Advanced Materials Research Vols. 194-196

Abstract: The hot corrosion behavior of pure Co, Co-10Cr and Co-10Cr-5Al alloys coated with (4～4.5) mg/cm² (Na, K)₂SO₄ deposits has been studied at 900 °C in air by thermogravimetry and SEM/EDX analysis. The results show that hot corrosion rate of Co-10Cr alloy was obviously higher than that of Co-10Cr-5Al alloy and hot corrosion rate of pure Co was between those of the two cobalt-based alloys. Both alloys produced complex corrosion scales, containing an outermost layer of pure cobalt oxide and an inner layer where the oxides of both alloy components were simultaneously present on the Co-10Cr alloy, while a middle layer containing CoO and Cr₂O₃ and an inner layer of Al₂O₃ with a few aluminum sulfides appeared on the Co-10Cr-5Al alloy. The results were interpreted by taking into account the effect of active element and hot corrosion mechanism.

Abstract: The microstructures and mechanical properties of AZ91D magnesium alloy produced by two kind of fluxes were analyzed by using mechanical performance testing machine, optical microscope, differential thermal analysis (DTA), X-ray diffraction(XRD), scanning electron microscope（SEM）and energy dispersive spectrometer(EDS) analysis, etc.. The results show that the comprehensive properties of AZ91D magnesium alloy produced by the new flux named NF were better than traditional flux named RJ-2. Phase Mg₁₇Al₁₂ was improved enormously. In addition, not only the nuclear particle A1₄C₃ was formed, but also the grain of the alloy was refined remarkably，and the σ_b，σ_s and δ were increased eventually. The tensile fracture surface was made of deeper dimples with rolling patterns, which was relevant to the smaller microstructure.

Abstract: The effect of temperature on the recrystallization texture and microstructure of non-oriented silicon steel under asymmetrically rolling condition was quantatively studied using X-ray diffraction technology. The results show that the texture component accumulates around {111}<112> when annealed at 800°C. Texture intensity is high and grain size is uniformly distributed between 50μm and 100μm with best magnetism. When annealed at 850°C and 900°C, texture component is scattered and the grain size is also bigger. However, for the annealing at 750°C, the texture component is similar to cold rolled process. The grain size is small and non-uniform, which is unfavorable to magnetism. The difference of forces along the fast and slow side of the roller results in different deformation texture and further affects the intensity of recrystallization texture along the two sides of the roller.

Abstract: The effect of yttrium addition and heat treatment on the mechanical properties and microstructure of AM60 magnesium alloy have been investigated using X-ray phase analysis, microstructure investigation, tensile test, hardness measurement and fracture surfaces analysis. The results showed that the mechanical properties of the alloys were obviously improved with the addition of yttrium no more than 1.0%. The reinforcement of the alloys resulted from the appearance of Al₂Y phase. After solid-solution treatment (T4), the Mg₁₇Al₁₂ phase almost dissolved in Mg matrix, but the rare earth compounds Al₂Y phase was rather stable. The ultimate tensile strength σb was improved, but the yield strength σ_0.2 and elongation δ were only slightly changed. After solid-solution + aging treatment (T6), the Mg₁₇Al₁₂ phase precipitated again and their morphology was changed. The yield strength σ_0.2 was improved.

Abstract: In order to prolong the life of inner liner of coke can, the thermal fatigue property of Cr17Mn10Ni3 heat-resisting steel was analyzed and studied from cast metallurgical structure, the morphology of crack surface and cross-section, the injury factor by OM, SEM, photoshop and imagetool software. The results shows, Cr17Mn10Ni3 has a good thermal fatigue property because of the microstructure with good thermal conductivity, austenite matrix and break carbide lying in treelike crystals. It decreases the innerstress and postpones the time of crack formation and extension, during the process with 1100°C and room- temperature water cooling. The cracks mainly appear in the phase interfaces between carbides and matrix, ferrite and austenite, and grain boundaries. The thin and deep cracks with high concentration are beneficial to relax the elastic strain energy. But a single and thick crack easily widens and deepens to be detrimental to the thermal fatigue property.

