Papers by Keyword: Al-Si Alloy

Abstract: The microstructural characteristics of externally solidified crystals (ESCs) and porosities in a non-heat-treated high-pressure die-cast AlSi9MnVZr alloy are investigated under two distinct process conditions: one with the application of lower intensification pressure and the other with higher intensification pressure. Optical microscopy (OM), scanning electron microscopy (SEM), and computed tomography (CT) are employed to analyze the ESCs and porosity distribution. The alloy's microstructure primarily consists of primary α-Al, ESCs, Al-Si eutectic, and iron-rich phases. ESCs nucleate in the shot sleeve, while α-Al forms within the die cavity. When the lower intensification pressure is applied, larger dendritic ESCs are observed, along with significant gas porosity, shrinkage pores, and numerous smaller dispersed pores, resulting in a high porosity fraction. Conversely, the application of higher intensification pressure results in a notable refinement in ESCs morphology, with a significant reduction in their diameter and area fraction. Additionally, the size and fraction of porosity decrease substantially, indicating a marked improvement in casting quality.

Abstract: Recently, high strength at high temperature can be achieved by inducing kink bands in alloys having aligned lamellar microstructure. However, the kink-bands formation has been confirmed only in alloys with lamellar microstructures, where slip plane is limited to the plane parallel to the lamellar interface, and not confirmed in alloys with rod-like or Chinese script microstructures. In this study, we clarified the contribution of rod-like Si phases in Al-Si alloy on the mechanical properties and focused on the feasibility of introduction of kink bands in the alloys without lamellar structure. The results showed that in Al-Si eutectic alloys, the non-lamellar second phase, i.e., the Si phase, is aligned by directional solidification, and refined by rolling. The directionally-solidified sample showed high yield strength with long and aligned Si phase, while the rolled samples showed high ductility with refined microstructure. The rolled samples were uniformly deformed in all the samples with variety of reduction ratios, and wedge-shaped deformation bands were observed after the compression test, especially in the 5-10% rolled specimens. Crystallographic orientation analysis indicated that these deformation bands were not kink bands but were localized slip bands.

Abstract: A positive segregation is usually formed on the casting surfaces produced by high-pressure die casting (HPDC). In diecast Al-Si-Cu alloy components, this segregation shows a higher content of Si compared to the nominal composition of the alloy and it drastically affects the anodizing response of the casting surface. In the present work, HPDC components were produced by AlSi11Cu2(Fe) alloy, grit-blasted, and then anodized in a sulfuric acid electrolyte at the temperature of -4.5°C. Before the anodizing process, some regions of the casting were also milled, in order to completely remove the surface segregation. Microstructural investigations were carried out on grit-blasted and milled surfaces to characterize the initial substrates before anodizing, and to study their effect on the growth of the anodic layer. Scratch and wear tests were also performed to investigate the surface mechanical properties after anodizing. The results show that the surface segregation and the rough surface present on grit-blasted substrate leads to the formation of a thin and homogeneous anodic layer. On the contrary, a thicker and scalloped oxide film is formed on the milled surfaces. After anodizing, grit-blasted surfaces show lower wear and scratch resistance than milled substrates. The presence of surface segregation prevents the thickening of the anodic layer, negatively affecting the surface wear resistance due to the reduced oxide thickness.

Abstract: The inhomogeneous microstructure and its change by annealing for an AlSi10Mg lattice structure with a body-centered cubic unit cell additively manufactured via laser powder bed fusion (LPBF) were investigated. The as-built lattice structure exhibited a cellular microstructure consisting of a number of primary α-Al phases decorated with α-Al/Si eutectic structure. The developed microstructure varied depending on the locations of the node and strut parts of the lattice structure. At the location near the bottom surface of the node part, the cellular microstructure became coarser and more equiaxed than those at the location near the top surface. At the location near the bottom surface of the strut part, the columnar α-Al phases were often elongated along the direction of the strut part. After the annealing at 300 °C for 2 h, numerous Si particles finely precipitated within the primary α-Al phases and coarsening of the eutectic Si phases occurred. After the annealing at 530 °C for 6 h, the microstructural characteristics changed significantly. A significant coarsening of the Si particles and the formation of Fe-containing intermetallic phase (β-AlFeSi) with a plate-shaped morphology occurred. The microstructures became homogeneous in the whole area of the lattice structure annealed at 530 °C for 6 h.

