Effect of the Second Phase on the Microstructure of Magnesium Alloys during Cyclic Extrusion Compression

2008 ◽  
Vol 584-586 ◽  
pp. 523-527 ◽  
Author(s):  
Yong Jun Chen ◽  
Hans Jørgen Roven ◽  
Qu Dong Wang ◽  
M. Liu ◽  
Jin Bao Lin
Keyword(s):  
Grain Size ◽  
Magnesium Alloys ◽  
Three Dimensional ◽  
Second Phase ◽  
Shear Stresses ◽  
Ultrafine Grained ◽  
Mean Grain Size ◽  
Accumulated Strain ◽  
Second Phases ◽  
Cyclic Extrusion Compression

Cyclic extrusion compression (CEC) is an effective severe plastic deformation (SPD) process which can be used for fabricating ultrafine grained light materials such as magnesium alloys. This method introduces three-dimensional compression and shear stresses and the process can be repeated for a certain number of passes until the desired accumulated strain has been introduced. In order to reveal the effect of second phases on the microstructure developed in magnesium alloys during CEC, three different alloys (AZ31, AZ31-1wt.%Si and AZ91) were investigated after CEC 7 passes performed at 225°C. The experimental results show that the CEC process can effectively refine the microstructures of these alloys and the mean grain size achieved is 1.3µm, 1.5µm and 1.4µm, respectively. It is revealed that the grain size, grain shape and grain boundary structures are little affected by coarse phase Mg2Si but strongly affected by the fine phase Mg17Al12. The fine phase Mg17Al12 seems to increase the relative grain misorientations, hence enhancing the formation of high angle grain boundaries (HAGBs). It is expected that such changes are improving mechanical properties, subsequent forming behavior and surface quality.

Study of the Microstructure, Texture and Tensile Properties in as-Extruded AZ91 and ZM21 Magnesium Alloys

2011 ◽  
Vol 702-703 ◽  
pp. 659-662
Author(s):  
M. Thirumurugan ◽  
R. Madhavan ◽  
S. Kumaran ◽  
T. Srinivasa Rao ◽  
Satyam Suwas
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Tensile Properties ◽  
Structure Formation ◽  
Texture Analysis ◽  
Magnesium Alloys ◽  
Az91 Alloy ◽  
Second Phase ◽  
Mean Grain Size ◽  
The Mean

In this paper, the microstructure, texture and tensile properties of the magnesium alloys AZ91 and ZM21 extruded at 350°C to the ratio 25:1 are investigated. After extrusion, the mean grain size reduces from 400 µm to 30 µm in ZM21 alloy and from 350 µm to 40 µm in AZ91 alloy. Bulk texture analysis indicates the formation of characteristic extrusion texture in both the alloys. The occurrence of dynamic recrystallization, as revealed through necklace structure formation, and the precipitation of second phase (Mg17Al12) particles in the AZ91 alloy are observed.

Structure of second phases in TiAl alloys containing Cr and B

1991 ◽  
Vol 49 ◽  
pp. 576-577
Author(s):  
Ernest L. Hall ◽  
Shyh-Chin Huang
Keyword(s):  
Grain Size ◽  
Second Phase ◽  
Structure And Properties ◽  
Tial Alloys ◽  
Second Phases ◽  
Interstitial Elements

Addition of interstitial elements to γ-TiAl alloys is currently being explored as a method for improving the properties of these alloys. Previous work in which a number of interstitial elements were studied showed that boron was particularly effective in refining the grain size in castings, and led to enhanced strength while maintaining reasonable ductility. Other investigators have shown that B in γ-TiAl alloys tends to promote the formation of TiB2 as a second phase. In this study, the microstructure of Bcontaining TiAl alloys was examined in detail in order to describe the mechanism by which B alters the structure and properties of these alloys.

