Solidification Of Aluminum Alloys Research Articles

In situ X-ray imaging of α-Al(FeMn)Si grain evolution during solidification of an Al-Si alloy with electromagnetic stirring

During the solidification of aluminum alloys with high iron concentrations in conjunction with electromagnetic stirring, the electromagnetic force induces movement of precipitated intermetallic grains containing iron. This force is assumed to cause macrosegregation of such compounds, although the movement process is complex due to the additional effects of melt flow on growth kinetics. The present work used in situ X-ray imaging to obtain insights into the macrosegregation process induced by electromagnetic stirring. This imaging was employed to observe the evolution of primary intermetallic α-Al(FeMn)Si grains during the solidification of an Al-10Si-2Fe-2Mn alloy in the presence of a rotating magnetic field. The α-Al(FeMn)Si grains were found to be uniformly distributed in the horizontal direction of the alloy without electromagnetic stirring but tended to congregate at the periphery of the specimen with stirring. In situ X-ray imaging confirmed that electromagnetic stirring also promoted growth of α-Al(FeMn)Si phase grains from the periphery into the center of the alloy. The α-Al(FeMn)Si phase at the sample periphery comprised a single grain, indicating that stirring led to dendrite growth. These observations together with ex situ crystallographic analyses demonstrated that macrosegregation in an Al-10Si-2Fe-2Mn alloy solidified with electromagnetic stirring resulted from grain coarsening of the α-Al(FeMn)Si phase at the sample periphery.

Wear behavior and impact breakage characterization of PCD teeth of circular saw blades during high-speed sawing of hard aluminum alloy

Polycrystalline diamond (PCD) wear is a classic issue limiting the widespread use of PCD circular saw blades, impairing the final cost and productivity. However, previous studies have rarely focused on the wear of PCD layers of saw teeth considering the vibration effect. Hence, this study aimed to elucidate the wear behavior and impact breakage characteristics of PCD teeth in sawing hard aluminum alloys. Sawing experiments were conducted, while vibration signals and force signals were captured in real-time. Then, wear morphologies of different zones of the PCD tooth were finely characterized and studied by SEM. The results suggested that the main wear types of cutting edges are abrasion, chipping, and adhesion. The abrasive wear was found on the cutting edges, side edges, rake faces, and flank faces. Interestingly, the breakage in chipping zones is mostly marked by grain spalling and cleavage fracture due to binder strength limitations. Adhesive wear occurs in wear zones by EDS analysis. A schematic of the impact wear evolution mechanism is given to explore in detail the wear morphologies of PCD layers. The wear behavior and morphological characterization of the PCD layer are finely discussed considering impact load and sawing factors (e.g., adhesive chips). This study sheds insight into the wear behavior of PCD teeth and guides the design of PCD layers.

Recover the tensile strength of hard aluminum alloy through laser assisted cold spray

In the present study, Al6061/Al2O3 composite coating was produced to repair the notched Al7075 substrate by cold spraying (CS) and laser assisted cold spray (LACS) technology. The preparation process and parameter selection of high-performance coating were discussed by combining simulation and experiment. Results showed that the LACS experiment guided by simulation results achieved high-quality bonding of single particle with the substrate. In addition, the tensile strength of samples repaired by LACS recovered to the level of original substrate, and the ductility was significantly higher than that of CS process. This is attributed to the introduction of laser irradiation heating, which improves the plastic deformation ability of particles and produces atomic-level metallurgical bonding between the particles. This study provides a possibility for the repair and remanufacture research of high-quality components, and has great development potential in future research.

Differential scanning calorimetry of age-hardenable aluminium alloys: effects of sample preparation, experimental conditions, and baseline correction

Precipitation processes in age hardenable aluminium alloys are often investigated by differential scanning calorimetry (DSC). The endothermic and exothermic peaks of the DSC signal correspond to the dissolution and formation of phases, respectively. However, parasitic effects can lead to an unintended curvature of the DSC signal. Although a baseline correction can be used, some imperfections typically remain. Additionally, sample preparation and experimental conditions can influence the precipitation sequence itself and, therefore, the DSC curve. In this study, we investigate the influence of sample preparation by milling and punching on DSC curves for three different aluminium alloys: EN AW-2024, EN AW-6082, and EN AW-7075. Additionally, the influence of quenching and natural ageing was investigated for EN AW-6082. We found that deformation introduced by punching the DSC samples with a piercing die after heat treatment leads to a change in the precipitation kinetics in 2xxx, 6xxx, and 7xxx series alloys. The influence was strongest for punching the samples after solution heat treatment and less significant for punching after artificial ageing. The influence of sample preparation can be avoided by punching the samples before solution heat treatment. If this is not practicable, milling of the samples is a good alternative. The choice of quenching medium and short storage at room temperature before measurement (5 min) had only small effects on the DSC curves. Moreover, the start temperature of the measurement was found to be crucial. For observing phases forming below 100 °C and for low-bias baseline correction, the measurement should start at low-temperatures (i.e. ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} − 50 °C).

