Papers by Keyword: Semi-Solid Metal

Abstract: Semi-solid die casting technology has great advantages at defects control and has been successfully used to produce high quality aluminum alloy components for several years. In this process, semi-solid metal with high apparent viscosity and low plunger velocity are used to avoid surface turbulence which is the main source of entrapped gas in conventional die casting processes. But, entrapped gas still has other sources, such as melting, pouring, surface flooding and confluence weld. Solution heat treatment is always used to strengthen semi-solid die castings. The entrapped gas leads to blister defects, which directly decreases the acceptance rate of semi-solid die castings. So, the entrapped gas is still a serious issue in semi-solid die casting process. We studied the floating behavior of entrapped gas bubble in semi-solid metal. Two floating models were established for gas bubbles with different sizes. These models were used to analyze the possibility of entrapped gas escaping from semi-solid metal in casting practice. The results showed that entrapped gas from feed billet could not escape from the semi-solid metal in the casting process of impeller, which was proved by experiment results. These results emphasized the importance of clean melt and semi-solid metal. Some advices were given at last for avoiding or removing the entrapped gas in semi-solid die casting process.

Abstract: Near-net shape casting of wrought aluminium alloys has proven to be difficult due to hot tearing. The Council for Scientific and Industrial Research (CSIR) has successfully processed wrought aluminium alloy 2139 into plate castings using the Rheo-high pressure die casting process (R-HPDC). Alloy 2139 is a Ag-containing aluminium alloy from the Al-Cu-Mg 2xxx series family. The addition of Ag enhances the age hardening response through the formation of co-clusters that act as precursors to the formation of plate-like Ω precipitates. These co-clusters typically form during natural ageing and 12-24 h of natural pre-ageing is normally specified before artificial ageing in Ag-containing Al-Cu-Mg alloys. The T6 hardness and tensile properties of R-HPDC 2139 alloy were investigated with and without natural pre-ageing. It is shown that there is no significant difference in both peak hardness and tensile properties in R-HPDC alloy 2139 with and without natural pre-ageing. The possible precipitation phenomena in both cases are discussed.

Abstract: The aim of this research was to study semi-solid state joining of SSM A356 aluminum alloys which welded at its semi-solid state temperature by using oxygen – acetylene heat source. Then a stirrer was used to stir the weld seam. The joining parameters were rotation speed 1,110 with welding speed 120 mm/min and rotation speed 1,320 rpm with welding speed 160 mm/min. The joining temperatures were 575-590 and 590-610 oC. Joining was performed under nitrogen shielding gas and under argon shielding gas. Physical appearance, macrostructure, microstructure and mechanical properties were analyzed. The results indicated that the weld’s microstructure consisted of globular structure. In addition, porosities were found at the top of weld. However, minimum porosities were obtained from joints under argon shielding gas. The highest tensile strength was achieved from rotation speed at 1,110 rpm with welding speed at 120 mm/min under argon shielding gas with the value of 173 MPa. The joint efficiency was 86 % compared to the base metal.

Abstract: Abstracts: This paper presents an overview of measured mechanical properties of thixoformed aluminium 7075 feedstock produced by the direct thermal method (DTM). The DTM feedstock billets were processed with a pouring temperature of 685 °C and holding periods of 20 s, 40 s and 60 s before being quenched and subsequently thixoformed. A conventionally cast feedstock billet was produced with a pouring temperature of 685 °C and was allowed to solidify without quenching. The feedstock billets were later formed by an injection test unit in the semi-solid state. Tensile testing was then conducted on the thixoformed feedstock billets. Tensile properties for 7075 DTM thixoformed feedstock billets were found significantly influenced by the thixoformed component density. Samples with longer holding times were found to have higher density and higher tensile strength.

Abstract: The study aimed at development of mechanical properties to make a comparison between Sn-50wt%Zn and Sn-50wt%Bi were investigated by properly design experiments, respectively, different mold temperature affecting the particle size of Sn-50wt%Zn, mechanical properties and microstructure were developed by GISS process, hardness test were used to compare both alloys. The results show that mold temperature has an effect on the grain sizes and grain characteristics. Gas Induce Semi-Solid (GISS) caused granular grains to affect the good mechanical properties.

