Al Si Research Articles

Research on thermal efficiency and weld forming coefficient prediction of ultra-high strength steel welded joint under different energy inputs

As an ultra-high strength steel, Al–Si coated 22MnB5 hot stamping steel is widely used in the manufacturing of body-in-white structural parts. Compared with traditional welding technology, laser welding is widely used in the field of automobile body-in-white manufacturing due to its high energy density, small heat affected zone, and high weld quality. For ultra-high strength steel laser welded joints, the weld forming coefficient is an important index to reflect the welding quality. In order to investigate the influence of weld forming coefficient on the Al content and the thermal efficiency, laser welding experiments of ultra-high strength steel under different laser energy inputs are carried out. The melting of the base metal and coating under different laser energy inputs is also considered. Particle swarm optimization (PSO) algorithm is introduced into radial basis function (RBF) neural network model to optimize the central parameters as the RBF neural network model alone is not sufficient in predicting the outcomes. The results shows that if the laser power density is constant (7 × 105 W/cm2), when laser energy inputs are 400 J/cm to 1200 J/cm, the Al content in welded joints is 1.458%–1.886%, the melting efficiency of welded joints is 0.23–0.26, the energy conversion efficiency of welded joints is 0.45–0.46. When the laser energy inputs are lower than 522 J/cm, the Al content of the laser welded joint increases gradually. When the laser energy inputs are higher than 522 J/cm, the Al content of the laser welded joint decreases. The root mean square error(RMSE) of PSO-optimized RBF neural network testing sets prediction results is 0.1551, R-square (R2) is 0.771 and mean absolute percentage error (MAPE) is 2.758%. The prediction accuracy of the PSO-optimized RBF neural network model for the upper surface weld width, waist weld width, and lower surface weld width is 93.9%, 91.1%, and 92.2%.

Solution treatment of core-shell structured particle reinforced A356 composite prepared by powder thixoforming: Effects of partial remelting temperature

In-situ core-shell structured particle Ti@(Al–Si–Ti)p reinforced A356 Al alloy matrix composites were prepared by powder-thixoforming at different partial remelting temperatures, and then were solid solution treated at 545 °C for 1 h. The results indicate that the reaction between Ti cores and Al matrix operates to form nano τ2 particles during solutionization, while the original (Al, Si)3Ti phases transform into τ2 phases, and simultaneously, the early-formed nano τ2 particles grow into large-sized plates. These behaviors are enhanced with rising the remelting temperature. The content of eutectic Si and solubility of Si in α-Al phase in the solutionized composites further decrease with rising remelting temperature, due to the reaction and phase transformation, and de-dissolution of Si, respectively. The tensile properties of the solutionized composites first increase and then decrease as the temperature rises, and the composite thixoformed at 595 °C has the highest comprehensive mechanical properties, an ultimate tensile strength of 267.0 MPa, yield strength of 178.6 MPa and elongation of 21.0 %, increased by 3.1 %, 13.3 % and 15.4 % compared with those of the as-fabricated counterpart.

Metallurgical characteristics of AA6061 aluminium and AZ31B magnesium dissimilar joints by fusion welding technique.

