Wyniki wyszukiwania - Biblioteka Nauki

1

Vliv technologie výroby odlitku ze slitiny AZ 91 na jeho kvalitu a strukturu

100%

Ptácková M. , Klakurková L. , Juřička I.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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tom Vol. 321, z. 89

41-41

EN

The paper summarizes the results of structure analyses focused on differences in the technologies of manufacturing AZ91-alloy castings. The following technologies were used: A) die casting B) gravity casting into ceramic moulds As to their shape complexity the two castings are similar and are of roughly the same wall thickness. The die casting was selected form the manufacturing process while the precision casting made in a ceramic mould (shell mould) was cast individually within the process of verifying the potentials of manufacturing precise castings by the technology of investment casting into ceramic moulds.

2

Possibilities of mechanical properties and microstructure improvement of magnesium alloys

88%

Greger M. , Kocich R. , Čížek L. , Dobrzański L. A. , Juřička I.

Archives of Materials Science and Engineering

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2007

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tom Vol. 28, nr 2

83-90

EN

Purpose: Magnesium alloys are the very progressive materials whereon is due to improve their end-use properties, which. Especially, wrought Mg alloys attract attention since they have more advantageous mechanical properties than cast Mg alloys. Design/methodology/approach: The presented article shows some specific physical-metallurgical characteristics of magnesium alloys of the AZ91 kind after hot forming. Special attention has been focused on the analysis of mutual relations existing between the deformation conditions, microstructural parameters, and the achieved mechanical properties. Findings: The discussed topic includes namely the monitoring of the structures in the initial cast state and after the heat treatment of the T4 kind and the influence of rolling in hot state at different temperatures on this structure. The results of torsion tests of AZ91, AZ61 and AZ31 were added. Research limitations/implications: The results of this paper evinces that a combination of ECAP technology with conventional rolling is very effective tool for improve a final properties of magnesium alloys in practical use. Practical implications: It would be appropriate a extrusions processes for increasing of mechanical properties on their treatment by plastic deformations in a rolling mills. Originality/value: It is explained a big consequence of the ECAP integration between classical forming techniques.

3

Mechanical properties of magnesium alloy AZ91 at elevated temperatures

75%

Čížek L. , Greger M. , Dobrzański L. A. , Juřička I. , Kocich R. , Pawlica L. , Tański T.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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tom Vol. 18, nr 1-2

203--206

EN

Purpose: Purpose of this article is to extend a complex evaluation of magnesium alloys which requires very often knowledge of elastic-plastic properties at elevated temperatures. These properties are connected with microstructure that is influenced by metallurgical and technological factors and conditions of exploitation. Design/methodology/approach: Methodology Testing of magnesium alloys was based on tensile test in dependence on temperature. The methods of the light microscopy and SEM for metallographic and fracture analyses of alloys after testing were used. Findings: Objective of this work consisted in determination of changes of elastic-plastic properties of magnesium alloy AZ91 in dependence on temperature, including investigation of fracture characteristics. It was confirmed that during heating at chosen temperatures there occurs partial dissolution of minority phases. Homogenisation of microstructure is, however, accompanied by simultaneous forming of inter-granular non-integrities, which is unfavourable from the viewpoint of strength and plastic properties, especially at higher temperatures. Failure occurs practically at all temperatures basically by inter-crystalline splitting along the boundaries of original dendrites. At temperature testing near melting point of alloy the interdendrite areas melting were observed. Research limitations/implications: The experiment was limited by occurrence a void in cast alloys. Practical implications: The results may be utilized for a relation between plastic and strength properties of the investigated material in process of manufacturing. Originality/value: These results contribute to complex evaluation of properties magnesium alloys at higher temperatures namely for explanation of fracture mechanism near the melting point.

4

Mechanical properties and structure of magnesium alloys with graduate content of aluminium at elevated temperatures

63%

Čížek L. , Hanus A. , Greger M. , Juřička I. , Rusz S. , Prażmowski M. , Tański T. , Hernas A.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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tom Vol. 321, z. 89

91-92

EN

At the contemporary stage of the development of the engineering thought, and the product technology itself, material engineering has entered the period of new possibilities of designing and manufacturing of elements, introducing new methods of melting, casting, forming, and heat treatment of the casting materials, finding wider and wider applications in many industry branches. Therefore the development of engineering aims at designs optimizing, reducing dimensions, weight, and extending the life of devices as well as improving their reliability [1-3]. Contemporary materials should possess high mechanical properties, physical and chemical, as well as technological ones, to ensure long and reliable use. The above mentioned requirements and expectations regarding the contemporary materials are met by the non-ferrous metals alloys used nowadays, including the magnesium alloys. Magnesium alloys and their derivatives, characterize of low density (1.5-1.8 g/cm3) and high strength in relation to their weight [1,3]. Knowledge of the relaxation properties of metal materials at elevated temperatures is necessary for the verification of susceptibility of castings to the creation of defects during the production and forming processes [1,4]. Temperature limits of materials where highest tension values are generated may be detected with tensile tests under high temperatures. Experimental investigation was made on magnesium alloy AZ91 - samples A and AZ61 - samples B (after ASTM Standard) in initial state as cast. The purpose of the measurement was the study of deformation and tension changing with temperature at the tensile test and in time with simultaneous acoustic emission (AE) measurement (in the case of alloy AZ61). These dependencies were also monitored at various temperatures of sample heating from 15°C to 400°C with crosspiece shift of 6mm/min. The measurement included material sample stress at the given temperature by tension at the INOVA electro hydraulic loading machine with a loading force of 20 kN with possibility of the acoustic emission (AE) monitoring. The test bar with 0 4 mm was warmed up in a graphite furnace in inert atmosphere (argon). The AE scanner records released elastic waves (overshoots) in a frequency band between 30 kHz and 400 kHz. The output from the scanner is carried to the AE preamplifier where it is amplified and impedance-adjusted so it is possible to be transferred to more far-reaching places. The signal is further carried to the EMIS 01 system and to the PC's hard disk and they are processed in the EXCEL. Microstructure of the alloys in initial state is formed by solid solution and by minority phases Mgn(Al,Zn)i2 in massive and dispersion form and showed dendritic segregation. During heating magnesium alloy AZ91 at chosen temperatures there occurs partial dissolution of minority phases. Homogenisation of microstructure is, however, accompanied by simultaneous forming of inter-granular non-integrities, which is unfavourable from the viewpoint of strength and plastic properties, especially at higher temperatures. Failure occurs practically at all temperatures basically by inter-crystalline splitting along the boundaries of original dendrites. Trans-crystalline plastic character of fracture in small areas at 300°C was occurred. Similar temperature dependence was occurred in the case of alloy AZ61. In this case the plasticity properties were at high level. An acoustic emission method was used for a better analysis of the course of the deformation action at the tensile test. The AE method especially enables a study of dynamics of these processes at various temperatures. The opportunity to study deformation processes preceding initiation of cracks and monitoring of initiation and crack growth as up to the macroscopic scale is a big advantage of the AE. The method is therefore used in the technical diagnostics and at a check of technological operations in the production process.