精密铸造锅炉管件用耐热奥氏体钢的研究

为了优化耐热奥氏体钢在锅炉管件精密铸造中的工艺,选取典型焊接接头进行分析,预热温度≥5℃,电压13~14V,焊层数3层,电流190~200 A,层间温度50~230℃。结果显示,600~1200℃温度环境下,AFA25-15为单相奥氏体基体,析出相为NiAl、σ相、M_(23)C_(6)、MC碳化物。通过适当冷变形处理之后,强度明显提升,AFA-50%与AFA-20%抗拉强度均有所降低,断后伸长率变动差异表现不明显。材料氧化腐蚀程度与温度呈正比关系,S31042材料抗氧化腐蚀能力最强,S31035与C-HRA-5材料抗氧化腐蚀能力基本相当。通过本文的研究与探讨,有利于改善锅炉管件用耐热奥氏体钢的综合性能,提升拉伸性能。

Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy

Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

Tensile behavior of 3104 aluminum alloy processed by homogenization and cryogenic treatment

The mechanical properties of 3104 aluminum alloy processed by different combinations of cryogenic and homogenization treatments were studied. The 3104 aluminum alloy processed by the cryogenic treatment followed by homogenization exhibited an enhancement in the tensile strength, yield strength, and elongation by 29%, 41%, and 11%, respectively, as compared with a sample processed by the conventional homogenization treatment. The stress-strain curve of the sample processed by the homogenization treatment exhibited the Portevin-Le Chatelier effect, whereas the sample processed by the cryogenic treatment did not. Further, the cryogenic treatment could accelerate the precipitation of secondary phase particles for the sample processed by a deep cryogenic treatment, followed by a homogenization treatment, which enhanced the dislocation pinning effect of the solvent atoms and thus improved the critical strain.

Quantitative contributions of solution atoms, precipitates and deformation to microstructures and properties of Al-Sc-Zr alloys

In order to investigate the effects of solid solution atoms, precipitated particles and cold deformation on the microstructures and properties of Al-Sc-Zr alloys, the Al-Sc-Zr alloys prepared by continuous rheo-extrusion were treated by thermomechanical treatment, analyzed for conductivity and mechanical properties by tensile and microhardness testing, and characterized using optical microscope, TEM and STEM. A mathematical model was established to quantitatively characterize the contribution of solid solution atoms, precipitates and cold deformation to the conductivity of the alloy. The results show that the strength of Al alloy can be significantly improved by solid solution, aging and cold deformation, and the quantitative impacts of solution atoms, precipitates and cold deformation on the conductivity of Al alloy are 10.5%(IACS), 2.3%(IACS) and 0.5%(IACS), respectively. Aging and cold deformation treatments are the keys to obtain high-strength and high-conductivity aluminum alloy wires.

Effect of cold deformation and heat treatment on microstructure and mechanical properties of TC21 Ti alloy

In the present research work on TC21 titanium alloy(6.5 Al-3 Mo-1.9 Nb-2.2 Sn-2.2 Zr-1.5 Cr), the effects of cold deformation, solution treatment with different cooling rates and then aging on microstructure, hardness and wear property were investigated. A cold deformation at room temperature with 15% reduction in height was applied on annealed samples. The samples were solution-treated at 920 ℃ for 15 min followed by different cooling rates of water quenching(WQ), air cooling(AC) and furnace cooling(FC) to room temperature. Finally, the samples were aged at 590 ℃ for 4 h. Secondary α-platelets precipitated in residual β-phase in the case of solution-treated samples with AC condition and aged ones. The maximum hardness of HV 470 was obtained for WQ + aging condition due to the presence of high amount of residual β-matrix(69%), while the minimum hardness of HV 328 was reported for FC condition. Aging process after solution treatment can considerably enhance the wear property and this enhancement can reach up to about 122% by applying aging after WQ compared with the annealed samples.

Influence of deformation and heat treatment on electrical conductivity of CuMoCr alloy

The solution heat treatment,cold deformation and subsequent aging were performed on CuMoCr alloy.And the influence of deformation and aging treatment on the electrical conductivity of CuMoCr alloy was studied through metallograph,transmission electron microscopy(TEM) and electrical conductivity measurement.Results show that deformation without subsequent aging can reduce the electrical conductivity of CuMoCr alloy,but deformation followed by the optimum aging treatment can effectively improve the electrical conductivity of CuMoCr alloy.Aging at 500 ℃ for 4 h after 80% deformation,the much better electrical conductivity of CuMoCr alloy can be obtained.Reduction of Cr content in the Cu matrix could be the reason for the enhancement of electrical conductivity.

Deformation and heat treatment ability of three-layer 6009/7050/6009 Al alloy clad slab prepared by direct-chill casting

Three-layer6009/7050/6009aluminum alloy clad slab was fabricated by an innovative direct-chill casting process.To study the response of the clad slab to plastic deformation and heat treatments,homogenization annealing,hot rolling,solution and aging were successively performed on the as-cast6009/7050/6009clad samples.The results revealed that excellent metallurgical bonding between7050alloy layer and6009alloy layer was achieved under optimal parameters.The clad ratio obviously decreased when the annealed sample was rolled to55%hot reduction level,and then changed slightly with further rolling.Furthermore,the content of rodlike Zn-rich phases increased significantly in7050alloy layer in the homogenized clad samples after rolling at55%,65%and75%hot reduction levels,and the higher level of hot reduction resulted in narrower diffusion layer.Subsequent solution and aging significantly improved the hardness in7050alloy layer,interfaces and6009alloy layers of the rolled samples except for the thin side for the75%hot reduction sample.