Aluminium (Al) and magnesium (Mg) alloys are extensively used in the automobile sector because of their high strength-to-weight ratio, excellent castability low density and simplicity of recycling. Al-Mg structures used in the automotive sector can potentially reduce their weight. Although there is a significant opportunity for substantial cost reduction, the use of magnesium in aluminium structures remains restricted. This study aims to weld 3 mm-thick rolled sheets of AA6061 Al and AZ31B Mg alloy using the cold metal transfer (CMT) arc welding process. Three different filler wires (ER1100, ER4043, and ER5356) were used in the experiment. In this article, the mechanical and microstructure characteristics of Al/Mg dissimilar joints manufactured by CMT are evaluated and discussed in detail. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used to analyze the CMT-welded Al/Mg dissimilar joints. Of the three filler wires used, ER4043 (Al-5%Si) filler wire yielded defect-free sound joints due to the presence of Si, which improves the flow ability of molten filler during welding. The presence of Mg-rich intermetallics-Al12Mg17)and Al-rich intermetallics-Al3Mg2 were observed. The fractured area of the CMT-welded Al/Mg dissimilar joints revealed the presence of the Mg-rich intermetallics (Al12Mg17), which is responsible for the decrease in tensile strength. The reduction of intermetallics, particularly of Mg-rich intermetallics (Al12Mg17) is important for improving joint strength. RESEARCH HIGHLIGHTS: Cold metal transfer (CMT) arc welding was used to control the Al-Mg-rich intermetallics in the Al/Mg dissimilar joints. The microstructure, morphology and phase composition of the welded joints were studied by OM, SEM, TEM, EDS and XRD. The weld metal and AL substrate bonded with a strong interface, while weld metal and Mg substrate were joined at the epitaxial solidification area where the intermetallic compounds of Mg2Al3, Mg17Al12 and Mg2Si are generated. The weld metal on the Mg side experienced brittle fracture, with a continuous distribution of Mg2Al3, Mg17Al12 and Mg2Si.

Perspectives on Tribological Properties of Spray Formed Al–Pb Alloys

AbstractThis article addresses the tribological characteristics and the influence of mechanical work on the porosity of spray formed Al–Si–Pb alloys. Al‐alloys are extensively utilized in industry due to their self‐lubricant qualities, particularly in the bearing company. In the case of immiscible alloys, the spray approach is the most convenient way to adopt since it allows for single‐step fabrication. The spray process has a high cooling rate, which affects the microstructure of alloys and results in equiaxed grain morphology. Spray deposition and several factors affecting to it are discussed here. This study examines the effect of secondary processes such as cold rolling, hot rolling, extrusion, and so on on porosity, hardness, tensile strength, and tribological behavior. A comprehensive knowledge of the principles of spray techniques and their respective influence on tribological properties are discussed in this perspective by comparing the available literatures, and a future scope for better development is emphasized.

Sintered Al–Si–Ni Alloy: Structure and Properties. I. Powder Obtaining

Sintered Al–Si–Ni Alloy: Structure and Properties. I. Powder Obtaining

Effects of Al–Si alloy powders on mechanical properties and slag resistance of unfired magnesia refractories: In air and carbon-embedded atmospheres

Ultra-low carbon magnesia refractories used in working lining of ladle are crucial components to meet the smelting requirements for producing purity steel. However, the decreased carbon content weakened thermal shock resistance and slag resistance of refractories, resulting in the hampered practical applications. To resolve the mentioned problems, Al–Si alloy powders were introduced into unfired magnesia refractories with glucose and citric acid as binders to form combination of oxides and non-oxides, and performances of refractories were researched systematically in air and carbon-embedded atmospheres according to different service conditions, respectively. The results show that reaction mechanisms in 2 atm led to different effects on microstructure of refractories with added Al–Si alloy powders. The formation of AlN whiskers and plate-shaped MgAl2O4 and Mg2SiO4 with intersecting structure resulted in higher mechanical strength, fracture surface energy and thermal shock resistance of refractories in air atmosphere than that in carbon-embedded atmosphere. The in-situ formed ceramic phases (AlN, MgAl2O4 and Mg2SiO4) in pores led to enhanced slag resistance for refractories. Meanwhile, in carbon-embedded atmosphere, the reduced reactions of Fe2O3 in molten slag increased slag viscosity, presenting higher slag penetration resistance for refractories than that in air atmosphere. Considering the lowered compactness of refractories with excessive alloy powders by large volume expansion from the formation of ceramic phases, refractories with 3 wt% alloy powders showed high mechanical properties, thermal shock resistance and slag resistance. This study provides a reference for the development of ultra-low carbon magnesia refractories used in working lining of ladle, and the research results also indicated that the evaluation of different atmosphere conditions is important for the design of high performance refractories.

