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The effect of pre-stretching and under-aging treatment on microstructure and fatigue crack resistance of Al-4.1Cu-1.27Mg-0.47Mn-0.02Ti alloy has been investigated in present work. The results showed that the fatigue strength corresponding to 107 stress cycle numbers of the sample pre-stretched 4% and under-aged at for 2 hours reached up to 280MPa, 80MPa higher than that pre-stretched 0% and peak-aged at for 8 hours. Microstructural observations showed that fine and uniformly dispersed S’ plates were present in the sample treated by pre-stretching and under-aging, whereas, a coarse S’ plate was formed in the sample when treated by 0% pre-stretching and peak-aging. It is indicated that the pre-stretching and under-aging treatment promotes the dispersoid formation of strengthening particles, enhancing the fatigue crack resistance and resultant fatigue strength. Keywords: Al-Cu-Mg alloy, fatigue, pre-stretching, aluminum alloy casing pipe

In the present paper, the non-intrusive Probabilistic Collocation (NIRPC) method is introduced in detail and used to simulate the effects of tip clearance uncertainty on the aerodynamic performance of NASA Rotor 37, which is combined with a commercial CFD software. The tip clearance height is supposed to be a stochastic variable in Beta distribution with four schemes of uncertainty in the random height of the plain tip clearance, the leading edge, the trailing edge and both the leading and trailing edges, respectively. The statistical properties of total performance of the rotor and flow structure within the blade passage in different flow conditions are analyzed. The results show that the Std. of total performances caused by the uncertain plain tip clearance decreases with reducing of the outlet pressure. The maximum of the standard deviation of Mach number appears in the regions where the leakage flow, the shock wave and the separation flow locate, which decreases from the tip to the hub. When the tip clearance is linear distributed, the uncertainty of tip clearance height at the leading edge is the main factor under high mass flow conditions. With the mass flow reaches to choking point, the Std. of total performances caused by the uncertainty of tip clearance height at the trailing edge drops sharply.

Mechanical properties and microstructural evolution of an Al-Cu-Mg-Ag alloy during thermal exposure at elevated temperature were characterized by means of tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. The tensile test results suggested that tensile strength (σBbB) and yield strength (σBsB) reduced with both increasing exposure time and temperature. When exposed at 150°C, the Al-Cu-Mg-Ag alloy exhibits good structural stability due to the splendid thermal stability of the Ω phase. SEM results showed that the specimen was fractured in a combined manner of intergranular and transgranular fracture. TEM results suggested the reduction of mechanical properties of samples was attributed to the coarsening of Ω phase and the precipitation of θ phase during thermal exposure.

The software CFDesign was used for the analysis of flow field simulation of two different kinds of drilling bit. The results showed that, if the waterway design of drilling bit was unreasonable, it could result in the following phenomenon: the local position of drilling bit could get severe erode of drilling fluid; the return of flow and eddy currents could be observed in the bottom of drilling well; negative pressure could be detected and might result in cavitation corrosion; the direction vector of flow field were diffused and resulted in cross flow. The waterway structure of arc-bottom bit was more reasonable comparing that of flat-bottom bit.

Using the Wilson equation and an extended Miedema model, the thermodynamic effect of silver on the stability of reinforced particles in the Al and Al-Cu matrix were evaluated. The formation of Al3Ti, AlB2, and TiB2 phases are promoted with the addition of silver atoms in Al matrix. Minimum values of excess free energy of reinforced particles were found in the Al-Cu-Ti-B-Ag system. Evidently, Low content of silver atoms actually has the profound effect in promoting the reinforced particles in Al-Cu matrix.

The effect of aging condition on elevated temperature tensile strength and microstructure of an Al-Cu-Mg-Ag alloy was investigated. The tensile strength of 165°C/14h samples was greater at room temperature and 200°C, while the 165°C/2h samples got superior tensile properties at 250°C and 300°C. The microstructure contained mainly of Ω plates in both conditions, and as the increasing of exposure temperature, the coarsening of Ω precipitates occurred by the solution of small particles and the growth of large particles, resulting in an increase in the average particle size, and the decrease in the number of precipitates.

Effect of thermal exposure on FCG of Al-Cu-Mg alloys with low Cu/Mg ratio in artificial and natural ageing conditions were modeled and analyzed. Three FCG rate models, namely Collipriest, Priddle, and Modified Forman model were examined to research the effect of thermal exposure on FCG of Al-Cu-Mg alloys with low Cu/Mg ratio in artificial and natural ageing conditions. The results showed that Priddle model provided the best fit. Priddle model was used to fit FCG data of (a) 170°C/30min ageing; (b)170°C/30min ageing +100°C/2000h exposure; (c)T351 ageing+100°C/2000h exposure; (d)T351 ageing. The fitted results indicated that the FCP resistance can be increased by slight artificial aging, and artificial aging can delay the degradation of the fatigue properties

Mechanical properties and microstructural evolution of an Al-Cu-Mg-Ag alloy during thermal exposure at elevated temperature were characterized by means of tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. The tensile test results suggested that tensile strength (σb) and yield strength (σs) reduced with both increasing exposure time and temperature. When exposed at 150°C, the Al-4.87Cu-1.2Mg-1.0Ag alloy exhibits good structural stability due to the excellent thermal stability of the Ω phase. SEM results showed that the specimen was fractured in a combined manner of intergranular and transgranular fracture. TEM results suggested the reduction of mechanical properties of samples was attributed to the coarsening of Ω phase and the precipitation of S' phase during thermal exposure.

