Papers by Keyword: Grain Refiner

Abstract: Grain refinement is one of the most important and popular melt treatment process for Al-Si alloy casting. Microstructure and mechanical properties of commercially available Aluminium Silicon alloy LM6 can be improved with the addition of grain refiners and modifiers as these provide technical and economic advantages. This paper is an effort to study the effects of addition of grain refiners and modifiers to the eutectic Al – Si alloy LM6. Commercially available Al - Si alloy LM6 (eutectic = 12% Si) is grain refined with Al-5Ti-1B and Al-3B; and modified with Al-10Sr master alloys. These were added individually and then tested for its unique mechanical properties such as ultimate tensile strength, hardness and wear; which are co-related with the machining tests such as turning, surface roughness and drilling. The test results are compared with microstructure of the samples observed through SEM.The mechanical properties of this alloy can be altered after addition of master alloys, which in turn alter the grain size. Thus the results conclude that the mechanical properties of Al-Si alloys in general are controlled by a number of principal microstructural features. A fine grain size is desirable, leading to improvement of mechanical properties.

Abstract: The commercial application of wrought aluminum alloys to semi-solid casting would be extremely beneficial, as wrought alloys often exhibit better strength-ductility combinations than cast aluminum alloys. Semi-solid casting typically reduces the hot tearing tendency, as it requires a globular microstructure and produces grain refinement, but hot tearing often still occurs during the semi-solid die casting of complex-shaped components produced from wrought alloys. This study examined the impact of intensification pressure and grain refinement on the hot tearing tendency of an Al-Zn-Mg-Cu alloy. Semi-solid slurries were produced using the SEED (Swirled Equilibrium Enthalpy Device) process. A specially designed constrained rod mold was used to evaluate hot tearing. Results showed the tendency for hot tearing decreased with increasing of intensification pressure. Grain refinement (with 0.06Ti) was also found to be beneficial to the elimination of hot tearing.

Abstract: Hot tearing is a common and severe defect encountered in aluminium alloys castings. It is affected by alloy composition as well as processing conditions and variables. In Al–7Si-3Cu presence of copper increases mechanical properties of the alloy, but it makes the alloy susceptible to hot tearing. The observations on the microstructures and the fracture surfaces propose that the hot tearing initiated at the grain boundaries and propagated along them through the thin liquid film. Grain refinement limits the hot tearing tendency of the Al-Si-Cu alloy. An attempt has been made to record the effect of annealed Al-5Ti-1B master alloy on minimizing hot tearing tendency in the gravity die cast of Al-7Si-3Cu alloys. It is observed that grain refining efficiency of Al-5Ti-1B master alloy is increased with increase in annealing temperature. This is attributed to the increased fraction of TiAl₃ particles and the possible formation of (Ti,Al)B₂ phase. Characterization study has been carried out by OM, SEM and XRD analysis.

Abstract: Aluminum and its alloys are the second used materials after steels due to their useful and attractive properties. In this paper, the effects of 4% copper addition to commercially pure aluminum grain refined by 0.15% vanadium are investigated. In particular, the effects of alloying on the mechanical behavior, fatigue life and strength are considered. The main objective of this study is to improve the mechanical strength and the fatigue strength of aluminum by refining its columnar microstructure. The obtained results show that the addition of 4% copper and 0.15%V to commercially pure aluminum significantly refined its grain size, and hence improve its mechanical strength as well as its fatigue life and strength.

Abstract: In this paper, the effect of addition of 4%wt. copper to commercially pure aluminum grain refined by 0.15% vanadium on its grain size, hardness, ultimate tensile strength, UTS, ductility and surface roughness is investigated. It is found that when they are added individually or together causes pronounced reduction in grain size, i.e., effective refiners. Similarly, they increase its hardness and ultimate tensile strength but reduce its ductility. Regarding their effect on the surface quality, they enhance the surface quality if added individually. However, they reduce it if added together, i.e. they increase its surface roughness.