Influence of Morphological Change of Eutectic Si during Homogenization Heat Treatment on the Microstructure and Strength at Elevated Temperatures in Wrought Al–Si–Cu–Mg–Ni Alloy

Influence of Morphological Change of Eutectic Si during Homogenization Heat Treatment on the Microstructure and Strength at Elevated Temperatures in Wrought Al–Si–Cu–Mg–Ni Alloy

Effect of Melt Stirring on Microstructure Formation During Solidification of Sr-Modified Near-Eutectic Al–Si Alloys

Effect of Melt Stirring on Microstructure Formation During Solidification of Sr-Modified Near-Eutectic Al–Si Alloys

Theoretical Investigation of Thermodynamic Properties of the Al-Si-Fe Ternary Alloy.

Aiming at the current lack of thermodynamic parameters related to the preparation of aluminum-silicon-iron alloys from spent refractory materials in aluminum electrolytic cells, the Miedema model was used to calculate the thermodynamic parameters of Al-Si, Al-Fe, and Si-Fe binary alloys. On this basis, the Toop model was combined to calculate the mixing enthalpy ΔH, excess entropy SE, excess Gibbs free energy GE, and component activity α of Al-Si-Fe ternary alloys. The results show that ΔH, SE, and GE of binary alloys are all negative values. The properties of the Al element and Si element are similar, and they are different from the Fe element. The ternary alloys also have negative values of ΔH, SE, and GE in the alloy composition range, and their values change obviously in the region where the content of Fe is high or low. The activity values of all components decrease dramatically along with the diminishing of the corresponding molar fractions, and the activity values of Al, Si, and Fe are smaller in the central portion of the triangle of ternary components. It indicates that there is a strong interaction between the three elements, which easily forms ternary intermetallic compounds.

Multipass friction stir welding of dissimilar Al–Si and Al–Mg cast aluminum alloys

In this study, dissimilar cast Al–Si and Al–Mg alloys were joined together using friction stir welding (FSW) technique, employing different levels of heat input and various numbers of FSW passes. For this purpose, two sets of welds were prepared with either low or high heat inputs. Each sets consisted of three welds with one, two, or three FSW passes. The microstructure of the welds was examined using optical and scanning electron microscopes on the weld cross section. The phases in the stirred zone (SZ) were identified using x-ray diffraction method. Hardness profiles and tensile properties were examined to understand joint efficiency. Based on the microstructural analysis results, three distinct regions were identified in the SZ of all welds, including the deformed Al–Mg base metal (region 1), the deformed Al–Si base metal (region 2), and the region with interdiffusion of the two base metals (region 3). Increasing the number of FSW passes increases the fraction of region 3 in the SZ, indicating enhanced stirring and interdiffusion of the two base metals. Following these microstructural changes in the SZ, the welds exhibited a significant improvement in strength and ductility with an increasing number of FSW passes and heat input. The weld with three FSW passes and higher heat input demonstrated the highest strength and ductility, reaching the strength of 187 MPa and ductility of 8.3 % which corresponded to 92 % of the strength and 106 % of the ductility of the Al–Si (the weaker) base metal, respectively. It was concluded that an increase in the number of FSW passes, altered the bonding mechanism from predominantly mechanical interlocking in single-pass welds to robust metallurgical bonding in three-passes welds.

Atomic-level mechanisms of short-circuit diffusion in materials

Abstract This paper reviews the recent progress in understanding the atomic mechanisms of short-circuit diffusion along materials interfaces, such as grain and interphase boundaries, as well as lattice and interfacial dislocations/disconnections. Recent atomistic computer simulations have shown that short-circuit diffusion is dominated by collective atomic rearrangements in the form of strings and rings of mobile atoms. The process is dynamically heterogeneous in space and time and has many features in common with atomic dynamics in supercooled glass-forming liquids. We discuss examples of grain boundary, interphase boundary, and dislocation diffusion in metals and alloys, including the solute effect on the diffusion rates and mechanisms. Interphase boundaries are exemplified by Al–Si interfaces with diverse orientation relationships and atomic structures. The hierarchy of short-circuit diffusion paths in materials is reviewed by comparing the rates of grain boundary, interphase boundary, and dislocation diffusion. Future directions in the field of short-circuit diffusion in defect core regions are discussed.