Internal Stresses in Nanocrystalline Nickel and Nickel-Iron Alloys

2012 ◽  
Vol 706-709 ◽  
pp. 1607-1611 ◽  
Author(s):  
J.D. Giallonardo ◽  
Uwe Erb ◽  
G. Palumbo ◽  
G.A. Botton ◽  
C. Andrei
Keyword(s):  
Grain Size ◽  
Internal Stress ◽  
Structural Difference ◽  
Intrinsic Stress ◽  
Internal Stresses ◽  
Second Phase ◽  
Nickel Iron ◽  
Second Phase Particles ◽  
Second Phases ◽  
Rule Out

Nanocrystalline metals are often produced in a state of stress which can adversely affect certain properties, e.g. corrosion resistance, wear, fatigue strength, etc. This stress is referred to as internal or “intrinsic” stress since it is not directly caused by applied loads. The structural causes of these stresses in nanocrystalline materials are not fully understood and are therefore an area of particular interest. The internal stresses of nanocrystalline Ni and Ni-16wt%Fe were measured and found to increase with the addition of iron. Characterization using HR-TEM revealed no signs of porosity, second phase particles, or a high density of dislocations. Both materials possessed well defined high-angle grain boundaries. The main structural difference between the two materials was found to be grain size and correspondingly, a decrease in grain size resulted in an increase in internal stress which supports the applicability of the coalescence theory. The current study also provides evidence to rule out the effect of voids (or porosity), dislocations, and second phases as possible causes of internal stress.

Microstructure and Aging Behavior of Al-0.2wt%Zr Alloy Heavily Deformed by ARB Process

2008 ◽  
Vol 584-586 ◽  
pp. 728-733 ◽  
Author(s):  
Takatoshi Sato ◽  
Daisuke Terada ◽  
Nobuhiro Tsuji
Keyword(s):  
Grain Size ◽  
Microstructural Evolution ◽  
Coarse Grain ◽  
Aging Behavior ◽  
Roll Bonding ◽  
Solution Treated ◽  
Ultrafine Grained ◽  
Mean Grain Size ◽  
Treated State ◽  
Zr Alloy

An Al-0.2wt%Zr alloy was severely deformed up to a strain of 8.0 by accumulative roll bonding (ARB) process, started from the solution-treated state. The microstructural evolution during ARB and its aging behavior were investigated. With increasing the number of ARB cycles, Vickers hardness of the specimens increased and reached to a constant value. The microstructural evolution during the ARB could be understood in terms of grain subdivision. The ultrafine grained (UFG) materials whose mean grain size was 0.4 -m were obtained by 10-cycle ARB process. In aging of the ARB processed specimens at high temperatures above 673K, the UFG microstructures quickly coarsened. On the other hand, it was suggested that the precipitation behaviors of the ARB specimen at 623K were quite unique and completely different from those of the conventionally solution-treated material with coarse grain size.

Effect of Calcium and Magnesium Addition on the Cast Microstructure Grain Size of HSLA Steel

2014 ◽  
Vol 685 ◽  
pp. 22-26
Author(s):  
Yan Liu ◽  
Kai Wang ◽  
Yang Liu ◽  
Jian Ming Wang
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Hsla Steel ◽  
Second Phase ◽  
Mean Grain Size ◽  
The Mean ◽  
Calcium And Magnesium ◽  
Observation Method ◽  
Cast Microstructure ◽  
Magnesium Addition

A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding calcium and magnesium into the steel in the form of Si-Ca alloy and Mg-Zr alloy, respectively. The effect of calcium and magnesium addition on the cast microstructure grain size of HSLA steel was analysed. The grain size of the cast microstructure in each sample was measured by the metalloscope observation method. The results show that a large amount of oxides generated from the adding Ca and Mg elements into the steel can accelerate the nucleation and refrain the grain growth, so the grains are refined. In the process of improving temperature, the oxides of Ca and Mg elements located in the interior of austenite can accelerate the nucleation and impede the grain growth. Almost every grain becomes finer after adding Ca and Mg elements. When adding 5wt% Mg, the mean grain size is the smallest, 0.712 mm, while the biggest grain size is 1.115mm in raw steel. The grain size in Mg 5wt% steel is refined by 36.1% in contrast with the raw steel. According to the adding amounts of Ca and Mg elements in experimental steel, the range of the mean grain size is from 0.712 mm to 0.975 mm.