Effect of natural aging by multifunction cavitation on plane bending fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys and its fatigue strength estimation

The effect of natural aging by multifunction cavitation (MFC) on the fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys was examined. Surface observation and plane bending fatigue tests were conducted for the MFC-treated aluminum alloys at a stress ratio, R, of −1. The hardness of aluminum alloy without T6 treatment was significantly increased by MFC due to both the work hardening and natural aging. MFC treatment improved the fatigue lives and the fatigue strength at N = 107 cycles of aluminum alloys due to the generation of compressive residual stress and increasing the surface hardness; however, surface pits were large enough to easily nucleate an initial fatigue crack. In addition, the fatigue strength at N = 107 cycles of MFC-treated aluminum alloys can be estimated considering the residual stress, pit size and surface hardness.

Effect of equal-channel angular pressing on microstructure, aging kinetics and impact behavior in a 7075 aluminum alloy

Among the precipitation hardenable 7xxx series aluminum alloys, AA7075 alloys (one of the most important engineering alloys) due to their low density (lightweight), high toughness and strength, and enhanced fatigue behavior have been used over the years in aerospace, aircraft, automotive, construction and marine applications. In the present study, the influence of the artificial aging through conventional heat treatment (i.e., precipitation hardening) and the thermomechanical treatment (equal-channel angular pressing (ECAP) + post-ECAP aging) on the quasi-static tensile, impact toughness and precipitation behavior as well as on the microstructure of an AA7075 alloy is investigated systematically. The results indicate that the ECAP process as well as post-ECAP aging result in considerably increased strength and hardness of the AA7075 alloys because of the superimposed effects of grain boundary strengthening (Hall-Petch relation), strain hardening (by means of the increased dislocation density) and precipitation hardening (due to the fine precipitates formed in Al matrix). Multi-pass ECAP processing has been found to result in a considerable decrease of the impact toughness (from 15.3 J·cm−2 to 7.6 J·cm−2) associated with the failure mode (i.e., ductile-to-brittle transition) of the AA7075 alloys, whereas the artificial peak aging leads to a marked improvement (∼67 %) in the impact toughness in ECAPed conditions. Moreover, the ECAP process noticeably accelerates the precipitation kinetics of AA7075 alloys: The peak aging time in the ECAPed alloy is reduced significantly – from 30 h to 4 h. The results of the present study provide a deeper understanding of the combination of ECAP and heat treatment, and their effect on the fracture mode and toughness under impact loading, the aging kinetics and the microstructural evolution of an AA7075 alloy.

Optimization of Surface Roughness of Aluminium RSA 443 in Diamond Tool Turning

Context—Rapidly solidified aluminium alloy (RSA 443) is increasingly used in the manufacturing of optical mold inserts because of its fine nanostructure, relatively low cost, excellent thermal properties, and high hardness. However, RSA 443 is challenging for single-point diamond machining because the high silicon content mitigates against good surface finishes. Objectives—The objectives were to investigate multiple different ways to optimize the process parameters for optimal surface roughness on diamond-turned aluminium alloy RSA 443. The response surface equation was used as input to three different artificial intelligence tools, namely genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE), which were then compared. Results—The surface roughness machinability of RSA443 in single-point diamond turning was primarily determined by cutting speed, and secondly, cutting feed rate, with cutting depth being less important. The optimal conditions for the best surface finish Ra = 14.02 nm were found to be at the maximum rotational speed of 3000 rpm, cutting feed rate of 4.84 mm/min, and depth of cut of 14.52 µm with optimizing error of 3.2%. Regarding optimization techniques, the genetic algorithm performed best, then differential evolution, and finally particle swarm optimization. Originality—The study determines optimal diamond machining parameters for RSA 443, and identifies the superiority of GA above PSO and DE as optimization methods. The principles have the potential to be applied to other materials (e.g., in the RSA family) and machining processes (e.g., turning, milling).

Impact Toughness of Selected Precipitation Hardening Aluminium Alloys

Impact Toughness of Selected Precipitation Hardening Aluminium Alloys

Solidification of aluminium alloys in different conditions

The development of modern nanotechnology has influenced the principles, design and characteristics of machines and parts. This applies mostly to materials that are used in the space industry. The first aspect concerns the technologies of synthesis, and the second - the qualities and applications of the materials.To date, a limited number of scientific publications describing the preparation and production of materials in space conditions have been published. This article describes the equipment used during the second Russian-Bulgarian flight. In 1988, in space, on the MIR orbital station, 3 experiments related to materials science were conducted by Bulgarian researchers. One of the experiments is “Structure” led by N. Stoichev (BAS). A multifunctional apparatus “Kristalhizator CSK-1” manufactured in Czechoslovakia was used.

