Papers by Keyword: Electromagnetic Stirring

Abstract: The effects of modification, electromagnetic stirring and compound treatment (modification and electromagnetic stirring) on the microstructure and thermal stability of Al-13% Si alloy are experimentally investigated. The results show that the three melt treatments can change the microstructure of the alloy. The modification has obvious refining effect on primary silicon and eutectic silicon grains, electromagnetic stirring has refining effect on primary silicon grains, and eutectic silicon grains appear coarsening phenomenon. The latent heat is obviously decreased by electromagnetic stirring, while the latent heat is increased by modification. Refining eutectic silicon grains will increase the latent heat of phase transformation of the alloy. When 560 °C remains unchanged, the melting temperature of the alloy generally decreases with the increase of holding time, but fluctuates, with a decrease of 7 °C. The latent heat decreases with the increase of constant temperature time, and the decrease amplitude reaches 8.4%.

Abstract: Al-Si alloy is widely used as a casting alloy. The α-Al phase in the semi-solid state has low Si content in the Al-Si alloy. Then by separation of these α-Al phases from semi-solid Al-Si alloy, refining of aluminum can be possible. But, in near eutectic Al-Si alloy, few primary α-Al phases can be crystallized. If the fraction ratio of the α-Al phase can be increased, near eutectic Al-Si alloy can refine, and this method can be used for recycling. In this study, the effect of electromagnetic stirring (EMS) on the microstructure, especially the amount of the α-Al phase particles was investigated. A rotational magnetic field was applied to JIS ADC12 alloy which has near eutectic content during slow cooling from the liquid state to the solid-state, by using a three-phase AC coil. By applying EMS at solidification, the shape of the α-Al phase became particle shape from dendrite shape, and the amount of α-Al phase particles was increased. Moreover, by applying unidirectional intermittent EMS, the volume fraction of α-Al phase particles was decreased with increasing intermittent applying time. In ADC12 alloy, the primary α-Al phases can be crystallized only 10% generally, but it could be obtained over 40% by applying EMS. This means that the semi-solid slurry of near eutectic alloy with over 40% of fraction solid can be obtained by applying EMS.

Abstract: The Φ730 / Φ340 mm hollow ingots of 2A14 aluminium alloy were produced by conventional and electromagnetic stirring (EMS) DC casting with extremely fine grain morphology. The results indicate that the metallographic microstructure of the alloy was more uniform and homogeneous in the EMS hollow ingot and the finer grain size was obtained. The average grain size dramatically decreased from 115 μm to 70 μm with applying EMS. The macrosegregation patterns of Cu element in EMS and conventional hollow ingots along the radial direction were both following the similar trend that positive segregation occurred in inner subsurface and middle section. Meanwhile negative segregation occurred in section offset to inside of centerline and outer surface. The extent of macrosegregation in EMS hollow ingot was severer than that in the conventional one. The mechanism of EMS was discussed to reveal its effect on the microstructure and macrosegregation.

Abstract: A three phase electromagnetic stirrer was used to agitate aluminum A356 slurry and a dry and oxygen free argon gas was introduced in to the slurry by a porous graphite core at a same time. The prepared semi-solid slurry was then transferred into a metallic mold and was compacted by a drop weight. Results demonstrated a favorable increase in shape factor, decrease in aspect ratio and average diameter size at different intensities of stirring. The intensity of stirring was changed by altering the current passed through the magnetic coil and also bubbling intensity via the porous graphite diffuser. Different time intervals for electromagnetic stirring and gas induction were applied. Agitating the slurry for 90 Sec. separately by electromagnetic stirrer and GISS method, gave better results in terms of shape factor, decrease in average diameter of the globules and aspect ratio.

Abstract: The effect of the different electromagnetic stirring frequency after low temperature pouring on microstructures and mechanical properties of Al-7Si-0.42 Mg-0.1Cu alloys was studied. It was found that the primary α-Al becomes smaller and tended to be spherical morphology, and the particles were uniformly distributed after electromagnetic stirring. The tensile strength of alloys improved gradually from 193.02 MPa to 212.54 MPa, and the elongation increased from 3.73% to 6.67% when the stirring frequency was 10 Hz. From the fracture morphology, the fracture for alloy stirred at frequency of 10 Hz showed more dimples than that without stirring. When the stirring frequency increased to 15 Hz, the microstructures of primary α-Al appeared to be dendritic structures, and the grains became coarse. As a result, the 10 Hz was the best electromagnetic stirring frequency.

