Wyniki wyszukiwania - Biblioteka Nauki

1

Forging and rolling of magnesium alloy AZ61

100%

Greger M. , Kocich R. , Čižek L.

|

tom Vol. 20, nr 1-2

447-450

EN

Purpose: The paper summarises results of experiments aimed at development of structure of modified alloy AZ61 at hot deformation. Design/methodology/approach: Deformation behaviour of alloy was verified at the temperature of 420 degrees centigrade by rolling at 380 degrees centigrade by forging, respectively. Findings: Magnesium alloy AZ 61 have hexagonal structure and their forming is at room temperatures very difficult, that's why big plastic deformations are carried out in hot condition. After plastic deformations was obtained that original grain size decreased 15 times. Research limitations/implications: This paper provide data about magnitude of deformation, strain rate and temperature of forming at different techniques of plastic deformation. It was aimed to determine the conditions for non problem rolling and forging respectively. Practical implications: Initial structure was as cast and after heat treatment T4. Heat treatment appeared much better for forming as well as forging than rolling because of state of stress. Originality/value: Role of beta phase (Mg17Al12) in these alloys at plastic forming is very important, such that how it was obtained, best final properties of AZ 61 alloy supports very fine particles, distributed into Mg matrix. Next a relevant information is that multi stage forming process is much better in comparison with a big single reduction.

2

Struktura a vlastnosti vybraných hořčíkových slitin s příměsi křemíku a zirkonia

88%

Čížek L. , Greger M. , Pawlica L. , Prażmowski M. , Sozańska M.

|

2007

|

tom Vol. 321, z. 89

93-94

3

The influence of the surface defects concerning drawing processes of the micro-alloyed steel

75%

Rusz S. , Kubicek M. , Pastrnak M. , Filipec P. , Greger M. , Petruska J. , Janicek L.

|

2005

|

tom Vol. 72, nr 2

118-121

EN

This paper provides a report on the effect of the pass reduction concerning the strain course in wires made of micro-alloyed steel, 23MnB4; namely successively investigating three particular points - before the die, in the die itself, and at the die output section so that the strain condition is mapped in its very detail, which is of fundamental importance for the behaviour of surface defects in the process of drawing the wire.

PL

Artykuł przedstawia wpływ gniotu w przebiegu odkształcenia drutów wykonanych ze stali mikrostopowej 23MnB4, mianowicie w trzech następujących po sobie punktach: przed ciągadłem, w ciągadle i w strefie wyjścia z ciągadła, w ten sposób warunki odkształcenia zostały zobrazowane szczegółowo. Ma to istotny wpływ na zachowanie defektów powierzchni w procesie ciągnienia drutów.

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.

|

2007

|

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.