Applied Mechanics and Materials Vols. 217-219

Abstract: The thermomechanical treatment of a 2A12 aluminum alloy was researched and the influence of pre-ageing on microstructure and hardness was analyzed emphatically. The results reveal that the hardness of specimen increases when they are pre-aged, the hardness value rises at first and then decreases, reaching the maxmum value when pre-aged at 180°C×30min . After plastically deformed at 450°C, the hardness keeps on increasing, and the grains are equiaxed polygon structure. After all the workpieces are aged in the end, the small particles of the second phase precipitates completely and disperses within the original phase matrix, the particles interact with dislocations in upper state that formed during plastic deformation and lead to a great increase in hardness compared with as-received. the best pre-aging parameter is 180°C×30min.

Abstract: Finite element method (FEM) is applied to analyze the buckling performance of alloy aluminum stiffened panel subjected to uniform axial compression. With the skin thickness and stiffener pitch unchanged, the influence of flange thickness, flange length, stiffener thickness and stiffener height on compress buckling critical loads are studied by FEM. Important parameters influencing the buckling performance are identified and the results offer a referenced measure for the optimization design and engineering application of the structure.

Abstract: The microstructural features and heat treatment response of Cu-2.1Ni-0.5Si-0.2Zr-0.05Cr (wt.%) alloy have been investigated. The alloy was aged at 400°C、450°C and 500°C after a cold deformation of 70% reduction. The variation in hardness and electrical conductivity of the alloy was measured as a function of aging time. The results indicated the highest peak hardness value of approximately 205HV for the alloy aged at 400°C for 4h after the solution treatment and cold deformation. The alloy has two main phases, one is Ni2Si phase, and the other is Cr2Zr phase. The strengthening mechanisms of the alloy include spinodal decomposition strengthening, ordering strengthening and precipitation strengthening.

Abstract: The online-quenching process of 6005 aluminum alloy was simulated by using Abaqus software, the stress field of alloy profile in different quenching temperatures and quenching processing were obtained. The results indicate that during quenching the temperature of the profile is decreasing and the internal stress gradually increasing. At the same time the stresses of different parts of the profile are different, the maximum stress is at the corner, the second in the center and the rest lower. Under the premise of keeping the performance of the alloy, the internal stress after step quenching is significantly lower than that after one-time quenching.

Abstract: Ti-Al multilaminate composite was prepared by high-power EB-PVD technology, and under vacuum condition, the samples were annealed at different temperatures. The changed microstructure of the samples after annealing was characterized by XRD, SEM and EDS. The experimental results show that, with the increment of temperature, the ordered phases reduce due to the diffusion of Al into Ti, and the breakdown of layered architecture was induced mainly by pore formation, grain growth and the grain boundary grooving.

Abstract: The effects of contact pressure and sliding velocity and different environment conditions on the frictional coefficient of friction plate on MW wind power were studied by fatigue testing machine. The results show that the coefficient of static friction and difference between static and dynamic reduced with the increase of sliding speed, and reduced first and then increased and then reduced with the increase of contact pressure, and the change of dynamic friction coefficient was relatively flat with velocity and pressure under dry friction. The impact of water on the triological performance was the large, followed by oil when considering environment factors. Water and pressure and oil were the main influencing factors in considering all factors comprehensively.

Abstract: Low-carbon Al2O3-C refractories were prepared using white fused corundum, α-Al2O3 powders and flake graphite as main raw materials. The critical particle sizes of corundum selected in this experiment were 0.5mm, 1mm and 2mm. The effects of corundum critical particle size on physical, mechanical and thermo-mechanical properties of low-carbon Al2O3-C refractories were investigated. The results show that the increase of critical particle size is conducive to the improvement of thermal shock resistance and fracture energy, but little effect on thermal expansion. The cold modulus of rupture after thermal shock test of samples using 0.5mm critical particle size corundum was 2.09MPa, while using 2mm critical particle size corundum was 2.98MPa. And the fracture energy increased from 265N/mm to 588N/mm when the critical particle size increased from 0.5mm to 2mm. The effects of critical particle size on apparent porosity, bulk density and modulus of rupture were insignificant.

Abstract: Copper-based bearing material containing Bi was prepared by running powder metallurgy process, the influence of the content of Bi on the tribological performance of copper-based bearing materials was inspected and Bi’s impact on frictional wear performance of copper-based bearing materials was studied by a MM-200 frictional wear tester. The research shows that, Bi, with a lower melting point, tends to melt and separate out, in friction process which may reduce shear strength of the friction pair surface and improve the performance of antifriction and adhesiveness resistance. When Bi content gets higher to produce more brittle phases, which will fall off directly from the matrix, the antifriction and antiwear of friction pair will weaken.

Abstract: To research the effect of electromagnetic stirring process parameters on the parts’ quality in semi-solid forming of aluminum alloy, the material of ZL017 was heated and melted, and electromagnetic stirred under different frequency and power, then material microstructure gained by different process parameters was observed. The elementary alteration rule of fluid field was analyzed with the alteration of stirring frequency, current density, stirring time，stirring temperature and fluid viscosity. Suitable process parameters for electromagnetic stirring of ZLl07 was concluded.

Abstract: In order to control the grain structure of K4169 superalloy blade which affects its mechanical performance and ability of resistance to corroding in high temperature state, the transient temperature field distributions were analyzed by using equivalent thermal entropy method with the consideration of the practical boundary conditions, such as, heat exchange and heat radiation in solidification, and the relationships between temperature and time of every point on vertical section and cross section during phase change heat transference process of K4169 superalloy were obtained. The changes of solid phase fraction after every time step were calculated basing on the model of equiaxed dendrite growth solute diffusion put forward by Rappaz and other persons. we used the data to modify the temperature in the same step when phase change latent heat was released. The Cell Automaton technology was adopted to coupled simulate the grain structure formation process of K4169 superalloy blade with its temperature fields using continuous nucleation model and kinetic model of dendrite tip growth. These simulation results which coincided much well with the ones of experiment test have played a very important role in studying superalloy mechanical performance and ability of resistance to corroding of K4169 alloy blades.