Effects of pin diameter and number of cycles on microstructure and tensile properties of friction stir fabricated AA1050-Al2O3 nanocomposite

Nanocomposites of Al-Al2O3 are fabricated by means of friction stir processing (FSP). Effects of pin diameter and number of FSP cycles on tensile properties of the nanocomposites are investigated and the variations are correlated to the evolution of microstructure and distribution of nanoparticles in addition to agglomeration of Al2O3 nanoparticles. Investigation of agglomeration has been considered as an indirect indication for efficiency of the process for distribution of nanoparticles. The ductility of the nanocomposite is found to improve due to grain refinement during FSP. However, the ductility is likely to degrade if Al2O3 particles agglomerate and form coarse particles. The composite fabricated using the 6-mm pin indicates the maximum ductility which is attributed to formation of fine grain structure and efficient distribution of nanoparticles in the composite. Although, the grain structure in the composite fabricated using 8-mm pin is well refined, this sample shows significantly lower ductility with respect to the other samples. This was attributed to formation of coarse agglomerated particles. The second pass of FSP is found to slightly improve ductility and strength in composites fabricated using 4- and 6-mm pins but enforce significant improvements in the one with 8-mm pin. This is indeed because the second pass results in significant change in the distribution of nanoparticles or agglomerated particles in the latter case and negligible in the former ones. Grain structure and nanoparticle distribution and agglomeration can all affect the fracture surface of the tensile specimens of the fabricated nanocomposite to be ductile or brittle

Modeling of Microstructural Evolution during Homogenization and Simulation of Transient State Recrystallization leading to Peripheral Coarse Grain Structure in Extruded Al-4.5Zn-1Mg Alloy

Materials Science & EngineeringMechanical, Maritime and Materials Engineerin

Application of physical and numerical simulations for interpretation of peripheral coarse grain structure during hot extrusion of AA7020 aluminum alloy

In this research, hot compression test is used to simulate the metallurgical phenomena occurring in the peripheral part of AA7020 aluminum alloy extrudates during hot extrusion and leading to the formation of the peripheral coarse grain (PCG) structure. The temperature profiles at a tracking point in the peripheral part of extrudates are predicted using finite element method (FEM). A special thermal treatment representing the predicted thermal profiles during extrusion is designed and applied to specimens after hot-compression testing. The effects of deformation conditions, i.e., temperature and strain rate, and the subsequent special thermal treatment on the formation of coarse grains in the AA7020 alloy are investigated. The as-deformed microstructures of specimens as well as the microstructures of specimens after the special thermal treatment are examined and the average grain size and homogeneity of grain size distribution determined. It is observed that with increasing deformation temperature or decreasing strain rate, the average recrystallized grain size increases. A fine and homogenous grain structure is obtained by increasing strain rate. According to the results of this investigation, formation of coarse grains at the periphery of the extrudate is attributed to high temperatures raised during extrusion rather than high strain rates.Accepted Author ManuscriptBiomaterials & Tissue Biomechanic

The effect of multi-pass friction stir processing on microstructure and mechanical properties of dual-phase brass alloy

This research aims to improve the microstructure and mechanical properties of C38000 brass alloy by multi-pass friction stir processing (MPFSP). In this study, The MPFSP was carried out on a dual-phase brass alloy sheet with a thickness of 5 mm at fully annealed conditions. To determine the effect of the number of passes on microstructure and mechanical properties of this alloy, rotational and traverse speeds were chosen at 750 rpm and 100 mm∖min, respectively. This process was performed in 1, 2, 4, and 6 passes. Metallography, microhardness, tensile, wear, and fractography are tests done to investigate the changes in microstructure and mechanical properties after processing. Finally, the relation between the microstructural and mechanical properties of MPFSPed specimens was discussed. Studying the tests mentioned above resulted that the MPFSP has caused a decrease in the grain size of the matrix and second phase (β′) particles. Furthermore, mechanical properties such as yield strength, ultimate tensile strength, and hardness were enhanced. It was obtained that elongation to failure has a decreasing trend with increasing the number of FSP passes. Tribological behaviors were also improved after performing MPFSP. The levels of grain size refining and improving the mechanical properties are directly related to increasing the number of passes. However, after performing six passes of FSP, there was no significant change in the microstructure and mechanical properties in comparison to that after 4 passes of FSP. The properties of 4 and 6 passes FSPed specimens showed that these had the most refined microstructures and enhanced mechanical properties with remarkable elongation

