Browsing by Author "Ghobadlou, Ali Hosseinzadeh"

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Effect of friction stir processing on the fatigue performance of AZ31 magnesium alloy
(Wiley, 2023-05) Yapıcı, Güney Güven; Sajadifar, S. V.; Ghobadlou, Ali Hosseinzadeh; Wegener, T.; Sobrero, C.; Engelhardt, A.; Niendorf, T.; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh
Herein, the cyclic mechanical behavior of AZ31 magnesium alloy after multipass friction stir processing (FSP) is investigated up to the very high-cycle fatigue (VHCF) regime. The grain refinement and texture evolution after processing are evaluated to enhance the understanding of the fatigue response. Although ultimate tensile strength and ductility of the friction stir processed AZ31 increase up to about 320 MPa and 25%, respectively, the fatigue performance deteriorates in comparison with that of the as-received condition due to the low yield strength and texture evolution after processing. Furthermore, analysis of fracture surfaces of the samples after cyclic loading reveals that the as-received AZ31 is more prone to brittle fracture with multiple-origin fatigue failure even at low stress amplitudes. On the contrary, the dominant failure mechanisms of the friction stir processed samples are initiation and propagation of cracks originating from the surface, porosities, and grain size inhomogeneity. Nevertheless, the capability of FSP for providing superior crack initiation resistance in the VHCF regime is demonstrated as a significant contribution. Based on a detailed study of prevalent microstructural features, processing–property–damage relationships are established indicating the major effect of FSP on the final performance of the AZ31 magnesium alloy.
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Effect of layer architecture on the mechanical behavior of accumulative roll bonded interstitial free steel/aluminum composites
(Elsevier, 2021-06-22) Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh
Multi-layered interstitial free (IF) steel/aluminum (Al) composites were fabricated by the accumulative roll bonding (ARB) method. Two types of IF steel/Al6061 dissimilar layered metal composites (LMC) with varied stacking of aluminum layers were processed to examine the effect of the layer architecture. Microhardness and uniaxial tensile experiments were applied to analyze the surface and bulk monotonic mechanical properties. Besides, the cyclic mechanical response of the processed materials was investigated via high cycle fatigue (HCF) tests with positive mean stress. Microstructure and mechanical characteristics of composites with various layer architectures were analyzed up to five ARB passes. It is revealed that the monotonic and cyclic performances of all LMCs are significantly enhanced as compared to the base alloy with an aluminum layered structure. Moreover, composites with aluminum as the outer layer exhibited the highest fatigue life, due to crack branching at the interface region during propagation from the softer to the harder layer. Fracture morphology analysis of composites demonstrated that in addition to the significant impact of surface cracks on the outer layers, propagation of cracks initiating from the interface layers led to failure under cyclic loading.
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Evaluating the mechanical behavior of ARB processed aluminum composites using shear punch testing
(Trans Tech Publications Ltd, 2020) Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh; Mısırlı, Mustafa; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh; Mısırlı, Mustafa
Multi-layered metal composites have received considerable attention due to their improved mechanical and physical properties. In this study, Al6061/Al2024 composite was processed by accumulative roll bonding (ARB) as a severe plastic deformation technique. Mechanical properties of processed material were evaluated using the uniaxial tensile test and shear punch test method (SPT). The correlation between the results of the tension experiments and shear strengths was calculated. Experimental results demonstrated that the shear strength enhanced with increased number of ARB passes. However, the elongation under shear manifested a reduction when the number of ARB passes increased. Inspection of the results of tensile tests and SPT revealed that they follow a similar trend for both strength and ductility. Therefore, it can be asserted that the shear punch test represents a useful and complementary tool in the mechanical analysis of the ARB sample.
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High temperature characteristics of Al2024/SiC metal matrix composite fabricated by friction stir processing
(Elsevier, 2018-07-25) Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh
In the present study, friction stir processing (FSP) is used for the synthesis of an aluminum metal matrix composite (MMC) reinforced by SiC particles. MMC specimens with reinforced microstructures exhibited significant improvement in hardness (near 50%). Isothermal uniaxial tensile tests were employed for the as-received, friction stir processed and composite microstructures at ambient and high temperatures under strain rates ranging from 10−2 to 10−4 s−1 to investigate the effect of deformation rate on the mechanical behavior. At ambient temperature, notable improvement of the yield strength was observed reaching about 240% of the as-received samples while the ductility was reduced near to 4%. Elevated temperature flow curves were perceptibly sensitive to strain rate, especially for FSPed and MMC samples. Fracture surface observations hinted at the distribution of second phase particles along with possible damage mechanisms.
