Effect of friction stir processing on the microstructure of cast A356 aluminum (original) (raw)
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Microstructural characterisation of friction stir processed aluminium
Materials Science and Technology, 2011
Friction stir processing was carried out on commercially pure aluminium, and a detailed microstructural characterisation was performed by electron backscattered diffraction and transmission electron microscopy. Friction stir processing resulted in significant grain refinement with narrow grain size distribution. The microstructure showed fine and equiaxed grains, with some ultrafine grains being also observed. Electron backscattered diffraction studies showed majority of the boundaries to be high angle, confirming the occurrence of dynamic recrystallisation (DRX). Transmission electron microscopy observations revealed dislocation arrangement into subgrain boundaries, grains having different dislocation densities and in different stages/degrees of recovery. Electron backscattered diffraction analysis also revealed a progressive transformation of sub-grain boundaries into high angle grain boundaries. A multimechanism of dynamic recovery, continuous DRX and discontinuous DRX seems to be operating during the process. The microstructure is not affected by changing the rotation speed from 640 to 800 rev min 21 , except that the grain size was marginally larger for higher rotational speed.
Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructural and mechanical properties of 6082-T6 Aluminum Alloy. A constant rotational speed and three different traverse speeds were used for processing. In this article, the microstructural properties in terms of grain structure and second phase particles distribution, and also the mechanical properties in terms of hardness and tensile strength of the processed zone were addressed with respect to the number of passes and traverse speeds. The parameter combination which resulted in highest ultimate tensile strength was further compared with additional two rotation speeds. FSP caused dynamic recrystallization of the stir zone leading to equiaxed grains with high angle grain boundaries which increased with increasing the number of passes. The accumulated heat accompanying multiple passes resulted in increase in the grain size, dissolution of precipitates and fragmentation of second phase particles. Increasing the traverse speed on the other hand did not affect the grain size, yet reduced the particles size as well as increased the particle area fraction. Hardness and tensile test results of the stir zone were in good agreement where increasing the number of passes caused softening and reduction of the ultimate tensile strength, whereas, increasing the traverse speed increased the strength and hardness. Increasing the tool rotational speed did not have a significant influence on particle mean diameter, ultimate tensile strength and hardness values of the stir zone, whereas, it caused an increase in mean grain size as well as particle area fraction.
12th International Conference on Mining, Petroleum and Metallurgical Engineering, 2014
In this study, a 10 mm thick AA7020 plate is friction stir processed (FSP) to a depth of 6mm using two different tool geometries of threaded and unthreaded pin and different friction stir processing speeds of 20, 40, 60 and 80 mm/min at tool rotation rate of 560rpm. The microstructure is investigated initially using optical microscopy. The mechanical properties of the processed material are characterized using tension testing and hardness testing. The tension test is carried out along the FSP direction and the hardness is measured mainly for the processed zone and compared with the base material. Microstructure investigation showed significant grain refining in the processed zone. In all the conditions studied, the processed zone showed a lower hardness as compared to the base metal. This suggests the dissolution of precipitate particles due to the frictional heat that softens the material. The tensile strength of the FS processed specimens was significantly increased by up to 14% as compared to the base metal. All specimens invariably showed considerable increases in the ductility by up to 75%. The use of the unthreaded pin showed better ductility and strength.
Friction stir processing (FSP) is an emerging surface engineering technology that can eliminate casting defects locally by refining microstructures, thereby improving the mechanical properties of the material. In this study, the influence of the Friction Stir Processing (FSP) on the microstructure and mechanical properties in terms of hardness for commercially available AA6061 Al sheet metals was studied and investigated. Samples were subjected to FSP by varying the number of passes using cylindrical geometry type high speed steel tool fixed in the Vertical milling machine. Micro structural observations were carried out by employing optical microscopy on the modified surfaces. From the microstructural evaluation, it was observed that the grain size of the processed area was around 70% decreased as compared to unprocessed parent metal. This is expected due to grain refinement by the FSP tool in the materials during processing. The hardness results showed that by increasing the number of passes the hardness of the produced composite surfaces increases steadily. It was noted here that the strength of stirred surface area was around 1.75 times higher than the unstirred surface area.
