Bimodal-Structured Al–Mg Alloy with High Strength and Ductility Processed by High Strain Rate Rolling at Medium Temperature

Xinyu Li,Weijun Xia,Jihua Chen,Hongge Yan,Zhenzhen Li,Bin Su,Min Song 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

A bimodal grain distribution is generated in the Al-6.5Mg alloy deformed by high strain rate rolling (HSRR) at 320 °C, inwhich the fine grains with the average size of 2.1 μm and the coarse grains with the size of hundreds of microns containingultrafine sub-grains are developed. The deformed microstructures are detected by transmission electron microscopy, X-raydiffraction and electron backscattered diffraction. High strength and considerable ductility are achieved in the HSRRed alloyand the high strength is ascribed to solution strengthening, grain (sub-grain) strengthening and dislocation strengthening. The grain (sub-grain) strengthening is the dominant contributor (~ 146 ± 6 MPa) for yield strength. The generation of newfine grains is primarily observed along the deformation bands related to the high Mg solid content and the high strain rate at320 °C. The dynamic recrystallization related to the deformation bands is proposed to build the bimodal grain distributionfor achieving high strength and considerable ductility.

Effects of Zn Addition on Dynamic Recrystallization of High Strain Rate Rolled Al–Mg Sheets

Lu Zhao,Weijun Xia,Hongge Yan,Jihua Chen,Bin Su 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5

Effects of Zn addition (0, 0.5, 1.0 and 1.5 wt%) on dynamic recrystallization (DRX) behavior of Al-9.2Mg alloy during highstrain rate rolling (with rolling temperature of 400 °C and strain rate of 8.6 s−1) are carefully investigated. The Zn contentplays a significant role in the enhanced DRX of Al-9.2Mg alloy. The critical strain (εc) and the peak strain (εp) are reducedfrom 0.178 ± 0.002 to 0.102 ± 0.001 and 0.211 ± 0.003 to 0.139 ± 0.002 with the Zn content increasing from 0 to 1.5%,respectively. Almost complete DRX grains are obtained in the Al-9.2Mg-0.5Zn alloy. The DRX volume fraction (FDRX), theaverage DRX grain size (AGS), the volume fraction of high-angle grain boundaries (FHAGBs) and the average grain boundaryangle (θAV) are 91.5%, 5.6 μm, 91.1% and 37.6 º, respectively. The Zn addition can enhance the formation of deformationbands (DBs) and promote the DRX process by providing the nucleation sites for new grains, while the increased dynamicprecipitates inhibit DRX. Continuous dynamic recrystallization (CDRX) is the dominant DRX mechanism, while discontinuousdynamic recrystallization (DDRX) is also existent. Effects of Zn addition on DRX process of the Al–Mg alloys canbe ascribed to the more DBs, the reduced stacking fault energy (SFE) and the dynamic precipitates.

Effect of Heat Treatment on the Microstructure and Properties of High Strain Rate Rolled 7050 Aluminum Alloy

Yang Liao,Hongge Yan,Weijun Xia,Jihua Chen,Bin Su,Xinyu Li,Lu Zhao 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4

High strain rate rolling (HSRR) is developed to improve the strength, plasticity and stress corrosion resistance of 7050 aluminumalloy simultaneously. The volume fraction of the small-angle grain boundary in the HSRRed alloy sheet is 89.9%. TEM shows that the presence of dislocations and sub-grains promotes the precipitation of the second phase. The alloy inthe T6 state has the highest strength (622 MPa) and the biggest elongation to rupture (20.6%), but poor corrosion resistance. The over-aged state shows the best corrosion resistance. The RRA state can achieve the tensile strength equivalent to T6 of614 MPa, the highest yield strength of 561 MPa and corrosion resistance comparable to the over-aged state. TEM observationshows the existence of sub-grains and dislocations plays an important role in the nucleation of the second phase. Thehigh strength can be attributed to the higher volume fraction of the precipitates, and the high plasticity can be attributed tothe higher work hardening rate. The better corrosion resistance can be ascribe to the wider precipitate-free zones at the grainboundary and the presence of the larger size second phase particles.

