Al-Si Layer Research Articles

Dissimilar Probeless Friction Stir Spot Welding of Aluminum Alloy and USIBOR®1500-AS Steel Thin Plates

Lap joining of an aluminum AA6082-T6 plate and a UHSS steel plate coated with an Al-Si layer was performed using Probeless Friction Stir Spot Welding (P-FSSW). The dwell time and rotational speed were controlled in the range of 10–15 s and 1000–1500 rpm, respectively. For all the samples, thermo-mechanical deformation occurred solely within the upper AA6082 plate. A refined grain structure was formed in the aluminum plate close to the surface. The dwell time was responsible for the intensity of the material flow, resulting in stirring between the Al-Si layer and the aluminum plate at 15 s. The microhardness distribution corresponded to the microstructure features.

A simulation of Al-Si coating growth under various hot stamping austenitization parameters: An artificial neural network model

22MnB5 hot stamping steels are pre-coated with an Al-Si layer to prevent oxidation and decarburization during the austenitization process, which includes heating and soaking within a furnace. Above ∼577 °C, the Al-Si coating transforms into Fe-Al and Fe-Al-Si intermetallic phases because of diffusion and solidification. In the present work, a deep neural network (DNN) model was developed to predict coating intermetallic growth under various heating rates and soaking conditions. The DNN model was trained using experimental data (energy dispersive x-ray spectroscopy chemical scans) collected from our coating growth characterization work. The heating rate (r), heating time (th), soaking time (ts), and the distance of each measured point away from the coating surface (d) are defined as input parameters, and the outputs are the weight percentage of Al, Fe, and Si. The model successfully predicted the chemical composition of the training dataset, which consisted of a single-stage heating process, followed by a soaking stage at a constant temperature. To validate the model, complex two-stage heating tests were conducted, and the intermetallic coating growth was quantified. The DNN model successfully predicted the two-stage heating test coating profiles, despite a minimal error that was due to the variation in as-received coating thickness. The DNN model predicts the overall experimental trends that show the heating rate has little effect on the transformed intermetallic species, but it affects the transformation rate of the intermetallic phases. Moreover, the higher heating rate test (after 750℃) resulted in the formation of the island shaped τ1 and/or τ2 phase, while the heating rate before 750℃ does not affect the morphology of the τ1 and/or τ2 phase.

Construction of efficient silicon solar cells through polymetallic oxidation-reduction triggered by thermite reaction

Optimal metal-semiconductor contact interface is crucial for semiconductor devices, particularly for silicon solar cells aluminum-silicon contact is a key to improve the efficiency of the cell. In this work, a new type of Sb2O3-MoO3-B2O3 glass frits that can trigger a thermite reaction was utilized to improve the Al-Si interface. The low melting temperatures of these glass frits enhance the effect of thermite reaction by providing solid-liquid contact, which enables gradient distribution of the elements and leads to differences in the valence states of the Al-Si layer at the inner and surface regions. The valence states of Al and Sb at the inner layer are higher than those at the surface, while Mo is the opposite. Metallic Mo with a matched work function can lower the potential barrier, thereby improving hole selectivity and enhancing the potential skip-step. As a result, the fabricated solar cell achieved a high open-circuit voltage, a high short-circuit current, and a low series resistance. Consequently, a power conversion efficiency of 19.94% was obtained for a monocrystalline silicon solar cell with full Al-BSF. This work not only presents a new hole-selective contact for silicon solar cells, but also introduces a new approach for regulating the distribution and valence states of interface elements for enhanced efficiency.

Raman Spectroscopic Analysis of the Reaction between Al-Si Coatings and Steel.

Hot-stamped ultrahigh strength steel components are pivotal to automotive light-weighting. Steel blanks, often coated with an aluminum-silicon (Al-Si) layer to protect them from oxidation and decarburization, are austenitized within a furnace and then simultaneously quenched and formed into shape. The Al-Si coating melts within the furnace and reacts with iron from the steel to yield an intermetallic phase that provides some long-term corrosion protection. During the intermediate liquid phase, some of the coating may transfer to the furnace components, leading to maintenance costs and operational downtime. A detailed understanding of the coating transformation mechanism is needed to avoid such production issues while ensuring that final intermetallic coatings conform to specifications. We introduce cross-sectional Raman microscopic mapping as a method to rapidly elucidate the coating transformation mechanism. Raman spectroscopic fingerprints for relevant intermetallic compounds were determined using synthesized Al-Fe-Si ternary and Al-Fe binary compounds. These fingerprints were used to map the spatial distribution of intermetallic compounds through cross sections of Al-Si-coated 22MnB5 specimens that were heated at temperatures between 570 and 900 °C. These chemical maps show that the intermetallic fraction of the coating does not grow significantly until formation of η (Al5Fe2) at the steel interface, suggesting that η facilitates extraction of iron from the steel and subsequent diffusion through the coating. Under the heating conditions used here, a series of reactions ultimately lead to a silicon-rich τ2 (Al3FeSi) phase on top of the binary η phase. The technique presented here simplifies structural analysis of intermetallic compounds, which will facilitate prototyping of strategies to optimize hot stamping.

