Somjai Janudom

Industrial development of gas induced semi-solid process

The gas induced semi-solid (GISS) is a rheocasting process that produces semi-solid slurry by applying fine gas bubble injection through a graphite diffuser. The process is developed to be used in the die casting industry. To apply the GISS process with a die casting process, a GISS maker unit is designed and attached to a conventional die casting machine with little modifications. The commercial parts are developed and produced by the GISS die casting process. The GISS die casting shows the feasibility to produce industrial parts with aluminum 7075 and A356 with lower porosity than liquid die casting.

Effects of primary phase morphology on mechanical properties of Al-Si-Mg-Fe alloy in semi-solid slurry casting process

Abstract The gas induced semi-solid (GISS) process was developed to create semi-solid slurry with fine and uniform globular structure. The combination of local rapid heat extraction and vigorous agitation by the injection of fine inert gas bubbles through a graphite diffuser in molten metal held at a temperature above its liquidus temperature changes the morphology of primary a(Al) from coarse dendritic to rosette-like and finally to fine globular. The GISS process produced semi-solid slurry at low solid fractions and then formed the slurry by a squeeze casting process to produce casting parts. The effects of primary phase morphology on the mechanical properties of Al-Si-Mg-Fe alloy were investigated. The results show that the ultimate tensile strength and elongation are affected by the shape factor and particle size of the primary a(Al).

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid (GISS) technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 °C and 250 °C, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

Development of aluminum rheo-extrusion process using semi-solid slurry at low solid fraction

An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 mm. The semi-solid metal process used in this study was the gas induced semi-solid (GISS) technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fraction on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts.

Semi-solid gravity sand casting using gas induced semi-solid process

The semi-solid metal forming using high pressures has been applied for several years. In contrast, low pressure casting, such as gravity sand casting, has not been widely studied even though it may help reduce porosity defects and offer a better casting yield. A semi-solid gravity sand casting process using the Gas Induced Semi-Solid process was investigated. The results show that the process can produce complete parts with no observable defects. The ultimate tensile strength and elongation data of semi-solid cast samples are higher than those of the liquid cast samples. In addition, the semi-solid sand casting process gives a better casting yield. It can be concluded that the semi-solid sand casting of an aluminum alloy using the GISS process is a feasible process.

Effects of Solid Fractions in a Slurry Die Casting Process on Defects of 7075 Aluminum Alloy

The effects of Gas Induced Semi-Solid (GISS) in the slurry die casting process on defects of 7075 aluminum alloy were studied, different initial solid fractions with 10, 15, and 20 sec of rheocasting time were investigated. The results showed that the percentage of porosity in semi-solid die casting was smaller than in the liquid die casting. In terms of the initial solid fraction in 7075 aluminum alloy, it was found that the defects were found when the initial solid fraction was high. In addition.

The Effect of Hot Tearing in Semi Solid Casting of Aluminum A201 Alloy

The effects of rheocasting times on the hot tearing defect in semi-solid die casting of aluminum A201 alloy have been investigated. This study found that no hot cracking formed in the semi-solid A201 alloy parts at a rheocasting time of 10 seconds, implying that the hot tearing suscepability (HTS) index value is zero. Moreover, the HTS index values for all semi-solid casting conditions were lower than those found in conventional casting samples. The microstructure of the as semi-solid casting parts consisting of non-dendritic structures and smaller grain size helped to improve the hot tearing resistance of aluminum A201 alloy. These results support the feasibility of semi-solid die casting of aluminum A201 alloy by using Gas Induced Semi-Solid (GISS) technique.

A Fluidity Study of Semi-Solid Rheo-Slurry of AC4C Aluminum Alloy in Gravity Sand Casting

A new approach to evaluate fluidity of semi-solid rheo-slurries was developed. The equipment was designed in order to reduce pouring error by using bottom tapping and heated tapping ladle. Commercial AC4C aluminum alloy slurries were tested in spiral sand mold by gravity casting. The slurries were prepared by introducing fine gas bubbles into molten metal above the liquidus temperature at different rheocasting times. Average fluidity and microstructures of cast spirals were reported. Results show that the spiral microstructure is non-dendritic and the fluidity of AC4C alloy decreases with increasing solid fraction. In conclusion, the spiral casting method using bottom tapping can be used to evaluate the fluidity of rheocast slurries in gravity sand casting.

Investigation on Properties of Anodized 7075 Slurry Cast Aluminum after Sealing

This work investigated the effects of sealing agents on properties of 7075 slurry cast substrate anodized in 1M sulfuric acid solution. The sealing agents tested were hot water, potassium dichromate, teflon, and nickel fluoride. It was found that anodized 7075 slurry cast Al oxide film sealed with teflon gave the highest hardness and the best corrosion resistance. It is possible that the porous oxide film was plugged by teflon, reducing porosity more than hot water, potassium dichromate, or nickel fluoride sealing.

Creep of Slurry Squeeze-Cast ZA-27 Zinc Alloy with Different Solid Fractions at 140 °C

This research work was aimed at studying creep of a slurry squeeze-cast ZA-27 zinc alloy. The Gas-Induced Semi-Solid (GISS) technique was used for preparing semi-solid metal slurry with two different solid fractions. The ZA-27 alloy slurry was squeeze cast to form plate-like specimens with dimension of 100×100×15 mm3. The tensile specimens were machined from the squeeze-cast plates and heat-treated before mechanical test. Tensile creep tests were performed at 140 °C, at stresses of 20, 40, 60 and 80 MPa, in an ambient air. Two groups of specimens, the low solid fraction ZA-27 alloy (GISS 5s) and the high solid fraction ZA-27 alloy (GISS 15s) were tested for comparison of creep property. The results show that the GISS 5s has longer creep life than the GISS 15s. The power-law creep stress exponents (n) of GISS 5s and GISS 15s are 1.45 and 1.04, respectively. Based on the creep stress exponents found from the present study, it could be concluded that at the temperature of 140 °C and stress between 20 and 80 MPa, creep of both alloys was governed by the diffusional creep mechanism.