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magnesium-alloy
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Structure and corrosion behavior of oxide layer with Zr compounds on AZ31 Mg alloy processed by two-step plasma electrolytic oxidation
, Article Surface and Coatings Technology ; Vol. 238 , 2014 , pp. 75-79 ; ISSN: 02578972 ; Lee, K. M ; Sani, M. A. F ; Yoo, B ; Shin, D. H ; Sharif University of Technology
Abstract
The formation of the oxide layer with Zr compounds on AZ31 Mg alloy processed by two-step plasma electrolytic oxidation (PEO) has been investigated. After the PEO process first in an alkaline phosphate electrolyte and second in an acid electrolyte containing K2ZrF6, the microstructure, chemical composition, and phase composition of the oxide layers were analyzed via SEM, EDS, and XRD, respectively. The electrochemical reaction and the high temperature caused by the plasma discharges in the electrolyte were the main factors leading to the fabrication of an oxide layer containing Zr compounds on AZ31 Mg alloy. The micro-pores were filled with ZrO2 formed during the PEO process. The results of...
Fatigue lifetime of AZ91 magnesium alloy subjected to cyclic thermal and mechanical loadings
, Article Materials and Design ; Vol. 53, issue , 2014 , pp. 639-644 ; ISSN: 02613069 ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
Abstract
In the present paper, thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) or isothermal fatigue (IF) lifetimes of a cast magnesium alloy (the AZ91 alloy) were studied. In addition to a heat treatment process (T6), several rare elements were added to the alloy to improve the material strength in the first step. Then, the cyclic behavior of the AZ91 was investigated. For this objective, strain-controlled tension-compression fatigue tests were carried out. The temperature varied between 50 and 200. °C in the out-of-phase (OP) TMF tests. The constraint factor which was defined as the ratio of the mechanical strain to the thermal strain, was set to 75%, 100% and 125%. For LCF tests,...
Numerical simulations of cyclic behaviors in light alloys under isothermal and thermo-mechanical fatigue loadings
, Article Materials and Design ; Vol. 56 , April , 2014 , pp. 245-253 ; ISSN: 02641275 ; Shamloo, A ; Felfeli, M ; Azadi, M ; Sharif University of Technology
Abstract
In this article, numerical simulations of cyclic behaviors in light alloys are conducted under isothermal and thermo-mechanical fatigue loadings. For this purpose, an aluminum alloy (A356) which is widely used in cylinder heads and a magnesium alloy (AZ91) which can be applicable in cylinder heads are considered to study their stress-strain hysteresis loops. Two plasticity approaches including the Chaboche's hardening model and the Nagode's spring-slider model are applied to simulate cyclic behaviors. To validate obtained results, strain-controlled fatigue tests are performed under low cycle and thermo-mechanical fatigue loadings. Numerical results demonstrate a good agreement with...
Stress–strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings
, Article Mechanics of Time-Dependent Materials ; Vol. 18, issue. 3 , 2014 , p. 475-491 ; Ghodrati, M ; Azadi, M ; Rezvani Rad, M ; Sharif University of Technology
Abstract
This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening...
Improvement of high temperature fatigue lifetime in AZ91 magnesium alloy by heat treatment
, Article Materials Science and Engineering A ; Volume 588 , December , 2013 , Pages 357-365 ; 09215093 (ISSN) ; Azadi, M ; Hossein Farrahi, G ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
In the present paper, an improvement in high temperature fatigue properties of the AZ91 magnesium alloy with rare earth elements has been obtained by a typical heat treatment, denoted by T6. For this objective, out-of-phase thermo-mechanical fatigue, room temperature and high temperature low cycle fatigue tests are performed to compare lifetimes. Several rare earth elements are initially added to the AZ91 alloy during a gravity casting process in permanent molds. Also, the type of the heat treatment is examined. Results of specimens with only the solution (the T4 heat treatment) and the solution with the ageing process (the T6 heat treatment) are compared under isothermal fatigue loadings....
