Sharif Digital Repository

Surfaces of cast 1100 aluminum were treated by multi-pass friction stir processing (MP-FSP), which is a solid-state microstructural modification technique using frictional heat and stirring action. An improvement in the mechanical properties was accomplished due to the microstructural modification and reduction of porosities. The yield strengths of the MP-FSPed specimens were significantly increased to about 1.4 times versus that of the base metal. The elongation of MP-FSP sample is about 30% higher than that of the base metal. Also the ultimate tensile strength and hardness of MP-FSPed specimens are improved. Moreover the effect of tool rotation rate and tool travel speed on the mechanical... 

The unique properties of NiTi alloy, such as its shape memory effect, super-elasticity and biocompatibility, make it ideal material for various applications such as aerospace, micro-electronics and medical device. In order to meet the requirement of increasing applications, great attention has been given to joining of this material to itself and to other materials during past few years. Laser welding has been known as a suitable joining technique for NiTi shape memory alloy. Hence, in this work, a comparative study on laser welding of NiTi wire to itself and to AISI 304 austenitic stainless steel wire has been made. Microstructures, mechanical properties and fracture morphologies of the... 

In-situ aluminum matrix composites were fabricated by 1-3 passes of friction stir process (FSP) using iron (Fe) particles with initial size of 10. μm. Although the initial reinforcing particles were relatively large in size and also agglomerated particles were formed in the obtained composites, all of the processed specimens fractured from the base metal during transverse tensile test. Longitudinal tensile tests revealed that the ultimate tensile strength (UTS) of the composites was up to 43% higher than that of the base metal; however, the strain to fracture of the composites reached to about 0.2. Al-Fe intermetallic compounds (IMCs) formed at the interface of the aluminum matrix and Fe... 

This paper presents the effect of martensite volume fraction (VM) on mechanical properties of AISI 4340 steel with ferrite-bainite-martensite microstructures. The steel bars were austenitized at 900°C for 1h followed by intercritical annealing at 740°C for 100min and quenching into a salt bath with temperature of 300°C and holding at different times to obtain triple phase (TP) microstructures with 34vol.% fraction ferrite and various martensite (or bainite) contents. Presence of three phases in adjacent to each other was confirmed by metallographic analysis and TEM studies. TEM observation also indicates higher density of dislocations within ferrite near martensite colonies compared to that... 

In this research, Araldite 2011 has been reinforced using different weight fractions of Reduced Graphene Oxide (RGO). Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses were conducted and it has been shown that introduction of the RGO greatly changes the film morphology of the neat adhesive. Uni-axial tests were carried out to obtain the mechanical characteristics of the adhesive-RGO composites. It has been observed that introducing 0.5 wt% RGO enhances the ultimate tensile strength of the composites by 30%. In addition, single lap joints using neat adhesive and adhesive-RGO composites were fabricated to... 

Welded sheets with different thicknesses are one of the interesting types of tailor-welded blanks (TWBs) that are widely used in metal-forming industries. In the present work, the formability behavior of different 1100-aluminum TWBs was studied. In this regard, the TWBs were made with different thickness ratios by using friction stir welding (FSW) at different welding rotational speeds (ω). The thickness ratios of 1.0, 1.3, and 1.7 were investigated where the thinner sheets had 1.5 mm thick for all conditions; i.e., the volume of welded material increased when the thickness ratio increased. Macrostructural observations, mechanical investigations, and sheet-forming limit tests were... 

MADI is new engineering material with very desirable properties such as higher strength at the same hardness compared to regular ductile iron, significantly better fatigue performance than regular ductile iron or austempered ductile iron, better machinability than regular austempered ductile iron and similar to as cast ductile iron. In this study,fatigue properties of Machinable Austempering Ductile was investigated using rotary -bend fatigue testing device. Chemical composition of sample was selected on the base of previous work which results in good mechanical properties and low hardness after austempering process. The results of this study,indicates that for an austempered ductile iron... 

In this study, Porous NiTi shape memory alloy has been produced by mechanical alloying of the elemental Ni and Ti powders. The compacting process was done at two temperatures (warm and cold press) and then sintering at 980 and 1050°C was performed on the specimens. Microstructure and mechanical prop-erties of the samples were investigated by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. Moreover, shear punch test (SPT) employed to investigate the effect of compaction pressure and sintering temperature on the mechanical properties of the fabricated samples. It was revealed that warm compaction/sintering resulted in 15% yield stress improvement and 20% ultimate... 

