Wenchen Xu

The formation mechanism of tear strips on stretched Ti-22Al-25Nb alloy sheets

This paper reports the presence of tear strips on the surface of a Ti-22Al-25Nb alloy sheet stretched at 960u2009°C. The test piece reveals a “bamboo”-shaped pattern on its surface, which severely affects the quality of the alloy. Microstructure analysis indicates that the formation mechanism of the tear strip is related to both the rich α2 phase layer and the interfacial B2 phase dynamic recrystallization layer between the α2 phase layer and the substrate metal.

Deformation behavior, microstructure evolution and hot workability of Mg-3.7Gd-2.9Y-0.7Zn-0.7Zr alloy

The deformation behavior of Mg-3.7Gd-2.9Y-0.7Zn-0.7Zr magnesium alloy has been investigated by thermal compression test conducted on a Gleeble-1500D thermal simulator in the temperature range of 375-475 °C and strain rate range of 0.001-1 s-1. It indicates that the addition of RE, the introduction of LPSO phases and the segregation of Zr element near the grain boundaries contributed to the high activate energy (Q = 354.08 kJ/mol) of the present Mg alloy. The long period stacking ordered (LPSO) phase could not only strengthen the alloy and contribute to the nucleation of dynamic recrystallization, but also re-precipitate in the recrystallization grains. The processing map based on MDMM and Murty’s instability criterion was more precise than the one based on DMM and Prasad’s instability criterion. The processing map exhibited two workable regions with sufficient dynamic recrystallization: 415-435 °C, 0.001-0.006 s-1 and 435-475 °C, 0.01-1 s-1. The flow instability was prone to occur at low temperature and high strain rate associated with the appearance of bands of flow localization and cracking.

Healing of Fatigue Crack in 1045 Steel by Using Eddy Current Treatment

In order to investigate the methods to heal fatigue cracks in metals, tubular specimens of 1045 steel with axial and radial fatigue cracks were treated under the eddy current. The optical microscope was employed to examine the change of fatigue cracks of specimens before and after the eddy current treatment. The results show that the fatigue cracks along the axial direction of the specimen could be healed effectively in the fatigue crack initiation zone and the crack tip zone under the eddy current treatment, and the healing could occur within a very short time. The voltage breakdown and the transient thermal compressive stress caused by the detouring of eddy current around the fatigue crack were the main factors contributing to the healing in the fatigue crack initiation zone and the crack tip zone, respectively. Eddy current treatment may be a novel and effective method for crack healing.

Microcrack healing in non-ferrous metal tubes through eddy current pulse treatment

This study proposed a novel method to heal microcrack within Mg alloy tubes using high density eddy current pulse treatment (ECPT). Through electromagnetic induction inside a copper coil connected with a high density pulse power source supply, the high density (greater than 5u2009×u2009109u2009A/m2) and short duration eddy current was generated in tube specimens of Mg alloy. The results show that the microcracks in tube specimens was healed evidently and the mechanical properties of the tubes subjected to ECPT were improved simultaneously. The crack healing during ECPT was ascribed to not only the thermal stress around the microcrack tips and the softening or melting of metals in the vicinity of microcrack tips, but also the squeezing action acted by the Lorentz force. In the inward-discharging scheme, both the compressive radial stress and tangential stress induced by the Lorentz force contributed to more sufficient crack healing and thus better mechanical properties of tube specimens after the ECPT experiment, compared to the outward-discharging scheme. The ECPT can heal microcracks automatically without directly contacting tubular specimens and is not limited by the length of tubular workpieces, exhibiting great potential for crack healing in non-ferrous alloy tubes.

Study on Hot Deformation Behavior and Processing Map of 20 Volume Percent Al 18 B 4 O 33w /2024 Composites

The hot deformation behavior and processing map of 20vol%Al18B4O33w/2024 composites were investigated by isothermal compression test within the temperature range of 380–500 ℃ and the strain rate range of 0.001–1 s−1. The results show that with the increase of temperature and decrease of strain rate, the flow stress decreased gradually during hot deformation. Due to dispersed strengthening caused by Al18B4O33 whiskers, the activation energy of the composite was much higher than the self-diffusion energy of pure Al. With the increase of deformation temperature, the deformation softening mechanism of the Al matrix composites was controlled both by dynamic recovery and dynamic recrystallization. The dynamic material model (DMM) was reliable in predicting the safe deformation regions. The Prasad’s instability criterion was appropriate in predicting the flow instability regions. The optimum deformation condition was 460–480 ℃ and 0.01–0.1 s−1, which was validated by near isothermal two-directional forging experiment. This study provided an effective guidance on hot working of Al18B4O33w whisker reinforced Al matrix composites.