Structure and Fatigue Properties of the Mg Alloy AM60 Processed by ECAP

2008 ◽  
Vol 584-586 ◽  
pp. 803-808 ◽  
Author(s):  
Rinat K. Islamgaliev ◽  
Olya B. Kulyasova ◽  
Bernhard Mingler ◽  
Michael Zehetbauer ◽  
Alexander Minkow
Keyword(s):  
Grain Size ◽  
Endurance Limit ◽  
Volume Fraction ◽  
Coarse Grained ◽  
Fatigue Properties ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Mean Grain Size ◽  
Fatigue Endurance ◽  
Misorientation Angles

This paper reports on the microstructures and fatigue properties of ultrafine-grained (UFG) AM60 magnesium alloy processed by equal channel angular pressing (ECAP) at various temperatures. After ECAP processing, samples exhibited an increase in fatigue endurance limit, which correlates well with a decrease in grain size. In case of lowest ECAP temperature, the mean grain size is as small as 1 2m which leads to an increase in fatigue endurance limit by 70 % in comparison to coarse-grained alloy. The temperature of ECAP not only governs the grain size and misorientation angles of grain boundaries but also the volume fraction of precipitates, thus affecting the probability of twinning and grain growth after fatigue treatment.

Effects of Strain Rate and Heat Treatment on the Tensile Property of 1Mn1Zn4Y Magnesium Alloy

2011 ◽  
Vol 311-313 ◽  
pp. 583-586
Author(s):  
Xiu Zhi Zhang ◽  
Ying Jie Li ◽  
Yi Shuai Zhang
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Strain Rate ◽  
Magnesium Alloys ◽  
Tensile Property ◽  
Tensile Tests ◽  
Second Phase ◽  
Dispersed Particles

In this paper, the effect of heat treatment and strain rate on the tensile property of extruding magnesium alloys 1Mn1Zn4Y is studied by using tensile tests. It can be concluded that because the grain size of the sample with solid solution (T4) is coarser than that of the sample without heat treatment，the elongation and the strength of the specimen treated with solid solution are lower. However, owing to many fine and dispersed particles of the second phase precipitated from the solid solution, the strength of sample treated with solid solution + aging (T6) is the highest.

The Mechanical Properties in the Vicinity of Grain Boundaries in Ultrafine-Grained and Polycrystalline Materials Studied by Nanoindentations

2004 ◽  
Vol 819 ◽  
Author(s):  
E. Schweitzer ◽  
K. Durst ◽  
D. Amberger ◽  
M. Göken
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Boundaries ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Polycrystalline Materials ◽  
Petch Relation ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Second Phases

AbstractThe strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

Microstructure and Mechanical Properties of Ultrafine-Grained Mg-Zn-Ca Alloy

2017 ◽  
Vol 381 ◽  
pp. 39-43 ◽  
Author(s):  
Olya B. Kulyasova ◽  
Rinat K. Islamgaliev ◽  
Ruslan Z. Valiev
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
High Pressure ◽  
Chemical Composition ◽  
High Pressure Torsion ◽  
Notable Effect ◽  
Ultrafine Grained ◽  
Mean Grain Size ◽  
High Microhardness ◽  
Mean Size

This paper studies the structure and mechanical properties of the Mg-1%Zn-xCa system subjected to high-pressure torsion (HPT) treatment. It was found that the chemical composition had a notable effect on the processes of grain refinement in the alloy. As is shown, HPT of Mg-1%Zn-0.005%Ca resulted in the formation of grains with a mean size of 250 nm, while HPT of the alloy with an increased content of Са up to 0.2% led to the formation of a nanostructure with a mean grain size of 90 nm. It is demonstrated that high microhardness is typical of all HPT-processed samples. The formation of fine Mg2Ca particles was established to increase the heat resistance of the alloy.

Grain Refinement in Steels through Thermomechanical Processing

2005 ◽  
Vol 500-501 ◽  
pp. 39-48 ◽  
Author(s):  
Peter D. Hodgson ◽  
Hossein Beladi ◽  
Matthew R. Barnett
Keyword(s):  
Grain Size ◽  
Thermomechanical Processing ◽  
High Strength ◽  
Structural Steels ◽  
Dynamic Strain ◽  
Second Phase ◽  
Ultrafine Grained ◽  
Uniform Dispersion ◽  
Key Issues ◽  
Typical Range

The development of ultrafine grained microstructures in steels has received considerable attention in recent times. In many cases the aim is to produce high strength structural steels with minimal alloying. It is well established that for an equiaxed ferrite with a uniform dispersion of second phase, both the strength and toughness will be markedly improved if the grain size can be reduced to 1-2 µm, from the typical range of 5-10 µm. Means of achieving this through dynamic strain induced transformation are examined here, following a brief overview of some of the key issues encountered when attempting to refine the austenite in existing mill configurations. A number of deformation microstructure maps are developed to aid the discussion.

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