Bolong Li

Study on the Erbium Strengthened Aluminum Alloy

We have systemically studied the effect of the erbium on the microstructure and the mechanical properties in the 5xxx series aluminum alloys by using optical microscope, transmission electron microscope (TEM) and by tensile testing. The results demonstrate that the tensile strength increased quickly at the beginning of small contents of 0.1%Er both in the hot and cold rolled states, then slowly increased with increasing the contents of Er until 0.4%, at which the best balance of the strength and ductility (438MPa and 9.6%) were obtained. Microstructure observation in the hot rolled state was indicated that the grain structure in the Er free Al-5Mg alloy revealed fully recrystallized grain structure, while in the Al-5Mg containing Er was demonstrated deformation structure, indicating the Er addition delayed the recrystallization behavior by the formation of the precipitation of the Al3Er, which confirmed by means of the X-ray diffraction analysis. Furthermore in the TEM microstructure observation the precipitation of Al3Er was distributed both in the grain interior and subgrain or grain boundaries, which could be pinning the subgrain or grain boundary migration and dislocation movement as well. Consequently the beginning of the recrystallization temperature in the Al-5Mg containing Er was elevated about 50°C than in Al-5Mg without Er. This could be explained that the strength increased without the deterioration of the ductility was attributed to the microstructure refinement by the Er addition.

Effect of Thermo-Mechanical Deformation on the Microstructure Evolution in a High Temperature Ti Alloy with Erbium

The effect of thermo-mechanical deformation on the microstructure was investigated by isothermal compression and microstructure characterization. The mechanical response of as-casted Ti–6.2Al–3Sn–5Zr–0.5Mo–1.0Nb–0.4Si–0.2Er titanium alloy was sensitive to the deformation temperatures and strain rates. The true stress increased with the increase in the strain rate and decreased in temperature. The discontinuous dynamic recrystallization of β phase was promoted with the increase in temperatures. Global α phase generated during the deformation at a temperature of 980 °C. The (Ti, Zr)3Si and participated phase were dissolved into the matrix above 950 °C, which acted as the homogenizing annealing process. However, novel participated phases with an average diameter of 20 nm generated.

Aging Time on the Microstructure and Mechanical Properties of A356 Alloy by Semi-solid Processing

An investigation was carried out to study the effects of aging time on the microstructure and mechanical properties of A356 alloy by semi-solid processing. The alloy was subjected to solution treatment for 4 h at 540 °C, artificial ageing was carried out at temperature (170 °C) and different time (0–24 h). The results revealed that the needle-shaped eutectic Si phase in as-cast ingot was transformed to globular shape compared with that by solution treatment. Meanwhile the Chinese script π-Fe(AlMgSiFe) phase was transformed to smaller and uniformly distributed β-Fe(AlFeSi) phase, the elongation increased obviously. With the increasing of aging time, the elongation decreased, and the ultimate tensile strength increased. When the aging time was 4 h, the alloy achieved the optimal mechanical properties. The micro-hardness was 121HV, ultimate tensile strength was 329 MPa, and the elongation was 15%. From the fracture morphology, the fracture for alloy aging for 4 h showed more dimples. With the increasing of aging time, the ultimate tensile strength and the elongation decreased.

Study of Aging Precipitation of Al-Zn-Mg Alloys with Er Additions by Monte Carlo Simulation

Our former experimental study showed that the addition of Er to Al-Zn-Mg alloys speeded up the aging precipitation, accelerated the precipitation of and enhanced the effect of aging strengthening distinctively. In this paper, the Monte Carlo method was applied to simulate the microstructural evolution of Al-2.6Zn-(2.3Mg)-(0.07Er), Al-2.6Zn-2.3Mg-(0.12Er), and Al-2.6Zn-2.3Mg-0.1(Er,Zr) alloys during aging. The effects of Er addition to Al-Zn-Mg alloys on the clustering of Zn and Mg atoms are studied through analysis of the simulation results and the effects on the subsequent aging process are discussed as well. The results show that the Zn/Mg/Er clusters appear beside the Zn clusters, Mg clusters and Zn/Mg clusters in the Er addition Al-Zn-Mg alloys. The Zn clusters and Zn/Mg clusters are finer in the Al-2.6Zn-2.3Mg-xEr alloys than that in the Al-2.6Zn-2.3Mg alloys without Er addition. The size of the Zn clusters and Zn/Mg clusters in the Al-2.6Zn-2.3Mg-0.07Er is eight percent and nineteen percent smaller than that in the Al-2.6Zn-2.3Mg alloys without Er addition respectively. This precipitation refinement effect of Er addition to the Al-2.6Zn-2.3Mg alloys is enhanced with the increment of Er content. These above results are consistent with the experimental results that the precipitation in the Al-Zn-Mg alloys with Er is finer and denser than that in the Al-Zn-Mg alloys without Er. The Er addition changes the clusters distribution in the Al-Zn-Mg alloys by its interaction with the main solute atoms and the vacancy, and thus influences the precipitations during subsequent aging processing.