Materials Science Forum Vol. 850

Abstract: In the present investigation, a physically based numerical model was developed to predict the yield stress of Al-7Si-Mg cast alloy during processing. It covered the integrated unit step models of the physical metallurgy of solidification, solid-state of homogenization, and structural hardening of precipitation. The as-cast microstructure of Al-7Si-Mg alloy was calculated based on the cellular automaton method and the evolution of the precipitated phase during aging process was achieved by a precipitation kinetic model involved nucleation, growth and coarsening. The yield stress prediction was achieved by a strengthening model including the effects of as-cast microstructure, solution strengthening and precipitate hardening. The predictions of this model were verified by comparing with experimental measured yield stress which shows that this model is successfully applied to predict the yield stress evolution of Al-7Si-Mg cast alloy.

Abstract: In plastic deformation, the strain rate is a crucial factor to influence the constitutive behavior of materials such as the flow stress evolution, dislocation slipping, and deformation heat generation. In the present work, a formula based on the volume flow rate rule in plastic deformation was proposed to estimate the average strain rate of materials during equal-channel angular pressing (ECAP). It has been found that both the deformation parameters (channel angle Φ, corner angle Ψ, channel width d, and pressing speed v) and material characteristics (strain hardening behavior) can influence the average strain rate during ECAP. The present model was compared with two other models for estimating the strain rate and numerical values calculated by four different finite element methods (FEM). The result of the present model is in good agreement with the numerical strain rate values by FEM at various values for channel angle Φ and corner angle Ψ.

Abstract: Quantitative structure and activity relationship (QSAR) method is becoming more desirable for predicting of corrosion inhibition properties. The inhibition efficiency of organic compounds is dependent on many basic molecular descriptors, including structural descriptors, thermodynamic descriptors, information content descriptors, topological descriptors as Wiener index, Zagreb index and molecular connectivity indices. A genetic function approximation approach was used to run the regression analysis and establish correlations between different types of descriptors and measured corrosion inhibition efficiency for imidazole derivatives. A QSAR equation was developed and used to predict the corrosion inhibition efficiency for 18 imidazole derivatives. The prediction of corrosion efficiencies of these compounds nicely matched the experimental measurements.

Abstract: The thermodynamic database has been developed for Au-RE binary systems. Based on the experimental data including thermodynamic properties and phase equilibrium, the thermodynamic assessments of phase diagrams in the Au-RE (RE: Nd, Dy, Yb, Gd, Tb, Sm, Lu) binary systems were carried out by using the CALPHAD (Calculation of Phase Diagrams) method. The Gibbs free energies of the solution phases were described by substitutional solution model, and all of the intermetallic compounds were described by sublattice models. The calculated phase diagrams are congruent with the available experimental data. Combined with the assessed Au-RE (RE: La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) binary systems, the thermodynamic database of Au-RE binary systems has been developed, and some significant information of thermodynamic properties and phase equilibrium could be calculated, which is important for the further development of Sn-Au-RE high-temperature lead-free solders.

Abstract: Sc-based alloys have been used as aero-structures materials, and Sc addition on wrought alloys has positive effects on weldability and welding properties. Phase diagrams play an effective role during the development of new type of alloy with good properties. Therefore, to establish the thermodynamic database of Sc-X binary systems is important and necessary.In the present work, the thermodynamic assessments of Sc-X (Ag, B, Cr, Er, Gd, Mo, Th, W, Y, Zr) binary systems was carried out by using CALPHAD (Calculation of Phase Diagrams) method based on the experimental data including thermodynamic properties and phase equilibria. The Gibbs free energies of the solution phases were described by the sub-regular solution model with the Redlich-Kister equation, and those of the intermetallic compounds were described by the sub-lattice model. A set of self-consistent thermodynamic parameters were derived for describing the Gibbs free energies of each solution phase and intermetallic compound. The calculated phase diagrams and thermodynamic properties are in good agreement with experimental data. The thermodynamic database of the Sc-X (Al, Ag, B, Ca, Co, Cr, Cu, Er, Fe, Ga, Gd, Ge, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Ru, Sn, Th, W, Y, Zn, Zr) binary systems have been developed, which can provide much important thermodynamic information for multicomponent Al-Sc based alloys.

