Microstructure-Property Relationship for Friction Stir Processed Magnesium Alloy (original) (raw)
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Metallurgical and Materials Transactions B, 2012
The main aim of the current study is the analysis of friction stir processing (FSP) of Mg-based alloys as a possible tool for nanocomposites production. The study reports microstructural changes taking place in a Mg-based alloy (AE42) subjected to FSP under different cooling conditions. The FSP process was carried out with single as well as multipass options. The friction stir processed samples were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), focused ion beam (FIB)-scanning ion microscopy (SIM), and X-ray diffraction (XRD). It was observed that FSP tends to fragment the elongated precipitates and produces near homogeneous distribution of fine particles. The smallest particle size was observed to be produced by double-pass FSP supplemented by rapid cooling, thereby generating in situ nanocomposites. Vickers microhardness testing was done along the thickness (transverse direction) of the specimen to study and understand the variation of hardness with thickness. Nearly a two-times increase in the microhardness of AE42 was observed in the case of double-pass, FSP AE42 with cooling at temperature of approximately 253 K (-20°C). To confirm these observations, another magnesium alloy AM50 was also friction stir processed under similar conditions. The fine submicron grain structure produced in AE42 alloy contributed immensely toward grain boundary strengthening and Orowan strengthening had only marginal influence. Subgrain boundary pinning by in situ nanoparticles contributed significantly in the strengthening process.
Archives of Metallurgy and Materials, 2016
The samples of the as-cast AM60 magnesium alloy were subjected to Friction Stir Processing (FSP). The effect of FSP on the microstructure of AM60 magnesium alloy was analyzed using optical microscopy and X-ray analysis. Besides, the investigation of selected properties, i.e. hardness and resistance to abrasion wear, were carried out. The carried out investigations showed that FSP leads to more homogeneous microstructure and significant grain refinement. The average grain size in the stirred zone (SZ) was about 6-9 μm. in the thermomechanically affected zone (TMAZ), the elongated and deformed grains distributed along flow line were observed. The structural changes caused by FSP lead to an increase in microhardness and wear resistance of AM60 alloy in comparison to their non-treated equivalents. Preliminary results show that friction stir processing is a promising and an effective grain refinement technique.
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.
Friction stir processing (FSP) of a new rare earth-free Mg-5Al-3.5Ca-1Mn (AXM541) alloy resulted in significant microstructural refinement and mechanical properties comparable to existing AXM series Mg alloys. Severe refinement of the Al-Ca (C36) phase during FSP led to uniform dispersion throughout the microstructure. The synergistic effect of high heat input and the presence of these 1-4 µm size particles resulted in dynamic recrystallization via particle stimulated nucleation (PSN), with an average grain size of 4.5 µm after FSP. Further, improved mechanical properties of the AXM541 alloy along the processing direction produced a tensile yield strength (TYS) of 322 ± 14 MPa and a total elongation of 16 ± 3%. The increase in strength was also attributed to the dispersion strengthening effect associated with Al-Ca and Al-Mn (D810) particles. Moreover, the AXM541 alloy showed a better mechanical response compared with other AXM alloys irrespective of high Ca/Al ratio, due to the effective refinement and redistribution of Al-Ca phases resulting from FSP. However, strain hardening ability and TYS of the AXM541 alloy could be further improved if the Mn/Al ratio could be tailored, as Al-Mn particles do not break down during FSP.
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.
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...
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.
Friction stir processing of magnesium alloys used in automobile and aerospace applications-A Review
A new microstructural modifications technique was developed by the Welding Institute (TWI) of United Kingdom in 1991 is known as Friction stir processing (FSP). The FSP is a newer technique used for refining and homogenizing the grain structure of metal sheet. Friction stir processing is a great potential in the field of super plasticity and metal matrix composites. Many investigators observed that the FSP greatly enhances super plasticity in many Al alloys. It is a is a solid-state processing technique based on friction stir welding technique in which a specially designed rotating cylindrical tool that comprises of a probe and shoulder. The probe of the tool is inserted into the sheet material while rotating and the shoulder moves over the surface of the sheet, and then traverses in the desired direction. The contact between the rotating probe and the sheet material generate heat due to friction which softens the material and the mechanical stirring caused by the probe, the material within the processed zone undergoes intense plastic deformation yielding a dynamically-recrystallized fine grain microstructure. This paper mainly deals with friction stir processing of magnesium alloys with different reinforcement and different input parameters. The study consist of the effect of different reinforcement addition methods that i.e. groove method and drill hole method on tribological and mechanical properties. The result shows that the addition of reinforcements improves the ultimate tensile strength, strain rate and wear resistance.
Friction stir processing of cast magnesium alloys
2007
This thesis investigates the feasibility and benefits of using friction stir processing as a thermo-mechanical microstructural modification tool for local property enhancement or casting repair of magnesium alloys, specifically high strength EV31A and WE43. Castings often have usage limitations due to the inherent microstructural inhomogeneity from solidification; in addition magnesium cast alloys generally suffer from poor ductility and relatively low strength, yet the low density of magnesium is very attractive for weight critical applications. Friction stir processing (FSP) is a proven tool for enhancement of aluminum alloys, imparting a fine-grained, homogeneous microstructure. The alloys in this study are designed for elevated temperature service in the aerospace and high performance automotive industries and are suitable in applications were lightweight and exceptional strength are desired. WE43 has excellent temperature resistance up to 300°C, and EV31A is a more industry cost-effective alternative to WE43 and has excellent strength retention up to 200°C. Results from the present work showed that both alloys are easily adapted to the use of FSP, and significant strength and ductility gains were achieved in both alloys over their respective as-cast peak strengthened states. v ACKNOWLEDGMENTS I thank first and foremost my advisor; Dr. Rajiv Mishra, for his patience, guidance and support throughout my undergraduate and graduate studies. Dr. Mishra's dedication to the group and his students has demonstrated that kindness fosters diligence. His generosity and mentorship have made my stay at UMR not only possible in many ways, but also enjoyable.
Friction stir processing of magnesium alloys used in automobile and aerospace applications
A new microstructural modifications technique was developed by the Welding Institute (TWI) of United Kingdom in 1991 is known as friction stir processing (FSP). The FSP is a newer technique used for refining and homogenizing the grain structure of metal sheet. Friction stir processing is a great potential in the field of super-plasticity and metal matrix composites. Many investigators observed that the FSP greatly enhances super plasticity in many Al alloys. It is a solid-state processing technique based on friction stir welding technique in which a specially designed rotating cylindrical tool that comprises of a probe and shoulder. The probe of the tool is inserted into the sheet material while rotating and the shoulder moves over the surface of the sheet, and then traverses in the desired direction. The contact between the rotating probe and the sheet material generate heat due to friction which softens the material and the mechanical stirring caused by the probe, the material within the processed zone undergoes intense plastic deformation yielding a dynamically-recrystallized fine grain microstructure. This paper mainly deals with friction stir processing of magnesium alloys with different reinforcement and different input parameters. The study consist of the effect of different reinforcement addition methods that i.e. groove method and drill hole method on tribological and mechanical properties. The result shows that the addition of reinforcements improves the ultimate tensile strength, strain rate and wear resistance.