High-performance solid-state lithium metal batteries achieved by interface modification

Garnet-structured ceramic electrolyte Li6.75La3Zr1.75Ta0.25O12 (LLZTO) attracts significant consideration in solid-state Li metal batteries due to its wide electrochemical window and favorable compatibility with Li metal. However, the deployment of LLZTO is severely hampered by poor contact between LLZTO and Li metal anode. In this paper, an ultra-thin Al-Si interface buffer layer (10 nm) is constructed on LLZTO by a magnetron sputtering method, which allows superior wetting of Li onto the LLZTO surface due to the alloying reaction between the Al-Si layer and Li metal. The resulting Li/Al-Si coated LLZTO (ASL)/Li symmetrical cell delivers an interfacial resistance of 15.0 Ω cm−2, which is much lower than that of 1140.3 Ω cm−2 for the bare LLZTO symmetrical cell. Moreover, the Li/ASL/Li symmetrical cells exhibit stable plating/striping performance (800 h) with small voltage hysteresis at 1.0 mA cm−2. Besides, the full cell with LiFePO4 cathode reveals a high capacity of 124.1 mA h g−1 after 600 cycles at 0.5C with a low-capacity decay of 0.032% per cycle. We believe this work will facilitate the development of solid-state rechargeable batteries.

Laser welding of tailored blanks made of Al-Si-coated 22MnB5 steel using a filler wire and a variable energy distribution laser optics

Laser welding of Al-Si-coated steels for hot stamping in automotive applications is problematic due to the mixing of the coating layers inside the molten pool that weakens the resulting weld seam. In this case, the most common welding procedure to overcome this issue consists in removing the Al-Si layer through laser ablation prior to the joining. This method continues to be the most widely used by major producers of tailor welded blanks, although in situ ablation of the Al-Si coating can be costly and time consuming. In this work, a novel approach consisting in joining as-received (i.e., not decoated) materials using a filler wire and an innovative variable energy distribution laser optics is introduced and tested on tailor welded blanks made of 22MnB5. Tensile tests of specimens obtained from a 33 full factorial design of experiment have shown an average value of ultimate tensile strength of 1523 MPa, which is much higher than the one usually observed in as-received welded then hot-stamped conditions and aligned with hot-stamped base material values. Hardness test results (494–543 HV0.5) were in the typical hot-stamped base material range of values as well, while SEM–EDS analyses detected no ferrite inclusions inside the fusion zone. Variations of the main process parameters have been considered on an iso-thickness and iso-material configuration, empirically demonstrating the stability and reliability of the proposed methodology as well as its suitability for production purposes.

Microstructure and shear strength on ultrasonic-assisted soldered the Si/Cu joint using Sn-3.5Ag solder

The thermal stress, resulting from the big difference of CTE between Si and Cu, could reduce the strength of joints. In this study, Silicon and Cu were soldered by a two-step process (pre-metallization and brazing), which could alleviate the stress. Firstly, a Al-Si metallization layer (consisting α-Al matrix and Si phase) was prepared on the surface of monocrystalline Si by using Al metal powder at 900 ℃. Then the joint of pre-metallized Si and Cu was successfully achieved by ultrasonic-assisted soldering method with Sn-3.5Ag filler at 250 ℃ in air. The effects of ultrasonic time on microstructure and shear strength of the Si/Cu joints were investigated in details. It was found that the oxide layer was broken and gradually dissolved with the ultrasonic action, which was attributed to the high velocity (3055 m/s), high pressure (2.32×108 Pa), and the high temperature (5700 K) generated by the cavitation bubble collapse. Besides, the Ag2Al compounds and Si phases at the solder/metallization layer interface were observed. And the Cu6Sn5+Cu3Sn compounds were detected forming at the solder/Cu interface. As the ultrasonic vibration duration time increased, Ag2Al compounds attached to the Al-Si layer gradually increased, and ultimately entered into the filler. Attentionly, the maximum strength of Si/Cu joint was 32.4 MPa with the ultrasonic time of 6 s, and the fracture occurred inside the monocrystalline Si. The results show that ultrasonic action affects the distribution of Ag2Al compound and Si phase, which has an important influence on the joint strength.