Modelling the spatial evolution of excess vacancies and its influence on age hardening behaviors in multicomponent aluminium alloys

Excess vacancies play crucial roles in the precipitation of age-hardening precipitates in aluminium alloys, but their spatial evolution across grains during heat treatments is less known. In this work, a numerical model is developed to predict the spatial evolution of non-equilibrium excess vacancies during cooling from solution treatment and during ageing heat treatments of multicomponent aluminium alloys. A finite volume scheme is applied to derive the spatial distribution of vacancy site fraction across grains by solving the diffusion equations of vacancies under the influence of solute elements. Binding energies between solute atoms and vacancies predicted by first-principles calculations has been used to handle the trapping of excess vacancies by solute atoms and atom clusters. The annihilation rates of excess vacancies at grain boundaries and at dislocation jogs have been derived based on a rigorous description of the annihilation mechanisms of vacancies. The evolution of the density of dislocation jogs due to vacancy annihilation has been taken into account. The model is successfully applied to interpret the age hardening behaviors of experimental alloys subjected to different thermomechanical processing conditions. This model will help to reach a deeper understanding of the roles of excess vacancies in precipitation kinetics and therefore is important to further optimize thermomechanical processing parameters and alloy composition to improve the macroscopic mechanical properties of age hardening aluminium alloys.

Wear mechanisms of aluminum 5083/6061/7075 with and without T6 treatment

The application of hardened aluminum alloys on the drive elements must be safe and reliable, T6 treatment is often used to improve their mechanical properties and dimensional stability. However, the impact of T6 treatment on operating life is not easy to evaluate. Hence, the effects of T6 treatment on the wear of aluminum 5083/6061/7075 were studied by a steel ball on disk tester. The results showed that T6 treatment tended to reduce the values of the friction coefficient about 9%. Moreover, T6 treatment had no significant effect on the frequency of the change of the friction coefficient of 5083 and 6061, but significantly affected that of 7075. T6 treatment can also reduce the size of wear particles about 16%. Based on the results, the wear mechanisms of aluminum 5083/6061/7075 with and without T6 treatment are described in this paper.

The beneficial effect of minor iron additions on the crack susceptibility of rapidly solidified aluminum alloy 6060 toward additive manufacturing applications

Solidification cracking presents a challenge for additive manufacturing of many materials, such as heat treatable aluminum alloys. The objectives of this article are to demonstrate the beneficial effect of minor Fe additions on crack elimination in rapidly solidified Al alloy 6060 and to elucidate the underlying mechanism. Blocks of 6060 + xFe (0 ≤ x ≤ 0.5) were cast and single-track laser melting trials were performed on the surface of the blocks to emulate solidification rates characteristic of additive manufacturing. Analysis of the melt pool cross sections revealed that cracks were present in all processing conditions for the baseline 6060 alloy, but a monotonic decrease in cracking was observed with increasing Fe content with no cracks observed in any conditions for the 6060 + 0.5Fe sample. Serial SEM imaging and FIB milling were used to reveal the 3D morphology of nanoscale particles in the melt pools, while TEM analysis was used to identify the phases. Discrete and nodular δ-AlFeSi particles were observed in samples containing 0.1–0.2 wt% Fe, while elongated and branched α-AlFeSi particles were observed in the 6060 + 0.5Fe sample. The crack mitigation mechanism is proposed to be due to bridging of the Al matrix by the AlFeSi particles, through the formation of a strong interface and mechanical interlocking, thereby resisting the thermally induced loads. It is concluded that minor Fe additions can effectively eliminate cracking in Al 6060, and that this cannot be explained by conventional mechanisms such as grain refinement or an increase in eutectic liquid.

Study of supersaturated solid solution decomposition during quenching of sheets from Al-Mg-Si aluminum alloy

This paper presents the results of a study of the stability of a supersaturated solid solution (SSS) of sheets made of thermally hardened aluminum alloy of the Al-Mg-Si system with a small addition of copper (Al-0.6Mg-1.0Si-0.2Cu) under various quenching modes. The samples were subjected to isothermal or continuous quenching with different quenching cooling rates, after which artificial aging was carried out at a temperature of 170°C. From the results of thermodynamic modeling of the equilibrium phase composition of the alloy, it was found that for the temperature range from 300 to 530°C, the presence of the β-phase (Mg2Si) is most likely. With the use of transmission electron microscopy and X-ray spectral microanalysis, it was found that during quenching, the decomposition of SSS leads to the precipitation of undesirable large particles of metastable β-type phases or equilibrium β-phase. The nucleation of the secretions is realized in the form of rod-shaped particles by a heterogeneous mechanism mainly on the surface of the α-phase dispersoids (Al15(Mn,Fe)3Si2), which thus significantly increase the quenching sensitivity of the alloy. The formation of these secretions at a low quenching rate causes, during subsequent aging, a decrease in the proportion and density of formation of strengthening particles of the β" phase, and also leads to an increase in their size and heterogeneity of distribution in the aluminum matrix, which reduces the potential of dispersion hardening during aging and corrosion resistance of the material.