-The high strength Al-Zn-Mg alloys (7xxx series) have some specific properties such as spontaneous ageing nature, high strength-to-weight ratio and effect of Sc addition makes it hard. This alloy is largely used in aircraft and automobile industries. Scandium (Sc) addition in aluminium alloys have great technological advantages to reducing the cast grain sizes and generate large volume fraction of constituent particles (Al 3 Sc) and promoting the precipitation of a more uniform dispersoid distribution. The grain refinement effect and the age-hardening behaviour of Al-Zn-Mg alloys are studied on the basis of Optical microscopy (OM), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and Vicker's hardness measurements. Friction stir processing (FSP) is an emerging surface-engineering solid state technology which locally eliminates casting defects and refines microstructure to enhance specific properties to some considerable depth. During FSP, the severe plastic deformation and thermal exposure of material significantly enhanced microstructural changes. FSP results in significant temperature rise within and around the processed zone. The stir zone (SZ) grains suggest effective strains together with a microstructural evolution that occurs by a combination of plastic deformation and a dynamic recovery or recrystallization. The temperature rise of 450-500 o C has been noted within the SZ for aluminium alloys. Intense plastic deformation and temperature rise results in significant microstructural evolution, therefore, fine recrystallized grains of 10.97±1.45 μm, precipitate dissolution and coarsening, textural changes and micro residual stresses. In general, processed zone is characterized by a recrystallized fine grain with uniformly distributed ή and Al 3 Sc particles. So, FSP enhances mechanical properties many folds as comparison to heat treated aluminium alloys. In this regard, many researchers have proposed energy-based model for the FSW/FSP in their experimental work. Finally, the mechanical properties have been evaluated after FSP and estimated likely to 0.2% proof strength increase to 200.2%, ultimate strength increase to 231.1%, ductility increase to 125.5%, and hardness increase to 17.7% as compared to T 4 condition, respectively.
Microstructural and Mechanical Characterization of Friction Stir Processed 5086 Aluminum Alloy
In the present investigation friction stir processing (FSP) is carried out by single and multipass FSP on a 5086 aluminum alloy to modify microstructure and mechanical properties. The processing is carried out at constant rotation speed of 1025 rpm and at a traverse speed of 30 mm/min. Inhomogeneous microstructural distribution was observed across the processed zone. EBSD analysis has been done to evaluate the microstructure. Overlapping passes is showing same grain size as in single pass FSPed material. Material processed using multi pass FSP at 30 mm/min is showing higher mechanical strength as compared to base material. The bulk material produced due to multipass seems to be good for superplastic forming applications.
Materials Science and Engineering: A, 2006
An improvement in the mechanical properties was accomplished due to the microstructural modification of an aluminum die casting alloy by multi-pass friction stir processing (MP-FSP), which is a solid-state microstructural modification technique using a frictional heat and stirring action. The hardness of the MP-FSP sample is about 20 Hv higher than that of the base metal. The tensile strengths of the MP-FSPed specimens were significantly increased to about 1.7 times versus that of the base metal. This is due not only to the disappearance of the cold flake in the base metal, but also to a structural refinement, such as uniform distribution of Si particles. Thus, the application of the MP-FSP is a very effective method for the mechanical improvement of aluminum die casting alloys.
Friction stir processing and characterisation of A380 cast aluminium alloy
The surfaces of cast A380 aluminium alloy plates were modified by friction stir processing. A milling machine was utilised with a tool rotating at 1400 rev min 21 and traversing at a rate of 16 mm min 21. The 400 mm–2 mm processed layers were obtained on the surfaces of the cast aluminium sheets. It was seen from the optical microscope examinations that the Si particles were homogeneously distributed in the Al matrix. The hardness of the cast aluminium sheets increased from 60 to 90 HB10 after friction stir processing. Samples were subjected to wear tests with 6 mm diameter alumina balls in dry condition. Wear tracks were examined by scanning electron microscope and profilometer. Wear rate of surface modified aluminium sheets were found to be 50% lower than the ones without surface modification.
Acta Metallurgica Sinica (english Letters), 2016
The influence of overlap multi-pass friction stir processing on the microstructure and the mechanical properties, in particular, strength, ductility and hardness of die cast Al-7Si-3Cu aluminum alloy was investigated. It was observed that increase in the number of overlap passes friction stir processing resulted in significant refinement and redistribution of aluminum silicon eutectic phase and elimination of casting porosities. The microstructural refinement by the friction stir processing not only increases the ultimate tensile strength from 121 to 273 MPa, but also increases the ductility as observed by the increase in fracture strain from 1.8% to 10%. Analysis of the fractured surface reveals that the microstructural refinement obtained by friction stir processing plays a vital role in transforming the fracture mode from completely mixed mode to the ductile mode of the fracture with increasing number of passes. The change in the size, shape, morphology and distribution of eutectic silicon particles and elimination of the porosities are the main reasons for the increases in tensile strength and ductility due to friction stir processing.