Wrought Al Alloys Research Articles

Upset Protrusion Joining (UPJ) characteristics of cast AM60 magnesium alloy to join with dissimilar material

Magnesium alloys have a significant benefit over the steel and aluminum alloys in manufacturing of components for many automotive and structural applications because of their extreme lightweight, low density, and high strength to weight ratio. However, one of the glaring impediments to the success of steels, aluminum, and magnesium-based multi-material integration for automotive industries is the ability to join these materials together without any cracking and corrosive damages during a performance. The present work aims to demonstrate a cost-effective, novel, and versatile joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly (1–2 s) join die-cast AM60 alloy to aluminum alloy sheet and evaluate its UPJ characteristics. Cast Mg plate has a cylindrical protrusion (11 mm diameter and 14 mm height) emanated perpendicular to its flat surface, and an aluminum sheet has a hole that accommodates the protrusion. Mg and Al alloy components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expanded circumferentially to fill the hole as well as the region above the hole, and entrapped the Al sheet between the deformed (in a mushroom shape) head and the Mg plate. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance is studied. The process demonstrated repeatability at given process conditions, and optimum process parameters were identified that produce visibly good joints (defect-free) and sufficient joint strengths when tested in the lap-shear mode under uniaxial tension. AM60 alloy showed a great promise as a candidate alloy to suit the UPJ method to adapt to automotive and other industrial manufacturing units to join with dissimilar wrought Al alloy sheets.

Al Alloys and Casting Processes for Induction Motor Applications in Battery-Powered Electric Vehicles: A Review

With the rapid expansion of battery-powered electric vehicles (BEVs) in the automotive industry, research interest in lightweight Al alloys as well as their casting processes and applications has increased considerably. The substitution of castable aluminum alloys with superior strengths and electrical conductivity for copper reduces the weight and size of electric induction motors, and improves the energy efficiency and driving range of the BEVs. The present article was intended to give a general introduction into the common cast Al aluminum alloys and their relevant processes, as well as to motivate the development of high strength and conductive Al alloys for the practical realization of Al applications in the motors of the BEVs. A number of cast alloy systems containing Cu, Si, Ni, Mg, Fe, and Ti were evaluated, in comparison to nanostructured wrought Al alloys. The conventional casting processes suitable for Al alloys, high pressure die casting, squeeze casting, and sand casting were described. Strengthening mechanisms including solid solution strengthening, precipitation strengthening, dislocation accumulation strengthening, and grain boundary strengthening were presented. The phenomenon of electrical conduction for Al alloys was outlined. The mechanical properties and electrical properties of the recently developed Al alloys for casting and deformation processes were comprehensively listed and critically reviewed in association with microstructural characteristics.

Effect of Aging State on Impact Toughness of Wrought Al Alloys

Effect of Aging State on Impact Toughness of Wrought Al Alloys

Effect of aging state on fatigue property of wrought aluminum alloys

The high-cycle fatigue (HCF) behaviors of wrought Al alloys are vitally important for their industrial application. To optimize the fatigue property of the wrought Al alloy, the effects of aging conditions on the fatigue properties of 7N01, 7075 and 2024 Al alloys were studied. The results show that the overaged samples have the lowest tensile strength among the three aging states, but their fatigue strength is the highest. Further investigations on the dislocation morphologies indicates that the dislocations are easy to accumulate and annihilate at the second phase boundaries for the overaged state, which reduces the fatigue damage degree at the grain boundaries. Besides, the discontinuous distribution of the grain boundary precipitates and the increased width of the precipitate-free zone also contributed to the improved fatigue property of the overaged state. Those results should be significantly important for the optimization of their fatigue properties and the industrial application of wrought Al alloys.

Selective laser melting of high-strength TiB2/AlMgScZr composites: microstructure, tensile deformation behavior, and mechanical properties

