DYNAMIC RECOVERY AND DYNAMIC RECRYSTALLIZATION OF 7005 ALUMINIUM ALLOY DURING HOT COMPRESSION

Dynamic recovery and dynamic recrystallizatin behaviors of AA7005 aluminium alloy (Al - Zn - Mg) during hot compression are investigated by isothermal compression testing.The interdependence of flow stress,stress, strain rate,true strain and deformation temperature for the alloy is analyzed by introduc- ing Zener-Hollomon parameter. A steady - state flow of the 7005 alloy is confirmed to be a thermal- ly activated process.which is governed by rate-controlling mechanisms of dislocations.A hyperbolic sine relationship can satisfactorily correlate temperature, strain rate with flow stress through an Arrhe- nius term that involves thermal activation parameters. The dynamic recovery mechanisms of the alloy are discussed.Cross- slip of jogged screw dislocations is the main dynamic recovery mechanism over the deformation temperatures and strain rates.Subgrains are highly developed in the originally elongat- ed grains.The size of the subgrain increases with decrease of the natural logarithm of Zener- Hol - lomon parameter.Local dynamic recrystallization is operative when the alloy is deformed at temperature of 500℃ and strain rate of 0. 001s - 1.

Kinetics for static recrystallization after hot working of 0.38C-0.99Cr-0.16Mo steel

The restoration mechanisms for static recrystallization of work-hardened austenite were investigated by using double-pass compression tests performed on medium-carbon steel containing chromium and molybdenum. The softening fraction was defined by 2% offset method. The results show that Avrami exponent of about 0.21 is insensitive to deformation temperature, indicating that the action of steel grade should be considered. The time of 50% recrystallization (t0.5) decreases noteworthily with the increase of deformation temperature. Apparent activation energy for static recrystallization of 195 kJ/mol, which is close to that of vanadium microalloyed steel, is obtained by calculating. The increasing trend of the driving force for recrystallization is opposite to that of the deformation temperature, which is attributed to the number of operative slip system increasing as temperature increasing.

Effect of thermo-mechanical processing parameters on the dynamic restoration mechanism in an Mg-4Y-2Nd-1Sm-0.5Zr alloy during hot compression

Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures(350-500℃),strain rates(0.01-5 s^(-1)),and strains(0.2,0.4,and 0.8).A strong dynamic softening is observed in all stress-strain curves,even at higher strain rates(1 and 5 s^(-1))due to an adiabatic heating effect.Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation.With the prediction of the processing map,an optimal processing domain has been determined to be the temperature range 450-500℃and strain rate range 0.01-0.1 s^(-1)at a strain of 0.8.The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate.For the effect of TMP parameters on the dynamic restoration,the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)synergistic effect occur throughout the whole process at high temperature and high strain rate.In terms of high temperature and low strain rate,DDRX characteristics at a low strain and then the DDRX+CDRX synergistic effect is observed at a higher strain.Although the DRX process is weak at low temperature and low strain rate,deformation twins have occurred and provided nucleation sites for DRX grains.

Dynamic mechanical behavior, microstructure evolution, and restoration mechanism of a β‐Ti alloy during hot compression deformation

Metastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density.Thermal-mechanical processing(TMP)is one of the most effective ways to improve the mechanical properties of such alloys.This paper describes a systematic TMP investigation on a new metastableβtitanium alloy,including its dynamic mechanical behavior,and microstructure evolution,via isothermal compression tests and electron back‐scattered diffraction characterizations.The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature.After yielding,the compression stress-strain pattern shows flow‐softening behavior at a low temperature and a high strain rate,while sustaining a steady flow state at a high temperature and a low strain rate.The temperature‐rise effect contributes to a large degree of flow softening at high strain rates.After the correction for temperature rise,the stress-strain constitutive relationships are established,showing that the compression behavior varies in different phase regions.Based on the microstructure characterizations,it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations inβphase region and at low strain rates,while the deformation band as an additional product is found inα+βphase region and at high strain rates.The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database forβ‐Ti alloy applications in lightweight mechanical systems.

A New Backup-VP Priority Restoration Methodfor ATM Survival Networks

In this paper, we propose a new backup-VP priority restoration method for ATM survival net-works. in order to improve the survivability performance of higher priority VPs in case of multi-failure under the minimum amout of spare capacity required. This method is a part of a hybrid restoration ,mechanism (to be presented later), which integrates a backup-VP, method￣[2] and a distributed flooding algorithm￣[3] in theATM layer. This method is a path restoration between VP terminal nodes, completes the restoration with bi-directional message transmission by ustng pre-assigned backup VP's in case of single failure, and improvesthe restoration time of higher priority VPs in case of multi-failure, but it should cooperate with anotherorganic part of the hybrid restoration mechanism-a floodting algorithm to restore the remaining lower priorityVPs. This method can use resource more efficiently and obtain a better cost-performance feature.