Aluminium matrix composites reinforced with submicrometre and nanosize Al 2O 3 particles were successfully manufactured in the form of sheets through eight cycles of accumulative roll bonding process. The mechanical properties of the produced composite are compared with accumulative roll bonded commercially pure aluminium. It is shown that only 1 vol.-% of submicrometre or nanosize alumina particles as reinforcement in the structure can significantly improve the yield and ultimate tensile strengths. Scanning electron microscopy revealed that particles have a random and uniform distribution in the matrix especially in the less volume fraction of alumina particles, and strong mechanical... 

A high-quality butt joint of aluminum to copper (Al/Cu) can rarely be achieved by conventional fusion and solid-state welding processes. In this research, the appropriateness of friction stir welding (FSW) for making high-quality Al/Cu welds was studied. A sound Al/Cu butt joint was achieved with relatively high strength in uni-axial tensile tests. Mechanical properties and microstructure of the sound friction stir welds were examined. The ultimate tensile strength of the joints reached about 75 percent of the aluminum base metal, with the fracture occurring at aluminum side. The metallurgical study of the welds before and after their failure in tensile tests showed that the heat affected... 

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.... 

The present study investigated the effects of initial Hydrogen level and cooling rate on ultimate tensile strength of commercial Al-A319 alloys. Three hydrogen levels (0.01, 0.2, and 0.41 mL/100 grams of melt) and five cooling rate were studied. Total of 45 tensile test bars was prepared (three hydrogen levels × five cooling rate × three repeats). The UTS of the samples was determined though uniaxial tension tests. Furthermore, the microstructures of the samples were studied by standard metallographic technique and image analysis software. Finally the relationship between UTS and microstructurai features—SDAS and fraction of porosity (Fp%)—of the alloys was investigated.Results of tensile... 

In this study, evolution of intermetallic layer of the cold roll bonded bilayer of Aluminum-Steel sheets, during severe plastic deformation (SPD) followed by annealing has been investigated. The effect of such evolution on mechanical properties has been discussed. For this purpose, Constrained Groove Pressing (CGP) was used as a SPD process. Field emission scanning electron microscope equipped with energy dispersive spectroscopy and optical microscopy were used for examination of intermetallic compounds morphology and composition. Meanwhile, tensile properties of the bilayer sheets were evaluated. According to microstructural observations, continuous intermetallic layer was formed during... 

The friction stir welding of AA2024-T6 to AA6061-T6 plates with a 4 mm thickness has been studied at constant traverse and rotational speeds of 1000 rpm and 100 mm/min, respectively. The position of alloys and the effects of precipitation hardening heat treatment in retreating and advancing side in the friction stir welding were analyzed. The tool with taper threaded pin was used for welding. Macro and microstructural analysis were investigated by using Optical and Field Emission-Scanning Electron Microscopes (FE-SEM) to check out the welded joints. Micro-hardness and Tensile tests were also done to study mechanical attributes of the joints. Microstructural analysis revealed some grain... 

This paper presents the creep behavior of various FRP (GFRP, CFRP, and hybrid) bars in order to investigate the effects of different parameters, including the applied stress levels, bar diameter, and the type of fiber and resin in the creep behavior of FRP bars. The creep strains versus time curves were experimentally obtained for 83 days. Moreover, a statistical study, including analysis of variance (ANOVA) and linear Bayesian regression was conducted to investigate the contribution of the studied parameters. The results showed that in GFRP bars the ratio of ultimate creep strain to the initial elastic strain decreased when the applied stresses on the bars exceeded 30% of their ultimate... 

In this study a severe plastic deformation method called constrained groove pressing (CGP) is used for imposing a high magnitude of strain into the low carbon steel sheets. Microstructural changes during process are examined by X-ray diffraction and optical observations. The grain size evolution during severe plastic deformation is studied using Williamson-Hall analysis on XRD pattern of the deformed samples. In effective strain of 4.64, ferrite grains with a submicron size of 200-300nm are achieved. The results show that constrained groove pressing can effectively refine the coarse-grained structure to an ultra fine grain range. Mechanical properties changes due to microstructure evolution... 

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection.... 

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn-Ag-Cu/CeO 2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO 2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and... 

Friction stir processing (FSP) can be used to improve surface composites. In this study, a modified method of FSP called friction stir vibration processing (FSVP) was applied to develop a surface composite on AZ91 magnesium alloy. In this technique, the workpiece is vibrated normal to the processing direction. The results illustrated that compared with the FSP method, the FSVP caused a better homogeneous distribution of SiC particles in the microstructure. The results also showed that matrix grains of friction stir vibration processed (FSV-processed) samples ((26.43 ± 2.00) µm) were finer than those of friction stir processed (FS-processed) specimens ((39.43 ± 2.00) µm). The results...