Advanced Materials Research Vols. 264-265

Abstract: Ring rolling process, especially hot rolling is characterized by 3D deformation, continuous change of thickness and height, high nonlinearity, non-steady flow and asymmetry. It involves both mechanical and thermal behaviors. Most mechanical and physical properties and boundary conditions are temperature related. The heat flow and stress analysis cannot be analyzed separately. In this study, both isothermal and coupled thermo-mechanical (CTM) 3D rigid-plastic finite element (FE) models of the hot ring rolling (HRR) process are developed to investigate their differences in accurately and quickly predicting the process. The results show that the latter should be more advantageous to the more accurate prediction and control of microstructure and properties of the ring.

Abstract: There has been a growing usage of high strength steels (HSS), particularly in automobile applications mainly as structural parts in view of their light weight and high strength properties. These materials are also being considered for dynamic applications. However, the multi-phase microstructure, which is at the base of the strengthening mechanisms in most of these steels, leads to unacceptably high stresses during forming and significant springback phenomena, thus making traditional sheet metal forming technologies unsuitable. To avoid the disadvantages, a new process method was introduced – Hot Press Forming. Hot press forming (HPF) process is a forming method which can provide various advantages such as excellent mechanical properties and formability, good weldability and little springback. Here, the experiment parameters which include locations of the cooling holes and the flow rate of the cooling water play an important role in the HPF process. In this paper, the Al-Si coated boron steel sheet was researched by heating it up to 930oC for 5 min and formed by a hydraulic press. In this study, microstructural evolutions and the associated mechanical properties were investigated in terms of the flow rates of the cooling water.

Abstract: In this study, a combination of starch, glycerol, linear low density polyethylene (LLDPE) and other additives was utilized as the binder composition. The effect of different parameters such as thickness, temperature and time on debinding process of green parts was investigated. Discs of different thicknesses consisting of 2, 2.7 and 3 mm were submitted to the water bath in order to obtain curves of time versus remaining mass of binder. Moreover, the injected tensile bar test specimens was utilized to observe specially the effect of temperature on rate of binder extraction from the green parts. The experiments were conducted at three sets of temperatures including 70, 80 and 90°C. The rate of binder removing considerably increased by decreasing the thickness of the discs. On the other hand, proportion of removed binder in injected tensile bar specimens increased in higher temperatures. The debinding process was successfully performed on injected tensile bars and the components did not suffer from any cracks and swellings. Moreover, the results show that more than 80% of the binder system can be extracted in 6 hours, which is in the acceptable time range. The investigation confirms that from the viewpoint of debinding, starch has a good potential as a binder component in MIM process.

Abstract: Welding sequence is one important factor which affects the residual stresses and distortions produced during welding, thus determines the welding quality and performance. In this paper, 3D numerical simulation of temperature distribution, residual stresses and distortions of the T-joint fillet weld with respect to the variation of welding sequence is presented. The finite element simulation involved thermo-mechanical analyses. Four welding sequences (WS) considered are one direction welding (WS-1), contrary direction welding (WS-2), welding from centre of one side (WS-3) and welding from centres of two sides (WS-4). The simulation results revealed that peak temperature achieved in the welding was greatly affected by the welding sequence and residual stress and angular distortion produced cannot both hold in minimum for a WS. The smallest residual stresses and the smallest angular distortions are related respectively to WS-2 and WS-4. The distributions of temperature, longitudinal and transverse residual stresses as well as angular distortions were also presented.

Abstract: Tube-compression is one of the usual forming methods for variable diameter parts. Due to the influence of compression instability, buckling and wrinkling are prone to occur in tube-compression process, especially for the thin-wall parts, which restricts the diameter reduction ratio limit. In this paper, the viscous pressure forming (VPF) method is proposed for the problems in tube-compression. Utilizing the mechanical property and easily achieved loading mode of viscous medium, the buckling in the tube-compression process can be delayed and wrinkles caused by buckling can be eliminated, so as to increase the diameter reduction ratio limit. The multi-steps forming can divide the large total deformation into much small deformation, thus the small deformation can be controlled in the range of buckling and wrinkling. The process has the more ability to improve material’s forming capability than one-step forming. The deformation of the multi-steps tube-compression process by VPF is analyzed by finite element method (FEM). The variation of length-to-diameter and wall thickness after each step forming has influence on the next step compression. This forming method can also be used in tube-compression of high strength materials and can realize precise plastic forming of parts with high strength, thin-wall and large diameter variation ratio.

