Advanced Materials Research Vols. 97-101

Abstract: The hot deformation behaviors of a high strength low alloy steel have been studied using the processing map technique, which is based on the variations of efficiency of power dissipation with forming temperatures and strain rates. The results show that: (1) The average grain size of the deformed alloy steel increases with the increase of forming temperatures and decreases with the increase of strain rates. (2) The efficiency of power dissipation increases as the forming temperature is increased. However, the efficiency of power dissipation changes with strain rates in the form of bulgy parabola, and the maximum value exists at the strain rate of 0.1 . (3) A domain for reasonable dynamic recrystallization (DRX) exists in the temperature range of (1050–1150) and strain rate range of (0.01–3) , with its peak efficiency of 32% at about 1140 °C and 0.23 , which are the optimum hot working parameters for the studied high strength low alloy steel.

Abstract: The microstructures of 30Mn20Al3 non-magnetic steel after different finishing temperature and cooling rates have been studied by multi-pass compression test in a thermal-mechanical simulator. The results show that the microstructure of this steel is totally of austenitic with amounts of twins. At the same cooling rate, larger amount of thicker twins appear when lowering finishing temperature. The austenite grain size is related to finishing temperature and cooling rate. The critical temperature of austenite recrystallization is determined as 950~1000°C. When the finishing temperature is about 1000°C and cooling rate higher than 15°C/s, fine and uniform austenite grains can be obtained.

Abstract: 10vol. % Csf/AZ91D composites were fabricated by extrusion following vacuum infiltration process with self-developed experimental device and measuring system. The relationships of load vs displacement during process and surface quality of composites at various extrusion temperatures were investigated. SEM microscope was used to observe the microstructure of fabricated composites. The experimental results showed that the extrusion process can be divided into three deformation stages. The extrusion temperature had a great influence on the maximum extrusion load. Based on proper infiltration parameters, a extruded bar with good surface quality was obtained at extrusion temperature of 420°C.

Abstract: Two different methods were utilized to synthesize intermetallic nickel aluminide alloy. The first method was combination of powder metallurgy and reaction synthesis (IMC_RS) and the second method was plasma melting to form homogenous plasma melted samples (IMC_PM). XRD patterns for both samples showed complete formation of single phase Ni3Al. Saturation magnetization value for IMC_RS was 0.445 emu/g and IMC_PM was 0.157 emu/g. This was comparable with Ms value of commercial Ni3Al from Alfa Aeser (0.398 emu/g). The reduced elastic modulus, Er value of IMC_PM and IMC_RS were 441.09 MPa. 408.2 MPa respectively. Both samples were exposed to 1%SO2/air gas mixture at 1000oC for 24-hour duration. The isothermal kinetic results for both samples were parabolic indicating rate limiting step. The oxide scales consisted of NiO, NiAl2O4 and Al2O3.

Abstract: Aluminum alloy joints are a key component of a light-weight bus body, hence, they have a complicated structure and high strength requirement. A vacuum die casting mould has been developed and joints have been manufactured using a CAE simulation, a “whole-process-vacuum exhaust” vacuum die casting process and a decreased cross-section design for vacuum-pumping. The joint’s internal porosity has been noticeably reduced and its mechanical properties have been considerably improved in comparison with joints manufactured from die casting.

Abstract: In this paper, finite volume method (FVM) is adopted to simulate complex irregular aluminum profile extrusion process. The basic theory of FVM, the materials model, friction model, and a computer aided optimization (CAO) model based on orthographic experiments, artificial neural network (ANN) and genetic algorithm (GA) are presented. A complex aluminum profile extrusion is simulated and optimized. The results show FVM simulation is a good way for the description of material flow, and mesh distortion could be avoided effectively. Optimal values of multi parameters are also obtained. Experiment shows good fit among the simulation, optimization and the experimental results.

Abstract: The mathematic model of three-dimensional aluminum profile extrusion processes using finite volume method (FVM) was established in this paper. Basic theory and key technologies of this model were researched and built. Non-orthogonal blocked structured girds were used to fit complex geometries. Volume of Fluid (VOF) scheme was used to capture the free surface of the deforming materials. A program AE-FVM was written according to the above theories and equations. A thin walled aluminum profile extrusion process was simulated and optimized using AE-FVM. The simulation results were also compared with that simulated by Deform-3D and SuperForge in the same conditions. The feasibility of the mathematic model built in this paper was demonstrated by the simulation results comparison.

Abstract: Local increases in product sheet thickness effectively contribute to reducing total product weight. Products could be designed efficiently if a designer could predict and control the thickness distribution of formed products. This paper presents a numerical simulation and evaluation of the local thickness increment of products formed during the ironing process. To clarify the mechanism of the local increase of sheet thickness, a 3-D numerical simulation during ironing was performed by the Finite-Element Method. Tool shapes (contact angles with the original materials and contact length of the punch with the material) that primarily affect thickness changes of original materials were evaluated. It was found that the sheet thickness distribution could be controlled if the original material were relatively thick, when appropriate manufacturing conditions could be selected.

Abstract: The growing demand for lightweight products has been increased by the rapid development of automobiles in order to reduce fuel consumption. One of the keys to reduced fuel consumption is to utilize high-strength, light materials like stainless steel that are difficult to form due to their high strength. This paper discusses the development of pressing technology that forms relatively high-strength stainless-steel pipe with surface screw threads. Our new press-forming process was tested to obtain accurate screw threads on stainless-steel pipe. A 3-D digitizer was used to measure the accuracy of pipes manufactured by the proposed pressing method. Our proposed press-forming method decreases pipe thickness more effectively than conventional roll-forming technology. The maximum decrease in material thickness produced by conventional roll forming was 40%. The maximum decrease in material thickness produced by our press-forming process was 20%.

Abstract: Contact friction is of crucial importance for the accurate modelling, optimum design and control of industrial rolling processes. Hot rolling tests were carried out to investigate the deformation of oxide scale and friction during hot rolling of stainless steel 304L. The morphology of oxide scale layer and the surface roughness transfer under the conditions of hot rolling were obtained. The friction condition at the roll-strip interface was determined.