A TiB2/AlMgScZr composite was fabricated by selective laser melting (SLM) with direct powder mixing. The microstructure and mechanical properties of SLM-fabricated TiB2/AlMgScZr composites were investigated. Nearly fully dense and crack-free SLM-fabricated TiB2/AlMgScZr parts were obtained. The results showed that TiB2 formed a coherent relationship with the matrix and was swallowed by the solid–liquid interface as a nucleation point to refine grains during the SLM process. In addition, some TiB2 particles did not form a coherent relationship with the matrix, moving the solid–liquid interface at the grain boundary, which reduced the recrystallization fraction and refined the grains significantly. TiB2 also promoted the precipitation of Al3Sc and Al3Zr phases and increased the volume fraction of the Al3Sc and Al3Zr phases during the SLM process. The SLM-fabricated TiB2/AlMgScZr composites showed a very high ultimate tensile strength of ∼483 MPa and excellent ductility of ∼15.8%, which are higher than those of wrought Al alloys. The solid solubility of the Mg element slightly increased in the SLM-fabricated TiB2/AlMgScZr composites because of the high heating and cooling rate during the SLM process. The high heating and cooling rate caused discontinuous strain and Portevin–Le Chatelier effect and weakened the strengthening effect of TiB2 in SLM-fabricated TiB2/AlMgSc composites.

A review of Laser Powder Bed Fusion Additive Manufacturing of aluminium alloys: Microstructure and properties

Additive manufacturing (AM) of metallic alloys for structural and functional applications has attracted significant interest in the last two decades as it brings a step change in the philosophy of design and manufacturing. The ability to design and fabricate complex geometries not amenable to conventional manufacturing, and the potential to reduce component weight without compromising performance, is particularly attractive for aerospace and automotive applications. This has culminated in rapid progress in AM with Ti- and Ni-based alloys. In contrast, the development of AM with Al-alloys has been slow, despite their widespread adoption in industry owing to an excellent combination of low density and high strength-to-weight ratio. Research to date has focused on castable and weldable AlSiMg-based alloys (which are less desirable for demanding structural applications), as well as on the development of new AM-specific AlMgSc alloys (based on 5xxx series). However, high strength wrought Al-alloys have typically been unsuitable for AM due to their unfavourable microstructural characteristics under rapid directional solidification conditions. Nevertheless, recent research has shown that there is promise in overcoming the associated challenges. Herein, we present a review of the current status of AM with Al-alloys. We primarily focus on the microstructural characteristics, and on exploring how these influence mechanical properties. The current metallurgical understanding of microstructure and defect formation in Al-alloys during AM is discussed, along with recent promising research exploring various microstructural modification methodologies. Finally, the remaining challenges in the development of AM with high-strength Al-alloys are discussed.

The Investigation of Machinability and Surface Properties of Aluminium Alloy Matrix Composites

Aluminum matrix composites (AMCs) are crucial to the progress of composite application areas due to their remarkable mechanical properties. Their usage has expanded into different fields such as the aerospace, automobile, and defense industries. The present study used wrought Al alloy AA6061 as the matrix, while ilmenite (FeTiO3) particles were used as reinforcement at different weight percentages to prepare metal matrix composites. One of the most economical and simple casting routes among the several available fabrication techniques for the preparation of composites is the stir casting method, which was applied in the present investigation to prepare the AMCs. The machinability of the fabricated composites and the surface roughness property after machining were studied to understand the effect of speed and feed during machining. The results showed that an increase in speed decreased the cutting forces and the surface roughness. Meanwhile, an increase in surface roughness was observed with an increase in feed.

Additive manufacturing of aluminium alloy 2024 by laser powder bed fusion: microstructural evolution, defects and mechanical properties

PurposeThe purpose of this study is to investigate the microstructural evolution of high-strength 2024 Al alloy prepared by the laser powder bed fusion (L-PBF) additive manufacturing (AM) route. The high-strength wrought Al alloy has typically been unsuitable for AM due to its particular solidification characteristics such as hot cracking, porosity and columnar grain growth.Design/methodology/approachIn this research work, samples were fabricated using L-PBF under various laser energy densities by varying laser power and scan speed. The microstructural features that developed during the solidification are correlated with operating laser parameters. In addition, finite element modelling (FEM) was performed to understand the experimentally observed results.FindingsMicrostructure evolution and defect formation have been assessed, quantified and correlated with operating laser parameters. Thermal behaviour of samples was predicted using FEM to support experimental observations. An optimised combination of intermediate laser power and scan speed produced the least defects. Higher energy density increased hot tearing along the columnar grain boundaries, while lower energy density promoted void formation. From the quantitative results, it is evident that with increasing energy density, both the top surface and side wall roughness initially reduced till a minimum and then increased. Hardness and compressive strength were found to decrease with increasing power density due to stress relaxation from hot tearing.Originality/valueThis research work examined how L-PBF processing conditions influence the microstructure, defects, surface roughness and mechanical properties. The results indicates that complete elimination of solidification cracks can be only achieved by combining process optimisation and possible grain refining strategies.

