Heat Treatment and Friction Stir Processing Effects on Mechanical Properties and Microstructural Evolution of Sc Inoculated Al-Zn-Mg Alloys (original) (raw)
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-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.
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.
Friction stir processing of 7075 Al alloy and subsequent aging treatment
Transactions of Nonferrous Metals Society of China
The effect of temperatures and time of post-process aging on the microstructure, mechanical properties and wear behavior of friction stir processed 7075 Al alloy was investigated, using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers microhardness tester. The results indicate that homogeneous, equiaxed and fine recrystallized microstructure is obtained with the grain size of 4−5 μm. The hardness value increases up to 30% and 80% in the stir zone and the base material, respectively. Based on the TEM observations, it is concluded that the improved properties following the duplex friction stir−aging process can be attributed to the very fine precipitates. Comparing the single and double aging conditions, the hardness of single aging sample is higher than that of double aging one which can be attributed to the high fraction of very fine spheroidal precipitate in single aging sample. The wear rate is reduced by the aging of Al alloy and a more decrease is achieved after the aging of FSPed sample.
Microstructural modification of as-cast Al-Si-Mg alloy by friction stir processing
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2006
Friction stir processing (FSP) has been applied to cast aluminum alloy A356 plates to enhance the mechanical properties through microstructural refinement and homogenization. The effect of tool geometry and FSP parameters on resultant microstructure and mechanical properties was investigated. The FSP broke up and dispersed the coarse acicular Si particles creating a uniform distribution of Si particles in the aluminum matrix with significant microstructural refinement. Further, FSP healed the casting porosity. These microstructural changes led to a significant improvement in both strength and ductility. Higher tool rotation rate was the most effective parameter to refine coarse Si particles, heal the casting porosity, and consequently increase strength. The effect of tool geometry was complicated and no systematic trend was observed. For a standard pin design, maximum strength was achieved at a tool rotation rate of 900 rpm and traverse speed of 203 mm/min. Post-FSP aging increased strength for materials processed at higher tool rotation rates of 700 to 1100 rpm, but exerted only a marginal effect on samples prepared at the lower rotation rate of 300 rpm. Two-pass FSP with 100 pct overlapping passes resulted in higher strength for both as-FSP and post-FSP aged conditions.
Engineering Journal, 2020
The effect of post ageing treatment (140 o C for 2h) on the microstructure and mechanical behaviour of FSPed 7075 Al alloy has been studied by Optical microscopy (OM), Field emission scanning electron microscopy (FESEM), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and mechanical properties. Friction stir processing (FSP) is a solid-state surface modification technique to apply for cast aluminium alloys. FSP has a similar metal working principle like FSW (friction stir welding). The alloy has strong age-hardening response with scandium (Sc) inoculated Al-Zn-Mg alloy, on the other hand novelty of FSP only few studies have been carried out to the effect of post ageing treatment on the microstructure, size, morphology and fine dispersion of coherent Al 3 Sc(L1 2) type precipitates or ή-phases and its mechanical properties of friction stir processed 7075 Al alloy. The FSPed enhances grain boundary (GB) formation and increases suitable sites for the precipitation of nucleation in post aged 7075 Al alloy. Themechanical properties have been evaluated such as proof strength (σ 0. 2) of 122. 9 MPa, ultimate tensile strength (σ u) of 256. 4 MPa, ductility (δ) of 8. 6%, Vicker's hardness in stir zone of 101 HV, strain hardening exponent (n) of 1. 82, and heat input during FSPed of 2. 15 kJ/mm, respectively. Keywords-Al 3 Sc and ή precipitates, FSP, mechanical properties, post aged 7075 Al alloy, TEM.
Engineering review, 2015
This paper presents the influence of friction stir welding (FSW) on the microstructure, mechanical and corrosion behavior of precipitation hardening Al-Zn-Mg alloy AA7039. The microstructure of weld joints was investigated using an optical microscope. The grains in weld nugget zone (WNZ) and thermo-mechanically affected zone (TMAZ) of weld joints were finer than in the base metal and a reverse trend was observed for heat affected zone (HAZ). Mechanical properties of friction stir weld joints were determined by tensile and micro hardness test. The ultimate tensile strength of weld joints was found approximately equal to the base metal while yield strength and ductility of weld joints were found lower than in the base metal. HAZ of weld joints was more susceptible to corrosion than WNZ, TMAZ and base metal. The HAZ exibits the highest current density followed by the base metal.
Materials
In this study, two successive methods were used to improve the grain structure and the mechanical and physical properties of Al 5052 aluminum alloy. The modifying elements, 0.99 wt.% of titanium (Ti) and 0.2 wt.% of boron (B), were added during the casting process. After solidification, single- and double-pass friction stir processing (FSP) were performed to achieve additional grain refinement and disperse the newly formed phases well. The addition of Ti–B modifiers significantly improved the mechanical and physical properties of the Al 5052 aluminum alloy. Nevertheless, only a 3% improvement in microhardness was achieved. The ultimate strength (US), yield strength (YS), and elastic modulus were investigated. In addition, the electrical conductivity was reduced by 56% compared to the base alloys. The effects of grain refinement on thermal expansion and corrosion rate were studied; the modified alloy with Ti–B in the as-cast state showed lower dimension stability than the samples tre...
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.
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.