Abstract: Based on the green and saving concept, a complex process preparing semisolid alloy slurry was developed, which was composed of the low superheat pouring and low frequency electromagnetic stirring. The semisolid A356-La slurry was prepared by the complex process, and the microstructure of the semisolid A356-La alloy was researched under the different preparing parameters in the complex process, such as the pouring temperature, electromagnetic stirring frequency, stirring time and micro-addition of La. The results indicated that it was feasible to reduce the addition of La and consumption of energy during the preparation of semisolid alloy slurry by optimizing the preparing parameters in the complex process. The suitable preparing parameters were obtained by the experiment, in which the pouring temperature was 630 °C, the frequency of electromagnetic stirring was 30 Hz, and the stirring time was 8 s. When semisolid A356 alloy slurry added 0.3 wt% La was prepared by the suitable preparing parameters in the complex process, the refining effects on microstructure in the semisolid A356-0.3La alloy was indistinguishable with that of the conventional addition amount of 0.6 wt% La in semisolid A356 alloy prepared by low superheat pouring.

Abstract: An enthalpy equilibrium electromagnetic-stirring process was introduced to semisolid metal processing for rheoforming route. AZ91D was die-casted under normally liquid state of Mg alloy, semisolid state of Mg alloy stirred using traditional EM-stirrer and an enthalpy equilibrium EM-Stirrer, respectively. Further step, effect of pouring temperature on microstructures and tensile properties of castings was researched in the introduced process. Experimental results indicated that samples of rheo-diecasted in the introduced process showed globular primary solid particle microstructure and better comprehensive mechanical properties, typical microstructures consisting of globular primary α-Mg grains and pseudoeutectic organization was observed in the castings with low solid fraction, while in higher solid fraction, the microstructure comprised of agglomerating primary solid particles and Mg₁₇Al₁₂ of divorced eutectic. With decreasing pouring temperature, the density of primary solid particles increased greatly, the size of primary solid particle evolved to coarse.

Abstract: In semisolid state forming the thermodynamic control of the solid liquid transition is necessary but not sufficient condition for having a good processing. For thixoforming it is critical to have a refined microstructure that during the heating to the semisolid state, achieve a mixture of small spheres immerse in liquid, which is crucial in order to get the best rheological properties for the slurry. This work compares the morphological evolution at the semisolid state of the Al-7wt%Si-2.5wt%Cu alloy produced by a) direct chill casting under electromagnetic stirring (EMS) combined with grain refinement and b) processed via one single pass in an equal channel angular pressing. EMS introduces metal flow during solidification that allows the better distribution of the nuclei provide by the grain refiner. ECAP has emerged as a promising technique capable of imposing large homogeneous deformations in metals, that could leads to a optimal grain refining. The ECAP deformation occurs in a die that contains two channels of the same cross-sectional area and form an angle of 120°. The raw materials were submitted to a heating treatment in order to reach 60% liquid fraction, at soaking times of 0s, 30s, 90s and 210s and the microstructure was evaluated via B&W and color metalography. Comparing the two production processes, it is observed that the ECAP process is highly efficient: while the traditional EMS method produced grains about 150 μm size, ECAP technique achieved grains of 60 μm, providing a fully globular structure, which exhibit favorable characteristics for the thixoforming process reaching to apparent viscosity about 2*10⁴Pa.s.

Abstract: The paper considers the influence of low-frequency pulsed force of an electromagnetic field on the formation of a solidifying metal structure, investigated experimentally. Pulses in the range from 0.1 to 10 Hz were applied to the melt, during the ingots growth in the cylindrical volume, to create the conditions of the forced convection. The final metal structure and deformation of the samples free surface, solidified in different conditions was analyzed. The reduction of porosity in metal ingots was stated for the cases of forced convection under the pulsed frequencies from 0.1 to 1 Hz, in comparison to the structure, formed by permanent electromagnetic stirring. The specimens, grown under the pulsed forcing with equal time of the pulses and the pauses have concave free surface, as well as in the cases of natural convection and permanent stirring. A flatter form of the free surface was obtained during the solidification process under the short pulses of electromagnetic force. Intorduction

Abstract: Present study reports the effect of electromagnetic stirring (EMS) on reciprocating wear characteristics of A390 alloy. The microstructure features showed the refinement of eutectic silicon and reduction in size of primary silicon particles due to the effect of EMS. Hardness of the A390 alloy (100.28 BHN) prepared by EMS was higher than conventional A390 alloy (66.86 BHN). Reciprocating wear tests were carried out at different contact loads (15N to 90N) and speeds (0.2m/s to 1m/s) using pin-on-reciprocating plate tribometer for a constant sliding distance of 500m. As the reciprocating velocity increases from 0.2m/s to 1m/s, the wear loss of both EMS stirred and without stirred A390 alloys were found to decrease gradually up to the critical velocity 0.6m/s. It was noticed that above critical reciprocating velocity 0.6m/s, the wear loss was found to increase abruptly. Also, as the load increases from 15N to 90N, the wear loss of both the alloys were found to increase gradually up to 45N and thereafter abrupt increase in wear loss was noticed up to 90N. This clearly indicates a transition in the mode of wear from mild oxidative to severe metallic wear regime. Wear rate of without stirred A390 alloy in the region 45N to 90N showed predominant increase compared to EMS stirred A390 alloy. This trend suggests that EMS stirred A390 alloy is more coherent and stable under dry sliding wear conditions than without stirred A390 alloy.