► The performance of AlTi5B1 falls short of expectations with the AlSi10Mg and AlSi12Cu alloys. ► When inoculated with AlB3, their grains are very small for the entire range of holding times. ► Fine ...grains, invariably smaller than 200
μm, are readily obtained with the addition of 200
ppm B. ► AlB3 offers remarkable grain refining efficiency and a strong resistance to fading.
The potential of AlB3 master alloy in the grain refinement of AlSi10Mg and AlSi12Cu foundry alloys was investigated and compared with that of the AlTi5B1 master alloy, the standard grain refiner for most aluminium foundries. The latter refines the grain structures of both alloys. However, this performance is not nearly as good as that obtained in wrought aluminium alloys with the same grain refiner. The Ti-free AlSi10Mg and AlSi12Cu alloys, on the other hand, exhibit very small grains for the entire range of holding times when inoculated with AlB3. This implies a remarkable grain refining efficiency, typical of grain refined wrought aluminium alloys, as well as a strong resistance to fading of the grain refinement effect. Lack of Ti in the melt allows the entire B to form AlB
2 particles, the perfect substrates, shortly before α-Al starts to crystallize. Aluminium castings can enjoy grains as small as those of the wrought alloys, well below 200
μm, with an addition of 0.02
wt% B provided that their Ti content is controlled.
The stress-free misfit strain obtained from simulation, neglecting the constraint from the matrix phase, serves as the inhomogeneity eigenstrain. On the other hand, the experimentally measured misfit ...strain under the constraint of the matrix phase serves as the constrained strain. This study demonstrates two ways to calculate the equivalent eigenstrain for precipitates through Eshelby inclusion theory: the inhomogeneity eigenstrain way (IEW) and the constrained strain way (CSW).
Aluminium alloys are being increasingly utilised in the automotive and aerospace industries to reduce the weight of vehicles. Extensive research has been conducted to overcome the poor ductility of ...aluminium alloys at room temperature and improve formability of the materials, to enable complex-shaped panel components to be manufactured. To this end, this paper contains a comprehensive review of widely used forming processes for aluminium alloys, under cold, warm and hot forming conditions, and the material characteristics and equipment used for each process. Based on a detailed analysis from the view of industrial requirements, recent progress in experimentation techniques are reviewed addressing the limitations and improvements of specific forming processes. Furthermore, material modelling methods at both cold and elevated temperature forming conditions have been presented. In addition, finite element (FE) simulations with the implementation of material models are discussed. This review article intends to provide a systematic guide for process designers to choose the most appropriate sheet forming technique for specific industrial applications.
Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to ...increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.
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This work presents a model for deformation enhanced precipitate growth and coarsening kinetics in pre-aged 7xxx aluminium alloys under warm forming conditions (100 to 200 °C). A ...multi-class Kampmann–Wagner framework is used to describe the evolution of precipitate size distribution, where the effect of deformation is incorporated through enhanced solute diffusivity resulting from deformation induced excess vacancies. A classical phenomenological model is used to describe the accumulation of excess vacancies. The model is validated with experimental warm deformation data from the literature, and applied to investigate a wide range of deformation conditions to predict the effect of strain, strain rate and temperature on precipitate growth and coarsening kinetics. It is demonstrated that the interaction of solute supersaturation and excess vacancy concentration can lead to complex non-monotonic precipitate growth rate variation for certain regimes of strain rate and temperature.
An in-situ nano-TiB2 decorated AlSi10Mg composite (NTD-Al) powder was fabricated by gas-atomisation for selective laser melting (SLM). Fully dense and crack-free NTD-Al samples were produced using ...SLM. In contrast to the NTD-Al powder without cell-like microstructure, the SLMed NTD-Al had a textureless microstructure, consisting of fine grains and cells, with well dispersed nano-TiB2 particles inside the grains and rod-like nano-Si precipitates inside the cells. Both nano-TiB2 particles and nano-Si precipitates exhibited a highly coherent interface with the Al matrix, indicative of a strong interfacial bonding. The formation of this microstructure was attributed to the sequential solidification of non-equilibrium and eutectic Al-Si upon rapid cooling during SLM. As a result, the SLMed NTD-Al showed a very high ultimate tensile strength ∼530 MPa, excellent ductility ∼15.5% and high microhardness ∼191 HV0.3, which were higher than most conventionally fabricated wrought and tempered Al alloys, previously SLMed Al-Si alloys and nano-grained 7075 Al. The underlying mechanisms for this strength and ductility enhancement were discussed and a correlation between this novel microstructure and the superior mechanical properties was established. This study provides new and deep insights into the fabrication of metal matrix nanocomposites by SLM from in-situ pre-decorated composite powder.
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Re-examination of the structure of Ω precipitate in Al-Cu-Mg-Ag alloys through first-principles density functional theory (DFT) calculation reveals that the widely-accepted orthorhombic structure of ...the ‘metastable’ Ω phase is actually tetragonal that is identical to that of the equilibrium θ phase in binary Al-Cu alloys. When the tetragonal θ (i.e. Ω) is embedded in α-Al matrix as thin plates, the elastic distortion imposed by the surrounding α-Al matrix can reduce the original 4-fold symmetry of the tetragonal structure to the 2-fold symmetry of the orthorhombic structure. The DFT calculation results also indicate that the presence of Mg and Ag at the θ/α-Al interface can dramatically facilitate the θ formation. The clarification of the Ω structure and the role of Mg and Ag in θ formation provides insights into how to facilitate precipitation of an intrinsically strong equilibrium phase as a key strengthening constituent in the microstructure.
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Metal Additive Manufacturing (AM) processes, such as selective laser melting (SLM), enable the fabrication of arbitrary 3D-structures with unprecedented degrees of freedom. Research is rapidly ...progressing in this field, with promising results opening up a range of possible applications across both scientific and industrial sectors. Many sectors are now benefiting from fabricating complex structures using AM technologies to achieve the objectives of light-weighting, increased functionality, and part number reduction, among others. AM also lends potential in fulfilling demands for reducing the cost and design-to-manufacture time. Aluminium alloys are of the main material systems receiving attention in SLM research, being favoured in many high-value applications. However, processing them is challenging due to the difficulties associated with laser-melting aluminium where parts suffer various defects. A number of studies in recent years have developed approaches to remedy them and reported successful SLM of various Al-alloys and have gone on to explore its potential application in advanced componentry. This paper reports on recent advancements in this area and highlights some key topics requiring attention for further progression. It aims to develop a comprehensive understanding of the interrelation between the various aspects of the subject, as this is essential to demonstrate credibility for industrial needs.
This paper investigates comprehensive knowledge regarding joining CFRP and aluminium alloys in available literature in terms of available methods, bonding processing and mechanism and properties. The ...methods employed comprise the use of adhesive, self-piercing rivet, bolt, clinching and welding to join only CFRP and aluminium alloys. The non-thermal joining methods received great attention though the welding process has high potential in joining these materials. Except adhesive bonding and welding, other joining methods require the penetration of metallic pins through joining parts and therefore, surface preparation is unimportant. No model is found to predict the properties of jointed structures, which makes it difficult to select one over another in applications. The choice of bonding methods depends primarily on the specific applications. The load-bearing mechanism of bolted joints is predominantly the friction that is the first stage resistance. Hybrid joints performance is enhanced by combining rivets, clinch or bolts with adhesives.
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