Microstructural modification of as-cast Al-Si-Mg alloy by friction stir processing (original) (raw)
Related papers
Effect of friction stir processing on the microstructure of cast A356 aluminum
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006
Commercially pure aluminium was subjected to friction stir processing (FSP) to study the microstructure developed and its effects on the mechanical properties. Friction stir processing refined the grain size to 3 m in a single pass from the starting coarse grain size of 84 m. Electron backscattered diffraction (EBSD) results showed occurrence of dynamic recrystallization and also revealed existence of different orientations within the stir zone and across the transition zone. Transmission electron microscopy (TEM) revealed fine grains with well defined boundaries. The arrangement and absorption of dislocation into the sub-grain boundaries, formed by dynamic recovery, was also revealed by TEM. The yield strength of the material was improved by a factor of 2.4 after FSP owing to grain refinement. The most important feature of the friction stir processed material was that even after this significant improvement in strength there was little loss of ductility. The hardness also improved by 34% with the peak hardness being observed towards the advancing side.
In this study, mechanical behaviour and microstructural evolution in friction stir processing (FSP) of casting hypereutectic A390 aluminium alloy have been investigated. The mechanical behaviour of FSP samples was investigated by measuring the strain rate sensitivity using shear punch testing. The room-temperature shear punch tests were conducted at shear strain rates in the range of 10 −4 -10 −1 s −1 . The results indicate that the strain rate sensitivity index increases from about 0.015 to 0.120 for as-cast A390 after third FSP pass and then experiences a further growth in FSP passes. The increase in the grain size and CuAl 2 intermetallic particle size result in a reduction in strain sensitivity index as well as shear strength after third FSP pass.
Scripta Materialia, 2006
As-cast Cu-9Al-4.5Ni-4Fe NiAl bronze alloy (NAB) was subjected to multiple-pass friction stir processing (FSP) with a 50 pct overlap. After FSP, the coarse microstructure of the base metal (BM) was transformed to defect-free material with fine microstructure. While the torchlike patterns in the stir zone (SZ) and the uplifted grains in the transitional zones (TZs) between two passes were observed in the multiple-pass FSP region, no grain coarsening was found in the remnant zone of the previous SZ after subsequent FSP pass. The hardness value of the FSP materials was higher than that of the BM and was homogeneously distributed throughout the entire multiple-pass FSP region. The FSP materials showed greatly improved tensile properties compared to the BM, and the TZs showed similar tensile strength and ductility to the single-pass FSP materials. The BM broke in a mixture mode of brittle cleavage and microvoid coalescence fracture, whereas the FSP and TZ samples failed in the latter fracture mode. The results showed that the multiple-pass overlapping (MPO) FSP was feasible to modify the microstructure of large-sized plate of the NAB.
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.
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.
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.
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.
Microstructure and Properties of Friction Stir Processed Cast Al-Fe Alloy
2011
Among available processing technologies of heat-treatable aluminum alloys such as the 2219 aluminum alloy, the use of both friction stir welding (FSW) as joining technology and electromagnetic forming (EMF) for plastic formation technology have obvious advantages and successful applications. Therefore, significant potential exists for these processing technologies, both of which can be used on the 2219 aluminum alloy, to manufacture large-scale, thin-wall parts in the astronautic industry. The microstructure and mechanical properties of 2219 aluminum alloy under a process which compounded FSW, heat treatment, and EMF were investigated by means of a tensile test as well as via both an optical microscope (OM) and scanning electron microscope (SEM). The results show that the reduction of strength, which was caused during the FSW process, can be recovered effectively. This can be accomplished by a post-welding heat treatment composed of solid solution and aging. However, ductility was still reduced after heat treatment. Under the processing technology composed of FSW, heat treatment, and EMF, the forming limit of the 2219 aluminum alloy decreased distinctly due to the poor ductility of the welding joint. A ribbon pattern was found on the fractured surface of welded 2219 aluminum alloy after EMF treatment, which was formed due to the banded structure caused by the FSW process. Because of the effects of induced eddy current in the EMF process, the material fractured, forming a unique structure which manifested as a molten surface appearance under SEM observation.
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.