Main Restoration Mechanism Research Articles

Deformation behavior of AA2017–SiCp in warm and hot deformation regions

Abstract In this work, the flow stress behavior of a metal matrix composite AA2017–10% SiCp was studied by means of the uni-axial compression test. The composite was first produced by stir casting technique and then, hot extrusion with the ratio of 18:1 was carried out to achieve a microstructure with a homogeneous distribution of SiC particles. In the next stage, the isothermal compression tests were conducted on the cylindrical specimens up to the true strain of 0.6. The experiments were performed at temperatures between room temperature to 400 °C and strain rates of 0.003, 0.03 and 0.3 s−1. Negative strain rate sensitivity was observed in the temperatures less than 250 °C indicating the occurrence of dynamic strain aging. However, at higher temperatures a regular hot deformation behavior associated with dynamic recovery as the main restoration mechanism was detected while the apparent activation energy for hot deformation was calculated about 303 kJ/mole.

Dynamic globularization and restoration mechanism of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy during isothermal compression

Dynamic globularization and restoration mechanism of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy during isothermal compression were investigated by employing a high-resolution electron backscatter diffraction technique (EBSD). Quantitative analysis was made in detail for further understanding the microstructure evolution. The results reveal that the dynamic globularization of primary α grains of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy is accomplished by the formation of high-angle boundaries (HABs) and the penetration of the β phase during isothermal compression, and an increase in deformation temperature leads to a more globular microstructure. The main restoration mechanism in the β phase of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy during isothermal compression is dynamic recovery (DRC) at a strain rate of 0.01s−1, while continuous dynamic recrystallization (CDRX) occurs as the strain rate increases to 1.0s−1/5.0s−1 and the α grains play an important role in recrystallization. The recrystallization in the β phase of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy during isothermal compression is promoted with the decreasing of deformation temperature and the increasing of strain rate. A strong 〈001〉 fiber texture develops where only DRC occurs and the deformation texture is weakened to a large extent after recrystallization of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy during isothermal compression.

Microstructure development in hot deformed AA6082

Age hardenable aluminium alloys are suitable for hot deformation at temperatures between 300 and 600°C, depending on the alloy and on the process. During thermo mechanical processes, dynamic and/or static restoration mechanisms take place. In this work, hot compression tests of hot rolled AA6082 and of a hot extruded AA6082 were carried out by means of a Gleeble® 1500 thermo-mechanical system, between 450 and 550°C and at 0.1–10s−1 of strain rate followed by fast cooling. The materials were thermo-mechanically processed before hot deformation to transform the complex initial microstructure into a fully recrystallized microstructure. Some compression tests of non recrystallized samples were carried out for comparison. All the samples were examined using electron backscatter diffraction (EBSD), followed by a determination of grain size and subgrain size distributions as well as of the local misorientation distribution. The as received samples showed a duplex microstructure consisting of elongated grains oriented in the rolling and extrusion directions, and some small recrystallized grains. The main restoration mechanism for all the materials is shown to be dynamic recovery, and the Zener–Hollomon parameter, as well as the flow stress was correlated to the subgrain size. The hot rolled material flow behaviour was sensitive to the initial microstructure, and geometric dynamic recrystallization was found.

Hot workability and processing maps of aluminium based discontinuously reinforced composites

Hot deformation behaviour under tensile conditions of Al6061/20%Al2O3 , Al2618/20%Al2O3, and Al2618/20%SiC particle reinforced composites and of an unreinforced 6061 aluminium alloy was investigated in the temperature range 350–500°C and in the strain rate range 10–3-10–1s–1. Processing maps were generated from the obtained data and the domains of optimal hot workability were identified for the different materials. Microstructural analyses on deformed specimens allowed it to be stated that dynamic recovery was the main restoration mechanism for the composites investigated. The concurrent evaluation of ductility and flow stress data also suggested that differences in reinforcement properties can play a significant role on property definition.