Effect of temperature on the mechanical properties of Al–Si–Cu–Mg–Ni–Ce alloy

High-temperature performance is a key factor to concern for the application of cast Al–Si alloys. The evolution of microstructures and mechanical properties of a multiphase Al–Si–Cu–Mg–Ni–Ce alloy during tension in a temperature range from 25 °C (ambient temperature) to 425 °C was investigated. The results show that the main strengthening precipitates of the alloy are θ′ and Q phases. They are stable at 25–250 °C, while dissolve rapidly above 250 °C during tension. The damage initiates and propagates in the form of cracking of brittle phases. The fracture mechanism transforms from quasi-cleavage to coexistence of quasi-cleavage and dimple as temperature increases. The Ce-bearing phase Al20Ti2Ce promotes the damage occurrence below 350 °C while hinders crack propagation at 425 °C. The ultimate tensile strength (UTS) and yield strength (YS) decrease as the tensile temperature increases. The decreasing rate of UTS can be divided into three stages which is associated with the decreasing rate of strengthening precipitates. An empirical constitutive equation is proposed to describe the relationship between UTS and tensile temperature. It provides a good estimation for both cast and wrought Al alloys and the predicted strengths are in good agreement with the experimental results.

Making selective-laser-melted high-strength Al–Mg–Sc–Zr alloy tough via ultrafine and heterogeneous microstructure

For most safety-critical applications, the achievement of both high strength and high toughness is one of the key requirements for structural materials. However, strength and toughness are generally mutually exclusive. Here, we report a selective-laser-melted Al–Mg–Sc–Zr alloy with a good combination of strength and toughness, which is comparable to those of 7075-T651 high-strength wrought Al alloy. Despite the brittle crack associated with order-induced planar slip due to secondary Al3(Sc,Zr) nano-precipitates, the fracture toughness was effectively improved via diverse intrinsic/extrinsic toughening mechanisms associated with its ultrafine and heterogeneous microstructure. The present work provides a potent strategy for fabricating high-strength and high-toughness Al-based alloys.

Prediction of Mechanical Properties of Wrought Aluminium Alloys Using Feature Engineering Assisted Machine Learning Approach

Data-mining based machine learning (ML) method is emerging as a strategy to predict aluminium (Al) alloy properties with the promise of less intensive experimental work. However, ML models for wrought Al alloys are limited due to the difficulty in feature digitalization of the variety of manufacturing processes. Hence, most previous studies were constrained to specific alloy designations, which impeded the applicability of those ML models to broader wrought Al alloys. In the present work, we propose a novel feature engineering, called procedure-oriented decomposition (POD), assisting prediction framework to address the complexity introduced by manufacturing processes for wrought Al alloys. In this model, both chemical compositions and manufacturing processes are integrated as features. Correlation mapping of these features to the wrought Al alloys mechanical properties is established using the support vector regressor (SVR) model. The prediction framework demonstrates a high prediction accuracy and potential to design new alloys.

Examining the Effect of the Aging State on Strength and Plasticity of Wrought Aluminum Alloys

A general rule of strength and plasticity is proposed for three typical wrought Al alloys (2xxx, 6xxx, and 7xxx) subjected to different aging times. Investigations of the work-hardening processes and dislocation configurations in tensile and compressive testing reveal that this general rule arises because there is a common mechanism for these three kinds of wrought alloys whereby the tendency for cross-slip increases monotonously with aging time. By analyzing the work-hardening exponent and the stacking fault energy, it is demonstrated that the change in the dislocation slip mode is attributed mainly to the formation of second phases rather than to the matrix composition. Accordingly, a new work-hardening model is proposed for wrought Al alloys containing second phases and this explains the interaction between dislocations and second phases and other relevant experimental phenomena. This study is therefore beneficial for quantitatively investigating and optimizing the strength and plasticity of wrought aluminum alloys.

