Papers by Keyword: Semi-Solid Processing

Abstract: The inclined Cooling Plate process can be considered as a reliable method for the production of semi-solid ductile cast iron. By utilizing aforesaid method, the main limitation of common semi-solid methods, i.e. Mg fading, will be eliminated. The present research is intended that the importance of alloying design through the inclined cooling plate method and its profound effect on obtaining the optimum solidification range for thixo-forming process have been illustrated. The optimization of solidification range for thixo-forming process has been gained by the simulation in both equilibrium and non-equilibrium conditions. Afterwards the alloy selection has been performed amongst several alloying composition with a view to their effect on the thixo-forming process and austempering.

Abstract: High chromium cast iron samples of 14% Cr and 24% Cr were produced in sand and permanent mold using semi-solid casting process. A series of experiments were carried out to clarify the effect of copper cooling plate and mold cooling rate on microstructure, particularly morphology and sphericity of primary austenite, hardness and heat treatment cycles. Results show that for 14% Cr and 24% cast irons casting at 10 and 15 degrees of inclined plate result in better sphericity and distribution of primary austenite and carbides. Moreover hardness comparison of both semi-solid iron alloys using copper cooling plate at of this special morphologies resulted from cooling plate investigated by making them heat treat at 1050 centigrade °C for 1 and 2 hours. Hardness results show both heat treated 14 and 24% Cr alloy in 1 hours have hardness comparable with those alloys traditionally cast optimum angles with respect to conventional casting show higher hardness in every condition. Effect but heat treated in 2 hours. Finally X-Ray diffraction pattern taken from specimens before and after heat treatment confirmed with observed phases in optical microscopy before and after heat treatment.

Abstract: Semi-solid processing of metals is becoming popular as a new potential manufacturing technology for parts and components in automobile, electronic and machine industries.Up to now semisolid welding technology have not been used in industrial applications. A new process of semisolid metals welding is proposed; the process shows excellent formability and joining ability of semisolid metals, and differs from the process of melt welding or mechanical joining with screws or nails. In the process, semisolid 2A14 aluminum alloy was joint together and was rapidly solidified under pressure. The heat affected zone of the joint was decreased and the grain size of the joint was become small. The application range of the process is wide, i.e., from the electronic industry to arts. The advantages of this new semisolid welding process are (1) ease of joining, (2) good joining microstructure, and (3) ease of carrying out mass production.

Abstract: Recently, semi-solid processing is paid to attention in the field of the light alloys. By this method, it is improved ductility and fatigue strength. Although, because of those mechanical properties of the elongation and toughness is not excellent, the range that can be the application to parts is limited. On the other hand, it is reported that grain refinements cause improvement of ductility and appearance of super plasticity. Then, Equal-Channel Angular Pressing (ECAP) method is reported to be effective to the sample making of a bulk and ultra fine grain in various alloys in recent years. In this study, it tried to improve ductility and durability due to making ultra fine grain in AC4CH alloys by the ECAP method, and the influence of ECAP processing on the mechanical property of AC4CH was investigated. As the result, the ductility of AC4CH has improved by ECAP processing. However, the tensile strength of AC4CH declined along with the increase in the number of passes. So, for the purpose of additional improvement of tensile strength, ECAP-Back Pressure (ECAP-BP) method that was reported to be more effective for grain refinements than ECAP method was applied to semi-solid AC4CH and compared with ECAP method. As the result, the tensile strength of AC4CH was maintained by use of ECAP-BP. Moreover, both ductility and toughness of that have been also improved.

Abstract: This work investigates the viability of production of thixotropic semisolid Ti-Cu alloys by controlled partial melting. Samples were submitted to different holding times at temperatures above solidus, from different initial microstructure conditions. In some cases, deformation by rolling before heating to semisolid was imposed. It is investigated the influence of deformation ratio and holding time in the obtained structure. Results show that thixotropic semisolid can be easily produced; pre-deformation leads to fine, globular primary phase in the liquid for short holding times. Therefore, thixoforming of Ti alloys is feasible, and can bring a whole new concept on forming complex shapes of these alloys, at low energy consumption, and new possibilities in engineering components with special properties.

