Lingfei Cao

The Influence of Composition on the Clustering and Precipitation Behavior of Al-Mg-Si-Cu Alloys

The natural aging (NA) and artificial aging (AA) behavior of Al-Mg-Si-Cu alloys with different Mg/Si ratios and Cu additions were systematically investigated by means of hardness test, atom probe tomography, transmission electron microscopy, and Monte Carlo simulation. The Si-rich low-Cu alloys displayed higher hardness compared to the Mg-rich equivalents because Si atoms play a dominant role in clustering of solute atoms during both natural and artificial aging. In the high-Cu alloys, Cu did not obviously change the cluster distribution during NA, but significantly refines the clusters and precipitates due to the strong interaction of Cu atoms with Mg atoms during AA. In contrast to the low-Cu alloys, the Mg-rich high-Cu alloys exhibit higher hardness in the early and over-aged stages of artificial aging, with similar or slightly higher hardness in the peak aging condition compared to their Si-rich counterparts. Three types of precipitates (β″, Q′, and L) are favored in the high-Cu alloys. The Mg-rich high-Cu alloy has more L phase, while the Si-rich variant is abundant in Q′ phase. The negative effect of NA on subsequent AA behavior is less dependent on Mg/Si ratio in the high-Cu alloys due to a synergistic action of the residual Si and Cu atoms, but is closely related to Mg/Si ratio in low-Cu alloys.

Flow behavior and microstructure evolution of 6A82 aluminium alloy with high copper content during hot compression deformation at elevated temperatures

The flow behavior and microstructure evolution of 6A82 aluminum alloy (Al–Mg–Si–Cu) with high copper content were studied on a Gleeble–1500 system by isothermal hot compression test in the temperature range from 320 to 530 °C and the strain rate range from 0.001 to 10 s−1. The results reveal that the flow stress of the alloy exhibits a continuous flow softening behavior at low temperatures of 320–390 °C, whereas it reaches steady state at high temperatures (≥460 °C), which are influenced greatly by the Zener–Hollomon parameter (Z) in the hyperbolic sine with the hot deformation activation energy of 325.12 kJ/mol. Microstructure characterizations show that prominent dynamic recrystallization and coarsening of dynamic precipitation may be responsible for the continuous flow softening behavior. Due to deformation heating at high strain rates (≥1 s−1), dynamic recrystallization is more prominent in the specimen deformed at 530 °C and 10 s−1 than in the specimen deformed at 460 °C and 0.1 s−1 even though they have very close ln Z values.

Microstructure characterization of Al-cladded Al–Zn–Mg–Cu sheet in different hot deformation conditions

Abstract Al-cladded Al–Zn–Mg–Cu sheets were compressed up to 70% reduction on a Gleeble–3500 thermo-mechanical simulator with temperatures ranging from 380 to 450 °C at strain rates between 0.1 and 30 s−1. The microstructures of the Al cladding and the Al–Zn–Mg–Cu matrix were characterized by electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). The microstructure is closely related to the level of recovery and recrystallization, which can be influenced by deformation temperature, deformation pass and deformation rate. The level of recovery and recrystallization are different in the Al cladding and the Al–Zn–Mg–Cu matrix. Higher deformation temperature results in higher degree of recrystallization and coarser grain size. Static recrystallization and recovery can happen during the interval of deformation passes. Higher strain rate leads to finer sub-grains at strain rate below 10 s−1; however, dynamic recovery and recrystallization are limited at strain rate of 30 s−1 due to shorter duration at elevated temperatures.

Improvement of strength and ductility of Al-Cu-Li alloy through cryogenic rolling followed by aging

Abstract To develop an improved approach in achieving an excellent combination of high strength and ductility, the solutionized Al-Cu-Li plates were subjected to rolling at cryogenic and room temperatures, respectively, to a reduction of 83%, followed by aging treatment at 160 °C. The results indicate that Al-Cu-Li alloys through cryogenic rolling followed by aging treatment possess better mechanical properties. Rolling at cryogenic temperature produces a high density of dislocations because of the suppression of dynamic recovery, which in turn promotes the precipitation of T 1 (Al 2 CuLi) precipitates during aging. Such high density of T 1 precipitates enable effective dislocation pinning, leading to an increase in strength and ductility. In contrast, room temperature rolled alloys after aging treatment exhibit lower strength and ductility due to low density of T 1 precipitates in the grain interior and high density of T 1 precipitates around subgrain boundaries.

Strain accommodation of -normal direction-oriented grains in micro-shear bands of high-purity tantalum

AbstractThe <110>ND(<110>//normal direction)(<110>ND) grains in micro-shear bands in high-purity tantalum were investigated using electron backscatter diffraction and X-ray line profile analysis. The generation of the <110>ND grains and their subdivision and rotation behaviors upon the subsequent deformation were characterized by multi-scale analysis methods based on information about the slip systems, misorientation angle/axes and stored energy. The obtained results show that in the transverse plane, <110>ND grains are oriented at angles of 15°–25° to the adjacent deformed matrices in the 60% rolled specimen, and at angles of 25°–35° in the 87% rolled specimen. The <110>ND grain provided strain accommodation during the shear deformation. Moreover, the energy of the <110>ND grains in the 87% rolled specimen is approximately three times larger than that in the 60% rolled specimen, indicating that the role of strain accommodation is enhanced with the increase in the micro-shear stress concentration in a local region in tantalum.