Papers by Keyword: Gravity Casting

Abstract: Interfacial thermal resistances of Al-Si alloys were evaluated by comparing the measured thermal conductivities and the simulated thermal conductivities. Al-7%Si, Al-18%Si and Al-18%Si held in the solid-liquid coexistence temperature for 90 minutes were fabricated by gravity casting. Thermal conductivities were measured with the steady state thermal conductivity measuring device. Thermal conductivities were also simulated by using optical microscope images. Comparing the measured thermal conductivities and the simulated thermal conductivities, interfacial thermal resistances in Al-Si interfaces were evaluated as about 2.5-4.8×10^-9 m²K/W.

Abstract: This article deals with the problematics of the production of small castings using gravitational investment casting. These are castings with a relatively complex shape, which are used as parts of trigger assembly for musical wind instruments. During their production, various defects occur which are connected with the casting process. The aim of this article is to describe the defects and suggest possible methods for removing them. The first step was to find and identify these defects using metallographic and EDX microanalysis. Furthermore, a simulation calculation of the casting process was used to determine the influence of the casting geometry on casting quality. Based on these analyses, the most suitable alloy and casting system geometry were proposed for the production of the casting.

Abstract: Al-Mg alloys with 3, 4.7, 6, 8, and 10%Mg were fabricated using gravity casting with a copper mold at a cooling rate of 30.6 °C/s. Hot forging was conducted at 500 °C with 50% reduction. An increase in Mg content increased the tensile stress but decreased the elongation in the as-cast ingot. The tensile stress and especially the elongation were increased by hot forging. The tensile stress, 0.2% proof stress, and elongation for hot-forged Al-8%Mg were 337 MPa, 154 MPa, and 24%, respectively. These mechanical properties were obtained without heat treatment. The results show that Al-Mg is suitable for cast forging in terms of mechanical properties and energy consumption.

Abstract: Al-4.7%Mg alloy with 0, 0.2, 0.4, 0.6 and 0.8% Fe added was cast using a copper mold and an insulator mold. The cooling rates of ingots cast using the copper mold and the insulator mold were 30.6 ^°C/s and 0.5 ^°C/s, respectively. The tensile stress and elongation of the ingots cast by the copper mold were superior to those cast by the insulator mold. The addition of Fe did not lead to tensile stress, but the elongation became smaller as the Fe content increased. The elongation of the ingot cast using the copper mold became much smaller on addition of only 0.2% Fe. The tensile stress and elongation were improved by hot forging with 50% reduction. The elongation of the ingots with Fe added was significantly improved by the hot forging. The degree of improvement of the tensile stress and elongation for the ingots cast using the insulator mold was remarkable.

Abstract: A model heat-spreader of Al-30vol%SiCp was cast by gravity casting. The plate size of the model was length 120 mm, width 90 mm, and thickness 6 mm. The effects of the metal head and die temperature on the metal filling in the die were investigated. A sound model heat-spreader of Al-30vol%SiCp was cast with a metal head of 150 mm at a die temperature of 300°C, and an ingot clad was cast. This study proposes the die to cast the ingot clad of Al-30vol%SiCp and 1070 aluminum alloy.

Abstract: A356 alloy was widely used in automobile industry due to its excellent castability and comprehensive mechanical properties. But, with increasing demands of strictly safety of components, fatigue life of A356 alloy became the key properties which were considered seriously. To evaluate the time-consuming properties, elongation, as a replaced property, was employed for its easy testing and the relationship which was proportional to the fatigue life of materials. Semi-solid processing was proved that it can improve the elongation of materials while the mechanical properties still kept at the same level as original alloy. Presently, many semi-solid techniques were developed to produce various products, in which the additional equipment was necessary to form the semi-solid microstructure. Therefore, this work is aimed to development an easily technique to obtain the semi-solid microstructure. In present study, A356 alloy with typical semi-solid microstructure was obtained by addition of RE elements during melt processing. In addition, the melting and pouring process was kept the same as the normal gravity casting of A356 alloy. After the treatment, the elongation was 19.5% for A356 alloy with RE addition, which was much higher than that of 13% for normal A356 alloy. Microstructure observation showed that the morphology of Si was changed significantly, and the shape of spheroid was dominantly appeared other than short rod shape. The improvement of elongation was attributed to the morphology change of α-Al and eutectic Si.

Abstract: Effects of sprue base size and design on flow pattern during aluminum gravity casting have been investigated by employing different sprue base sizes and using computational fluid dynamics (CFD). Calculations was carried out using SUTCAST simulation software based on solving Navier-Stokes equation and tracing the free surface using SOLA-VOF algorithm. Flow pattern was analyzed with focusing on streamlines and velocity distribution in sprue base, runner and in-gate. Increasing well size was produced a vortex flow at the bottom of sprue base which increased the urface velocity of liquid metal in runner. Using a rather big sprue well could eliminate vena contracta, but in-gate velocity was observed independent from well size. It assumes that in-gate velocity may be more influenced by other casting considerations. Using a curved sprue base could remove vortex flow at the bottom of sprue while keeping a nearly full contact between liquid metal and runner wall.

Abstract: In the design of runner systems, ceramic foam filters are used for reducing the velocity of liquid metal in order to avoid so called bifilm defect resulting from a high gating velocity (over its critical gating velocity) in aluminum gravity casting. In this study, two types of runner systems incorporated with the ceramic foam filters were designed. In order to observe the flow phenomena in these two runner systems with and without the filters, a water analogy experiment in a transparent plastic mold was utilized. Furthermore, in order to understand the effect of the filters used in these systems, an aluminum sand casting experiment was conducted. The quality of the cast metal in the outlet area of the filter for these systems was investigated. The defect content of this casting sample was measured by the re-melt reduced pressure test (re-melt RPT) and followed by measuring its bulk density. An optimized runner system with the filter was suggested in this study. Keywords: ceramic foam filter, runner system design, gravity casting, critical gating velocity, bifilm defect.

Abstract: The effects of different microstructural features on the mechanical properties of a conventional and semi-solid gravity sand cast AM60B alloy are investigated. The Rapid Slurry Forming (RSF^TM) technology and a step casting geometry, with a range of thickness from 5 to 20 mm, have been used. Tensile specimens have been drawn from the middle and external regions of the casting. The results show that the microstructure of conventionally gravity cast step castings consist of primary α-Mg dendrites, while those cast from the semi-solid state show the presence of globular and rosette-like α-Mg phase. Partially divorced Mg-Mg₁₇Al₁₂ eutectic and fine intermetallic Al_xMn_y compounds, distributed among the interdendritic channels and along grain boundaries, are also revealed. Due to low solidification rate, discontinuous precipitation of Mg₁₇Al₁₂ also takes place. The presence of primary blocky α-Mg phase and lower eutectic fraction tend to increase the mechanical properties of semi-solid cast Mg alloy.

Abstract: A rheocasting technique called the Gas Induced Semi-Solid (GISS) is being developed for commercial applications in Thailand. The process creates semi-solid metal slurries by applying the injection of fine inert gas bubbles through a graphite diffuser to induce localized convection and heat extraction. The slurries are then formed into parts using different casting processes such as die casting, squeeze casting, gravity casting, and semi-solid infiltration process. This paper reports some of the current applications of the GISS forming processes, including prosthetic adaptors, lapping plates, sacrificial anodes, and armor plates. Preparation of semi-solid slurries of the alloys used in these applications, which are aluminum 356, Sn-Sb, Al-Zn-In, and 7075 alloys, is also reported and discussed.