg-Al-10Ho alloys after casting and heat treatment was studied by means of metallographic and scanning electron microscopy. The phase characterisation was carried out by X-ray diffraction and by energy dispersive X-ray microanalyser. The hardness changes during aging of both alloys were determined by Vickers hardness. Findings: It was found that as-cast microstructure of Mg-7Al alloy doped with 3% Nd, and 10% Ho, is characterized by �ż-Mg solid solution with eutectic mixture of �α-Mg and Mg17Al12 phases, intermetallic compounds Al2Nd and Al11Nd3, and Al2Ho respectively. During solution heat treatment eutectic phase was dissolved and intermetallics were transformed into Al3Nd and Al3Ho, whilst Al11Nd3 phase was remained in microstructure. Aging of investigated alloys plays slight role in mechanical properties at ambient temperature. Research limitations/implications: The microstructure of supersaturated Mg-7Al-10Ho alloy is composed of ��α-Mg and thermally stable, fine and randomly distributed Al3Ho phase, what may considerably improve the creep behaviour this alloy at elevated temperature. The creep tests in connection with microstructural analysis will be done in the future. Practical implications: The development of creep resistant Mg-Al alloys with individual rare earth elements allows to apply these materials as responsible structural members working at elevated temperature. The present results extend the knowledge about effect of Nd and Ho addition on the microstructure of Mg-7Al alloys. Originality/value: Microstructural studies of two new Mg-7Al alloys doped with 3% Nd and 10% Ho were presented.