Papers by Keyword: Semi-Solid

Abstract: The as-cast and friction stir processed (FSP) hypereutectic AlSi29Fe3 were reheated to the semi-solid state, the coarsening dynamics of the Fe-rich phase during the process of remelting were investigated by the means of quantitatively metallurgical analysis. The results indicated that the coarsening of the Fe-rich phase in semi-solid state for both microstructures followed the Lifshitz-Slyozov-Wagner (LSW) theory:. However, the coarsening exponent n of the Fe-rich phase in the as-cast microstructure was 3, in the FSP microstructure was 2. Therefore, the growth rate of the Fe-rich phase in the FSP microstructure was larger than in the as-cast microstructure. In the meantime, the morphology of the Fe-rich phase changed to short bar from granular in the FSP microstructure.

Abstract: The deformation behavior of semi-solid aluminum alloy is strongly dependent on the microstructure. This paper illustrates several experimental research works concerning thixoextrusion of 7075 aluminum alloy which was carried out at “Arts et Métiers ParisTech” of Metz. Inductive re-heating of the aluminum billet is the method used in order to obtain the target liquid fraction for thixoextrusion. To minimize the heat losses, a sample obtained from a direct extruded bar is inserted in a die for reheating in semisolid state and thixoextrusion. During the experimental re-heating process, the temperature was directly controlled by using thermocouples for temperature measurements in the sample and also in the die. The influence of different working ram speeds and reheating temperature on the microstructure evolution was studied by optical microscopy. The experimental results on extrusion load and microstructure evolution of the component are reported.

Abstract: The semisolid slurry of A356 Al alloy was prepared by low superheat pouring and weak traveling-wave electromagnetic stirring (LSPWES), and then the slurry was further soaked for proper time and finally rheo-cast into a rheo-casting sample in this paper. The experimental results show that if the melt of A356 Al alloy is poured at 630-650°C and meanwhile stirred by weak electromagnetic field for a short time, the most primary α-Al grains solidified in the slurry are spherical and only a few are rosette-like. The shape of primary α-Al becomes more spheroidal and more homogeneous distribution in the microstructure by the process of the uniform temperature fields. The experimental results also show that the slurry temperature, injection pressure and speed have a great influence on filling ability. The higher the slurry temperature, injection pressure and speed, the higher the slurry filling ability, the more easily the die cavity is filled. With the given rheo-casting sample, if only the slurry temperature should be equal to or more than 585°C, or the injection pressure is equal to or more than 20 MPa, or the injection speed should be equal to or more than 0.24m/s, the rheo-casting sample die cavity can be filled completely. The microstructure of the castings indicates that the shape, size and numbers of the primary α-Al grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 160 °C for 16 h, the tensile strength, elongation rate and hardness of the rheo-casting samples with the above process are respectively 321.5 MPa, 8.03% and 105.9HB.

Abstract: Based on the SCR process, semisolid shearing-rolling process was proposed. Effect of strip size on neutral angle during the process was analyzed. Neutral angle decreases gradually with the increment of the strip width. When the strip width is less than 40 mm, the neutral angle decreases more obviously with the increment of the strip width. When the strip width is greater than 40 mm, the neutral angle decreases slowly with the increment of the strip width. The neutral angle decreases gradually with the decrease of the strip thickness. Neutral angle is mainly affected by the strip thickness.

Abstract: Spherical grains can be obtained by several semisolid processes in aluminium alloys. One of these methods is called Strain Induced Melt Activated (SIMA). In this work, commercially available 2024 and 7075 alloys were subjected SIMA process. First, optimised process parameters were investigated for the homogeneous spherical grain structure. This was followed by solution heat treatment of the parts. For the quenching medium, room temperature and 80°C boiling water was selected. The effect of different quenching temperatures over the mechanical properties was tested. Hardness, tensile and fatigue tests were applied. In addition, reduced pressure test was used to assess alloy quality and the results were compared with the mechanical tests.

Abstract: Semisolid A356 alloy was prepared by low superheat pouring. The effects of La as a kind of refinement on the size and morphology of the primary phase in semisolid A356 alloy were researched. The results indicated that semisolid A356 alloy contained certain La addition with particle-like and rosette-like primary phase could be prepared by low superheat pouring. The size and morphology of primary phase in A356 alloy are markedly improved by the suitable addition of La. The refining mechanism of La on the size and morphology of the primary phase in semisolid A356 alloy were concerned with the eutectic reaction induced by La in the alloy.

Abstract: The semisolid A356 alloy slurry was prepared by low superheat pouring and slightly electromagnetic stirring (LSPSES). The effects of frequency conversion on the slurry were researched for energy-saving. The results indicated that it was feasible to prepare the slurry with particle primary phases by LSPSES. The application of frequency conversion technique into the preparation of the slurry by LSPSES was favorable to satisfying the requirements of rheo-forming and reducing the energy consumption.

Abstract: The as-cast and semi-solid microstructures of quasicrystal reinforced AZ91 alloys were investigated. The results show that the main phases of as-cast AZ91ZY1 and AZ91ZY2 alloys are all α-Mg, I-phase, Mg17Al12 and Al2Y phase. The grain boundary phases contents increase with increasing Y and Zn contents. The better semi-solid processing technological parameters of AZ91ZY1 and AZ91ZY2 alloys are 580 °C, 30 min and 560 °C, 30 min respectively. The better semi-solid processing temperature of AZ91ZY2 alloy is lower than the one of AZ91ZY1 alloy is mainly attributed to the higher contents of the grain boundary phases in the AZ91ZY2 alloy.

Abstract: Extending extrusion process of semisolid AA2017 alloy was achieved. Metal flow during the process was analyzed by the finite element simulation. It was shown that alloy flow velocity decreases gradually from the center part to the sides of the mould, sometimes a transitional turbulence region appears in the middle. A smaller declining angle θ and without step d is suggested in the design mould. Alloy flow velocity at the center of the forming region decreases linearly with increases of the extending ratio s1/s0.

Abstract: It is demonstrated that the fine spheroidal and equiaxed non-dendritic microstructures required for semisolid casting can be formed by low superheat pouring and weak traveling-wave electromagnetic stirring (LSPWES). The effects of pouring temperature and then soaking treatment on the microstructure of A356 slurry were investigated. The results show that if A356 alloy is poured at 630 or 650°C and meanwhile stirred by an electromagnetic field at low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak traveling-wave electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a large region, which leads to the spherical microstructure of primary α-Al grains. When the A356 alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semisolid forming of A356 alloy.