Solid State Phenomena Vols. 192-193

Abstract: The RheoMetal process (previously called the Rapid S- and RSF- process) is a novel method to produce cost effective, high quality, semisolid slurries for component casting. The RheoMetal process uses an Enthalpy Exchange Material (EEM) as cooling agent to absorb heat and produce a slurry. Critical process parameters to create a slurry by robust melting of the EEM are alloy content, stirring speed, EEM to melt ratio, EEM temperature, EEM microstructural characteristics and melt superheat. In this paper, the melting sequence and melting rate of the EEM was studied experimentally. The effect of EEM composition, as well as superheat, on evolution of shape and dimension of the EEM during stirring was investigated. Initial material freezing onto the EEM was observed, followed by a stationary phase with subsequent gradual melting of the EEM. It was shown that the characteristics of freeze-on layer were strongly correlated to melt superheat, EEM temperature, as well as material composition, hence also has significant influence on the melting sequence.

Abstract: The electromagnetic stirring combined with mechanical stirring (EMSCMV) method was developed for preparing the AlSi9Mg alloy semi-solid slurry. The experimental results demonstrate that, the preparation of semi-solid slurry by EMSCMV is sufficient to obtain fine microstructure of billet. The primary -Al particles are small, spherical and uniform throughout the microstructure. When increasing the stirring power and the vibrating power, the size of primary -Al particles decreases while the shape factor increases, and its distribution is more uniform. The fine microstructure of billet prepared by EMSCMV was obtained at the stirring power of 2.0~2.4 kW and vibrating power of 0.8 kW.

Abstract: The semi-solid slurry of A356 aluminum alloy was prepared through a serpentine pouring channel, which is a new method proposed recently for semi-solid forming process, and the effect of pouring temperature and bend number in the channel on the slurry microstructure was investigated and the slurry was finally rheo-die cast. The results show that when the pouring temperatures are between 640oC and 680oC, the slurry of A356 aluminum alloy with spherical primary a-Al grains can be prepared under the given conditions. The more the bend numbers in the channel are, the better the slurry is, i.e. the primary a-Al grains are more spherical and finer. The results also show that the as-cast ultimate strength and elongation of the rheo-die castings can reach 250MPa and 8.613.2% respectively. After T6 heat treatment, the ultimate strength and elongation of the rheo-die castings can reach 320MPa and 8.011.3% respectively. The work undertaken demonstrates eventually that the serpentine pouring channel process is a good method for semi-solid rheo-die casting or rheo-forming of metallic materials, the process is simple and the slurry cost is not expensive.

Abstract: In the Semi-Solid Processing of indirect squeeze casting, runners were needed for each part cavity. In our experiment, it was found that some of the runners were blocked, and some parts were not filling in full mold. Numerical simulation was applied to analyze this phenomenon, and the results show that it was the shell which emerged on the chamber surface that blocked the runner. Experimental results also confirmed our interpretation. Some measures have been used to correct it, such as runner design, two-layer coating, and process improvement which eliminated blocking of the runner.

Abstract: The semi-solid slurry of 7075 aluminum alloy was prepared by using an innovative non-stirring technology that can be called inverted cone-shaped pouring channel process (ICSPC). The effect of pouring temperature and structural parameters of the channel on the microstructure of semi-solid 7075 aluminum alloy slurry was investigated. The experimental results reveal that when keeping the pouring temperature within some range, the slurry with spherical primary α(Al) grains can be prepared by ICSPC process, and with the decline of the pouring temperature, the microstructure of semi-solid 7075 aluminum alloy is more desirable under the same channel. The appropriate combination of channel length and interior surface slope can also give rise to a transition of the growth morphology of primary α(Al) from coarse dendritic to coarse particle-like and further to fine-globular at the same pouring temperature. In ICSPC process, numerous effective heterogeneous nucleation takes place in the melt as it flowed along the interior surface of the channel and the morphology of primary α(Al) grains is virtually determined by the degree of contact condition between the superheat melt and the interior surface of the channel. A better contact condition stands for a stronger heat extraction from the melt, and will finally appear as a remarkable increase of primary α(Al) grains survived in the melt, which will conspicuously promote the spherical growth of the primary α(Al) grains.

Abstract: A self-developed forced convection rheomoulding (FCR) machine for light alloy semisolid slurry preparation is introduced, which is high efficient, reliable and easy to maintain. Its core component contains a shearing system, a central temperature processing system and a discharge system. Flow characteristics and the parameter of FCR process affecting semisolid slurry organization are analysed. Taking 7075 aluminium alloy as experimental material, experimental results show that the FCR process could obtain semisolid microstructure with the small primary α-Al particles of nearly spherical and uniformly distributed. The melt of aluminium alloy involves complex convection mixing characteristics when flowing in FCR device. As the pouring temperature decreases, the primary particles become fine and homogeneous with the mean size diminished and the shape factor increased.

Abstract: It is known that ultrasonic waves promote nucleation and globulization of solid particles in aluminium alloys. However, the studies performed up to date have been conducted, in the laboratory, using small volumes of aluminium. This article aims to establish the application of ultrasound effect in the A357 aluminium-silicon alloy in amounts of about 2 kg of material. The experiments have been conducted with different parameters of ultrasonic treatment, evaluating the microstructure of the slurry quenched from the semi-solid state. The globulization effect of aluminium α phase by ultrasounds is very effective in the area close to the ultrasonic horn tip and the transmission system, but its effect highly reduces in the regions far away from the source of ultrasonic waves.

Abstract: The purpose of this study was to develop a new method for formation of non-dendritic microstructure during sand casting of aluminum alloys without any previous special processing. For this purpose, sand molds with three different types of running systems were designed. The first design included a traditional reverse tapered vertical sprue. The second design was similar to the first one except for a conical sand core placed inside the lower half portion of the sprue creating a narrow gap for the flow of the melt into the mold. In the third design, the core was fitted with metal chills. Molten A356 alloy was then cast from fully liquid state under gravity and centrifugal casting conditions in the molds and the microstructures of the castings were studied. The results showed that non-dendritic microstructure could be achieved by using the last design under low superheat temperature and centrifugal casting conditions. The findings can pave the way for small quantity production of semisolid castings in expendable molds.

Abstract: For the semi-solid casting process it is very important to make high quality slurry with high speed and low cost. Recently the double-axis-electromagnetic stirrer is developed as the slurry-making tool. This stirrer has rotating magnetic field (RMF) and linear traveling magnetic field (TMF). This new technology shows several advantages in the quality of slurry. The cup design is also important to make uniform quality slurry. In this paper the new stirrer and its advantages from test report and technology of cup design is introduced.

Abstract: Despite the lightweight demands, precision die casting products with high dimensional/ die-transcriptional accuracy is still made by zinc die-casting, because the conventional aluminum die-casting cannot satisfy the requirement. While light weight precision die casting demand for electric devices /automobile parts has been encouraging the material replacement from zinc to aluminum, it cannot be realized yet. We applied the Semi-Solid die casting technique to the precision casting, and verified possibility of replacement of the material from zinc to aluminum