Sharif Digital Repository

In this research, Al 3003/Zn sheets with different Zn layer thicknesses (as filler layer) have been soldered to the monolithic Al 3003 sheets. The effects of Zn layer thickness and soldering time at the peak temperature on the joint strength of soldered Al 3003 alloy by pure Zn filler (as the soldering sheets) have been evaluated. Furthermore, microstructure and fracture mechanism of Al 3003/Zn/Al 3003 soldered joints have been studied. The results indicate that by decreasing the Zn layer thickness and increasing the holding time at the peak temperature of soldering, the joint strength improves. Additionally, microscope examinations show that the fracture type of the Al 3003/Zn/Al 3003... 

Al-3003/Zn bi-layer soldering sheets were produced using roll bonding process at different reductions in both cold and hot conditions. The bond strengths of the bi-layer sheets were measured by peel test before and after supplemental annealing treatment. The peeled surfaces were examined using optical and scanning electron microscopy. The results indicate that by increasing the reduction in thickness during rolling and/or the annealing treatment the bond strength improves. Additionally, the decrease of initial sheet thickness and increase of rolling temperature can effectively improve the bond strength. Microscopic examinations show that the fracture type of Al-3003/Zn sheets is... 

Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by... 

This paper aims at understanding the role of liquation and solidification phenomena on the tensile properties of arc welded cast AZ91 magnesium alloy. Owing to its refined microstructure, the fusion zone exhibited improved ductility/strength compared to the base metal. It is demonstrated that the partially melted zone (PMZ) which is characterised by constitutional liquation of eutectic β-Mg17Al12 phase is the weakest link in the weldment. The reduced strength and ductility associated with the liquation phenomena are due to the increased volume fraction and thickness of the eutectic β-Mg17Al12 in the PMZ as well as the formation of liquation micro-cracks in a network of brittle intermetallic... 

Semisolid casting and forming have attracted growing attention of both research and industry. A suitable semisolid microstructure consists of globular grains in a matrix of lower melting point phase and may be produced by various methods, including the cooling slope technique. The combined effect of cooling slope angle and mould vibration on the semisolid microstructures of AI7075 is reported. The results indicate that mould vibration decreases average grain size significantly and that the effect increases with increasing size of primary crystals entering the mould through the cooling slope. Mould vibration was also found to improve the shape factor of alloy grains after appropriate... 

In this work, friction stir soldering (FSS) as a new approach for fabrication of copper/copper lap joints was introduced. This process is principally based on the friction stir processing (FSP) that can be performed using FSP tools with and without pin on the top sheet. In the present study, Pb-Sn foil was used as a solder which would be melted and then extruded in the area between the copper sheets during FSS process. This process was carried out using tools with and without pin at various rotation speeds of 1200, 1400, and 1600 rpm and traverse speed of 32 mm/min. Also, the same joint was fabricated using furnace soldering to compare the mechanical properties obtained with FSS and furnace... 

In this study, Al-5083 and St-12 alloy sheets were friction stir lap welded at different travel (7- 23 cm min -1) and rotation (750-1125 rev min -1) speeds of the welding tool. The welded joints were characterised by various methods including shear tensile and Vickers microhardness tests, optical and scanning electron microscopies and X-ray diffraction analysis. The results showed that the weld zone defects decreased, and the joint strength also improved significantly with the reducing tool travel speed from 23 to 7 cm min -1. The travel speed of 11 cm min -1 was an optimum speed within the travel speeds investigated in this work. Additionally, raising the tool rotation speed enhanced the... 

In the present study, the roll bonding behaviour of Al-3003/Al-4043 and Al-3003/Zn sheets were compared. The bi-layer sheets were produced by a roll bonding process at different reductions in thickness and rolling temperatures. The joint strengths of the sheets were evaluated by peel and bend testing before and after supplemental annealing treatment. The peeled surfaces were examined using a scanning electron microscope. The results indicated that the Al-3003/Al-4043 sheets were bonded with higher joint strength and lower threshold reductions in thickness with respect to the Al-3003/Zn sheets. In contrast to the Al-3003/Zn sheets, significant improvement was observed in the joint strength of... 

