Investigation into the hot workability of the as-extruded WE43 magnesium alloy using processing map (original) (raw)
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WE43 magnesium alloy – material for challenging applications
Metallic Materials, 2019
WE43 magnesium alloy is a commercial lightweight material developed for application at temperatures up to 250 • C. This alloy is also considered for applications in medicine as a biodegradable material. The present study provides microstructure characterization and related mechanical properties of the WE43 alloy prepared by different processing techniques including casting, extrusion, rotary swaging and heat treatment. Results indicate huge differences in observed microstructures, such as precipitation of secondary phases, grain coarsening, texture formation and also concomitant changes of mechanical properties, such as tensile yield strength, ultimate tensile strength, compressive yield strength, ultimate compressive strength and elongation to fracture. Although this material is well-known, WE43 prepared in this study by a combination of extrusion and rotary swaging offered highly improved mechanical properties, including a tensile yield strength of 370 MPa and elongation of 15 %. Such a combination of values is rarely seen in literature and is not generally offered for commercially produced materials although both preparation methods are easily commercially available.
Magnesium alloys containing RE elements (WE grade) are considered as potential materials for high temperature structural applications. To this end, it is crucial to study the flow behavior and the micro-structural evolution of these alloys at high temperatures. In present work, the hot compression testing was employed to investigate the deformation behavior of a rolled WE54 magnesium alloy at elevated temperatures. The experimental material failed to deform to target strain of 0.6 at 250 and 300 C, while the straining was successfully performed at 350 C. A flow softening was observed at 350 C, which was related to the depletion of RE strengthener elements, particularly Y atoms, from the solid solution and dynamic precipitation of b phases. It was suggested that the Zener pinning effect of the latter precipitates might retard the occurrence of dynamic recrystallization. As the temperature increased to 450 and 500 C, the RE elements dissolved in the matrix and thus dynamic recrystallization could considerably progress in the microstructure. The comparative study of specimens cut along transverse ad normal direction (TD and ND specimens) implied that the presence of RE elements might effectively reduce the yield anisotropy in WE54 rolled alloy. Microstructural observations indicated a higher fraction of dynamically-recrystallized grains for the ND specimens. This was discussed relying on the different shares of deformation mechanism during compressing the TD and ND specimens.
Hot workability analysis of extruded AZ magnesium alloys with processing maps
Materials Science and Engineering: A, 2010
The processing conditions applied to deform wrought magnesium alloys greatly affect their final microstructure and mechanical properties. Defining an applicable processing window in terms of the ranges of temperatures and strain rates to achieve a homogeneous microstructure is a prerequisite for process optimization, since magnesium alloys show a peculiar deformation behaviour. By using trustworthy input data from uniaxial hot compression tests, processing maps were constructed for the alloys AZ41, AZ61 and AZ80. These maps clearly indicate the conditions leading to dynamically recrystallized homogeneous microstructures after hot deformation, as verified by analysing the microstructures after hot deformation under different conditions. It is found that a strain rate of 5 s −1 and a temperature of 375 • C for AZ41 and 325 • C for both AZ61 and AZ80 would result in dynamically recrystallized homogeneous microstructures.
Experimental and numerical analyses of magnesium alloy hot workability
Journal of Magnesium and Alloys, 2016
Due to their hexagonal crystal structure, magnesium alloys have relatively low workability at room temperature. In this study, the hot workability behavior of cast-extruded AZ31B magnesium alloy is studied through hot compression testing, numerical modeling and microstructural analyses. Hot deformation tests are performed at temperatures of 250°C to 400°C under strain rates of 0.01 to 1.0 s −1. Transmission electron microscopy is used to reveal the presence of dynamic recrystallization (DRX), dynamic recovery (DRY), cracks and shear bands. To predict plastic instabilities during hot compression tests of AZ31B magnesium alloy, the authors use Johnson-Cook damage model in a 3D finite element simulation. The optimal hot workability of magnesium alloy is found at a temperature (T) of 400°C and strain rate (ε) of 0.01 s −1. Stability is found at a lower strain rate, and instability is found at a higher strain rate.
Dislocation Movement in WE43 Magnesium Alloy during Recovery and Recrystallisation
MATERIALS TRANSACTIONS, 2011
The mobility of dislocations has been investigated in WE43 magnesium alloy during recovery and recrystallisation for samples deformed plastically, at different degrees of plastic deformation and temperatures. The dislocation density decreases within the temperature range 550 K-650 K, in good agreement with the characteristic recovery temperature of this alloy, 630 K. New dislocations located at the grain boundaries start their movement from 650 K onwards. During recrystallisation, which has a characteristic temperature of around 700 K, the density of dislocations decreases and the possibility of movement of the dislocations also decreases, due to the development of internal stresses during the growth of new strain-free grains. The excess of vacancies promoted by the plastic deformation in cold worked samples is consumed up to temperatures of 550 K. New thermal vacancies which assist the movement of grain boundaries and dislocations are created after annealing at temperature above 650 K. Hot worked samples which exhibit dynamic recovery or recrystallisation, depending on the degree of plastic deformation; have a structure with both a scarce dislocations mobility and also a small dislocations density.
Wrought Magnesium Alloys ZM21, ZW3 and WE43 Processed by Hydrostatic Extrusion with Back Pressure
Archives of Metallurgy and Materials, 2012
Wrought Magnesium Alloys ZM21, ZW3 and WE43 Processed by Hydrostatic Extrusion with Back Pressure Cold hydrostatic extrusion with and without back pressure of commercial ZM21, ZW3 and WE43 magnesium alloys has been performed at originally designed hydrostatic extrusion press operating up to 2000 MPa with back pressure up to 700 MPa. Alloys were cold extruded in one pass into rods between 5 and 9 mm in the outer diameter with product velocities between 1 and 10 m/min and extrusion ratios above 2. Application of back pressure extended formability of all magnesium alloys. It was due to hydrostatic pressure superimposed on the extruded product what inhibits the cracks generation and propagation. Cold deformation restrained the grain growth and softening processes while severe deformation in one pass increased grain refinement and density of internal defects. Ultimate tensile strength ranging from 370 MPa (ZM21) through 400 MPa (ZW3) up to 410 MPa (WE43), with respective yield stresses f...
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.
Hot deformation behavior of AZ91 magnesium alloy in temperature ranging from 350°C to 425°C
Transactions of Nonferrous Metals Society of China, 2012
The flow behavior and microstructure evolution of AZ91 magnesium alloy during a thermomechanical process, hot compression test， was investigated. The specimens were hot compressed at a temperature ranging from 350 °C to 425 °C and at strain rate of 0.1 s −1 to the strains of 0.3, 0.5 and peak. Microstructural evolutions were studied using optical and scanning electron microscopes. The results show that during the compression process, the recrystallized grains nucleate along the pre-existing grain boundaries. The amount of dynamically recrystallized grains is increased with strain in a sigmoid scheme followed by Avrami equation. The size of dynamically recrystallized grains also increases at the beginning and decreases after reaching the maximum value.