Hot deformation behavior of AZ91 magnesium alloy in temperature ranging from 350°C to 425°C (original) (raw)
Related papers
Journal of Alloys and Compounds, 2011
Dynamic recrystallization of the AZ91 alloy was studied by conducting hot compression tests at temperature range of 325-400 • C and strain rate of 0.001-1 s −1. The influence of the hot deformation variables on flow stress as well as recrystallized grain size was investigated. The results showed that by decreasing temperature and increasing strain rate, flow stress increases while dynamically recrystallized grain size decreases. A power-law relation developed between the characteristic peak strain and Zener-Hollomon parameter and the exponent was determined as 0.17. Besides, the linear regression between the Zener-Hollomon parameter and dynamically recrystallized grain size developed another power law equation, with a stress exponent equivalent to −0.13.
Analysis of high-temperature deformation and microstructure of an AZ31 magnesium alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
High-temperature plastic deformation and dynamic recrystallization of AZ31 extruded (EX) and heat treated (FA) alloy was investigated in the temperature range between 200 and 400 • C. High-temperature straining resulted in partial dynamic recrystallization above 250 • C; in the EX alloy recrystallization was complete at 300 • C, while a moderate grain growth was observed at 400 • C. The peak flow stress dependence on temperature and strain rate are described by means of the conventional sinh equation; the calculation of the activation energy for high temperature in the whole range of temperature deformation gives Q = 155 kJ/mol, i.e. a value that was reasonably close but higher than the activation energy for self diffusion in Mg. The microstructure resulting from high-temperature straining was found to be substantially different in EX and FA alloys; in particular, the EX alloy was characterized by a lower flow stress, a higher ductility and by a finer size of the dynamically recrystallized grains. These results are then discussed on the basis of the "necklace" mechanism of dynamic recrystallization.
Grain refinement in AZ91 magnesium alloy during thermomechanical processing
Materials Science and Engineering: A, 2003
Microstructural changes during high-temperature extrusion and torsion of an AZ91 alloy (Mg Á/9Al Á/1Zn, wt.%) were investigated. In the experimental domain studied, dynamic recrystallisation (DRX) occurs and the effect of temperature and strain rate on the resulting recrystallised grain size was investigated. Complete recrystallisation in torsion is associated with the development of a stress plateau after softening from the peak stress, which is systematically observed in the first steps of straining. The resulting grain size can be related to the value of the peak stress. It appears that the precipitation of the Mg 17 Al 12 phase does not affect significantly the torsion behaviour of the alloy in the experimental domain investigated here. This study supports the idea that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 mm) can be easily produced by DRX during hightemperature extrusion of the AZ91 alloy.
Flow behavior and microstructure of ZK60 magnesium alloy compressed at high strain rate
Transactions of Nonferrous Metals Society of China, 2014
Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250−400 °C and the strain rate range of 0.1−50 s −1. The results showed that dynamic recrystallization (DRX) developed mainly at grain boundaries at lower strain rate (0.1−1 s −1), while in the case of higher strain rate (10−50 s −1), DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 °C, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10−50 s −1 and in the temperature range of 250−350 °C was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.
HIGH TEMPERATURE PLASTIC DEFORMATION OF A HEAT-TREATED AZ31 MAGNESIUM ALLOY
High-temperature plastic deformation and dynamic recrystallization were investigated in an extruded and heat-treated AZ31alloy in the temperature range between 200 and 400°C. High-temperature straining resulted in partial dynamic recrystallization above 250°C; at 400°C recrystallization was complete and a moderate grain growth was observed. The peak flow stress dependence on temperature and strain rate was described by means of the conventional sinh equation; calculation of the activation energy for high temperature in the whole range of temperature deformation gave Q=155 kJ/mol, i.e. a value that is reasonably close to, but greater than, the activation energy for self-diffusion in Mg. When the data obtained at the lowest temperature were excluded from the calculation, the activation energy increased to 180 kJ/mol. This difference in the activation energy value can be explained by the occurrence of dynamic recrystallization in the high-temperature regime; this observation was substantially confirmed by the plots of strain-hardening rate as a function of stress that were used to identify the onset of dynamic recrystallization.
