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Mechanical properties of a squeeze cast Mg-Al-Sr alloy

Trojanová Z., Drozd Z., Lukáč P., Chatey A.

Archives of Materials Science and Engineering

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2008

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Vol. 29, nr 2

97-104

EN

Purpose: The aim of the present work is to study the influence of temperature on tensile properties of the magnesium alloy AJ50, and to discuss possible hardening and softening mechanisms and thermally activated processes. Design/methodology/approach: Deformation behaviour of a Mg-Al-Sr magnesium alloy has been studied in tension as well as compression in the temperature interval from room temperature up to 300°C. Stress relaxation tests were performed with the aim to find applied stress components (internal stress and effective stress) and parameters of the thermally activated process/-es. Findings: The yield stress as well as the maximum stress of the alloy are very sensitive to the testing temperature. The work hardening coefficient O=dδ/dε decreases with increasing stress and temperature. Performed analysis of the O-α plots determined the hardening and softening mechanisms operating during the deformation. The internal stress decreses with increasin temperature, while the effective stress component increases. Practical implications: Estimated values of the activation volume as well as the activation energy indicate that the main thermally activated process is connected with the rapid decrease of the internal stress. Originality/value: An analysis showed that the main hardening process is the storage of dislocations at impenetrable obstacles. The activation

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Compressive behaviour of a squeeze cast AJ50 magnesium alloy

Trojanová Z., Drozd Z., Lukáč P.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

47-50

EN

Purpose: There is very limited information about the mechanical properties of Mg-Al-Sr alloys and therefore it is important to investigate mechanical properties at different temperatures and to estimate the mechanisms responsible for the deformation behaviour of Mg-Al-Sr alloys at elevated temperatures. Design/methodology/approach: Deformation behaviour of a Mg-Al-Sr magnesium alloy has been studied in compression in the temperature interval from room temperature up to 300 degrees centigrade. Stress relaxation tests were performed with the aim to find parameters of the thermally activated process. Findings: The yield stress as well as the maximum stress of the alloy are very sensitive to the testing temperature. Analysis of the work hardening coefficient determined the hardening and softening mechanisms operating during the deformation. Practical implications: The estimated activation energy and values of the activation volume indicate that the main thermally activated process is very probably the glide of dislocations in the non-compact planes. Originality/value: An analysis showed that the main hardening process is the storage of dislocations at impenetrable obstacles. The activation volume values indicate that the main thermally acivated process is connected with recovery process.

3

Microstructure and behaviour of ZC63 alloy and composite

Trojanová Z., Lukáč P.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 9

541-548

EN

Purpose: of this paper is to study the damping behaviour of ZC63 magnesium alloy and the same alloy reinforced with short Saffil fibres. Design/methodology/approach: Samples were thermally cycled between room temperature and increasing upper temperature of the thermal cycle and the logarithmic decrement were measured at room temperature. Findings: The strain amplitude dependence of the logarithmic decrement can be divided to two components: the amplitude independent and the amplitude dependent. While the thermal treatment does not change the amplitude independent component, the amplitude dependent part increases with increasing upper temperature of the thermal cycle. Research limitations/implications: Redistribution of solute atoms during thermal cycles is the reason for the observed changes in the amplitude dependence of decrement. Thermal stresses arise in the composite at the interfaces between the matrix and the reinforcement owing to a considerable mismatch of the thermal expansion coefficients of the matrix and that of the reinforcement. Practical implications: The ZC63/Saffil composites may be used as damping materials. Originality/value: New results on the damping behaviour of ZC63 alloy and its composite including internal friction were obtained.

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Deformation behaviour of ZC63 magnesium matrix composite

Trojanová Z., Lukáč P.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 6

361-364

EN

Purpose: of this paper is to give information on the deformation behaviour of ZC63 magnesium alloys reinforced with 10 vol. % of SiC particles. Design/methodology/approach: The deformation behaviour of the ZC63/10SiCp composite was investigated in tensile tests over the temperature range from 23 to 200 °C at an initial strain rate of 8.3 x 10 -3 s -1. Findings: The flow stress decreases with increasing temperature. Both the yield stress and the maximum stress decrease with increasing temperature for temperatures higher than 100 °C. Research limitations/implications: The paper indicates significant softening mechanisms that take place at high temperature deformation. Practical implications: The ZC63/10SiCp composite may be used for applications at temperatures above 100 C. Originality/value: New results on the temperature dependence of the yield stress and maximum stress were obtained.