Papers by Keyword: Al-Si

Abstract: Steel 22MnB5 is widely used in the automotive industry for manufacturing high-strength structural car body parts. To achieve desired mechanical properties, hot-stamping is used, during which the Al-Si coating plays a critical protective role against oxidation. This study investigates the structural evolution of the Al-Si coating under various austenitization durations at 920 °C. Intermetallic phase formation and coating morphology are analyzed.

Abstract: In addition to property anomalies, a distinguishing feature of the intermediate phase is the qualitative change of the crystallization or recrystallization interval (Q∆LS) that occurs at congruent and incongruent melting phases, at eutectic or eutectoid points, at the ends of eutectic or eutectoid horizontals, and also at any nonmonotonicity of the liquidus, since the solidus or solidoid is a horizontal in eutectic or eutectoid systems. A technique has been developed that allows us to associate anomalies in the properties of industrial alloys with state diagrams based on the first established criterion - a qualitative change (length in temperature) of the crystallization (recrystallization) interval (Q∆LS), as well as with a difference in the structural heredity (genealogy) of the component atoms that make up dual system. A joint analysis of the anomalies in the properties of binary alloys with state diagrams (based on the established criterion (Q∆LS)) allows us to relate the latter to the presence of intermediate phases in Al − Si, Fe − C, Al − Cu systems. The intermediate phases AnBm-Q∆LS explaining the anomalies of properties are declared: ~Al₇Si, Al₄₁Cu₉ − correspond to the eutectic point; Fe₂₄C − eutectoid point; Al₁₁Si, AlSi₆ − the bend of the liquidus; Fe₄₂C − bending liquidoid; Al₄₉Cu, Al_98.5Si_1.5 − the end of the eutectic horizontal; Cu₄Al, Cu₇Al₃ − to the ends of the eutectoid horizontal.

Abstract: Hypereutectic Al-Si alloys can be used in applications that require high wear resistance. Such wear resistance is achieved by the presence of hard primary silicon particles, allied to the formation of Mg₂Si intermetallic phase when magnesium is added in this alloy. Centrifugal casting generates a gradient in the microstructure of hypereutectic Al-Si alloys that can favor such applications. Cylindrical components of Al-19%Si alloy containing added copper and magnesium contents were processed by centrifugal casting. The purpose of this study is to investigate the formation and segregation of particles of primary silicon (β) and Mg₂Si in Al-19%Si alloy containing additions of copper and magnesium. Because the density of silicon (2.33 g/cm³) and Mg₂Si (1.88 g/cm³) is lower than that of aluminum (2.67 g/cm³), centrifugal casting causes primary silicon (β) and Mg₂Si particles to concentrate more at the outer wall of the centrifuged pipe. In this study, primary silicon (β) and Mg₂Si particles were found to be retained at the outer wall of the pipe. It is believed that the rapid cooling of the molten metal in the region of contact with the mold, whose temperature is lower than that of the molten metal, allied to the centrifugal force, prevented the particles from migrating to the inner wall of the pipe. The microstructure shows a gradient in the distribution of these phases, enabling the production of a functionally graded material. The addition of copper and magnesium leads to the formation of Mg₂Si and Al₅Cu₂Mg₈Si₆ phases, reducing the amount of primary β phase (Si) particles. In all the evaluated conditions, a tendency is also observed for a gradual increase in the segregation of silicon towards the inner wall along the entire length of the centrifuged pipe.

Abstract: Hot stamping is often used in the automotive industry to combine formability and strength. However, during forming process at high temperatures, friction and tool wear are determining factors that can affect the efficiency of the whole process. The goal of this paper is to investigate the effects of temperature on the local coefficient of friction and tool wear and to provide an insight in the phenomena which take place at the tool-sheet metal interface during hot stamping processes. For this purpose, hot friction draw tests between uncoated tool steel and Al-Si coated press hardening steel were carried out at several temperatures between 500-700°C. Consecutive tests were performed to mimic industrial hot stamping process and to investigate the effect of tool wear on the friction phenomenon. Finally, tool-sheet metal tribological behavior and the interaction between the friction and tool wear mechanisms were analyzed using different imaging and chemical characterization techniques. The results show that several stages can be distinguished at the interface between tool and sheet metal coating during hot stamping: flattening due to initial normal contact, ploughing of tool asperities through coating, secondary ploughing in the coating by adhered material on the tooling, and abrasive wear in the tool by embedded particles in the sheet metal coating. Furthermore, tool wear shows some major differences in the temperature range of 500-700°C. At high temperature a larger abrasive area and more severe compaction galling occurs that can be explained by material properties of Al-Si coating at elevated temperatures. The results of this study can be used for more efficient process design and a more realistic modelling of the hot stamping process.

