Effect of Equal Channel Angular Pressing and Annealing Treatment on the Evolution of Microstructure in AlMg0.7Si Aluminum Alloy

In this research, samples of AlMg0.7Si aluminum alloy are deformed up to three passes using equal channel angular pressing (ECAP). Formation of a sub-micron structure after three passes of ECAP is demonstrated. Microstructural stability of the samples is investigated at temperatures of 300-500 °C. At 300 °C, fine recrystallized structure forms after 10 min which remains stable when the annealing proceeds up to 18 hrs. However, at 350 °C and higher, the microstructure is quite unstable. Even by 10 sec annealing, the samples exhibit recrystallized structure which turned to abnormal grain growth when temperature enhances to 500 °C and time up to 300 sec. &nbsp

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

A solidification model for prediction of castability in the precipitation-strengthened nickel-based superalloys

The Scheil equation was used to model the solidification path, microsegregation of alloying elements in the interdendritic regions, solidification temperature ranges, and to predict the formation of secondary structures and the castability behavior of as-cast superalloys. 4 experimental alloys with pre-specified -Ti,Nb,Al,Mo composition containing different Nb, Ti and Al contents were designed using vacuum induction melting furnace. The produced as-cast superalloys were characterized using optical and scanning electron microscopy equipped with energy dispersive X-ray spectrometer and TG–DSC analysis. The experiments showed logic conformity to the modeling results. The model and experiment confirmed the highest segregation behavior for Ti and Nb. All the experimental superalloys indicated the remarkable tendency to form secondary eutectic structures at the last stages of solidification. Superalloy with chemical composition of -3.5%Mo,1.8%Al,4%Ti,2.9%Nb showed the shorter solidification temperature range and the best castability

Prediction of Temperature Distribution in the Hot Torsion Test Specimen

Hot torsion test (HTT) has extensively been used to analysis and physically model flow behavior and microstructure evolution of materials and alloys during hot deformation processes. In this test, the specimen geometry has a great influence in obtaining reliable test results. In this paper, the interaction of thermal-mechanical conditions and geometry of the HTT specimen was studied. The commercial finite element package ANSYS was utilized for prediction of temperature distribution during reheating treatment and a thermo-rigid viscoplastic FE code, THORAX.FOR, was used to predict thermo-mechanical parameters during the test for API-X70 micro alloyed steel. Simulation results show that no proper geometry and dimension selection result in non uniform temperature within specimen and predicted to have effects on the consequence assessment of material behavior during hot deformation. Recommendations on finding proper specimen geometry for reducing temperature gradient along the gauge part of specimen will be given to create homogeneous temperature as much as possible in order to avoid uncertainty in consequent results of HTT

Modern fiber laser beam welding of thenewly-designed precipitation-strengthened nickel-base superalloys

In thepresentresearch,themodern fiber laserbeamweldingofnewly-designedprecipitation- strengthened nickel-basesuperalloysusingvariousweldingparametersinconstantheatinputhasbeen investigated.Fivenickel-basesuperalloyswithvariousTiandNbcontentsweredesignedandproduced by VacuumInductionMeltingfurnace.The fiber laserbeamweldingoperationswereperformedin constant heatinput(100Jmm2) anddifferentweldingpowers(400and1000W)andvelocities(40and 100mms1) using6-axisanthropomorphicrobot.Themacro-andmicro-structuralfeatures,weld defects, chemicalcompositionandmechanicalpropertyof3.2mmweldmentswereassessedutilizing optical andscanningelectronmicroscopesequippedwithEDSanalysisandmicrohardnesstester.The results showedthatweldingwithhigherpowerscancreatehigherpenetration-to-widthratios.The porosity formationwasincreasedwhentheweldingpowersandvelocitieswereincreased.Noneofthe welds displayedhotsolidification andliquationcracksin400and1000Wweldingpowers,butliquation phenomenon wasobservedinalltheheat-affectedzones.WithincreasingtheNbcontentofthe superalloystheliquationlengthwasincreased.Thechangingoftheweldingpowerandvelocitydidnot alter thehardnesspropertyofthewelds.ThehardnessofweldsdecreasedwhentheTicontentdeclined in thecompositionofsuperalloys.Finally,the400and1000W fiber laserpowerswithvelocityof40and 100mms1 havebeenofferedforhotcrack-freeweldingofthethinsheetofnewly-designed precipitation-strengthenednickel-basesuperalloys