Формування та структура шару Al–Si на контактній поверхні алюміній–реактивний флюс системи KF–AlF$_3$–K$_2$SiF$_6$

Формування та структура шару Al–Si на контактній поверхні алюміній–реактивний флюс системи KF–AlF$_3$–K$_2$SiF$_6$

Damping Behavior of Layered Aluminium and Aluminide Coatings on AISI 316 Austenitic Steel

Several coating configurations on AISI 316 steel were obtained by a hot dipping process followed by isothermal interdiffusion. Six different kind of multilayered specimens were produced and characterized. These coatings, typically employed as bond coat in thermal barrier coating (TBC), can also be effective as vibration reduction elements at intermediate and high temperatures. This preliminary work was focused on the microstructural design and processing effects of the coatings. The damping of the produced specimens was measured up to 450 °C and compared with that of the steel substrate. The most performing coatings contain an Al-Si layer and exhibit a steep damping increase above 200 °C, reasonably due to dislocation movements by plastic straining of soft alloy layer and to the interface sliding between layers with different elastic moduli.

Electrochemical behaviour of 22MnB5 steel coated with hot-dip Al-Si before and after hot-stamping process investigated by means of scanning Kelvin probe microscopy

Press-hardened steels are commonly protected with hot-dip Al-Si coating. Due to the electrochemical complexity of this system, either before or after hot-stamping process, SKPFM was used to investigate the influence of the thermo-mechanical process on the electrochemical behaviour of the galvanic coupling. The hot-stamping process changed significantly the anodic/cathodic coupling of the coating/steel due to iron enrichment in the coating layer. Hence, a concurrent mechanism was thoroughly established, i.e., while the press hardening enhances the corrosion properties of the steel system (steel and metallic coating) through diffusion, at the same time it diminishes the cathodic protection of the Al-Si layer.

Effect of Al-Si Coating on Weldability of Press-Hardened Steels

Resistance spot welding (RSW) of Al-Si-coated PHS was undertaken, and the effect of Al-Si coating on nugget formation and mechanical properties was investigated. Press-hardened steel (PHS) has long been applied to automotive body structure construction to support mass and corresponding greenhouse gas emission reductions. PHS materials are often combined with an Al-Si coating applied as an oxidation barrier though unfortunately, the Al-Si coating poses a challenge to the resistance spot welding (RSW) of PHS containing stack-ups. As a newly developed coating for the hot stamping process, the property of Al-Si coating is different from base metal and traditional coatings, and the influence mechanism of Al-Si coating on the welding process is not clear. It would remain at nugget edge and might cause severe stress concentration. To investigate this problem, RSW of 1.5-mm Al-Si-coated PHS was undertaken, and the results indicate that a large portion of the Al-Si coating is extruded and forms a sharp notch close to the nugget edge during the welding process. During the post-weld cooling stage, a thin layer of residual coating is formed between the nugget and notch root. The mechanical performance of the welded joints is limited by the thin residual Al-Si layer which acts as a preexisting crack and supports the interfacial fracture. The presence of the Al-Si coating at the faying interface also significantly delays nugget formation, though it contributes to a larger nugget size by inhibiting expulsion events at the faying interface.

Eutectic Formation, V/III Ratio and Controlled Polarity Inversion in Nitrides on Silicon[1

The crystallographic polarity of AlN grown on Si(111) by plasma assisted molecular beam epitaxy is intentionally inverted from N-polar to Al-polar at a planar boundary. The position of the inversion boundary is controlled by a two-step growth process that abruptly changes from Al-rich to N-rich growth conditions. The polarity inversion is induced by the presence of Si, which is incorporated from an Al-Si eutectic layer that forms during the initial stages of AlN growth and floats on the AlN surface under Al-rich growth conditions. When the growth conditions change to N-rich the Al and Si in the eutectic react with the additional N-flux and are incorporated into the solid AlN film. Relatively low levels of Al-Si eutectic formation combined with lateral variations in the Si incorporation lead to nonuniformity in the polarity inversion and formation of surprisingly narrow, vertical inversion domains. The results suggest that intentional incorporation of uniform layers of Si may provide a method for producing polarity engineered nitride structures.