Microstructure and properties of additively manufactured Al–Ce–Mg alloys

Additive manufacturing of aluminum alloys is largely dominated by a near-eutectic Al-Si compositions, which are highly weldable, but have mechanical properties that are not competitive with conventional wrought Al alloys. In addition, there is a need for new Al alloys with improved high temperature properties and thermal stability for applications in the automotive and aerospace fields. In this work, we considered laser powder bed fusion additive manufacturing of two alloys in the Al–Ce–Mg system, designed as near-eutectic (Al–11Ce–7Mg) and hyper-eutectic (Al–15Ce–9Mg) compositions with respect to the binary L → Al + Al11Ce eutectic reaction. The addition of magnesium is used to promote solid solution strengthening. A custom laser scan pattern was used to reduce the formation of keyhole porosity, which was caused by excessive vaporization due to the high vapor pressure of magnesium. The microstructure and tensile mechanical properties of the alloys were characterized in the as-fabricated condition and following hot isostatic pressing. The two alloys exhibit significant variations in solidification structure morphology. These variations in non-equilibrium solidification structure were rationalized using a combination of thermodynamic and thermal modeling. Both alloys showed higher yield strength than AM Al-10Si-Mg for temperatures up to 350 °C and better strength retention at elevated temperatures than additively manufactured Scalmaloy.

Influence of Mn and TiB<sub>2</sub> on the Microstructural Evolution of the Primary α-Al Grains and Fe Containing Intermetallic in the Wrought Al-Mg-Si Alloy

The most popular aluminium alloy used for the automotive applications is the wrought-Al alloy, where its popularity arises from its intrinsic characteristics such as, excellent formability, crash resistance, corrosion resistance and excellent specific strength. In the coming decades the use of aluminium alloys is expected to increase within automotive and aerospace industries, where this will source for an upsurge in Al recycling. Problems arise during Al recycling, where there is a steady build-up of Fe content, as this is recognised as being an impurity element. Fe has very little solubility in Al in its solid state and precipitation of these Fe intermetallics (IMC), in the Al matrix decrease mechanical properties, due to the Fe IMC brittle nature. These Fe-rich IMC also have very little cohesion to the Al matrix and can separate from the Al matrix resulting in the development of voids, where the initiation of microcracks becomes ostensible when subjected to thermomechanical processing. In order to curtail the damaging effect of the Fe IMC it so of importance to alter the nucleation and growth characteristic of the Fe rich IMC during solidification. Addition of trace elements and the manipulation of cooling rates have shown to be an effective technique to alter the Fe IMC morphology. In order observe the morphological evolution of the Fe IMC, various experiments were conducted using Al-1Si-1Mg-1Fe alloy with the addition of Mn and TiB2-based commercial grain refiner. Microstructural analysis of the primary α-Al and Fe IMC are observed and the morphological evolution of the Fe IMC is analysed with respects to the addition of Mn and TiB2. How the addition of these trace elements influence the growth characteristics and chemistry of the Al melt is also presented in this work.

Friction Stir Welding of Similar Aluminum Alloys Thick Plates: An Understanding of the Material Flow, Microstructure Evolution, and Mechanical Properties

A systematic study of friction stir welding in three precipitation hardened wrought Al alloys (2024-T351, 6061-T651, and 7075-T735) has been conducted. The material flow, microstructure evolution, defects and precipitates formation mechanisms, and mechanical properties for different tool rotation and traverse speeds have been systematically investigated for 15 mm-thick butt-welds of similar alloys plates. The nugget zones in all welds were determined to be formed by two material flows – shoulder-driven and pin-driven. The shoulder-driven flow at the top of the weld corresponds to bulk material transfer (i.e., bulk material flow), while the pin-driven flow occurs through a combination of layer-by-layer material transfer (i.e., layered extrusion flow, due to the pin’s extrusion effect) and bulk material flow. The relative volumes of the layered and bulk material flows are dependent on the material and processing parameters. Weld defects are formed when significant differences in flow stress between shoulder-driven and pin-driven flows exist, due to the inhomogeneous heat distribution across the large weld thickness. For materials with higher thermal conductivity, lower flow stresses and temperature gradients, as well as reduced heat inputs result in reduced defect formation. Different techniques, including TEM and DSC characterization, have been used to study the precipitation behavior in friction stir welds. Heterogeneity between the top and bottom regions of the nugget zone was observed. Increasing traverse speed improves the tensile strength and ductility of most studied alloys, and discussions on optimizing the resulting weld quality and mechanical properties using an integrated material flow-microstructure evolution understanding will be presented.