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High temperature mechanical characteristics of friction stir processed light alloys
(2018-08) Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Bundur, Zeynep Başaran; Oral, A.; Department of Mechanical Engineering; Ghobadlou, Ali Hosseinzadeh
Friction stir processing (FSP) is a recently developed process for surface modification of light alloys that has expanded into applications other than microstructure refinement by the concept of fabricating metal matrix composites (MMCs). FSP as a severe plastic deformation method also enables the manufacturing of high strength materials. Although considerable research has been done to observe the microhardness and corrosion resistance of MMCs and FSPed alloys, rather less attention has been paid to the high temperature mechanical properties and fracture mechanisms of aforementioned materials. This study investigates fabrication of aluminum and magnesium MMCs via FSP and tracks the ambient and high temperature mechanical behavior of processed materials. In order to understand the effect of FSP parameters on the tensile behavior, experimental design methods were utilized. The microstructure evolution and distribution of dispersed particles were observed. It was shown that embedding SiC reinforcements improved the microhardness of FSPed samples up to 50% and 80% relative to the as-received Al2024 and AZ31 conditions. Ambient temperature tensile tests were performed and the results revealed that the yield strength of Al2024 samples improved about 2.5 folds, in relation with the refined microstructure after FSP with the expense of decreasing ductility to about 4%. While FSP decreased the yield strength of AZ31 to 80 MPa along with increasing ductility up to 26%. Therefore, formability of AZ31 sharply increased at room temperature. High temperature tensile tests were conducted at 300˚C under strain rates of 0.01 s-1, 0.001 s-1, 0.0001 s-1 and strain rate sensitivity (m) of both Al2024 and AZ31 were determined for all conditions. The results exhibited that m value of Al2024 increased up to 0.16 for FSPed sample while m value of AZ31/SiC MMC was stable at 0.21 for all interval strain levels. Fracture surface analysis after high temperature loading revealed that the mechanism at high strain rate is dominated by intergranular fracture for fine grained FSPed and MMC samples of Al2024, while the as-received sample is generally fractured by coalescence of microvoids even under high strain rate. On the other hand, the ductile fracture of fine grained FSPed samples represented by equiaxed and relatively deep micro voids were observed for AZ31, whereas the annealed and MMC samples revealed a relatively brittle fracture.
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Influence of warm rolling and aging on the microstructural evolution and mechanical behavior of AZ31 magnesium alloy
(American Institute of Physics Inc., 2019) Mısırlı, Mustafa; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Mısırlı, Mustafa; Ghobadlou, Ali Hosseinzadeh
The microstructural evolution and tensile properties of AZ31 after warm rolling and different aging methods and conditions were investigated. The warm rolling was conducted on the as-received AZ31 after homogenization at 400°C for 3h. The rolled slabs were artificially aged at different temperature of 120°C, 180°C and for various durations. As an alternative approach, stress aging was applied on the samples. The results of tensile tests illustrated that the ultimate tensile strength of the as- received AZ31 after 24h aging at 120°C increased up to 300 MPa with the expense of 5% reduction in elongation. While the ductility of the sample aged at 180°C and 48h increased to 14% with the UTS of 285MPa. Also, the stress aging at 120 °C for only 1h increased the yield strength of as-received sample to over 240 MPa. This points to almost 50% increase in strength thermo-mechanical processing. Microstructural observations revealed that the grain growth firstly decreased the strength of rolled samples while improving the ductility. This is followed by the nucleation of recrystallized grains during ageing enhanced the strength with decent ductility as compared to the rolled samples.