Abstract: With available melting point and hardness, the Bi-based filler alloy is considered as one choice of high-temperature Pb-free solder. Phase diagram can play an important role in the design of new type of Pb-free solder.In the present work, the thermodynamic assessments of the Au-Nd and the Au-Lu binary systems have been carried out by the Calculation of Phase Diagram (CALPHAD) method based on the available experimental data. The Gibbs free energies of the solution phases were described by subregular solution models with the Redlich-Kister equation, and those of the intermetallic compounds were described by sublattice models. A set of self-consistent and reasonable thermodynamic parameters is obtained for the binary systems, which describes the Gibbs energies of the solution phases and the intermetallic compounds phases. Additionally, combined the reported Bi-Au, Bi-Lu and Bi-Nd binary systems, the thermodynamic database of the Bi-Au-Lu and the Bi-Au-Nd ternary systems have been developed, which will provide important thermodynamic information for the phase equilibria of the multicomponent Bi-based alloy systems.

Abstract: At present, the flame retardant system was adopted by Cnooc offshore oil engineering (Qingdao) co, LTD (COOEC) workshop ton class jacket platform, whose heat resistance temperature is no more than 80°C. The part of flame retardant area is burned by excessively high temperature and excessive on-site repair work at COOEC workshop due to reserved area of flame retardant is not accurate. In this paper the welding simulation software SYSWELD was used to analyze the temperature distribution of weld joint of typical assembly at workshop. The process parameters, material and model input parameters were adjusted by the field data feedbacks to obtain the optimized welding temperature distribution. The results show that the temperature distribution simulated by the SYSWELD was similar to the field actual measurements. The results of the temperature distribution of the weld joint give the accurate reserved area of flame retardant.

Abstract: A new mathematic approach was proposed to evaluate the temper embrittlement from the step cooling test. The approach was composed of two parts. A nonlinear model, which acted as weight factor, was used to fit the variance at different test temperatures, and the maximum likelihood method was used to determine the curve parameters. In the ASME specification SA-542, there was no instruction to be provided on how to determine the transition temperature from the test results. This method is adopted as an additional supplementary requirement to assess the temper embrittlement of Chromium-Molybdenum steel.

Abstract: Centrifugal pouring is often used in investment casting of large thin-wall Ti castings to promote filling. Shrinkage defects often appear in a Ti casting produced by centrifugal casting. Numerical simulation indicate that shrinkage is caused by these reasons: improper pouring system and thin-wall structure limited feeding of liquid metal from pouring system, and centrifugal force enlarged the shrinkage defects by strengthen feeding of liquid within the casting. Thus centrifugal casting is replaced by gravity casting and a new pouring system is adopted. Obvious shrinkage defects disappear in the new casting process.

Abstract: Backward Ultra-fast cooling (UFC) plays a key role in low-cost dual-phase steels production. Cooling process control system for backward UFC was developed to meet the process requirements. Basing on basic theory of heat transfer, cooling control model was established to accomplish temperature calculation. To deal with the influence of technological conditions fluctuations an adaption system, including self-learning function and feedback function was proposed to intelligently realize temperature correction. The developed cooling strategy can achieve diversified cooling path control. The controlling of significant technological parameters, including cooling rate and air cooling time for dual-phase steels, was also accomplished. Furthermore, flexible and diversified UFC strategies were developed aiming at high temperature precision and low temperature deviation control in thickness direction. The system has been applied successfully in dual-phase steel production with high stability and reliability. The precision of medium temperature (MT) can be controlled within ±10°C, and the UFC delivery temperature (UFC-T) can be limited within ±30°C of the target values.