Improving weldability of Al-Si coated press hardened steel using stepped current pulse schedule

Al-Si coated press hardened steel (PHS) were introduced into vehicle body structures for a balance of lightweighting and crashworthiness. However, the weldability of PHS is relatively poor, due to its high carbon equivalent and high strength and is characterized by severe heat affected zone, HAZ softening, and interfacial fracture. The interfacial fracture mode is defined in part by the presence of retained Al-Si coating as a sharp notch at the faying interface following the welding process, which limits the mechanical performance of the joint. To improve the weldability of PHS, a stepped current pulse schedule was proposed for the resistance spot welding (RSW) of 1.5 mm Al-Si coated PHS as a means to effectively promote nugget growth, inhibit expulsion and eliminate the residual Al-Si layer. In this manner the mechanical performance of joints were significantly improved and the desirable button pullout fracture mode was realized.

Tribological behavior of differently deposited Al-Si layer in the improvement of Inconel 718 machinability

Inconel 718 suffers from very poor machinability which limits its application and causes very high machining costs. Therefore, maximizing the tool performance is of prime importance for improving its machinability and reducing the high costs. Physical vapor deposition (PVD), of coatings on the tool material, is the common method, suggested by many studies, to improve the tool performance during cutting of difficult-to-cut materials. Previously, authors have introduced an easy and cost-effective process for depositing the target material on the tool as an alternative for PVD coatings. In the novel proposed process, referred to by the authors as the “pre-machining” method, the material is deposited on the tool surface during a few seconds of machining of the target workpiece. In the current study, the performance of the new proposed technique is compared with the conventional PVD method. The target material used for deposition is a very soft material (Al-Si) which itself has not been used before for coatings used for difficult-to-cut materials. Thus, for this study, a single layer of soft Al-Si material is deposited on the tool through two different techniques; a typical PVD technique under a high vacuum environment in a coater chamfer and the “pre-machining” technique. The comprehensive machinability analysis performed on the tools showed that application of Al-Si as the target materials through both techniques is very beneficial for the cutting tools used for cutting Inconel 718. Moreover, results showed that the performance of the new, easy to perform, and cost-effective deposition technique is very similar to the performance of conventional PVD coatings and even outperforms a PVD coating in some respects. The results showed that the tool life of the Al-Si-coated tool with 1- and 0.7-μm thicknesses and Al-Si pre-machined tool are significantly higher than that of the uncoated tool by 321%, 231%, and 205% respectively. They also outperform the conventional TiAlN hard coating used for machining of this class of material. The study also demonstrated that the cutting force decreased significantly by using Al-Si-coated and pre-machined tools. Furthermore, chipping, abrasion wear, adhesion, BUE formation, and machining-induced work hardening of the workpiece material reduced significantly by using the Al-Si pre-machined/coated tools. Investigation of the chips produced during the machining process and coefficient of friction measurements also confirmed the friction reduction and better flow of the material at the tool-chip interface as a result of Al-Si deposition with both techniques.

Analysis of Al-Si Layer on Steel Sheet during Thermo Mechanical Processing Using Microscopic Methods

High strength steel 22MnB5 according to DIN EN 10083-3 belongs to the group of HF steels frequently used in the production of coachwork. Using the thermo mechanical pressing can be achieved that these steels have strength of about 1500 MPa. The surface of this steel is provided with a protective coating to protect it from oxidation. Galvanic ally, a Zn-based layer is used to provide cathodic protection. The Zn-based layer is limited by the temperature which is insufficient for TMP. Hot-dip galvanizing is also applied to an Al-based layer that does not serve as a cathodic protection but is used as an effective oxidation barrier. The quality of the Al-Si layer is important with regard to the resulting quality of the formed blank. The properties of the surface Al-Si layer affect not only the conditions for their application to the steel blank but also the external conditions which are determined by the conditions of the thermo-mechanical processing into the shape of the finished product. To assess the properties of this layer, microscopy methods, namely light and electron microscopy, were used. On the basis of analyzes, conclusions were drawn that should lead to securing the Al-Si layer with the required properties.

A novel treatment for cutting tools for reducing the chipping and improving tool life during machining of Inconel 718