Abstract: Due to its attractive characteristics, thin wall ductile iron (TWDI), has been increasingly considered as a preference for reducing material consumption in order to save energy and contribute less environment pollutions as well as decreasing costs. In this research, the effect of two mould runner gating systems and mould coating on graphite nodule characteristics and hardness values of TWDI casting was studied. Strip samples with various thicknesses of 2.3, 3.3, 4.5, 5.4, 6.5, 7.5 and 8.5 mm were casted into CO2 Silicate moulds designed by two gating systems namely stepped and tapered runners. Half of the moulds were coated by graphite-based zircon material to investigate the effect of mould coating on the graphite nodule qualities and quantities. The molten metal prepared contained carbon equivalent (CE) of 4.29% and was poured at the temperatures of 1450°C. Optical microscope (OM) and Clemex Image Analyzer (CIA) were used to evaluate graphite nodule count, roundness and diameter of the nodules of the TWDI cast samples. Brinell hardness test was performed on all samples. The results show that roundness and graphite nodule counts in the microstructure of the samples produced in stepped runner gating system and uncoated mould decrease whereas graphite nodules diameter shows opposite behaviour. Furthermore, molten metal experienced a superior fluidity in coated moulds. Moreover, the TWDI samples achieved a significant improvement in the value of hardness.

Abstract: Thixoforming and related semi-solid processing (SSP) methods require thixotropic materials. One of the many SSP techniques is the cooling slope (CS) casting process, which is simple and has minimal equipment requirements, and which is able to produce feedstock materials for semisolid processing. When the feedstock is reheated to the semisolid temperature range, non-dendritic, spheroidal solid particles in a liquid matrix suitable for thixoforming are obtained. In this study, equipment for the CS technique was first established, and then the effects of the pouring temperature and inclined slope angle on the microstructures of A380 aluminum alloy (ISOAlSi8Cu3Fe) were studied. Optimum parameters for thixoforming experiments were selected, and it was found that the microstructure produced by the inclined plate depended on its angle and the pouring temperature.

Abstract: The main objectives of the present study are to develop/manufacture SiC reinforced aluminium matrix composite (SiCp/AMC) with different reinforcement combinations using stir casting method and investigate the effects of heat treatment on wear performance. AMCs were prepared using 20 vol% SiC with three different reinforcement combinations into aluminum matrix. Stir casting is a primary process of composite production whereby the reinforcement ingredient material is incorporated into the molten metal by stirring. The reinforcement combination consists of 20% (single particle size), 7% and 13% (double particle size) and 5%, 5% and 10% (triple particle size). The triple particle size (TPS) composite consist of SiC of three different sizes viz., coarse, intermediate and fine. The solution heat treatment was carried out on cast specimens at 540 0C for four hours followed by precipitation treatment. The wear test was carried out using a pin-ondisc type tribo-test machine under dry sliding condition. The wear morphology of the damaged surface was also studied using optical microscope and scanning electron microscope (SEM) in this investigation.

Abstract: Kinetic strength in grain growth is evaluated for HAZ of welded pipes. Austenite grain growth is dependant on the thermal cycle and the material properties. In this research the influence of thermal cycle is evaluated using characteristic time constant and characteristic temperature. These dimensionless parameters were calculated for the points lying in HAZ using temperature/time profile derived from Rosenthal equation for the heat transfer. The grain growth is assumed diffusion controlled and Arrhenius temperature dependency is applied for the rate of growth in grains. In an experimental investigation the welded pipes were sectioned longitudinally and the grain size in parent metal and HAZ were measured based on ASTM E 112 by using Planimetric Counting. The obtained data was compared with the result of the model and the appropriate kinetic constant which is calibrated the equation of grain growth is introduced for the seam weld and seamless pipes.

Abstract: Sintering is a key step in the metal injection moulding (MIM) process, which affects the mechanical properties of the sintered part. The mechanical property of the sintered compact is resulted from tremendous sintered part densification. The paper presents an optimisation of the sintering parameter for the best flexure strength of the fine SS316L water atomised powder compact. The L9 (34) orthogonal array is used in the study and four replication of the flexure strength has been recorded at each experiment trial. The analysis of variance (ANOVA) signifies the sintering variables are highly significant to the flexure strength, α = 0.005. The study demonstrates that the cooling rate is the most influential variable that contributes to the best flexure strength, followed by heating rate, dwell time and sintering temperature.