Materials Science Forum Vol. 1032

Abstract: Vibration stress relief (VSR) and thermal stress relief (TSR) are important method to eliminate the residual stress of structural parts. The thermal vibratory stress relief (TVSR) is a new method to decrease and homogenize the residual stress. Based on the stress relaxation tests and the equivalent vibration equation of modal analysis, the creep constitutive model and the bilinear isotropic hardening plasticity material model (BISO) are combined to establish the numerical simulation model of TVSR of 7075 aluminum alloy ring part. The simulation results show that four different initial blank residual stress levels are obtained after quenching process, and the residual stress elimination and homogenization effect of TSR and TVSR is better than that of VSR. TVSR has a better effect on both residual stress elimination and homogenization, and the residual stress relief rate can reach more than 20%.

Abstract: In this paper, the high temperature flow behaviors of 6061 Al alloy was studied by thermal compression experiments. The effects of temperature, strain rate and strain on the microstructure evolution and flow behavior of the alloy were investigated by experiments. The results show that the flow stress of the alloy increases with the increase of strain rate and it decreases with the increase of deformation temperature. The flow curve reaches the dynamic equilibrium under the interaction of work hardening and dynamic softening mechanism. The uprising deformation temperature promotes thermal excitation dynamic recrystallization of deformed microstructure. With the increase of strain, the microstructure of the alloy is transformed from equiaxed crystal morphology to fibrous structure and strain-induced dynamic recrystallization occurs. As strain rate increases, the action time of dynamic softening mechanism for the studied alloy is reduced, resulting in the fraction of dynamic recrystallized structure is reduced and the flow stress increases.

Abstract: The milling experiments were conducted carried out which Ti-6Al-4V alloys with different amount of hydrogen permeating were processed, in order to explore various problem in the machining process of hydrogenated titanium alloy. The main cutting force, microhardness and residual stress before and after milling were measured. The experiments result show that Ti-6Al-4V alloy with appropriate amount of hydrogen can effectively reduce the cutting force, improve the surface hardness and reduce the surface residual stress.

Abstract: TC16 titanium alloy is a martensite α+β two-phase high strength titanium alloy, which can improve its structure and enhance properties through heat treatment. Effect of annealing process on microstructure and tensile properties of TC16 titanium alloy was investigated using optical microscope, scanning electron microscope and universe tensile test machine. The results show that when annealed at 720°C for 4h then furnace cooling to ambient temperature, the tensile strength of the TC16 alloy reaches nearly 900MPa,the elongation reaches 19.6% and the reduction of area reaches 65%, which present a good comprehensive performance.

Abstract: The effect of natural aging on mechanical properties and bake hardening behaviors of Al-Mg-Si alloys was quantitatively investigated by a series of tensile experiments along the rolling direction. The natural aging period is from three days to three months after heat treatment. As the results, within three months, along the rolling direction, 0.2% offset yield strength and ultimate tensile strength respectively increased from 97 MPa to 145 MPa, 210 MPa to 248 MPa. The strain hardening exponent n-value and the increment of yield strength after bake hardening respectively decreased from 0.2804 to 0.2186, 127 MPa to 89 MPa. The percentage elongation after fracture varies from 22% to 24% during natural aging and varies from 13% to 16% after bake hardening. A large amount of detailed data has been given, which quantitatively describes the change in mechanical properties and bake hardening behaviors of Al-Mg-Si alloys during natural aging.

Abstract: The surface of Ti6Al4V alloy was rapidly carburized by high-frequency electromagnetic induction heating under vacuum. The microstructure and hardness of the carburized layer were studied. The wear properties of the carburized layer were tested at 50, 100 and 200 rpm using the end face friction and wear device, and the wear mechanism was analyzed. The results show that the TiC strengthening phase was formed on the surface of Ti6Al4V alloy after high-frequency induction carburization, and the surface grains were refined. The surface hardness reaches 1116 HV_0.25, but the brittleness of the carburized layer increases with increasing temperature. The amount of wear was reduced by 54% at 100 rpm. The roughness of the wear scar was reduced from 3.26 μm to 2.28 μm of Ti6A14V alloy matrix. The coefficient of friction and wear rate increases with increasing speed. The wear mechanism was transformed from adhesive wear and oxidative wear of the substrate to abrasive wear after carburizing.

Abstract: The finite element simulation technology can provide strong support for the optimization of processing technology and the treatment of detailed problems in the processing process. Two finite element methods applied to hot forming of high-strength steel plates are introduced, namely the incremental method and the deformation method. Two methods are used for simulation calculations. The finite element simulation based on incremental theory has high accuracy and requires more complete mold and process information. It is mainly used in the middle and late stages of product and mold design. And the finite element simulation based on deformation theory have fast calculation speeds and are mainly used in the early stages of product and mold design. Both types of methods have high practical value.

Abstract: This report outlines a succinct analysis of the contemporary casting methods in single-crystal turbine blades. Furthermore, this paper also provides an examination of the solidification procedure in mixed turbine blades. The couple cooling and heating operation system was advanced to obtain identical thermal positions for single crystal (SC) solidification in the blade group, thereby significantly diminishing the associated flaws in the contemporary Bridgman process. The chemistry science of Nickel based alloys planed for single crystal (SC) gas turbine blades has been notably improved upon, especially when considering the initial production of alloys. The second and third production within the total operation has been enhanced by the introduction of rhenium (Re). Surged density, grain flaws, and microstructural stableness have presented themselves as significant issues within this process. Additionally, it is imperative to minimize the concentrations of the different alloying components.

Abstract: Holistic thin-walled parts are common structural parts of modern aircraft to reduce the weight and increase the stiffness. Over 90% of the materials are removed from the blank, as a result, large machining deformations occur to the parts, which causes the manufacturing discrepancies and even the scrap parts. In this paper, numerical simulation models are established to predict the machining deformation of two typical aviation thin-walled parts. The blank initial and machining induced residual stresses, as well as the cutting parameters, are considered in the model. The deformations and stresses after machining are calculated using the proposed model, and the deformation and stress distributions are analyzed.

Abstract: Titanium alloys have been taken as Oil Country Tubular Goods (OCTG) owing to their higher strength, and better corrosion resistance, but there are some problems in their application process. The corrosion types of titanium alloys were emphatically discussed, and corrosion mechanism was analyzed in this paper. The results showed that the main corrosion type of titanium alloys in hydrochloric acid was pitting, and the surface roughness of titanium alloys could affect it. The critical current density of titanium alloys in phosphoric acid was closely related to temperature and phosphoric acid concentration. The passivation of titanium alloys could be carried out by the growing oxide film at low current density, to achieve the higher stability of passivating film in the concentrated sulfuric acid. Titanium alloys suffered from more serious corrosion in the CO₂-containing completion fluid environment than that in the CO₂-containing formation water environment. H₂S would cause electrochemical corrosion and stress corrosion of titanium alloy pipe, leading to hydrogen embrittlement and even cracking of OCTG. Passivating film was the key to corrosion resistance of titanium alloys, and its composition would change with the depth of the film, presenting N-type. The dynamic corrosion of titanium alloys was mainly controlled by charge transfer.