Papers by Keyword: Semi-Solid Forming

Abstract: Based on making principle of aluminum foams and semi-soild forming technology, a two-stage foaming process for Al-Si alloy foam named Semi-Solid Foaming (SSF) was put forward in this paper in order to control the cell structure of closed-cell aluminum foam. On the basis of introducing basic technology of SSF, effects of process parameters on foaming process and cell structure was investigated to obtain optimal parameters. The results show that the decomposing time of TiH2 can be controlled and two-stage foaming process, i.e. SSF, has been realized, to obtain Al-Si alloy foam of relatively homogenious cell structure with porosity of 74.6%, cell diameter ranging from 2.1mm to 3.2mm（average value is 2.3mm），and average circularity of 0.812. It is clarified that optimal parameters are as follows:agitation temperature is 580,the mixing time is 0.5min,the mixing speed is 1200r/min，re-foaming temperature of furnace is 720 and the heating time is 15min on condition of experiment.

Abstract: In this paper, the methods of electromagnetic stirring and isothermal extruding were used to study the semi-solid forming performance of ZA27 alloys. Through summarizing and analyzing the stirring experimental results, the reasonable parameter combination of electromagnetic stirring is that inputting voltage is 180V-200V and stopping stirring temperature is 465°C-475°C and cooling method is quenching. After ZA27 alloys are stirred by using above parameter combination,the spherical microstructures are obtained.Then the billets which were prepared by using above reasonable parameter combination were reheated to semi-solid temperature range for isothermal extruding.The extruding ratio was 4.Because the recrystallization occurs during extruding,the grains of ZA27 alloys become smaller and more uniform after isothermal extruding and per unit extruding force of semi-solid ZA27 alloys decreases by 1/4-1/5 times than that of general casting ZA27 alloys.These results provide a reliable experimental basis for production and application of ZA27 alloys.

Abstract: The semi-solid forming (SSF) of aluminum alloys offers many advantages over conventional casting processes. Nevertheless, the semi-solid forming is still far from its full commercial potential and mainly used in specific niche markets. The market positioning requires simple, low cost, and versatile SSF processes that are capable of processing a wide range of alloy composition including wrought alloy compositions. However, wrought alloys must be adapted to obtain the desired semi-solid processing ability and proper mechanical properties. The processing of these attractive alloys with the SEED process offers the possibility to better target specific applications and customers’ needs. In the present paper, the alloy development of AA-6061 aiming to minimize the hot tearing propensity during forming process is reported. An overview of the industrial SEED process used to produce the semi-solid AA-6061 feedstock is presented. The mechanical properties of the cast parts subjected to a specific heat treatment were evaluated. As part of the joint effort between Alcan International Limited and the National Research Council of Canada (NRC), the fatigue results obtained from the semi-solid AA-6061 die cast parts will be also reported.

Abstract: This paper presents an analysis of the effect of CO2 laser processing parameters on the surface modification and heat treatment of steels. The CO2 laser and sample movement process parameters are presented. The controlled operation of these in conjunction with each other is required to obtain better surface hardness and structure. H13 tool steel samples were rotated at high speeds to keep exposure times below 0.3s. Laser processed samples were analysed using EDX spectroscopy, optical microscopy, Vickers and Martens micro-hardness testing, and X-ray diffraction (XRD). Results show how the hardness profile through the surface is related to the laser treatment and resultant microstructures. Increased surface hardness was noted due to a complete microstructural transformation to an amorphous state in the glazed samples. The usefulness of such coatings on tool steels, in conjunction with other thermal barriers, for the forming of semi-solid steel alloys is presented.

Abstract: Thixo-forming is in the forefront of metal processing technology in the 21st century. The research on thixo-co-extrusion of multi-layer tube as extension and development of the semi-solid forming technology is a completely new processing method for the composite material forming and is of great significance, in which different semi-solid billets (slurries) are extruded at the same time to form multi-layer tubes. In this study, different sizes of column-shaped and ring-shaped billets of Al/Mg alloys were firstly prepared by using specially designed molds. Then they were reheated by electric-resistance furnace，microstructures from different heating laws were investigated. Lastly, FEM simulation on thixo-co-extrusion of double-layer tube with A356/AZ91 was conducted.

Abstract: The paper presents some experimental data about the thixoforming process applied to different aluminum alloys very used in the Romanian machine building industry. From many procedures for obtaining the semisolid slurry described in the paper, based on specialized literature [2, 3, 4] in particular, the accent is given to choose the mechanical mixture in the overheated mould until it reached the liquid alloy temperature. The main results are based on reducing of stirring time for increasing the benefits of the new technology. All procedures and results are described in the paper and also some specific conclusions are given. The experimental data of the research, were obtained in the specific testing laboratory from Transilvania University of Brasov.

Abstract: The evaluating rules for semi-solid microstructure were brought up, and the analysis software was developed on MATLAB 7.0 platform in this study. Furthermore, this system can be used not only in the Thixomolding AZ91D magnesium alloy microstructure analysis, but also in the other semi-solid processing microstructure.

Abstract: This paper describes a new integration algorithm for hyperbolic sine constitutive equation (HSCE) used in semi-solid forming. An intermediate variable Lambda ranged from zero to one is introduced to replace the inelastic strain rate in HSCE so that the inelastic strain rate can be solved indirectly from the Lambda. The proposed integration algorithm is based on the stress update concept and the effect of normal stress updating on the material compression is also discussed thoroughly in this paper. The investigation results show that the new algorithm can integrate the HSCE efficiently and the normal stress should keep constant as the deviatoric stress updating. An example of semi-solid extruding was given in the paper at last to illustrate the implementation of new algorithm and effect of normal stress updating on the compression of material.

Abstract: The Council for Science and Industrial Research has developed and patented a rheocasting process. The process involves the preparation of semi-solid slurries from liquid metal, by controlled cooling and MHD stirring using induction coils. An industrial prototype was designed and built to test the system in an industrial environment. A semi-solid high pressure die casting cell was set up with an industrial partner and the system was tested under normal production conditions. The production cell consisted of the CSIR rheocasting system, a six axis robot, dosing furnace and 400 ton H-400SC shot controlled Bühler HPDC machine. An engine mounting bracket originally designed for liquid HPDC was redesigned for SSM forming (casting) taking into consideration the flow and thermal behaviour of semi-solid casting process, the function of the component and the required mechanical properties. Although a full production run was not completed due to an ancillary equipment failure, sufficient castings were produced to perform preliminary evaluation of the components. The processing parameters used were, die temperature of 250°C, SSM casting temperature of 580°C ±1Cº and a piston injection velocity of 0.13 m/s. Initial evaluation showed evidence of casting defects due to a combination of factors: die design/manufacture, casting parameters and poor foundry practice. From the mechanical tests it was evident that if the die design, casting parameters and foundry practice are optimized components with adequate mechanical properties can be reliably produced.

Abstract: Thixoforming offers the possibility of forming complex aluminum parts with a superior quality and a reduction of processing steps. The production of a fine, equiaxed, globular microstructure is essential for thixoforming. Strain Induced Melt Activation (SIMA) and the Cooling Slope (CS) casting processes were employed to produce AA6082 thixotropic feedstock in the present work.. SIMA process produces such a microstructure through recrystallization of heavily deformed billets and a subsequent heat treatment in the mushy zone. Molten metal with a suitable superheat is cast over a water-cooled, inclined metal plate into a permanent mould to produce the thixotropic billet in the CS casting route. The effect of cold work and heating temperature and time were investigated for the SIMA process where as the effect of CS length, casting temperature on the final microstructures were investigated for a fixed set of heating conditions in the CS casting route.