Abstract: The enthalpy equilibration method is a novel technique to produce globular grain structure in semi-solid slurry preparation. In this process, the liquid is firstly poured into a metallic crucible, which possesses low thermal conductivity and high thermal capacity. Homogeneous distribution of temperature within the metallic crucible is achieved by rotating the crucible and cold down to a temperature between liquidus and solidus, determined by the requirement of solid fraction. The semi-solid slurry is then transferred to a high pressure die caster. In order to achieve a spherical microstructure morphologies in the entire slurry, effects of grain refiners, in addition to the enthalpy equilibration method, on the microstructure of the slurries of A357 alloy were investigated. Quantitative metallographic measurements were applied to evaluate microstructural evolution and processing parameters were optimized.

Abstract: In this study, the hexachloroethane (C₂Cl₆) as a refiner was introduced into a cylindrical squeeze casting of magnesium alloy AM60 with a diameter of 100 mm and a thickness of 25 mm. The casting was prepared under an applied pressure of 30 MPa. The results of tensile testing indicate the tensile properties for the C₂Cl₆-refined specimens were significantly improved over the untreated AM60 samples. Microstructure analyses with optical microscopes reveal the great grain refining capability of C₂Cl₆ on squeeze cast magnesium alloy AM60, which should be responsible for the enhanced tensile properties of the refined AM60.

Abstract: In this paper, the effect of addition of some grain refiners namely: molybdenum, titanium and titanium+boron to zinc-aluminum 22%, ZA22, alloy on its microstructure and mechanical characteristics is investigated in two conditions one in the cast condition and the other after pressing by the equal channel angular pressing, ECAP. Recently the ECAP process has been used to produce severe plastic deformation. It was found that addition of any of these elements to ZA22 alloy resulted in grain refinement of its structure both in the cast and after pressing by the ECAP conditions, being more pronounced after pressing by ECAP. The maximum decrease was %. Furthermore, it resulted in enhancement of its mechanical strength at, indicating softening of the alloy. Regarding the effect on its hardness, it decreased by th addition of either Mo or Ti+B. at any rate of Mo addition.

Abstract: Grain refining is one of the most important issues in the applications of Mg alloys, which directly determines mechanical properties and deformability. Therefore the understanding of grain refining mechanism during solidification will be benefit to develop new grain refiners. Herein refining role was elucidated by the first principles calculations based on adsorption behavior of a Mg atom on the closest-packed planes of grain refiners (Zr (001), Al₂Y(311) and Al₄C₃(102)). Taking into account different sites, the site with the maximum adsorption energy value generally corresponded to the most possible location. The adsorption energy results show that the possible refining turn follows Al₄C₃(102)>Zr (001)>Al₂Y(311). Meanwhile, the structural optimization confirmed that the Mg atom connected with two C atoms on the top of zig-zag plane of Al₄C₃(102), three Zr atoms at the hcp position on Zr (001), and two Y atoms and one Al atom at the bottom of zig-zag plane of Al₂Y(311). The density of states revealed that the variation of d-orbital electrons of Mg atom became apparent during adsorption process. The values of Mulliken charges were 0.898 e in Al₄C₃(102), 0.410 e in Zr (001) and 0.245 e in Al₂Y(311), respectively. This tendency agrees well with the previous experimental results. It indicates the adsorption energy on the closest-packed planes can be regarded as a prerequisite to select new grain refiners for Mg alloys in future.

Abstract: Grain refining has been studied in the semi-solid-metal (SSM) casting by addition of master alloy Al-5Ti-1B using inclined slope. A356 aluminium alloy was melted at 850 °C and poured at 660 °C on the inclined slope into the steel mould. Grain refiner was added in various percentages of 0.2%, 0.5% and 1.0% in A356 aluminium alloy melt. Microstructure and microhardness were characterized using optical microscope and Vicker’s microhardness tester. The addition of master alloy Al-5Ti-1B not only refined but also increased the globularity of the primary α-Al particles. The higher hardness was achieved with 1% addition of master alloy Al-5Ti-1B.