Abstract: In the current work, wear behavior of plasma processed LM6 alloy is investigated. LM6 alloy was prepared by plasma technique. The samples were aged at 350^°C & 450^°C for 2 hours followed by water quenching. A comparative study of the metallographic structure and properties viz. hardness, density and wear of the non-heat and heat treated alloy samples were carried out. A very fine lamellar structure is observed in case of 450^°C heat treated samples than that of sample heat treated at 350^°C and non-heat treated samples. Highest hardness value of 68.11 VHN is observed with the sample heat treated at 450^°C. Density is found to be the lowest in non-heat treated samples and it increases with increasing heat treatment temperature. Wear experiments were carried on a pin-on-disc set up (of Ducom make), varying applied loads (between 10-40Newton and varying sliding speed (from 0.94 m. s^-1 to 2. 83m.s^-1). Maximum wear resistance is observed with the specimen heat treated at 450^°C.

Abstract: The factors affecting the shape and size of burrs that form at the edges of strips cast by a vertical type twin roll caster were investigated in this study. The size of the burr was found to be affected by the Si content of the strip. When the Si content was larger than 7 mass%, the burrs became larger. The position of the lower edge of the side dam plate also affected the shape of the burr. The burrs that formed were generally perpendicular to the strip surface but changed to being parallel to the strip surface as the position of the lower edge of the side dam plate was displaced upward from the center of the rolls.

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 aim of the article is piston damage evaluation of a highly exposed combustion engine. The analysed piston was made of an AlSi-based alloy. Atypical damage, which occurred relatively early in the lifetime of the component, was evaluated by metallographic and fractographic analyses. The analysis took into account influences of mechanical and thermal fatigue processes in relation to the microstructure of the material. The metallographic observations of the microstructure revealed the occurrence of cracks extending over the secondary phases and precipitates. Cracks were initiated on the coarser Si phase particles. The crack initiation site is located at the root of the bridge between the sealing piston rings. The damage of the piston was metallographically documented in wide range.

Abstract: A horizontal-type twin roll casting method has been popular for producing aluminum alloy strips, however, it is characterized by a relatively low productivity (1~6 m/min). In contrast, a vertical-type high-speed twin-roll casting method possesses an extremely high productivity (60~120 m/min (1~2 m/s)) and an excellent heat extraction ability. The rapid cooling effect provided significant microstructure refinement and mechanical properties improvement in various kinds of cast aluminum alloy products. Not only “product to product recycling” but also “up-grade recycling” can be achieved by making good use of these merits. Two examples of application showing the potential of vertical-type high-speed twin roll casting method are presented. (1) Several kinds of Al-Si base alloy were cast into the strips. Not only strength and toughness but also formability was increased in the twin roll cast products. In particular, great improvement in deformability shows the potential of the twin-roll cast aluminum alloy products as substitutes for some wrought aluminum alloy products. (2) The vertical-type tandem twin-roll caster was able to fabricate a clad strip by single step. The A4045/A3003/A4045 aluminum alloy clad sheets produced by the twin-roll casting showed better mechanical properties than the conventional hot-roll bonded clad sheets.

Abstract: Microarc oxidation(MAO) was used to prepare the coatings on the surface of Al-Si alloy. Besides, scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) were utilized to research the microstructure characteristics, the components distribution, and the phase compositions, for the microarc oxidation coatings on Al-Si alloys. Furthermore, the growth process and wear properties of the coatings were explored. Results indicated that:the phase compositions of microarc oxidized coating consisted of mullite (3Al₂O₃·2SiO₂₎, α- Al₂O₃ and γ- Al₂O₃. With the increase of load, the friction coefficient of the coating decreased, however it was greater than that of Al-Si alloy substrate. The wear resistance of the coating were one time higher than that of the substrate.