Improving density and strength-to-ductility ratio of a 3D-printed Al–Si alloy by high-pressure torsion

Good combination of strength and ductility in metallic materials is always desired. To this end, this study assesses the combination of two modern manufacturing processes, namely additive manufacturing (AM) and severe plastic deformation, for an AlSi11Cu alloy. Laser powder bed fusion (L-PBF) produced an alloy with spherical pores with an average size of 42 μm, representing a volume fraction lower than 0.15%. At the mesoscale, the alloy showed a cellular microstructure made up of Al cells and Si-rich boundaries with an average size of 0.69 µm, which were broken down by the high-pressure torsion (HPT) process into ultrafine particles smaller than 0.41 µm. The HPT process transformed the columnar grains of the as-built material into ultrafine-grained grains around the disk edges, while the central zone conserved the as-built characteristics for a number of HPT turns smaller than ¼. HPT processing at room and warm temperatures gave rise to strength–ductility improvements with yield strengths and elongations larger than 400 MPa and 10%, respectively. The good strength–ductility trade-off was related to the porosity decrease, the breakdown of the interconnected network into particles of ultrafine size, the grain size reduction due to the dislocation density increase, and the formation of precipitates and Si-rich particles of different sizes. Thus, AM and HPT improved the grain boundary and precipitation strengthening, giving rise to an Al–Si alloy with superior mechanical properties.Graphical abstract

Preparation and properties of aluminosilicate aerogels from boehmite and waterglass

Aluminosilicate aerogels are promising thermal insulation materials for high temperature applications. In this study, aluminosilicate aerogels were effectively synthesised using affordable precursors: dispersible boehmite powder and waterglass solutions, with subsequent drying achieved by supercritical CO2 processing. According to the evaluation of their properties, the Al–Si aerogels exhibited low densities (0.11 g/cm3), low thermal conductivities (<0.021 W/m·K) and high specific surface areas (SSA) (516 m2/g for an Al:Si molar ratio of 3:1). When waterglass-based aerogel and aluminosilicate samples were treated at high temperature (1200 °C), the formation of mullite was demonstrated for the aluminosilicate aerogel with a molar ratio of Al:Si 3:1, which showed a higher value for SSA compared to the waterglass-based aerogel.

Upgrading recycling of Al–7 wt%Si alloys using electromagnetic force in directional solidification

The highly reactive chemical nature of aluminum makes it production energy-intensive or essentially impossible to extract alloying elements from Al-based liquids. Using molten salt fluxing and electrolysis processes can effectively refine coarse Al scraps. However, the generation of toxic gases and hazardous dross during these processes can cause significant environmental protection challenges and result in notable social concerns. Therefore, the primary recycling of post-consumer Al in industries currently proceeds mainly in a cascade manner, which is not sustainable when considering the Al cycle trends in the coming decades. Herein, we develop a novel process to separate primary Al from the crystallizing liquid when a constant electromagnetic force (EMF) is applied. Using this technique, we successfully upgraded Al–7mass%Si (hereafter, unless specified otherwise) alloy to approximately Al–3.6%Si in directional solidification. The separation mechanism was discussed in terms of the electrical properties of the respective phases during solidification. Fluid flow simulation results were applied to elucidate the separation behavior in the alloy. The upper and lower limits to separate the crystallizing alloy into an Al-rich and Si-rich areas were determined when the controlling factors were clarified, which made it possible to scale up the present laboratory-based setup to an industrial level. Moreover, the energy consumption of the process was slightly higher than that required for remelting only. Using the EMF technique to separate the crystallizing alloy into Al-rich and Si-rich regions did not produce hazardous dross or toxic gases. This energy-saving and eco-friendly process can provide a breakthrough to overcome the “dead metal” crisis and thus realize sustainability by upgrading recycling of post-consumer hypoeutectic Al–Si casting alloys.