Abstract: The demand for lightweight structures in the automotive and aerospace industry increases permanently, and the importance of lightweight design principles is also increasing in other industrial branches, aiming towards improved energy efficiency and sustainability. Light metals are promising candidates to realize security relevant lightweight components because of their high specific strength; and amongst them, aluminum alloys are the most interesting materials due to their high plasticity and strain to failure, good processability, passivation in oxygen containing atmosphere, and low cost. However, for many applications, their stiffness as well as strength and fatigue behavior at elevated temperature are insufficient. Metal matrix composite (MMC) formation by integration of reinforcements in the form of continuous or discontinuous (short) fibers can yield a high increase in the alloys’ specific mechanical properties at room temperature and at elevated temperature. The integration of fibers with conventional manufacturing techniques like squeeze casting, hot pressing or diffusion bonding leads to restrictions in the component’s geometry. Moreover, these techniques result in elevated process costs mainly caused by long cycle times and the need of additional protective fiber coatings. In the present paper, an alternative method for the manufacturing of aluminum matrix composites is described, combining thermal spraying and semisolid forming (thixoforging) technologies for the formation of fiber prepregs and subsequent forming with simultaneous densification. Therefore, prepregs with the matrix alloy as a thick surface coating on the reinforcement fibers are manufactured in a fast, automated coating process, while reheating, densification and shaping are performed in a separate process, allowing an optimization of both processes towards cycle times and resulting material properties. Continuous fiber and short fiber reinforced aluminum matrix composites are manufactured using woven or parallel arranged continuous fibers, or short fibers as a fleece or fiber paper material. For the coating process, twin-wire electric arc spraying is applied as a well established, cost efficient thermal spray technology. The coating process is optimized towards microstructure of the matrix alloy prior to semisolid forming, which requires a globular alloy microstructure, and reduced fiber damage during the high-temperature liquid melt deposition. The thermally sprayed fine-grained matrix material enables semisolid forming at liquid contents of 40-60 vol% of the alloy, with short flow paths, reduced mechanical loads and short cycle times. Thus, limited fiber damage and residual stresses will occur, leading to good mechanical material properties. A production line for industrial-scale coating of fiber fabric coils in a continuous process is introduced in order to provide prepregs of various fiber-reinforcement materials and fiber architectures; moreover, a winding equipment for simultaneous fiber winding and coating is presented that enables local reinforcement for components with adapted, tailored composite material design.

Abstract: Rheoforming is becoming the choice of the casting industry which relies on the semi-solid slurry for high integrity structural parts. The potential of rheoforming with LSPSF (Low superheat pouring with a shear field) for aluminum alloys was investigated in the present work. High quality semi-solid slurries of a series of aluminum alloys were manufactured by LSPSF process, such as casting alloy A356, high strength alloy 201, secondary die casting alloy A380 and wrought alloy 2024, 6082 and 7075, in which the primary α-Al presented spherical, small and homogeneous distribution, especially with zero-entrapped liquid. Applications of LSPSF in high pressure die casting process and squeeze casting process were presented. Results showed that LSPSF rheoforming could improve microstructures and increase mechanical properties.

Abstract: In this work we will explore the use of thermochemical simulation methods (Calphad) to support alloy selection and processing in the semi-solid state. Semi-solid processing has been investigated extensively for aluminium alloys, in particular A356, but there is also an increasing interest in using semi-solid processing for steels, in particular high carbon steels. A key property for the semi-solid processing is the fraction of liquid phase as function of temperature. It is necessary to know the fraction of liquid phase in order to be able to control the process and in order to simulate the viscous flow during various forming operations. The approach used here is to calculate the fraction of liquid phase from thermodynamic (and diffusion) data, using equilibrium calculations, Scheil–Gulliver calculations and diffusion simulation. Normally only the solidification behaviour is considered, but during thixoforming also the melting behaviour is of importance. However, there is very little information on melting of alloys to be found in the literature. Here an attempt will be made to discuss also melting as it cannot in all cases be regarded as the reverse of solidification. In addition some further properties, such as enthalpy, heat capacity and density as function of temperature will be discussed. The materials treated are the aluminium alloy A356 and the tool steel X210CrW12. Interestingly they show fairly similar solidification behaviour.

Abstract: Owing to its superior flow and mould-filling capability, a fully globular structure is essential for semisolid processing technologies. The present work was undertaken to identify the cooling slope casting process parameters that, upon heating to the semisolid state, gives the required globular structure for the ETIAL 160 alloy. Of the two pouring temperatures investigated, 605 °C and 615 °C, the lower pouring temperature was found to provide more globular grains surrounded by liquid phases.

Abstract: In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy showed that specimen's thickness and so, its strain affected zones influence on the globulization of dendrites. In addition, it was seen that at a given strain and constant diameter, increase of H/D ratio led to increase of needed time for reaching a certain sphericity in cylindrical samples. Also, it was showed that microstructural evolutions during SIMA processing of both rolled and unidirectional compressed samples were relatively identical. However, at a same condition, ultimate size of globulized dendrites in the rolled samples was smaller than those of compressed ones.