A new energy-based isothermal and thermo-mechanical fatigue lifetime prediction model for aluminium-silicon-magnesium alloy
, Article Fatigue and Fracture of Engineering Materials and Structures ; Volume 36, Issue 12 , 2013 , Pages 1323-1335 ; 8756758X (ISSN) ; Azadi, M ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
In this paper, a new fatigue lifetime prediction model is presented for the aluminium-silicon-magnesium alloy, A356.0. This model is based on the plastic strain energy density per cycle including two correction factors in order to consider the effect of the mean stress and the maximum temperature. The thermal term considers creep and oxidation damages in A356.0 alloy. To calibrate the model, isothermal fatigue and out-of-phase thermo-mechanical fatigue (TMF) tests were conducted on the A356.0 alloy. Results showed an improvement in predicting fatigue lifetimes by the present model in comparison with classical theories and also the plastic strain energy density (without any correction...
Experimental fatigue lifetime of coated and uncoated aluminum alloy under isothermal and thermo-mechanical loadings
, Article Ceramics International ; Volume 39, Issue 8 , December , 2013 , Pages 9099-9107 ; 02728842 (ISSN) ; Farrahi, G. H ; Winter, G ; Eichlseder, W ; Sharif University of Technology
2013
Abstract
This paper presents the fatigue lifetime of an aluminum-silicon-magnesium alloy, widely used in diesel engine cylinder heads, both with and without a thermal barrier coating (TBC) system. The coating system in this study consists of two layers including a 150 μm thick metallic bond coat and a zirconium oxide top coat 350 μm thick. These coating layers were applied on the substrate of A356.0 alloy by air plasma thermal spraying. The isothermal fatigue tests were conducted in low cycle fatigue (LCF) regime at various temperatures. Out-of-phase thermo-mechanical fatigue (OP-TMF) tests were also performed at different maximum temperatures and constraint factors. Experimental results demonstrate...
Mechanisms of joint formation throughout semisolid stir welding of AZ91 magnesium alloy
, Article Transactions of Nonferrous Metals Society of China (English Edition) ; Volume 23, Issue 9 , September , 2013 , Pages 2585-2590 ; 10036326 (ISSN) ; Aashuri, H ; Kokabi, A ; Sharif University of Technology
2013
Abstract
Joining in the semisolid state is considered a possible method to join alloys to each other. The mechanisms taking part in semisolid stir welding of AZ91 alloys were investigated. Two 7.5 mm-thick AZ91 pieces and a 2 mm-thick Mg-25%Zn interlayer piece were placed in a heating plate. After holding for 3 min at a desired temperature, the weld seam was stirred by a rotational tool. The heating plate was travelled on a trolley at a constant speed of 4.6 cm/min. In addition, one sample was welded without interlayer. Evolution of welding as a function of stirring rate, tool shape and temperature was studied throughout this welding process with scanning electron and optical microscopes. Interlayer...
Characterization of newly developed semisolid stir welding method for AZ91 magnesium alloy by using Mg-25%Zn interlayer
, Article Materials Science and Engineering A ; Volume 565 , 2013 , Pages 165-171 ; 09215093 (ISSN) ; Aashuri, H ; Kokabi, A. H ; Sharif University of Technology
2013
Abstract
Semisolid stir joining of AZ91 alloy was investigated by using mechanical stirring and Mg-25. wt%Zn interlayer. A 2. mm-thick interlayer was located between two 7.5. mm-thick AZ91 pieces. Then, they were heated to 530. °C, the semisolid temperature of both base metal and interlayer. A stirrer with a rotational speed of 1600. rpm was introduced into the weld seam. Optical microscopic and scanning electron microscope (SEM) investigation, microhardness test, shear punch test (SPT), and three points bending test were carried out to assess the properties of the joint. Results showed three distinctive zones: stir zone (SZ), compacted zone (CZ), and diffusional-mechanical affected zone (DMAZ). SEM...
Dissimilar Friction Stir Welding between Aluminum Alloy and Magnesium Alloy
, M.Sc. Thesis Sharif University of Technology ; Kokabi, Amir Hossein (Supervisor) ; Seyed Reihani, Morteza (Supervisor)
Abstract
In this project, Dissimilar Friction Stir Welding (FSW) between aluminum alloys (1100-H12 and 5083-O) and Magnesium alloy (AZ31B-O) with 3mm thickness were butt joined. Fusion welding of aluminum/magnesium alloys has failed because of forming much more intermetallic compounds. By using friction stir welded samples, effect of welding parameters such as tool travel speed, tool rotation rate, tool position respect to weld centerline, and sheet position respect to tool direction on mechanical (tensile strength, yield strength and elongation) and microstructural properties of the welds were investigated. After several tests, range of optimum parameters were obtained. In both 1100 and 5083 alloys,...
