Effect of ECAP on microstructure and tensile properties of A390 aluminum alloy

The purpose of the present research is to determine the tensile strength and elongation of the A390 alloy processed by ECAP and to reveal the relationship between the microstructure and tensile properties. Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for microstructural analysis of the samples. The results of the mechanical testing showed that the ultimate tensile strength (UTS) increased from 142 MPa for the as-cast sample to 275 MPa for the sample after the third ECAP pass. Increasing the ECAP passes up to 4 led to a remarkable enhancement of elongation compared with the as-cast sample. It was found that the improvement of strength and ductility of A390 alloy with increasing the number of ECAP passes was attributed to the homogenous distribution of particles, reduction of particle size, and elimination of voids especially adjacent to the primary silicon particles. The results of fractography demonstrated that when the number of ECAP passes increased to 4, the uniform round dimples formed and the relatively brittle as-cast sample transformed to a ductile alloy.

Microstructure, mechanical and tribological properties of A390/SiC composite produced by compocasting

Aluminum A390 alloys reinforced with 10 wt.%SiC composite,were produced by the compocasting method.The effects of temperature,time,and stirring speed of this compocasting method on the microstructure,mechanical and tribological properties of composite were investigated.The results indicated that with increasing the rotational speed from 450 to 550 r/min,the distribution of the SiC particles becomes more uniform.A sudden increase in porosity due to gas absorption results in a downtrend of elongation with an increase in stirring speed from 550 to 650 r/min.Furthermore,as the stirring time increases,the amount of agglomerates of primary Si particles is reduced,and a more uniform microstructure of SiC and Si particles is formed.Although the fracture mode is a combination of both brittle and ductile fractures,the main mechanism of the fracture in the compocast sample is ductile.The formation of a protective layer at a high temperature can result in a very low wear rate as compared to a wear test performed at a low temperature.Optimal particle uniformity and mechanical properties were obtained at processing parameters of 610刟C,550 r/min,and 20 min.

Microstructure and mechanical properties of AA6063 aluminum alloy wire fabricated by friction stir back extrusion(FSBE) process

In the present work,the friction stir back extrusion(FSBE)process was used as a novel method for the fabrication of AA6063 aluminum alloy wire.Scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS),tensile and hardness tests were performed.The FSBE via the rotational speed of 475 r/min resulted in fine equiaxed grains,and the mean grain size decreased from 179.0μm to 15.5μm due to the occurrence of dynamic recrystallization(DRX).Heat generated by the FSBE changed the size and volume fraction of the Mg2Si precipitated particles.The minimum particle size and maximum volume fraction obtained in the sample were processed by rotational speeds of 475 and 600 r/min,respectively.The 475-r/min sample had the maximum hardness value due to having the lowest grain size(i.e.,15.5μm)and the presence of many fine Mg2Si precipitates in the aluminum matrix.With increasing rotational speed up to 600 r/min,the hardness decreased,owing to the growth of both grains and precipitates.The FSBE process with a rotational speed of 475 r/min increased the tensile strength(from 150 to 209 MPa)and ductility(from 21.0%to 30.2%)simultaneously.

Retraction notice to"Computational investigation of powder coating of nanoparticles in supersonic and hypersonic impactors"[Particuology 11(2013)273-281]

This article has been retracted:please see Elsevier Policy on Article Withdrawal(https:/www.elsevier.com/about/our-business/policies/articlewithdrawal).This article has been retracted at the request of the Editor.The authors have plagiarized part of a paper by Omid Abouali and Goodarz Ahmadi that had already appeared in Journal of Nanoparticle Research(2005)7:75-88(https:/link.springer.com/article/10.1007/s11051-004-7910-3).

Computational investigation of powder coating of nanoparticles in supersonic and hypersonic impactors

In this study, numerical simulation of flow field in a supersonic/hypersonic impactor with one or two nozzles was carried out using a commercial computational fluid dynamics （CFD） software FLUENT. The objective was to investigate the effects of working parameters such as pressure ratio （50 〈 Po]Pb 〈 800）, nozzle diameters （D=0.23, 0.27, 0.45 mm）, nozzle to plate distance （0.5 〈L/D〈 50）, particle diameter （1 nm〈 dp 〈 100 nm ） and angle between two nozzles. A single-phase 3D unsteady-state model was implemented by the software. For this purpose, a user-defined function （UDF） was employed to implement nanoparticles for different assumptions of Cunningham correction factor. An axisymmetric form of the compressible Navier-Stokes and energy equations was used for both fluid flow and temperature; Lagrangian particle trajectory analysis was used for particle motion. Using the variable Cunningham cor- rection factor showed suitable agreement with experimental data in comparison with other methods. Results show that increase of the distance between nozzle and impaction plate causes increase of Mach number, the distance between bow shock and impaction plate, and the collection efficiency. Maximum jet velocity, distance between bow shock and impaction plate and collection efficiency increase by using two nozzles in supersonic and hypersonic imoactors.