Short-Term Outcomes and Safety of Computed Tomography-Guided Percutaneous Microwave Ablation of Solitary Adrenal Metastasis from Lung Cancer: A Multi-Center Retrospective Study

Min Men,Xin Ye,Weijun Fan,Kaixian Zhang,Jingwang Bi,Xia Yang,Aimin Zheng,Guanghui Huang,Zhigang Wei 대한영상의학회 2016 Korean Journal of Radiology Vol.17 No.6

Objective: To retrospectively evaluate the short-term outcomes and safety of computed tomography (CT)-guided percutaneous microwave ablation (MWA) of solitary adrenal metastasis from lung cancer. Materials and Methods: From May 2010 to April 2014, 31 patients with unilateral adrenal metastasis from lung cancer who were treated with CT-guided percutaneous MWA were enrolled. This study was conducted with approval from local Institutional Review Board. Clinical outcomes and complications of MWA were assessed. Results: Their tumors ranged from 1.5 to 5.4 cm in diameter. After a median follow-up period of 11.1 months, primary efficacy rate was 90.3% (28/31). Local tumor progression was detected in 7 (22.6%) of 31 cases. Their median overall survival time was 12 months. The 1-year overall survival rate was 44.3%. Median local tumor progression-free survival time was 9 months. Local tumor progression-free survival rate was 77.4%. Of 36 MWA sessions, two (5.6%) had major complications (hypertensive crisis). Conclusion: CT-guided percutaneous MWA may be fairly safe and effective for treating solitary adrenal metastasis from lung cancer.

Effects of Ga Content on Dynamic Recrystallization and Mechanical Properties of High Strain Rate Rolled Mg–Ga Alloys

Wensen Huang,Jihua Chen,Hongge Yan,Weijun Xia,Bin Su,Weijun Zhu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.6

The Mg–xGa (x = 1, 2, 3 and 5 in mass%) alloys are subjected to high strain rate rolling (HSRR) at 275 °C with the rollingstrain rate of 9.1 s−1 to develop high performance Mg alloy sheets with high plasticity. Effects of Ga content on microstructureand mechanical properties of the Mg–Ga alloys are investigated by SEM, XRD, tensile testing and etc. The Ga additioncan reduce the critical strain of DRX in Mg alloys, which is associated with the reduced stacking fault energy, the increasedtwinning density during deformation and the more DRX nucleation sites during HSRR. With the Ga content increasing from2 to 3%, the reduced DRX degree is attributable to the hindrance of dynamic precipitates. With the Ga content increasingfrom 3 to 5%, the slightly increased DRX degree can be ascribed to the relatively coarse precipitates. The Mg–2 Ga alloysheet, featured with complete DRX, exhibits an ultra-high plasticity (with the elongation to rupture of 36.6%) and a relativelylow anisotropy of yield strength and plasticity. The Mg–5 Ga alloy sheet has the best comprehensive mechanical properties,with the ultimate tensile strength of 292 MPa, yield strength of 230 MPa and elongation to rupture of 30.3%, which can beascribed to the combination of grain refinement strengthening and precipitation strengthening.

Effect of Strain Rate on the Microstructure and Texture Evolution of the ZK60 Alloy Sheets

Hongge Yan,Qin Wu,Jihua Chen,Weijun Xia,Min Song,Bin Su,Biao Huang 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.3