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Low-cycle fatigue behavior of friction stir-welded copper joints
(Springer, 2021-11) Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh; Salahi, Salar; Radi, Amin; Sajadifar, Seyed Vahid
Investigation of the fatigue response of friction stir-welded (FSWed) joints is especially important in the design and manufacturing of components with exposure to cyclic loading. In this study, cyclic response of FSWed pure copper joints is investigated in the low-cycle fatigue regime. Microstructural characterizations revealed that FSW introduced a severely deformed microstructure in the nugget zone (NZ). Fatigue response was determined at a strain ratio of 0.1 by varying the total strain amplitude from 0.1 to 0.6%. Cyclic softening was observed for the low strain amplitude of 0.1%, whereas hardening was detected at higher strain amplitudes. The hysteresis loops demonstrated symmetricity along with noticeable linear behavior after the reversals. Typical fractures occurred in the heat affected zone (HAZ) rather than the NZ or the base metal due to grain coarsening of the HAZ. Improved cyclic properties of the NZ along with stable behavior up to 1000 cycles at a total strain amplitude of 0.3% were attributed to its fine and homogeneous microstructure. Moreover, fracture surface analysis demonstrated a ductile behavior represented by dimples in the sample strained at 0.1% in contrast with a brittle fracture surface of the sample fatigued at 0.5% strain amplitude.
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On the mechanical behavior of accumulative roll bonded lightweight composite
(IOP Publishing, 2019-09) Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Aljashaami, Dhyai Hassan Jawad; Ghobadlou, Ali Hosseinzadeh
Multi-layered composites have received great interest due to their enhanced mechanical and physical properties. In this study, Al6061/Al2024 composites were processed by accumulative roll bonding as a severe plastic deformation technique. The processed structure after four cycles contained alternating layers of both aluminum compositions. For outlining the mechanical behavior, uniaxial deformation experiments in the monotonic and cyclic regime were performed. With increased number of processing cycles, decent progress in hardness levels was exhibited with varying degrees among constituent alloys. Accordingly, improvement levels of up to 1.5 and 2 times were recorded for Al2024 and Al6061 layers, respectively. The tensile strength of the bi-metallic composite reached over 320 MPa after two cycles, coinciding with more than two-fold of the weaker base composition. Fatigue strength was also improved, especially at the low cycle regime. Microstructural observations revealed the level of refinement down to sub-micron scale along with possible fracture mechanisms under tensile straining.
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Severe plastic deformation as a processing tool for strengthening of additive manufactured alloys
(Elsevier, 2021-08) Ghobadlou, Ali Hosseinzadeh; Radi, Amin; Richter, J.; Wegener, T.; Sajadifar, S. V.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Ghobadlou, Ali Hosseinzadeh; Radi, Amin
For the first time, the novel combination of multi-pass equal channel angular extrusion/pressing (ECAE/P) and selective laser melting (SLM) was investigated. Herein, four passes of ECAP via route Bc at 150 °C were applied as a severe plastic deformation (SPD) technique on the SLM as-built AlSi12 to promote superior mechanical properties. The microstructure and mechanical behavior of AlSi12 fabricated by SLM were studied before and after ECAP, applying several mechanical and microstructural characterization techniques. Results of the tensile experiments revealed that the yield point, the ultimate strength, and the ductility of the as-built sample were improved by 56%, 11%, and 55% after 4 passes of ECAP, respectively. This enhancement is attributed to the effective grain refinement and the persisting silicon phase network after SPD as evidenced by electron backscatter diffraction and elemental mapping results. Moreover, micro-computed tomography analysis disclosed that ECAP considerably reduces the remnant porosity of the post-treated SLM AlSi12 samples eventually further affecting the strength of the ultra-fine grained AlSi12 in a positive way. Findings presented herein indicate that it is viable to utilize ECAP as a post-AM processing tool for mechanical property improvement of laser powder bed fused microstructures with the virtue of enhanced densification. Even if geometrical restrictions exist in ECAP, results obtained herein are transferrable to other SPD techniques with suitable processing windows, which would pave the way to advanced properties of adequately post-treated conditions.
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Solid state routes for composite materials production
(Elsevier, 2021) Heidarzadeh, A.; Radi, Amin; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Brabazon, D.; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Ghobadlou, Ali Hosseinzadeh
Solid-state methods are frequently used to fabricate metal matrix composites, which usually lead to superior mechanical properties compared to liquid state routes. In this article, different solid-state routes including powder metallurgy, diffusion bonding, forging, accumulative roll bonding, extrusion, explosive bonding, and friction stir processing are elucidated for the production of metal matrix composites. For this aim, the different stages and capabilities of each of these processes are presented. This is an area in which both research and commercial activity is expected to grow significantly in the coming years.