Solid State Phenomena Vols. 116-117

Abstract: Recently, we have developed a slurry maker using a multiplex-type slurry cup for rheoforming process. In the present study, the optimum manufacturing condition of semi-solid slurry having a fine and globular structure of primary solid phase was investigated in the multiplextype slurry cup. A various manufacturing condition, such as a pouring temperature of melt, a preheating temperature of slurry cup, and a holding temperature and time of melt in slurry cup was varied to make a processing map of the semi-solid slurry for rheoforming process. Through the microstructural examination of primary solid phase of the interrupt-quenched semi-solid slurry of Al-7wt%Si-0.35wt%Mg alloy produced in the multiplex-type slurry cup under a various manufacturing condition, the optimum manufacturing condition of the semi-solid slurry for rheoforming process were a pouring temperature of melt of 650
, a preheating temperature of slurry cup of 300
, and an isothermal holding time of melt in slurry cup of 10min at 580
.

Abstract: An attempt has been made to investigate feasibility of thixoextrusion for AZ31 Mg wrought alloy through simple partial remelting. Microstructural evolution of AZ31 Mg wrought alloy for thixoextrusion was investigated as functions of isothermal holding temperature and time in the partially remelted semisolid state. The interesting point of this study was that the thixotropic structures of AZ31 Mg wrought alloy without additional pretreatment could be obtained through simple partial remelting. The uniform average grain size and liquid fraction according to the isothermal holding time were very important for the thixoextrusion. Because, it is must be considered on actual extrusion time. The liquid fraction was increased with increasing isothermal holding temperature and time. But, the liquid fraction was almost uniform after 10 min. The average grain size was decreased with increasing isothermal holding temperature. On the other hand, as the holding time increased, the average grain sizes were uniform at 615
and 622
. This phenomenon is very useful for thixoextrusion in terms of process control such as actual extrusion time.

Abstract: This paper is concerned with the dynamic characteristics of sinter-forged Cu–Cr alloy for various strain-rates. The amount of the chrome content is varied from 10 %wt to 30 %wt in order to investigate the influence of the chrome content on the dynamic characteristics. The dynamic response at the corresponding level of strain-rate should be obtained with an adequate experimental technique and corresponding apparatus due to the inertia effect and the stress wave propagation. In this paper, the high speed tensile testing machine is utilized in order to identify the dynamic response of the Cu–Cr alloy at the intermediate strain-rates and the split Hopkinson pressure bar is used at the high strain-rates. Experimental results from both the quasi-static and the high strain-rates up to the 5000/s are interpolated with respect to the amount of the chrome content in order to construct the Johnson–Cook and the modified Johnson–Cook model as the constitutive relation for numerical simulation of the dynamic impact behavior of electrodes.

Abstract: This paper is concerned with the thermo-mechanical behavior of steel sheet for an autobody including the temperature dependent strain-rate sensitivity. Tensile tests have been carried out with the high strength steel sheets such as SPRC35R, SPRC45E and TRIP60. The tensile tests were performed with the variation of the strain-rates from 0.001/s to 200/s and with the variation of environmental temperatures from -40
to 200
. The thermo-mechanical response at the quasi-static state is obtained with the static tensile test and the one at the intermediate strain-rate is obtained with the high speed tensile test. Both the strain-rate and the temperature sensitivity of the flow stress are calculated for the quantitative evaluation of thermo-mechanical behavior of steel sheets. The results demonstrate that as the strain-rate increases, the variation of the flow stress becomes more dependent on the temperature. The results also indicate that the material properties of SPRC35R are more sensitive to the strain-rate and the temperature than those of SPRC45E and TRIP60.

Abstract: Partially Remelted Mg alloys focused only to aspect of semi liquid forming until now. In presents study, for the purpose of proposition as economic lightweight hydrogen absorbing materials, the hydrogenation properties of pressure-composition-isotherm (PCI) apparatus. According to the results of experiments, globules (Mg rich solid phase) were regarded the storage system as a hydrogen absorption/desorption and eutectic/liquid droplets (quenched liquid phase) were considered the catalytic system as an improving factor of hydrogenation kinetics. Especially, the hydrogenation properties were depended on properties of globules and liquid fraction.

Abstract: The thixoforging process in which magazine plates of AZ91D magnesium alloy were thixoforged in semi-solid state using semi-solid billets prepared by common SIMA method and new SIMA method was investigated. The results show that the pressure has a great influence on the semi-solid billet’s ability to fill die’s cavity. When the pressure is 500KN, the semi-solid billet can’t fill the die’s cavity completely. When the pressure is 2000KN, the semi-solid billet can fill the die’s cavity completely. Room temperature mechanical properties, such as yield strength of 201.4MPa, ultimate tensile strength of 321.8MPa and elongation of 15.3%, can be obtained successfully when the technological parameters, including pressure of 200KN, die preheating temperature of 723K, holding for 20min at 818K, are satisfied. Comparing with common SIMA, mechanical properties of room temperature and high temperature at 373K
are enhanced heavily.

Abstract: Many rheocasting processes had been proposed because of the difficulty of recycling, the limit of material, and the high cost of raw material in thixocasting. But, these rheocasting processes also had disadvantages such as the high initial investment cost and the lower mechanical properties than thixocasting. In this study, a continuous fabrication of rheological material with pressure rotation equipment was newly devised to overcome the disadvantages of rheocasting process. In order to investigate the thixoformability, reheating experiments were carried out with the material fabricated by the newly devised equipment.

Abstract: The microstructural evolution of AZ61 semi-solid magnesium alloy during semi-solid remelting process was studied in this paper. The semi-solid billet was fabricated by strain-induced melt activation (SIMA) method. The results showed that the initial semi-solid grains melt mainly through coalescence. With the prolongation of isothermal holding time, the grains grew up and spheroidized, in which the mean diameter of grain and liquid volume fraction increased. In the meantime, the higher the holding temperature, the faster the grain grew and spheroidized. The suitable reheating temperature of AZ61 semi-solid magnesium alloy was 592
. The samples were susceptible to serious deformation beyond 597
.

Abstract: ZK60-RE is a kind of high strength magnesium alloy. Here, starting materials are casting ZK60-RE magnesium alloy and ZK60-RE magnesium alloy extruded by equal channel angular extrusion (ECAE), reheating to semi-solid state and studied on their partial remelting microstructures by means of microscope. The results show that ZK60-RE magnesium alloy extruded by ECAE are much finer and lead to the formation of spheroids quite rapidly while RE elements modified casting need a little longer time. At the same time, the mechanical properties of two kinds of ZK60-RE magnesium alloys are given. To do that, we want to find better magnesium alloys with high mechanical properties and good thixotropy, which adapt to semi-solid process to form the high quality complex component one time.