The dynamic recrystallization (DRX), precipitation and texture evolution of the ZK60 alloy sheets rolled at 300 °C withdifferent strain rates were studied, and the effects of texture on the plasticity were also clarified. The DRX grain sizes at fivestrain rates (5–25 s−1) are 1.4 μm, 1.2 μm, 1.8 μm, 2.4 μm and 2.8 μm, respectively, while the DRX volume fractions are35.8%, 75.0%, 82.0%, 88.0% and 93.0%, respectively. The maximum intensity values of the (0002) texture are 7.91, 8.22,7.64, 5.76 and 5.34 at five strain rates, respectively. The strongest (0002) texture is observed at the strain rate of 10 s−1,which is related to the relatively low DRX volume fraction and the precipitation density. The tensile strength (UTS) and yieldstrength (YS) increases firstly and then decreases, while the elongation (EL) gradually increases with increasing the strainrate, suggesting that the plasticity of the alloy sheet can be improved by decreasing the basal texture intensity and increasingthe dispersion degree of the basal texture. The optimal comprehensive mechanical properties are obtained at the strain rateof 10 s−1, with UTS of 358 MPa, YS of 291 MPa and EL of 21.5%.

Effect of Mg Content on the Damping Behavior of Al–Mg Alloys

Zhenzhen Li,Hongge Yan,Jihua Chen,Weijun Xia,Bin Su,Lu Zhao,Min Song 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

This article investigated the effect of Mg content (4.5, 6.5 and 9.2, in wt%) on the damping capacities of Al–Mg alloys. The results indicate that the damping behavior can be divided into three regions. Region I refers to the low strain amplituderegion (ε < 5 × 10−5), where the damping capacity decreases with increasing the Mg content and has almost no relation withthe strain amplitude. Region II is the middle strain amplitude region (5 × 10−5 < ε < 8 × 10−4), where the damping capacityincreases rapidly with the strain. Region III refers to the high strain amplitude region (8 × 10−4 < ε < 2 × 10−3), where thedamping capacity remains constant and is independent of the strain when the strain is high enough, but increases with the Mgcontent. The damping values Q−1 of Al–4.5Mg, Al–6.5Mg and Al–9.2Mg alloys are 0.01501 ± 0.00032, 0.01633 ± 0.00032and 0.01862 ± 0.00119 at the strain of 1 × 10−3, respectively. The damping capacity in Region I is mainly determined bythe lattice distortion caused by Mg addition and the restoring force caused by pinning points and Suzuki segregation. Theextended dislocations break away from the pinning effect of Mg atoms and become moveable in Region II, and the movementof extended dislocations is the dominant damping mechanism in Region III.

High Strength-Thermal Conductivity Mg–Ga–Ca–Ce Sheet by Hot-Extrusion and Rolling

Mouxin Wu,Xueqi Jiang,Jihua Chen,Hongge Yan,Weijun Xia,Bin Su,Yifu Deng 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.1

The thermal conductivity of magnesium alloys is increasingly required for fast heat dissipation in the automotive and electronicfields. However, the methods for mechanical property improvement such as grain refinement and alloying tend to deterioratetheir thermal conductivity. In this work, a novel low-alloy Mg–2Ga–0.6Ca–0.6Ce alloy exhibits a surprisingly goodcombination of high strength and high thermal conductivity compared with the other samples. The wrought alloys are of smallgrain sizes (< 2 μm), have high yield strength (> 272 MPa) and exhibit excellent thermal conductivity (> 143 W·m−1·K−1). The as-extruded alloy exhibits excellent yield strength (272 MPa) and high thermal conductivity (144.6 W·m−1·K−1) atroom temperature. After 30% rolling, the yield strength is further increased to 283 MPa, and the thermal conductivity isslightly reduced to 143.2 W·m−1·K−1. The effects of Ca and Ce addition on mechanical properties and thermal conductivityare analyzed from dislocation density, dynamic recrystallization fraction (fDRX), average grain size (dDRX) and texturecharacteristics. The higher yield strength can be attributed to the combination of grain boundary strengthening, dislocationstrengthening and second phase strengthening. Moreover, the addition of Ca and Ce can obviously reduce solute Ga atomsin α-Mg, which is the key to high thermal conductivity. Therefore, adding two alloying elements, Ca and Ce, significantlyimproves both tensile properties and thermal conductivity.