Abstract: The evolution of microstructure affect from different pouring temperatures and holding times using a direct thermal method is presented in this paper. The direct thermal method is one of the thermal techniques which are used to produce semi-solid metal feedstock. In this experimental work, aluminium 7075 alloy was used. The experiments were carried out by processing a sample with a 0.7 °C/s cooling rate to evaluate the formation of the microstructure. In direct thermal method experiment, a molten 7075 was poured into a cylindrical copper mould at different pouring temperatures of 680 °C and 660 °C meanwhile the holding time of 20 s, 40 s and 60 s before quenched into room temperature water. The sample processed by the cooling rate of 0.7 °C/s produced a large microstructure. The formation of a spheroidal microstructure was obtained with the combination of a suitable pouring temperature and holding time. The pouring temperature of 665 °C and the holding time of 60 s produced a finer and uniform microstructure that is suitable for semi-solid feedstock.

Abstract: SSM 356-T6 aluminium alloys generally present low weldability by fusion methods because of the sensitivity to weld solidification cracking, porosities, change microstructure in weld zone and other defects in the fusion zone. Diffusion bonding can be deployed successfully with aluminium alloys. This paper presents the technique to conserve the globular weld structure of SSM 356-T6 aluminium alloy. The effect of joining parameters on the microstructure and mechanical properties of diffusion bonding butt joints of semi-solid metal 356-T6 aluminium alloy were investigated by conditions as follows: contact pressure at 0.4, 0.9, 1.8, 2.4 and 2.7 MPa, for 3 hours holding time and temperature at 495°C under argon atmosphere at 4 liters per minute. The results showed that condition used contact pressure 2.4 MPa, with 3 hours holding time and temperature at 495°C, under argon atmosphere provided. The highest joint strength reaching to 182.2 MPa, which had joint efficiency of 61.34 percents compared with base material. In addition, microstructure in welded zone after welding is still in globular structure, but the grain size was increased when the higher bonding temperature was used. The results of this investigation have shown that an average hardness is around 121.2 HV.

Abstract: The purpose of this research is to investigate the semi-solid state joining of SSM 356 aluminum alloy which welded at its semi-solid state by using oxygen - acetylene as a heat source. Then a stirrer was used to stir the weld seam. Joining was performed under nitrogen shielding gas. The parameters of this study were rotation speed at 1,110 and 1,320 rpm, welding speed at 120 and 160 mm/min, semi-solid state temperatures 575-590 and 590-610 oC. The results indicated that the weld's microstructure consisted of irregular globular structure. In addition, porosities were found at top of weld metal. The highest tensile strength and elongation were obtained from rotation speed at 1,110 rpm, welding speed at 120 mm/min and joining temperature at 575-590 oC.

Abstract: In this research, the semi-solid state joining of SSM A356 aluminum alloy was investigated. The butt-joint of SSM A356 was heated by an induction heating coil to create a localized semisolid pool. Then a stirrer was applied into the joint seam in order to mix the weld metal. The accurate controlling of temperature during joining was measured. The effects of stirring rate on physical, macrostructure, microstructure and mechanical properties were studied. Experimental results showed that increase in stirring rates, the surface of the joint was smooth. The weld metal consisted of the globular microstructure and also voids. The density of weld metal zone increased by an appropriate stirring. The best tensile strength was achieved with 1750 rpm, 70 mm/min for 103.4 MPa.

Abstract: The SEED rheocasting process was used to produce semi-solid slurries of hypereutectic Al-17Si-4.5Cu (A390) and Al-15Si-10.5Mg-4Cu alloys respectively. The rheological properties of these alloys in the semi-solid state were characterized at different deformation rates and at variable solid fractions using the parallel plate compression viscometry. The viscosity at different shear rates was calculated using a Newtonian fluid model for increments of deformation during compression. Microstructures of both alloys, after partial solidification and compression, were examined in order to characterize the flow behavior during deformation. The comparison of the viscosity between the A390 and Al-15Si-10.5Mg-4Cu alloys indicated that the high Mg containing alloy possessed a higher viscosity for the range of shear rates and solid fractions investigated. Rheological results showed that at a given solid fraction, the viscosity of both alloys decreased significantly with increasing shear rates, indicating a shear thinning behavior. In addition, a separation of liquid and solid phases was also observed for both alloys in the microstructural study of compressed semi-solid billets.