New approach to achieve extremely high thermal conductivity of a powder extruded Al–50Si alloy

The Al–50Si alloy, designed for effective heat dissipation in electronic components, was subjected to a two-stage heat treatment process to optimize its microstructure and achieve high thermal conductivity (TC). Two distinct temperature stages were strategically chosen: 850 °C and 550 °C, respectively, with the former operating above and the latter below the eutectic point. The first stage at 850 °C led to the isolation of independent Si particles, each closely associated with individual Al crystal with grain size of approximately 1 mm. Subsequent heat treatment at 550 °C skillfully eliminated introduced eutectic Si through Ostwald ripening. Consequently, the impediments posed by grain boundaries to the movement of electrons and phonons were significantly reduced, yielding an exceptionally high TC of approximately 180 Wm−1K−1, closely approaching the theoretical TC value (∼193 Wm−1K−1) for the Al–50Si alloy. This work paved a new path for the design of outstanding thermal properties in Al–Si electronic packaging materials.

Achieving Metallurgical Bonding in Aluminum/Steel Bimetallic Castings

Aluminum castings are increasingly being used in automotive powertrain and structural applications for vehicle lightweighting. Cast aluminum parts often need to be machined and joined to steel components in multi-material systems. Bimetallic components produced by casting aluminum over steel substrate are advantageous due to the elimination of machining and traditional dissimilar material joining processes. However, forming a strong metallurgical bonding during overcasting process has been challenging. In this paper, the effects of processing conditions such as substrate surface preparation, pre-heating temperature, melt conditions as well as casting design were studied by investigating the bimetallic interfaces for aluminum A319 casting alloy and a high alloy steel substrate in a sand-casting process. Zn and Al-based substrate coatings were evaluated. The experimental results suggest a metallurgical bond between aluminum and steel can be formed during the sand-casting process via high temperature diffusion with or without coatings. Al-based substrate coating prior to overcasting results in the formation of a continuous layer of intermetallics at the bimetallic interface, with large Al–Si–Fe intermetallics penetrating the cast aluminum.

Insights into the dual effects of Ti on the grain refinement and mechanical properties of hypoeutectic Al–Si alloys

Hypoeutectic Al–Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance, and grain refinement is regarded as an important way to improve casting and mechanical properties. Titanium (Ti) is a basic element for grain refinement; thus, a certain amount of Ti is often included in Al–Si alloys. In the present work, the changes in the grain refinement, mechanical, and casting properties of Al–Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated. The specific roles of Ti in the heterogeneous nucleation of α-Al grains were summarized, and the formation mechanism of Ti-rich zones in Al–Si alloys was revealed. Excess Ti concentration could not efficiently reduce the grain size of Al–Si alloys and eventually resulted in inferior mechanical and casting qualities; hence, the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is ≤ 0.1 wt%. Furthermore, an optimized technique for the grain refinement of hypoeutectic Al–Si alloys was presented. A small amount of an Al–TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment. The addition of 0.5 wt% of the Al–TCB master alloy at the Ti concentration level of 0.06 wt% increased the ultimate tensile strength, elongation, and quality index of the Al–7Si–0.45Mg alloy to 328.8 ± 5.0 MPa, 14.4 % ± 0.6 %, and 970.7 ± 33.1 MPa, respectively.

Grain Refinement of Al–Si–Cu Alloys by AlB2 and (Al,Ti)B2

Grain Refinement of Al–Si–Cu Alloys by AlB2 and (Al,Ti)B2

Influence of the pulsed magnetic field of the amplitude strength on the parameters of the magnetoplastic effect in aged Al–Si–Cu–Fe aluminum alloy

The results of a comprehensive experimental study of the influence of the pulsed magnetic field of the amplitude strength on the properties and characteristics of an Al–Si–Cu–Fe aluminum alloy during aging are presented. Data are presented on the modes of thermomagnetic treatment and the results of measurements of the microhardness, lattice parameter, and fine structure parameters of the alloy aged at a temperature of 175°С for 4 h in a pulsed magnetic field with a strength amplitude of 79.6–557.2 kA/m and in its absence. The main regularities of changes in the structure and properties of the metal alloy during annealing are formulated.

The Impact of HIP Process and Heat Treatment on the Mechanical Behaviour of an Al–Si–Mg Alloy Component

AbstractThis study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.