Abstract: The surface of the large hydraulic track needs thermal treatment for hardening and tempering to improve its wear resistance and bearing capacities. Currently it is still difficult to simulate the hardened layer of the track. For that, this paper firstly put forward a surface layer hardness graded distribution model of the track, and then established a method to measure the hardness of the track in the finite element software. Based on the limit thinking, the meshes of the hardened layer of the track were refined, so as to achieve the purpose of using the discrete mesh to simulate the continuous change of the hardness graded distribution in the hardened layer of the track. Calculation results show that improving the hardness value and the thickness of the hardened layer of the track are benefit to the track’s bearing capacity and deformation stabilization.

Abstract: The effects of two-step aging temperature on exfoliation corrosion of an Al-Zn-Mg-Cu alloy were characterized by EXCO test, electrochemical test and TEM observations. Results suggested that the partial recrystallized structure is susceptible to exfoliation corrosion which is greatly influenced by intergranular corrosion. The transfer current of the sample aged at 170°C (second-step aging temperature) is higher than that of the sample aged at 155°C. The second-step aging temperature exhibits more contributation to the exfoliation corrosion in this investigation, compared to the first-step aging temperature.

Abstract: . To investigate the effects of thermomechanical treatments (TMT) on the microstructure and properties of Al-Mg-Si alloy, the cold deformation on the ageing precipitation of a solution-treated Al-Mg-Si alloy was studied. The results shows that the time of reaching the peak hardness is shortened with the increasing deformation and an obvious increasing in the peak hardness and tensile strength are occured with higher amount of deformations. The microstructures of peak hardness reveals that the average size of the precipitates becomes smaller in size and greater in number in the alloy with 50% deformations. The study is also carried out to investigate the changes in resistivity of alloys during the ageing time in the alloy with and without 50% deformation. It was found that there are rapidly increasing in resistivity followed by decreasing with the onset of ageing time in both cases. However, the extent of increasing and decreasing in resistivity is much stronger in the alloy with 50% deformation. These results were discussed according to the effects of cold deformation on the dislocations and precipitates in the Al-Mg-Si alloy.

Abstract: Studying effects of Ni content (0.6%, 0.8% and 1.0%) on structure and properties of aluminum brass (Cu-22.7Zn-3.0Al) as-cast ingot, cold-rolled and annealed sheet. The results show that: Ni can restrain the precipitation of β phase, and increase percentage of α phase during casting process. The proportion of α phase of ingot as-cast grows up with the increase of Ni content in the alloy. α phase refines gradually and shape changes to needle-like and distributes more uniform with the increase of Ni. The average grain size of α phase of ingot as-cast is 33.57μm, 31.78μm and 28.32μm respectively, and the percentage of α phase as-cast is 69.73%, 75.18% and 78.91% corresponding to 0.6%, 0.8% and 1.0% Ni respectively in the alloy. The tensile strength and hardness enhance and elongation drops with the increase of Ni content. The hardness, tensile strength and elongation is 238.7HV, 784.9MPa and 3.7% respectively for 0.2mm thickness cold-rolled sheet with 1.0% Ni in the alloy. The sheet from 1.0mm to 0.2mm thickness undergoes deformation and heat-treatment process. The hardness and tensile strength of cold-rolled strip of 0.2mm thickness are 205HV and 691.16MPa that increase 13.25% and 16.45% than cold-rolled sheet of 1.0mm thickness.

Abstract: Investigate effects of annealing temperature and holding time on the recrystallization temperature, hardness, microstructure and average grain size of Cu-20Ni-5Sn alloy by hardness tester, microscope and XRD. Research the kinetic mechanism of grain growth of recrystallization of Cu-20Ni-5Sn alloy. The research result shows that the recrystallization temperature declines with the increase of cold-deformation. The recrystallization temperature is at about 500°C ~650°C respectively for 50% and 60% total cold deformation, and is about 470°C ~620°C respectively for 70% and 85% total deformation. The grains grow up with the increase of annealing temperature and holding time.