Solid State Phenomena Vols. 116-117

Abstract: Ultra-fine grained and high hardened Al sheet was obtained by Equal Channel Angular Pressing (ECAP). During this process the microstructure, the hardness and the texture of AA 1050 Al alloy sheet are changed by a severe shear deformation. The plastic strain ratio after the ECAP and subsequent heat-treatment condition was investigated in this study. It was found that the average r-value of the equal channel angular pressed and subsequent heat-treated specimen was 1.7 times higher than that of the initial Al sheet. This could be attributed to the various texture formations through the ECAP and subsequent heat-treatment of AA 1050 Aluminum alloy sheets.

Abstract: This paper is concerned about the precision material property measurement of a micro metal thin foil used in MEMS technology. Evaluations of reliability such as the life cycle endurance test, impact test, and residual stress test are necessary for MEMS components, because MEMS components require great precision and accuracy. However, in practical reliability tests, we should consider various factors that make them hard to perform. In this manner, we use the analytical method to evaluate the reliability of MEMS component rather than actual testing. In general, the analytical method is utilized by software tools. Nevertheless, it is obviously necessary to acquire fundamental properties of materials through real test methods. In this paper, we proposed the micro scale material property measurement system to measure the oriented mechanical properties of aluminum thin foil.

Abstract: Semi-solid slurry for a rheocasting process requires a fine and globular structure of primary solid phase. In the present study, in order to find an optimum preheating temperature of a multiplex-type slurry cup in the slurry maker that we recently developed for the rheocasting process, the semi-solid slurry was held for a various time of up to 60 min. in a multiplex-type slurry cup preheated at a different temperature. A size and morphology of primary solid phase of the semisolid slurry was measured and analyzed with the difference of the recorded cooling curve during the solidification with respect to a preheating temperature of the slurry cup. Also, a microstructural evolution and globularization mechanism occurred during the isothermal holding were discussed. Finally, as considering the effect of a different casting condition on the morphology of primary solid phase the optimum manufacturing condition of the semi-solid slurry for the rheocasting process was proposed.

Abstract: The feasibility study for thixoextrusion of 7075 Al wrought alloys was carried out with respect to reheating profile, isothermal holding temperature and time during the partial remelting through simple partial remelting. The reheating rates were 40
/min and 60
/min. The isothermal holding temperatures were controlled at 609
, 622
, 628
and 632
for 0, 2, 5, 10 and 30 min. The interesting point of this study was that the thixotropic structures of 7075 Al wrought alloy without additional pretreatment could be obtained through simple partial remelting. The average grain size was significantly smaller in the quickly heated specimen. The liquid fraction was increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min is considered very useful for thixoextrusion in terms of actual extrusion time.

Abstract: The mechanical properties of electromagnetically stirred billet of Al alloy during continuous casting such as a tensile, impact, and fatigue property was examined with respect to a size and roundness of primary α phase to examine the influence of the globularization and refining of primary α phase on the dynamic mechanical property. The billet was continuously cast in a casting speed of 100 to 600 mm/min during the electromagnetic stirring with a magnetic flux density of 700 Gauss and then was heat-treated. All tensile properties were enhanced with decreasing the size of primary α crystal and the ultimate tensile strength (UTS), yield strength, and elongation was obtained 320MPa, 235MPa, and 17.8%, respectively, at a size of primary α phase of 77 um. The fatigue life at fracture was largely improved by 37% from 1.25×105 to 1.7×105 cycles and the fracture toughness was obtained approximately 7.25 joules as a maximum value at a minimum size of primary α phase on the present experiment condition. Therefore, it indicates that all mechanical properties can be improved at the higher casting speed owing to the fine microstructure of a primary α phase and also eutectic phase due to the higher cooling rate.

Abstract: In this paper, the influence of electromagnetic stirring on the grain size of A356 alloy inoculated by Al-5Ti-B was investigated. It is found that when stirring is applied at the same time with Al-5Ti-B, the inoculation effect will be disabled. X-ray determination and SEM observation show that stirring hinders the deposition of TiB2 particles; consequently hinder the formation of TiAl3 particles, which were proved to be the nucleus of primary α aluminum phase. If the stirring time is short, the grain size will be abnormally coarse. This experiment also confirms that the grain refinement of rheocasting is caused by dendrite fracture instead of modified nucleation.

Abstract: Semi-solid AZ91 magnesium alloys were produced using a cooling plate followed by quenching in the mold. The cast and T6 heat treated microstructures were microscopically characterized and subjected to hardness tests. It was found that the resultant microstructure in water quenched semi-solid specimen were finer than that in conventional permanent mold cast specimen. The hardness tests also showed that the hardness of quenched semi-solid cast specimen was higher than that of permanent mold cast specimen. This was attributed to large amount of precipitates which results from fine precipitation of eutectic phase at intergranular areas during the aging treatment after its complete dissolution.

Abstract: A 20vol.%SiCw/ZK51A Mg-based composite was fabricated by the process of semi-solid extrusion directly following liquid infiltration. The microstructure and mechanical properties of the composite were investigated in comparison with its squeeze cast and hot extruded counterpart. The results showed that, by semi-solid extrusion, the SiC whiskers were well aligned and microstructure defects associated with the casting technology were eliminated. In addition, as compared with the conventional hot extrusion, the damage to the SiC whiskers during semi-solid extrusion was reduced significantly. Consequently, the composite fabricated by the semi-solid extrusion presented the best whisker reinforcing effect, with its elastic modulus, 0.2% offset yield strength, and ultimate tensile strength achieving 82.5GPa, 383.6MPa, and 431.8MPa respectively.

Abstract: Semi-Solid metal (SSM) processing is now considered a commercially successful manufacturing route producing millions of near net shape parts per annum for the automotive industry. Although semi-solid process is currently widely used as a manufacturing process which produces near net-shape metal component, the processes those used for the preparation of semi-solid slurry still take a great deal of time, energy and money. Cup cast method – recently developed by the authors – is able to make semi-solid slurry preparation as easy as pouring water from a pitcher into drinking glass. In this method globular solid particles are prepared by controlling the turbulence and heat distribution in the melt through pouring instead of applying certain external stirring forces, in other common method. In the current study, cup cast method applied to Al-A356 alloy using simple cylinder. Vital factors of this method were optimized by investigating micro-structures.

Abstract: Production of semi-solid slurry with fine and uniform microstructures is one of the basic and key problems for the industrial application of semi-solid processing. The common disadvantages of existing techniques are as follows: continuous production difficulty, high process controlling requirement and low quality microstructure. In order to overcome those problems, the MSCP (Multielectromagnetic Stirring Continuous Preparation) process has been developed by GRINM. Experimental results show that annular chamber for feedstock production can improve the efficiency of electromagnetic stirring and reduce the difficulty of temperature grad control. Compared with single electromagnetic stirring, multi- electro magnetic stirring can achieve more uniform stirring. Strict temperature grad control in annular chamber is the key of continuous preparation of high quality semi-solid slurry. Semi-solid slurry of different solid fractions was obtained by MSCP.