Abstract: Al-Si alloys are the most common aluminium cast products owing to their high resistance to hot cracking and excellence fluidity during the molten state. They play important roles in aerospace, automobile and structural industries where high strength to weigh ratio, superior heat conductivity and good corrosion resistance applications are necessary. Alloying elements such as copper, magnesium, zinc and nickel are added into the Al-Si alloys for further strength enhancement. However, impurities such as iron are often present in Al-Si alloys, forming brittle intermetallic phases and hence reducing the mechanical strength of the alloys. In this paper, previous studies on the effects of alloying elements on physical and mechanical characteristics of Al-Si alloys will be accounted. Moreover, a comprehensive review on the Al-Si alloy casting methods will also be included.

Abstract: The addition of a high percentage of silicon and a small percentage of magnesium to aluminum are the main enhancers largely used to improve the mechanical characteristics. Our goal, here, is to make a direct contribution to the mechanical properties in traction, the hardness, the resilience and the structural properties of the AlSi13 alloy used in sand molding and shell metal molding, mechanical as well as manual. The reference state is designated by crude casting, noted: F. To increase the characteristics and obtain substantially large yield stresses and higher stiffnesses, the material of numerical designation 44100 is subjected to the specific heat treatments, quenching and annealing. This study aims to determine the influence of the chemical composition, the structural hardening of sand casting and metal shell casting by gravity on the evolution of the tensile behavior, hardness, resilience and microstructure of the binary alloy 44100.

Abstract: This study aims to investigate the effects of mechanical melt-shearing treatment during casting process on the morphological change of iron-containing intermetallic phases formed in the high-iron bearing Al-Si casting alloys. The process parameters of the melt-shearing treatment were controlled and optimized in order to modify the needle-like shape of the iron-containing intermetallic into a less harmful form. Throughout this study, it was found that the melt-shearing treatment shortened effectively the length of the needle-shaped iron-containing intermetallic phase in the Al-Si alloys. It was also confirmed that these modified morphology and microstructures result in the improvement of mechanical properties.

Abstract: Series of Al–P master alloys including binary Al–P and Al–Si/Zr–P master alloys containing pre-formed phosphides have been developed. Hypereutectic A390 alloys have shown fast refinement response to the addition of series of Al–P master alloys. After refined at 780°C for 30 min, the coarse primary Si can be refined obviously from 90 μm to less than 20 μm. In addition, the morphologies of primary Si are changed from coarse polygon to near-sphere shape, and the distribution is improved simultaneously.

Abstract: Aluminium Silicon reinforced with 50Vf% SiC has been produced by spontaneous infiltration at 900°C for 1 hour. Aluminium infiltrated preforms containing 1%wt Mg mixed with various of Si between 2 and 14wt%, as external dopant. However Al did not infiltrate a preform containing 1wt%Mg but if mixed with Si in the preform generated in more extensive infiltration. Effect of Si on characterisation of pure Al composites by spontaneous infiltration were studied and compared to Al-Si based matrix. Microstructural analysis of MMC as well as mechanical properties were also observed. It was found that increasing of Si content generated lower porosity thus increasing hardness due to aluminium could wet SiC preform well. Although the dopant was uniformly distributed throughout the perform but microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform as infiltration inwards from the top to the bottom of preform. The hardness of Al-Si composites is significantly increased with increasing of Si for both externally and internally doped system. This is associated with decreasing porosity with higher Si in composites.

Abstract: Friction Stir Processing (FSP) has potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry, by greatly refining the second phase particle size. In the present study, the homogeneity of particle refinement and second phase spatial distribution within the process zone, as well as the relationship to the processing parameters, were investigated in a gravity die cast Al-Si LM24/A380 alloy, subjected to a range of FSP conditions. Detailed image analysis and the dirichlet tessellation method were used to quantify particle clustering. ‘Stop-action’ experiments were also used to study the process of particle break up, by following the behaviour through the deformation zone surrounding the tool.