Effect of Aging State on Fatigue Property of Wrought Aluminum Alloys

The high-cycle fatigue (HCF) behaviors of wrought Al alloys are vitally important for their industrial application. To optimize the fatigue property of the wrought Al alloy, the effects of aging conditions on the fatigue properties of 7N01, 7075 and 2024 Al alloys were studied. The results show that the overaged samples have the lowest tensile strength among the three aging states, but their fatigue strength is the highest. Further investigations on the dislocation morphologies indicates that the dislocations are easy to accumulate and annihilate at the second phase boundaries for the overaged state, which reduces the fatigue damage degree at the grain boundaries. Besides, the discontinuous distribution of the grain boundary precipitates and the increased width of the precipitate-free zone also contributed to the improved fatigue property of the overaged state. Those results should be significantly important for the optimization of their fatigue properties and the industrial application of wrought Al alloys.

Microstructure and properties of a high temperature Al–Ce–Mn alloy produced by additive manufacturing

An Al–10Ce-8Mn (wt%) alloy was designed and fabricated by laser powder bed fusion additive manufacturing (AM). The rapid cooling rates of the AM process produced a refined microstructure with a large fraction of reinforcing intermetallic phases. The tensile properties of the alloy were characterized in the as-fabricated state and following thermal exposure. The properties of the as-fabricated microstructure showed exceptional high-temperature performance and strength retention at elevated temperatures up to 400 °C relative to benchmark wrought Al and AM Al alloy properties. Characterization of the microstructure and thermodynamic modeling of the ternary Al–Ce–Mn system rationalized the solidification and solid-state phase transformations. Analysis of the relevant strengthening mechanisms for both the as-fabricated and thermally exposed conditions was performed.

Current Progress in Rheoforming of Wrought Aluminum Alloys: A Review

Semi-solid processing (SSP), including rheoforming and thixoforming, offers a promising opportunity to manufacture net-shaped parts with complex structure and excellent mechanical properties. Owing to its low cost and short process, rheoforming has been the subject of extensive study over the last two decades. The interest in the rheoforming of wrought aluminum alloys is progressively growing among both the research and industrial communities. This review starts with reviewing the recent efforts and advances on preparation of semi-solid slurry of wrought Al alloys, followed by discussing the correlation between microstructure and performance of these alloys. Finally, special attention is paid in the industrial application and the future trends of rheoforming of wrought aluminum alloys.

Effects of the addition of silicon to 7075 aluminum alloy on microstructure, mechanical properties, and selective laser melting processability

Aluminum alloys that can be processed using the selective laser melting (SLM) technique have been restricted to cast alloys based on the Al–Si binary system. To increase the selection of materials available for SLM, researches on SLM processability using wrought Al alloys (e.g. 2xxx, 7xxx series) have been conducted. The 7075 Al alloy has excellent mechanical properties among aluminum alloys; however, 7075 alloy has the problem of severe cracking occurring in parts fabricated through the SLM process. Our study demonstrated that additional silicon enables the fabrication of 7075 SLM parts without major defects and that the amount of silicon content changes the favorable processing conditions, morphology of microstructure, and mechanical properties. As the silicon content increased, voids and cracking in SLM samples were suppressed, and volumetric energy density for sufficient densification was reduced. Vickers microhardness and 0.2% proof strength were enhanced with increments of additional silicon content. In contrast, excessive silicon content resulted in brittleness, which appeared as slight ductility measured on tensile testing and breakage of samples during SLM process. These conflicting effects indicated that silicon content must be adjusted depending on the underlying alloy to yield better processability and a balance between strength and ductility. For the 7075 alloy, the optimal silicon content could be concluded to be 5%, being the lowest amount of silicon content needed for the elimination of cracking with enhanced tensile strength and acceptable ductility.

Effects of nanosized TiC and TiB2 particles on the corrosion behavior of Al-Mg-Si alloy

Nanosized TiC and TiB2 particles (TiCp, TiB2p) can increase the mechanical properties of Al alloys. However, their effects on the corrosion performance of Al alloys are relatively less understood. The corrosion behavior of Al-Mg-Si alloys is improved by adding TiCp and worsened by adding TiB2p. These changes result from i. TiCp refining the grain structure by acting as nucleants and reducing the number of grain boundary phases and ii. TiB2p segregating at grain boundaries and accelerating the corrosion. This provides a selection criterion that can be utilized for reinforcement nanoparticles for wrought Al alloys that are applied in corrosive environments.