Chipping and high tool wear are considered the most challenging issues associated with machining of superalloys, including Inconel 718. Despite numerous attempts in this area, it is still considered a critical drawback of this class of materials for application in different industries. A new tool treatment technique is proposed for improving the tool wear and reducing the chipping during machining of Inconel 718. The treatment involves less than two seconds of machining on an aluminum-silicon (Al-Si) workpiece prior to the actual machining of Inconel. In this way, the “pre-machining process”, deposited a very thin layer of Al-Si on the tool face. During the subsequent machining of the Inconel bar, the Al-Si was melted due to the high temperatures of Inconel machining. The molten material channeled itself through the microcracks on the tool surface and seized their propagation. The sliding of the tool on the low friction Al-Si layer resulted in much lower forces, less sticking, seizure and built-up edge formation and, thereby, in less tool wear and chipping. Several beneficial lubricious and thermal barrier tribo-films were also formed on the tool face, which further protected the tool from chipping and severe tool wear. Reducing the contact pressure, friction and temperature during machining resulted in considerable reduction in the machining induced work-hardening of the workpiece material, which is considered as one of the most important factors affecting chipping during machining of this class of materials. Moreover, the ductility of Al helped to dampen the vibrations during machining and helped in tool chipping prevention. Finally, the preconditioning of the tool itself through this process resulted in tool performance improvement by lowering the tool wear at the running-in stage. The new method resulted in a significant reduction in tool chipping and an overall improvement in tool life. Considerable improvements in the surface integrity of the machined part were also obtained. The contributing mechanisms are discussed using detailed material characterization techniques.

Comparison of Electromagnetic and Marangoni Forces on Thin Coatings during Rapid Heating Process

The present paper is dedicated to the investigation of Marangoni and Lorentz forces in a rapid heating process. During the melting of aluminum-silicon (AlSi) layer on the bor-manganese steel 22MnB5, the liquid AlSi is shifting from the middle to the side and leaves dry spots on the steel due to a combination of both forces. In order to solve this process design issue, the impact of each force in the process will be evaluated. Evaluation is carried out using experimental data and numerical simulation.

A comparative investigation on bi-layer Al–Cr/Al–Si coating and mono-layer Al–Cr–Si coating synthesized on Ti–6Al–4V alloy substrate by mechanical alloying method

Abstract A bi-layer Al–Cr/Al–Si coating and a mono-layer Al–Cr–Si coating were respectively produced on the Ti–6Al–4V alloy substrate by mechanical alloying method. The bi-layer coating had an inner composite Al–Si layer and an outer composite Al–Cr layer, which was obtained by milling in Al–Si powder and Al–Cr powder successively. The mono-layer coating was a Sip and Crp reinforced Al matrix coating. The adhesion behavior, the microhardness, the friction and wear resistance, and the high-temperature oxidation resistance of the coatings were investigated and compared. The results indicated that the mono-layer coating had better adhesion behavior compared with the outer layer of the bi-layer coating. Both the mono-layer and the bi-layer coatings could improve the surface microhardness of the substrate. The mono-layer coating had higher surface microhardness. But the bi-layer coating had an inner cushioning layer to maintain the hardness and prevent its sharp decrease with the increase of coating depth. The mono-layer coating had better friction and wear resistance. The bi-layer coating had lower mass gain and oxidation rate compared with the mono-layer coating. A continuous Al3Ti layer formed during oxidation of the bi-layer coating, which could protected the substrate effectively at the elevated temperature. The mono-layer coating was severely oxidized and porous structure formed in the coating. The bi-layer coating had advantages in protecting the substrate at elevated temperature.

Elastic properties and electronic structures of NaAlSi ternary obtained with first-principle calculations

First-principle calculations were carried out on the ternary of sodium aluminium silicide to evaluate the elastic properties and electronic structures within the framework of the density functional theory. Six independent elastic constants were obtained from the coefficients of the polynomials determined by non-linear least squares fitting of the energy-strain functions, and the elastic parameters of the corresponding polycrystalline aggregates were estimated from the calculated single crystal elastic constants. The electronic structure and charge density distribution were explored to analyse and explain the nature of chemical bonding. The results showed that the sodium aluminium silicide compound is a mechanically stable and brittle material with a metallic character. The nature of the bonds formed a layer structure, with a layer of covalent bonding between the Si and Al atoms alternating with a Na atom layer which bonded the Al–Si layer by ionic interaction.

Inferring the specific heat of an ultra high strength steel during the heating stage of hot forming die quenching, through inverse analysis

In hot forming die quenching, furnaces are used to austenitize ultra high strength steel blanks. In the case of coated steels, like Usibor® 1500 P, furnace heating also transforms a protective Al–Si layer into a permanent Al–Si–Fe coating. Modeling this process requires knowledge of how the sensible energy and latent heat of austenitization change with blank temperature; while the former is known, there is considerable uncertainty regarding the latter. In this work the effective specific heat of Usibor® 1500 P is inferred through inverse analysis of temperature data collected on coupons heated in a muffle furnace. This technique is first used to validate the heat transfer model, and then used to investigate austenitization at higher temperatures. Finally, the methodology is applied to analyze temperature data collected from an instrumented blank heated in a roller hearth furnace.