Characterization of Ceramic Coating Synthesized on Magnesium Alloy Substrate by Plasma Electrolytic Oxidation Process
, M.Sc. Thesis Sharif University of Technology ; Faghihi Sani, Mohammad Ali (Supervisor)
Abstract
Plasma electrolytic oxidation (PEO) is currently recognized as an effective coating method on active metals such as magnesium. In this method, through occurrence of strong electric discharges on the surface of the anode accompanied by electrochemical and thermo-chemical reactions at plasma environment, a relatively thick ceramic coating with complex compounds grows on the metal surface which significantly improves its properties. Regarding the influence of PEO electrical parameters on the morphology and other properties of the coating, the objective of the present study is to prepare a quality ceramic coating on AZ31 magnesium alloy substrate via setting the process parameters, such as...
Micro Arc Oxidation Coating on Magnesium Alloy AZ31 and Study its CorrosionBehavior in Physiological Solution
, M.Sc. Thesis Sharif University of Technology ; Afshar, Abdollah (Supervisor)
Abstract
Magnesium and its alloys have been used as biodegradable implements in recent years. However Magnesium implements may corrode in the body before the natural healing process of the damaged tissue. MAO process was studied in order to reduce primary corrosion of Magnesium alloy in Simulated Body Fluid (SBF). MAO coating was created on AZ31 alloy in a nontoxic alkaline-silicate solution at DC current densities of 5, 10, 15 and 20 mA/cm2 for 30 minutes and the current was in form of 20-10-5 mA/cm2 steps that each were applied for 10 minutes. The maximum corrosion resistance was observed for the mentioned step applied current in a 30g/l Sodium Silicate solution. Furthermore the effects of adding...
Surveying The Biodegradation Behavior, Biocompatibility and Mechanical Properties of Mg-4Zn-xAl-0.2Ca Alloys
, M.Sc. Thesis Sharif University of Technology ; Afshar, Abdollah (Supervisor)
Abstract
Due to their favorable biodegradability, Magnesium and its alloys have always attracted such a lot of research interests for making temporary implants. With the same direction, Mg-4Zn-0.2Ca has recently absorbed lots of research interests, due to its excellent biocompatibility. As the most regarded draw back concerned with this alloy, poor corrosion resistance is frequently discussed. Accordingly, in the present work it has been tried to come over this problem by addition different amount of aluminum, including 1, 3, 5, 7.5, and 10 percent, to this alloy; without causing any negative effect on its biocompatibility, and to present a new alloy composition with modified degradation behavior....
Improvement of Mechanical Properties of a Mg-Zn alloy using the Micro Alloying Elements
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
The development of new wrought magnesium alloys for automotive industry has increased in recent years due to their high potential as structuralmaterials for low density and high strength/weight ratio demands. However, the poor mechanical properties of the magnesium alloys have led tosearch a new kind of magnesium alloys for better strength and ductility.In this research,a new type of magnesium alloy based on Mg-Zn-Si-Ca system has been developed using the permanent gravity casting process. For comparison, an alloy without Siby the same method was also produced. The effects of trace Si addition on the microstructure and mechanical properties in magnesium alloy with composition of...
An Investigation into the Effect Of Severe Plastic Deformation by Equal Channel Angular Extrusion (Ecae) Process on Mechanical and Microstructural Properties of a Mg-Zn Alloy
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
The specific properties of some of magnesium alloys have caused these alloys to be used in medical and industrial applications. Adding new elements and applying severe plastic deformation to these alloys have been considered as a clue for improving their mechanical properties. The aim of this project is to improve the mechanical properties of a magnesium alloy by using new alloying elements and applying the ECAP process.
In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution...
In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution...
Friction stir processing of an aluminum-magnesium alloy with pre-placing elemental titanium powder: In-situ formation of an Al3 Ti-reinforced nanocomposite and materials characterization
,
Article
Materials Characterization
;
Volume 108
,
October
,
2015
,
Pages 102-114
;
10445803 (ISSN)
; Simchi, A
; Kokabi, A. H
; Gerlich, A. P
;
Sharif University of Technology
Elsevier Inc
2015
Abstract
A fine-grained Al-Mg/Al3 Ti nanocomposite was fabricated by friction stir processing (FSP) of an aluminum-magnesium (AA5052) alloy with pre-placed titanium powder in the stirred zone. Microstructural evolutions and formation of intermetallic phases were analyzed by optical and electron microscopic techniques across the thickness section of the processed sheets. The microstructure of the nanocomposite consisted of a fine-grained aluminum matrix (1.5 μm), un-reacted titanium particles (<40 μm) and reinforcement particles of Al3 Ti (<100 nm) and Mg2 Si (<100 nm). Detailed microstructural analysis indicated solid-state interfacial reactions between the aluminum...
