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Modyfikacja mikrostruktury stopów magnezu Mg-7Al dodatkami metali ziem rzadkich oraz Mg-3Al metodą ECAP

Bryła K., Rokhlin L. L., Dutkiewicz J.

Inżynieria Materiałowa

2012

Vol. 33, nr 5

377--380

W pracy przedstawiono badania mikrostruktury i właściwości mechanicznych stopów Mg-7% Al z dodatkami 3% Nd i 10% Ho oraz stopu AZ31 po czterokrotnym przejściu przez kanał kątowy w temperaturze 150°C i 250°C. W mikrostrukturze stopów Mg-7% Al z dodatkami 3% Nd i 10% Ho po odlaniu obserwuje się roztwór α-Mg i mieszaninę eutektyczną α-Mg + Mg17Al12, fazy międzymetaliczne Al 2Nd i Al 11Nd3 oraz odpowiednio dla stopu z holmem Al2Ho. Po przesyceniu stopów w temperaturze 560°C w ciągu 3 godzin faza Mg17Al12 została rozpuszczona, fazy międzymetaliczne Al 2Nd i Al2Ho zostały wzbogacone aluminium, tworząc Al 3Nd i odpowiednio Al3Ho. Faza Al11Nd3 pozostaje w mikrostrukturze stabilna. Starzenie badanych stopów nieznacznie polepsza właściwości mechaniczne w temperaturze pokojowej. Obserwacje mikroskopowe stopu AZ31 po czterokrotnym przejściu przez kanał kątowy w 150 i 250°C ujawniają mikrostrukturę o bardzo drobnym ziarnie o średniej wielkości 1,5 μm i 3,2 μm dla wyższej temperatury procesu ECAP. W mikrostrukturze po procesie ECAP obserwowano zmiany świadczące o zachodzących procesach zdrowienia dynamicznego. Zmniejszenie wielkości ziarna powoduje zwiększenie twardości oraz wytrzymałości na ściskanie stopu AZ31 w temperaturze pokojowej.

In this work, the microstructure and mechanical properties of Mg-7% Al alloys doped with 3% Nd and 10% Ho and after four passes of ECAP at 150°C and 250°C of AZ31 alloy. It was found that as-cast microstructure of Mg-7% Al with 3% Nd and 10% Ho is characterized by α-Mg solid solution with eutectic mixture α-Mg and Mg 17Al12, intermetallic compounds Al2Nd and Al11Nd3, and Al2Ho respectively. During solution heat treatment Mg17Al12 phase was dissolved and intermetallics were transformed into Al3Nd and Al3Ho, whilst Al11Nd3 was remained in microstructure. Aging of investigated alloys increases slightly mechanical properties at ambient temperature. The microstructure of AZ31 alloy after four passes of ECAP at 150°C and 250°C consists of very fine grains with average size of 1.5 μm and 3.2 μm at higher pressing temperature. Processes of dynamic recovery during ECAP were observed. The grain refinement increases the hardness and compression strength of AZ31 alloy at ambient temperature.

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.