The effect of multi-pass friction stir processing on microstructure, mechanical properties, and corrosion behavior of WE43-nHA bio-composite

The influence of multiple passes during friction stir processing (FSP) on the evolution of microstructure, hardness, compressive strength, and corrosion behavior of a Mg-based bio-composite has been investigated. WE43 Mg alloy was used as the matrix of the composite and nano-sized hydroxyapatite (nHA) was added as the second material to form the composite. After fabrication of the composite by one pass of FSP, the process was repeated six times. Significant grain refinement and fragmentation of secondary phase particles were observed during FSP. Increasing the number of passes of FSP was found to be associated with pronounced grain refinement coupled with the uniformity in distribution of nHAs. Corrosion resistance is enhanced with an increasing number of FSP passes, which is attributed to the fragmentation and redistribution of secondary phase particles in addition to a homogeneous distribution of nHA

A novel approach to determine residual stress field during FSW of AZ91 Mg alloy using combined smoothed particle hydrodynamics/neuro-fuzzy computations and ultrasonic testing

The faults in welding design and process every so often yield defective parts during friction stir welding (FSW). The development of numerical approaches including the finite element method (FEM) provides a way to draw a process paradigm before any physical implementation. It is not practical to simulate all possible designs to identify the optimal FSW practice due to the inefficiency associated with concurrent modeling of material flow and heat dissipation throughout the FSW. This study intends to develop a computational workflow based on the mesh-free FEM framework named smoothed particle hydrodynamics (SPH) which was integrated with adaptive neuro-fuzzy inference system (ANFIS) to evaluate the residual stress in the FSW process. An integrated SPH and ANFIS methodology was established and the well-trained ANIS was then used to predict how the FSW process depends on its parameters. To verify the SPH calculation, an itemized FSW case was performed on AZ91 Mg alloy and the induced residual stress was measured by ultrasonic testing. The suggested methodology can efficiently predict the residual stress distribution throughout friction stir welding of AZ91 alloy.</p

Tribological properties of copper-graphene (CuG) composite fabricated by accumulative roll bonding

The main aim of this study is to clarify the effect of the number of accumulative roll bonding (ARB) cycles on the tribological properties of the copper-graphene composite. To conduct the wear test, the pin-on-disk method was utilized at an average normal force of 20 N and a sliding distance of 1000 m. Field emission scanning electron microscopy (FE-SEM) was used to investigate the worn surface resulting from the wear test and determine the wear mechanism. The results showed that the wear rate increased in the rolled copper sheet and copper-graphene composite as a result of increasing the number of cycles. The increase in wear rate and weight reduction in the composite were less than rolled copper sheet. SEM micrography and EDS analysis showed that adhesive, oxidation, and delamination wear mechanisms were active on the wear surfaces. With increasing the ARB cycles, the dominant wear mechanisms in the copper-graphene composite and copper sheet were delamination, which was associated with severe galling and cracking in high cycles and more accentuated in copper sheet samples

The effect of addition of hardystonite on the strength, ductility and corrosion resistance of WE43 magnesium alloy

A composite material based on the WE43 magnesium alloy and containing nano-sized hardystonite ceramic particles was processed by means of friction stir processing (FSP). Compressive strength and strain-at-failure of the WE43 alloy increased as a combined result of FSP and nanoparticle reinforcement. The results of potentiondynamic polarization and electrochemical impedance spectroscopy tests indicated that the corrosion mechanism of the nanocomposite is combination of uniform corrosion and localized pitting corrosion which is not different from the base metal. However, the corrosion rate is significantly decreased as a result of reduced localized corrosion of the base metal after FSP and the effect of hardystonite to reduce pitting corrosion. The polarization resistance is increased from 192.48 to 339.61 and 1318.12 Ω/cm2 by applying FSP on WE43 and addition of nano-sized hardystonite particles, respectively. Indeed, the fabricated nanocomposite shows significantly increased corrosion resistance. Enhanced strength, ductility and corrosion resistance were attributed to grain refinement in addition to the fragmentation and redistribution of second-phase particles in the magnesium matrix, occurring during FSP