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.

This work aims to develop a physically based numerical model to predict the microstructure evolution and residual yield strength of high Cu/Mg ratio Al-Cu-Mg-Ag alloys after thermal exposure. Based on the established interfacial energy model and the classical nucleation and growth theories, a thermodynamically based precipitation model had been established to describe competitive precipitation of two phases, being of different stability, in under-aged and the subsequent thermally exposed Al-Cu-Mg-Ag alloys. And the strengthening model based on Orowan mechanism was deduced to predict the residual yield strength after thermal exposure. The microstructural evolution and yield strength predictions of the model in this work are generally in good agreement with the experimental result.

Mechanical properties and microstructural evolution of an Al-Cu-Mg-Ag alloy during thermal exposure at elevated temperature were characterized by means of tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. The tensile test results suggested that tensile strength (σBbB) and yield strength (σBsB) reduced with both increasing exposure time and temperature. When exposed at 150°C, the Al-Cu-Mg-Ag alloy exhibits good structural stability due to the splendid thermal stability of the Ω phase. SEM results showed that the specimen was fractured in a combined manner of intergranular and transgranular fracture. TEM results suggested the reduction of mechanical properties of samples was attributed to the coarsening of Ω phase and the precipitation of θ phase during thermal exposure.

The effect of severe plastic deformation method on the dissolution of θ’phase in Al-Cu binary alloy was investigated by employing equal channel angular pressing(ECAP) and multi-axial compression(MAC). The results suggested that a more rapid dissolution of θ’ phase occurred in the MAC processed sample comparing with the ECAP processed sample, which was attributed to the stress state difference between ECAP and MAC processed samples .

The alloying behavior of RE element of Er in Al-Cu-Mg-Ag alloys with addition of Er were investigated in this paper. During solidification ,most of element Er segregated at grain boundaries in the form of primary Al8Cu4Er phase and part of Er dissolved in the α-Al matrix. After rolling, Al8Cu4Er phase could be fragmentated into dispersed particle which leaded to an increase of the grain boundary strengthening . TEM observation and tensile strength test showed that small addition of Er retarded the precipitation of Ω phase and prolonged the time corresponding to the peak aging,with a remarkable increase of ductility.

The evolution of second phases and its effect on tensile mechanical property in artificial ageing and RRA process of super-high strength aluminum alloy is investigated.The result of tensile test shows that the samples of Al-Zn-Mg-Cu-Ag alloy aged at lower temperature(100°C) not only have higher tensile strength up to 753Mpa but also relatively higher tensile elongation above 9% than normal temperature(120°C) in artificial ageing. The sample of Al-Zn-Mg-Cu alloy has the highest tension strength upto 788Mpa when aged at 100°C for 48 hours in single step of artificial ageing. Further more in RRA process samples of Al-Zn-Mg-Cu alloy preaged at 100°C for 24 hours retrogressed at 200°C for 7min and reaged at 100°Cfor 24 hours present the best tensile strength of 795Mpa than others. The tensile strength of Al-Zn-Mg-Cu alloy after RRA treated decreases with prolonging of retrogression time and reageing time starting from 7mins and 24 houres respectively. SEM observation shows that crack of the samples in tensile test is created at large particles in the fracture while there are more particles of undissolved phase in Al-Zn-Mg-Cu alloy containing Ag. TEM observation shows that the dominant strengthening particle corresponding to the peak strength of Al-Zn-Mg-Cu alloy containing Ag when aged at 120°C for 8 hours is η’ phase while dominant strengthening particle is G.P zone when aged at 100°C for 80 hours. However, η’ phase as the dominant strengthening particles corresponds to the peak strength of Al-Zn-Mg-Cu alloy without content of Ag when aged at 100°C for 48hours. TEM observation also shows that G.P zone as strengthening particle is dominant in the samples of Al-Zn-Mg-Cu alloy reaged at 100°C for 24 hours, and strengthening particles is coarsened when the sample is retrogressed at 200°C and reaged for a longer time. It is suggested that whether at the presence of coarse particles of undissolved phases or when G.P zone and η’ particle grow up in the retrogression ,sample needs deformable G.P zone instead of undeformable η’ in subsequent artificial ageing and reageing as dominant strengthening particle, in order to present a larger freedom spacing for dislocation to slip and let the sample not to behave too brittle to display high resistance to imposed plastic deformation or high tensile strength.

0.85Pb(Zn1/3Nb2/3)O3-0.10BaTiO3-0.05PbTiO3 (abbreviated as PZN-based ceramics hereafter) ternary system ceramics with Zn2+ deficiency were synthesized by the columbite method. The effect of deficient Zn2+ on phase structure, ordered micro-region size and dielectric properties was investigated in detail. The analysis of Raman scattering spectra demonstrated that Zn2+ deficiency sharply enlarged the ordered micro-region size. Zn2+ deficiency significantly increased the dielectric constant, and decreased the diffusion degree of phase transition. There is a close correlation between effective ordered micro-regions size and dielectric properties for the PZN-based ceramics.