In this research, Dynamic recrystallization of an Al-Li alloy was investigated in two temperatures, i.e. 350oC and 400oC. Wedge samples were subjected to hot rolling deformation in high temperature and one passes. For wedge specimens, reduction up to 70% was considered. Results showed that grain size of the specimens after hot rolling decreases from 100mm to 30mm because of Dynamic recrystallization phenomenon. Furthermore, it is observed that critical reduction for starting Dynamic recrystallization was 50% and 40% in 350oC and 400oC respectively.

In this research, grain size variation and grain distribution and the effect of different factors such as friction, tool rotational speed, linear velocity of the tool, cooling rate, tool geometry and tool penetration depth on the temperature change and grain size during the friction stir welding process of the aluminum alloy Al-2024 sheet with a thickness of 7. 8 mm has been investigated. In order to simulate the model of finite element friction stir welding, the Deform 3D software has been used. The tool is a rigid body and a sheet is considered as a formable plastic material. In order to validate, a comparison between simulation data and experimental results was performed. The effect of effective factors on the temperature of the welding and the amount of grain size variation in the cross section of the weld line have been discussed. Among the variables studied, increasing the cooling rate and the linear velocity of the tool reduce the temperature and grain size, and increase the temperature and grain size with increasing other variables. The results show that with the method presented in this paper, precise prediction of the effect of variation of the variables affecting temperature and grain size can be obtained. In the following, these results can be used to determine the optimum conditions for the friction stir welding process.

Dynamic recrystallization, DRX, behaviour of a precipitation hardened, PH, stainless steel was studied in connection with microstructural developments in a compression test, The experimental results showed that the dominant mechanism of softening is DRX, but at high strain rates and low temperatures,, high Zener-Holman parameter, Z. work hardening and Dynamic recovery, DRV, produced a pancked structure. When Z values decreased, the flow curves displayed DRX in two ways: single peak behavior observed at low Z values and multiple peak behavior at the lowest ones. In addition, the peak strain, ep, necessary for DRX is also determined as a function of peak , Stress sp, and Z. according to the observed and calculated data, at low sp values, ep is directly proportional to sp while in higher sp p values, ep rarely depends on it. Besides, ep expotenentially depends on Z.

The study of nucleation mechanism of new grains during severe plastic deformation of magnesium alloys is of great importance to control the characteristics of final microstructures. To investigate the role of discontinuous recrystallization, a wrought AZ31 magnesium alloy was deformed by accumulative back extrusion process at 330oC. The obtained microstructures were studied using optical and field emission microscopy as well as electron back scattered diffraction techniques. The results demonstrated that the fine and ultrafine grains formed along the prior grain boundaries yielding a bimodal structure. The EBSD analysis showed that the new grains exhibit a similar basal texture to deformed grains, which may confirm the operation of strain induced boundary migration mechanism.

Strain induced precipitation in HSLA-100 steel was investigated by conducting hot compression and relaxation tests at temperature range of 850oC to 1100oC and strain rate of 0.001 s-1 to 1s-1. The absence of Dynamic recrystallization at temperatures below 1000oC was attributed to the influence of Dynamic precipitation. The stress relaxation tests showed that strain induced precipitation is possible over a wide range of temperatures from 850oC to 1050oC. The starting and finishing times of precipitation were sensitive to temperature than strain rate. At temperature range of 950-1000oC and strain rate of 0.1s-1 the lowest times for precipitation were observed. The combination of precipitation-time-temperature and recrystallization-time temperature diagrams showed that at high temperatures and low strain rates, precipitation precedes Dynamic recrystallization, whereas at the opposite condition, Dynamic recrystallization goes in advance. The starting and finishing times for Dynamic precipitation were approximated about 40 percent lower that those for strain induced precipitation.

The present investigation is dealing with the evolution of simultaneous Dynamic and metaDynamic recrystallization (DRX)& (MDRX) phenomena by physical simulation for a 4-strock hot compression process, where flow curves were presented for each stroke. The primary alloy is a penetrator steel containing 0.3% C in addition to some Cr, Mo, Ni and 1.63 W. Calculated grain size after the onest of DRX & occurrence of MDRX decreases continuously with the increase of cumulative strain reaching to 0.289 µm. However, Electron Backscatter Diffraction (EBSD) investigation established that 99% of the grains, after the last compression stroke, were detected as <1.0 μm, with an average grain size 0.31 μm. Microstructure after simulation presents fine lath martensitic structure, coexisting with Cr-W carbides, which are crammed at the inter- martensite laths. Furthermore, 56% of the grains showed grain boundaries misoriention creating High Angle Grain Boundaries (HAGBs), which are promoting MDRX. The flow curve of each stroke definitely contains two complementary microstructure events, namely a DRX , and a MDRX phenomenon, where the peak stress (σp) of DRX is inversely proportional to the mean temperature of stroke.

In this paper the hot deformation behavior of Al-5083 commercial alloy is investigated. The aim is to investigate the formability of this alloy in hot tension under Dynamic recrystallization. For this purpose, the material is thermo-mechanically processed. Then hot tensile tests are carried out at various temperatures and strain rates. Velocity jump tests are performed to determine stress-strain rate curves at various temperatures and strains. The microstructures are studied by optical and electron microscopy (SEM). It is found that the thermo–mechanical process resulted in a homogeneous distribution of fine precipitates. Dynamic recrystallization occurs during hot deformation of the AA5083. Maximum elongation about 250% is obtained at 450 oC and strain rate of 0.005 s-1. Maximum strain rate sensitivity (m) is 0.3. The failure surface is narrow and failure occurs by necking.

The aim of this study is to investigate the nucleation of new grains by neck lacing mechanism during Dynamicrecrystallization (DRX). The material used is 316 stainless steel. In order to modeling the deformation behavior during hot rolling, one-hit compression tests were performed at temperature range of 950-1100°C with strain rates of 0.01-1s-1 The result shows that at the temperature of 1000°C with the strain rate of 0.1s-1 DRX developed by necklace mechanism, it is far from completeness over the steady state stress. By contrast the hardness increased by development of DRX. The final microstructure is very heterogeneous and comprises of very fine and coarse grains due to the occurrence of partial DRX. The results also show that the necklace structure developed by increasing Zener-Hollomonparameter (Z).