A processing map for hot deformation of an ultrafine-grained aluminum-magnesium-silicon alloy prepared by mechanical milling and hot extrusion
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 46, Issue 12 , December , 2015 , pp 5900–5908 ; 10735623 (ISSN) ; Rahbar Niazi, M ; Simchi, A ; Sharif University of Technology
Springer Boston
2015
Abstract
Uniaxial compression test at different temperatures [573 K to 723 K (300 °C to 450 °C)] and strain rates (0.01 to 1 s−1) was employed to study the hot deformation behavior of an ultrafine-grained (UFG) Al6063 alloy prepared by the powder metallurgy route. The UFG alloy with an average grain size of ~0.3 µm was prepared by mechanical milling of a gas-atomized aluminum alloy powder for 20 hours followed by hot powder extrusion at 723 K (450 °C). To elaborate the effect of grain size, the aluminum alloy powder was extruded without mechanical milling to attain a coarse-grained (CG) structure with an average grain size of about 2.2 µm. By employing the dynamic materials model, processing maps for...
Effects of stored strain energy on restoration mechanisms and texture components in an aluminum-magnesium alloy prepared by friction stir processing
, Article Materials Science and Engineering A ; Volume 642 , August , 2015 , Pages 204-214 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Gerlich, A. P ; Nosko, M ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Plates of AA5052 (Al-Mg) alloy in both annealed (solution-treated) and wrought (rolled) temper conditions were subjected to friction stir processing (FSP) at various w/. v pitch ratios from 4 to 28. rev.min/mm. The role of stored strain energy on the evolution of restoration mechanisms and crystallographic texture components were assessed in terms of microstructural features evaluated using electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) analysis. The results revealed that FSP significantly refined the grain structure and changed the crystallographic micro-texture components. The grain size of the annealed and wrought alloy was reduced from 49.4 and 9.7....
Effects of nanometric inclusions on the microstructural characteristics and strengthening of a friction-stir processed aluminum-magnesium alloy
, Article Materials Science and Engineering A ; Volume 642 , August , 2015 , Pages 215-229 ; 09215093 (ISSN) ; Simchi, A ; Kokabi, A. H ; Švec, P ; Simančík, F ; Gerlich, A. P ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
An aluminum-magnesium alloy was friction-stir processed in the presence of TiO2 nanoparticles which were pre-placed in a groove on the surface to produce a composite. Field emission-scanning and transmission electron microscopy studies show that solid state chemical reactions occur between the Al-Mg matrix and the ceramic particles upon the severe plastic deformation process. The microstructure of the aluminum alloy consists of a coarse grain structure, large complex (Fe,Mn,Cr)3 SiAl12 particles, and small Mg2 Si precipitates. After friction stir processing, a deformed grain structure containing rod-like Al-Fe-Mn-Si precipitates is attained, along...
Friction stir welding joint of dissimilar materials between AZ31B magnesium and 6061 aluminum alloys: Microstructure studies and mechanical characterizations
, Article Materials Characterization ; Volume 101 , March , 2015 , Pages 189-207 ; 10445803 (ISSN) ; Behnamian, Y ; Mostafaei, A ; Izadi, H ; Saeid, T ; Kokabi, A. H ; Gerlich, A. P ; Sharif University of Technology
Elsevier Inc
2015
Abstract
Friction stir welding is an efficient manufacturing method for joining dissimilar alloys, which can dramatically reduce grain sizes and offer high mechanical joint efficiency. Lap FSW joints between dissimilar AZ31B and Al 6061 alloy sheets were made at various tool rotation and travel speeds. Rotation and travel speeds varied between 560-1400 r/min and 16-40 mm/min respectively, where the ratio between these parameters was such that nearly constant pitch distances were applied during welding. X-ray diffraction pattern (XRD), optical microscopy images (OM), electron probe microanalysis (EPMA) and scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS)...