Materials Science and Engineering: A, 2012
The present study deals with the recrystallization behavior of homogenized AZ81 magnesium alloy with emphasizing on the role of mechanical twins and g precipitates. Towards this end a set of hot compression tests were conducted in the temperature range of 250-450 1C under strain rates of 0.003, 0.03 and 0.3 s À 1. The results indicate that the dynamic recrystallization (DRX) has been occurring in the large scales thereby considered as the main factor affecting the related flow stress characteristics. The twin related dynamic recrystallization (including DRX within twin bands and DRX at twin-twin intersections) possesses a great contribution to the formation of new recrystallized grains. The obtained results also confirm that the dynamic precipitation of g phase has a significant effect on hindering the growth of new DRX grains thereby resulting in an outstanding grain refinement. The role of mechanical twinning and dynamic precipitation on the DRX behavior of the alloy is more pronounced at higher and lower Zener-Hollomon parameter, respectively.
MATERIALS TRANSACTIONS, 2013
High temperature uniaxial compression deformation is conducted on AZ80 magnesium alloy at 673 and 723 K by varying the strain rates ranging from 1.0 © 10 ¹4 to 5.0 © 10 ¹2 s ¹1 in order to investigate the behaviors of deformation and texture formation. Particular attention is paid to the development of basal texture. Under the deformation conditions of this study, work softening is observed in all the stressstrain curves without exception. The results of the microstructure observation reveal occurrence of dynamic recrystallization. Formation of fiber texture during the deformation is confirmed. The main component is (0001) when the peak stresses appearing in the stressstrain curves are more than 15 20 MPa, and it develops together with an increase in the peak stress. In contrast, weak fiber textures having a main component at a position 29°a way from the basal plane are formed with deformation conditions giving peak stresses of less than 15 MPa. The stress exponent changes at a peak stress near 20 MPa, suggesting that change in the texture corresponds to the change in the deformation mechanism. It is concluded that the formation of basal texture is due to the continuous dynamic recrystallization resulting from the growth of the subgrains formed by the deformation.
Hot compression behavior of the AZ91 magnesium alloy produced by high pressure die casting
Journal of Materials Processing Technology, 2007
The hot deformation behavior of a Mg-9Al-1Zn alloy produced by high pressure die casting has been investigated by means of compression tests in the temperature and strain rate ranges of 125-300 • C and 1.6 × 10 −5 to 10 −1 s −1 , respectively. The samples were deformed in the high pressure die casting state or after an exposure at 415 • C for 2 h to evaluate any different response to deformation. A premature fracture at 45 • respect to the compression axis was observed in samples strained at low temperatures and high strain rates. The stress-strain curves are explained in terms of microstructure evolution, with emphasis on the eutectic phase and on dynamic precipitation phenomena occurring at low and high temperature of deformation. Constitutive parameters were evaluated in order to better understand the microstructure evolution. Light and scanning electron microscopy have been performed to correlate the microstructure to the deformation parameters in all the tested conditions.
Mechanical properties of magnesium alloy AZ91 at elevated temperatures
2006
AbstrAct 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.
Advanced Materials Research, 2012
The effects of heat treatment on the microstructure, tensile property and fracture behavior of as-extruded AZ91 magnesium alloy were studied with OM and SEM. The results show that the grains of as-cast AZ91 alloy are refined by hot extrusion due to dynamic recrystallization, and the mechanical properties are improved obviously. The ductility is significantly enhanced after solution treatment of the as-extruded AZ91 alloy, tensile strength is almost the same as before, and hardness is significantly reduced after solution treatment and artificial aging treatment. The tensile strength reduced and the ductility is significantly enhanced of as-extruded after annealing processes. The fracture surface of as-extruded AZ91 magnesium alloy has the mixed modes of ductile and brittle characteristics. But after T6 or annealing treatment, the dimple number increases evidently.