Al-5083 and St-12 alloys sheets were friction stir lap welded at various travel and rotation speeds of the welding tool. Microscopic examinations indicate that the joint strength is due to the macroscopic and microscopic mechanical lockings and also atomic diffusion. The reaction zone of the welded joints consists of mixed layers of ultra-fine grains and the intermetallic compounds. The microhardness and nano indentation results prove that the intermetallic phase layer is more brittle in comparison to base metals and ultra-fine grain region. The fracture surfaces are a combination of brittle and ductile fractures. The fracture loads show that the joint strength improves significantly by... 

In this work, the feasibility of friction stir lap welding an aluminium alloy (Al-5083) to the aluminium clad steel sheet was studied. The welded joints were characterised by various methods including shear-tensile test and optical microscopy and scanning electron microscopy. The results indicated that sound and defect free joints were obtained. The fracture loads of the samples reached up to 94% compared with that of the steel base metal. Moreover, the joint strength linearly increased with the decrease in thickness of the aluminium layer roll bonded on the steel sheet. It was also shown that welding rotation and travel speed variation did not considerably impact the fracture loads in the... 

Al-1100/St-12 aluminum clad steel sheets were produced using roll bonding process at different reductions in thickness and with various supplemental annealing treatments. Experiments were conducted by applying the Taguchi method to obtain optimum condition for maximizing the joint strength. The joint strengths of the bi-layer sheets were evaluated by peel test. The Al/Fe intermetallic phases at the joint interface and the peeled surfaces were examined using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) and Vickers microhardness test were performed to characterize the intermetallic compounds. The results indicate that at the optimum condition of 0.50 reduction in... 

The effect of a plasma electrolytic oxidation (PEO) pre-treatment on joining of AA 5052 aluminium alloy and polypropylene by friction stir spot welding (FSSW) is investigated using lap tensile shear tests. Two surface conditions of the AA 5052 alloy are compared, one with a PEO pre-treatment in a silicate-based electrolyte, another without any pre-treatment. The resultant specimens are examined by high resolution scanning electron microscopy, thermogravimetric analysis and attenuated total reflectance-infrared spectroscopy. The PEO treatment generated a thermally-insulating, porous ceramic coating, which has a highly porous, rough surface that is favourable for incorporating polypropylene... 

In this paper we propose a new method for estimating the mixing matrix, A, in the linear model X = AS, for the problem of underdetermined Sparse Component Analysis (SCA). Contrary to most existing algorithms, in the proposed algorithm there may be more than one active source at each instant (i.e. in each column of the source matrix S), and the number of sources is not required to be known in advance. Since in the cases where more than one source is active at each instant, data samples concentrate around multidimensional subspaces, the idea of our method is to first estimate these subspaces and then estimate the mixing matrix from these estimated subspaces. ©2007 IEEE  

The human protein disulfide isomerase (hPDI), is an essential four-domain multifunctional enzyme. As a result of disulfide shuffling in its terminal domains, hPDI exists in two oxidation states with different conformational preferences which are important for substrate binding and functional activities. Here, we address the redox-dependent conformational dynamics of hPDI through molecular dynamics (MD) simulations. Collective domain motions are identified by the principal component analysis of MD trajectories and redox-dependent opening-closing structure variations are highlighted on projected free energy landscapes. Then, important structural features that exhibit considerable differences... 

The current study is allocated to experimental evaluation of the multiphase flow of fine solid particles (FSPs) as well as comprehensive numerical study in an annular space under static, laminar, and turbulent flow conditions with consideration of the inner pipe eccentricity and rotation. The experimental investigation was carried out using an annular pipe flow loop. The numerical modeling and simulation of the multiphase flow in the annular space have been performed using the Euler-Euler approach. The unsteady-state multiphase model based on the kinetic theory of granular flow (KTGF) is developed to investigate the particulate flow characteristics in the annular space. Moreover, Standard...