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Quantitative analysis of microstructure in AE44 magnesium alloy after long-term annealing

Rzychoń T., Kiełbus A., Paszkowski G.

Inżynieria Materiałowa

2008

Vol. 29, nr 4

304-309

The microstructure and microstructural stability of die-cast AE44 (Mg-4A1-4RE) alloy were investigated by quantitative metallography, X-ray diffraction, scaning electron microscopy and transmission electron microscopy. It is shown that formation of A12RE after long-term annealing at 250°C is not related to the decomposition of AlnRE3, as reported in the literature, but, rather, it is associated with the supersaturation of rare earth atoms in the matrix and probably related to the decomposition of AI2.12RE0.88 phase. The high thermal stability of AlnRE3 compound located at the interdendritic regions impedes the grain growth in AE44 alloy at 250°C.

W artykule przedstawiono wyniki badań struktury i stabilności strukturalnej odlewanego ciśnieniowo stopu magnezu AE44 (Mg-4A1-4RE). Badania przeprowadzono z wykorzystaniem metalografii ilościowej, rentgenowskiej analizy strukturalnej, elektronowej mikroskopii skaningowej i transmisyjnej. Stwierdzono, że powstawanie fazy A12RE podczas długotrwałego wygrzewania w 250°C nie jest związane z przedstawionym w literaturze rozpadem fazy AlnRE3. Proces ten może być związany z przesyceniem roztworu stałego pierwiastkami ziem rzadkich i rozpadem fazy Al2.12RE0.ffl. Wysoka stabilność termiczna fazy AlnRE3, znajdującej się w przestrzeniach międzydendrytycznyeh, zapobiega rozrostowi ziarna w 250°C.

Microstructure of AE44 magnesium alloy before and after hot-chamber die casting

Kiełbus A.

Journal of Achievements in Materials and Manufacturing Engineering

2007

Vol. 20, nr 1-2

459-462

Purpose: AE44 magnesium alloy allows attractive high temperature mechanical properties, as well as diecastability and good corrosion resistance. It contains magnesium, aluminium, cerium and lanthanum. Typically, it is used in automotive industry for structural components working at elevated temperature (150-175 degrees centigrade). The aim of this paper is to present the results of investigations on the microstructure of the AE44 magnesium alloy before and after hot chamber die casting. Design/methodology/approach: Die casting was carried out on 280 tone locking force hot-chamber die casting machine. For the microstructure observation, a Olympus GX+70 metallographic microscope and a HITACHI S-3400N scanning electron microscope with a Thermo Noran EDS spectrometer equipped with SYSTEM SIX were used. Findings: Based on the investigation carried out it was found that the AE44 magnesium alloy before die casting is characterized by alpha-Mg solid solution with globular, lamellar and acicular precipitations of Al11RE3 and Al3RE phases. Moreover, there was found globular Mn-rich phase existence (probably Al8CeMn4 phase). After hot-chamber die casting the microstructure of AE44 alloys consist of equiaxed dendrites of alpha-Mg with precipitates of Al11RE3 and probably Al2RE phase. Research limitations/implications: Future researches should contain investigations of the influence of the hot chamber die casting process parameters on the microstructure and mechanical properties of AE44 magnesium alloy. Practical implications: AE44 magnesium alloy can be cast with cold- and hot-chamber die casting machine. Results of investigation may be useful for preparing die casting technology of this alloy. Originality/value: The results of the researches make up a basis for the investigations of new magnesium alloys containing rare earth elements for hot chamber die casting designed to service in elevated temperature.