Texture and weak grain size dependence in friction stir processed Mg–Al–Zn alloy (original) (raw)
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Scripta Materialia, 2010
The influence of strain rate and temperature during friction stir processing (FSP) on the texture and tensile behavior of a Mg alloy has been investigated. By varying key processing parameters systematically, i.e. rotation and travel rates of the tool, a series of FSP specimens were prepared with a wide range of thermo-mechanical inputs in terms of the Zener-Hollomon parameter (Z). Neutron diffraction results showed a dramatic change in texture as Z increased. The resulting tensile behavior in the stir zone also illustrates the influence of Z.
Achieving ultrafine grain size in Mg–Al–Zn alloy by friction stir processing
Ultrafine-grained (UFG) microstructures with an average grain size of 100–300 nm are achieved in solution-hardened AZ31 Mg– Al–Zn alloy prepared by friction stir processing equipped with a rapid heat sink. The mean hardness of the UFG region reaches $120H v , which is more than twice as high as that of the AZ31 matrix. The grain refinement kinetics are analyzed and the results are self-consistent.
Microstructural Evaluation of Friction Stir Processed AZ31B-H24 Magnesium Alloy
Canadian Metallurgical Quarterly, 2007
The microstructural characteristics in an AZ31B-H24 magnesium alloy after friction stir processing (FSP) were examined. The effects of FSP parameters including forge force and traverse speed on the microstructure were evaluated. It was observed that the grain size increased from about 4 mm in the base metal to about 8 mm at the centre of the stir zone after FSP. The aspect ratio of the grains decreased towards the centre of the stir zone. The changes in the grain size and shape resulted in a drop in micro-indentation hardness from 75 HV in the base metal to about 55 HV at the centre of the stir zone. Increasing the forge force or decreasing the traverse speed increased the grain size due to a greater heat input. It was also observed that the annealing effects (recrystallization and subsequent softening) of FSP were less pronounced with increasing distance horizontally or vertically from the pin tool due to the presence of temperature gradient. Furthermore, the Hall-Petch type relationships between the microhardness and the grain size were found to be valid after FSP.
MATERIALS TRANSACTIONS, 2014
Friction stir process (FSP) and post thermal exposure were carried out to a microstructure-thermostable cast Al5Mg0.5Mn alloy to examine the grain size dependence of tensile yield stress by using HallPetch relation, • y = • 0 + k y d ¹1/2. The measurement of preferred crystalline orientations and grain boundaries characteristic is used to explain the difference of the HallPetch parameters. FSP produces fine grain structure and, for the obtained average grain size from 3.7 to 12.8 µm, near-random crystalline orientations and certain proportion of rigid coincident site lattice boundaries (CSLs) is detected. Two-step post thermal exposure leads to a quick development of rotated ©001ª type crystalline orientations and the obtained coarse grains with average size from 229 to 508 µm are also commonly surrounded by general high angle boundaries. The calculation of Taylor factor and CSLs proportion reveals that stronger texture and grain boundary hardening effects exist in FSPed specimens than in thermal exposed specimens. These items are the major factors leading to larger • 0 and k y in FSPed specimens than in thermal exposed specimens.
Microstructure-Property Relationship for Friction Stir Processed Magnesium Alloy
Advanced Engineering Materials, 2014
Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure-property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys.
Effect of Velocity Index on Grain Size of Friction Stir Processed Al-Zn-Mg-Cu Alloy
Procedia Technology, 2016
Friction stir processing is an effective tool for microstructure modification by refining the microstructure in aluminum alloys. In this study, the effect of velocity index (tool rotation speed /traverse speed) on resulting grain microstructure of friction stir processed high strength Al-Zn-Mg-Cu alloy is reported. The velocity index is a key factor to decide the heat input during the process. Three samples were manufactured at different velocity index. The hardness measurement was performed to understand the hardness distribution in the processed region at different velocity index. The microstructure examination of the stir zone was performed by optical microscope. All the samples exhibited the stir zone with fine equiaxed grain microstructure. It is observed that grain size decreased with decrease in the value of the velocity index.
Microstructural and microhardness evolution of friction stir processing AZ31B-H24 magnesium alloy
2007
In this work, the microstructure, texture, phases, and microhardness of 45 • printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni 3 Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe 2 Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to γ phase dissolution and differences in grain morphology.
MATERIALS TRANSACTIONS, 2012
The workability and ductility of AlZnMg alloy are lower. In this study, the Zn content (4.446.34 mass%) was reduced and the Mg content (1.111.28 mass%) was raised to investigate the relationship between microstructures and tensile mechanical properties of AlxZnyMg aluminum alloys after friction stir process (FSP). The ZM35 alloy (Zn/Mg ratio is 3.5) and the ZM57 alloy (Zn/Mg ratio is 5.7) had a friction stir process and then three artificial aging treatments were performed to discuss the effects of Zn/Mg ratio on mechanical properties. After FSP and then natural aging for 12 days, the results of the experiment showed that the tensile strengths of ZM35 and ZM57 alloys were lower than the base metal (extruded material with T6, no FSP). Notably, the strength of as-FSP specimens was promoted after aging treatments. Through the mode I (80°C/16 h) treatments and the mode II (80°C/16 h + T6) treatment, the strengths of ZM35 alloy and ZM57 alloy were improved. However, after the mode III (T4 + 80°C/16 h + T6) treatment, the tensile strength and ductility of the ZM57 alloy reduced, and the deterioration rate of ductility reached to 65%; the ZM35 alloy possessed a better ductility, which confirmed the fact that decreasing Zn/Mg ratio improved the workability of friction stir AlZnMg specimens with an artificial aging treatments.
Influence of Process Parameters on Microstructure of Friction Stir Processed Mg AZ31 Alloy
2014
Friction stir processing (FSP) has been developed on the principles of friction stir welding (FSW) as an effective and efficien new method for grain refinement and microstructural modification, providing intense plastic deformation as well as higher strain rates than other conventional severe plastic deformation methods. FSP produces an equiaxed homogeneous microstructure consisting of fine grains, resulting in the enhancement of the properties of the material at room temperature. The objective of the present paper is to examine the influence of friction stir processing (FSP) parameters namely tool rotational speed (RS), tool traverse speed (TS) and tool tilt angle (TA) on the microstructures of friction stir processed AZ31B-O magnesium alloy. This investigation has focused on the microstructural changes occurred in the dynamically recrystallised nugget zone/ stir zone and the thermo mechanically affected zone during FSP. The results presented in this work indicate that all the thre...
Journal of Mechanical Science and Technology, 2016
In this paper, the effect of heat treatment and number of passes on microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy samples were investigated. From six samples of as-cast AZ91C magnesium alloy, three plates were pre-heated at temperature of 375°C for 3 hours, and then were treated at temperature of 415°C for 18 hours and finally were cooled down in air. Three plates were relinquished without heat treatment. 8 mm thick as-cast AZ91C magnesium alloy plates were friction stir processed at constant traverse speed of 40 mm/min and tool rotation speed of 1250 rpm. After process, microstructural characterization of samples was analyzed using optical microscopy and tensile and Vickers hardness tests were performed. It was found that heat treated samples had finer grains, higher hardness, improved tensile strength and elongation relative to non-heat treated ones. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg 17 Al 12). The micro-hardness characteristics and tensile improvement of the friction stir processed samples depend significantly on grain size, removal of voids and porosities and dissolution of β phase in the stir zone.