Multiscale modeling of particle-induced damage in AA7075 aluminum sheet at large plastic strains

Large plastic deformation and ductile damage in precipitation hardening aluminum alloy AA7075 is driven by plastic flow in the vicinity of particles as well as fracture and decohesion of second phase particles embedded in the matrix. The current work investigates the deformation and damage characteristics of Fe-rich intermetallic particles, and η and θ precipitates in AA7075-O sheet. A multiscale model simulation methodology is presented and applied to analyze large-scale plastic deformation and damage characteristics. The methodology utilizes nanoscale molecular dynamics simulation to obtain matrix-particle interface strength properties and Weibull statistics to capture experimental fracture characteristics of particles. The above sub-models are incorporated within a 2-D real particle microstructure-based finite element model to conduct a comparative study of the roles of decohesion and fracture in the development of plasticity and void damage in AA7075-O sheet. In addition, in-situ SEM uniaxial tensile tests are carried out to assess the effectiveness of the simulation methodology and to compare the experimental and numerical results. Post-test high resolution X-ray computed tomography (HR-XCT) was also carried out to qualitatively observe particle-induced voiding in the material. The numerical methodology is shown to capture well the experimental trends in damage evolution of the individual particles. It is observed that particle damage is a function of inherent particle properties, their morphological features, and matrix strain localization characteristics. Larger-size Fe-rich particles are observed to undergo damage at an earlier stage, and consequently, affect the strain localization characteristics the most. In contrast, η precipitates are found to be most resistant to particle damage, followed by θ precipitates. Higher stresses inside strain localization bands, caused increased void damage initiation and growth of η and θ precipitates. Overall, particle fracture is observed to be marginally higher compared to particle decohesion, irrespective of the particle type.

Analysis of wear mechanism and sawing performance of carbide and PCD circular saw blades in machining hard aluminum alloy

High-efficiency sawing is widely applied in primary and secondary machining sectors, but it faces limitations due to saw tooth life and manufacturing constraints. This research investigates the wear mechanism, wear characteristics, and sawing performance of carbide and polycrystalline diamond (PCD) saw teeth when machining hard aluminum alloy. The results show that the sawing forces with PCD saw teeth are less than those of carbide teeth, yielding better surface quality and longer tool life. The wear mechanisms of saw teeth of two materials with different tooth types are classified and characterized finely. Carbide teeth are subject mainly to abrasion and adhesion at the cutting edges, while adhesion, corrosion, and diffusion primarily contribute to flank face wear. PCD teeth mainly suffer from abrasion and micro-chipping on the cutting edges and faces. A comprehensive description of the wear evolution of carbide and PCD teeth is presented, with the cutting heat being the primary cause of carbide tooth wear and the presence of hard particles in the workpiece causing PCD tooth wear by SEM and EDS analysis. The friction coefficient of the PCD teeth is considerably lower than that of the carbide teeth by sliding friction and wear tests, which also proves its more superior thermal stability and wear resistance during wear evolution analysis. Systematic research analyzes and discusses the wear mechanism and wear characteristics of saw teeth in high-speed sawing process, which can further enhance the understanding of the saw tooth wear to provide theoretical guidance for saw tooth design and manufacturing.

Numerical modelling of the process chain for aluminium Tailored Heat-Treated Profiles

Lightweight construction in modern car design leads to an increased usage of various aluminium semi-finished products. Besides sheet material, aluminium extrusion profiles are frequently used due to their high stiffness and variety of possible cross-sections. However, similar to sheet material, aluminium profiles exhibit limited formability in comparison to mild steel materials. One possibility to increase the forming limits of precipitation hardened aluminium alloys is the so-called Tailored Heat Treatment technology. By a local short-term heat treatment, the material is softened and the material flow can be controlled to reduce stresses in critical forming zones. The purposeful definition of the heat treatment zones is mandatory to improve the forming results. Therefore, numerical methods are necessary. In this investigation, a numerical process chain is presented. It combines the thermo-mechanical simulation of a local laser heat treatment with a subsequent bending process of the heat-treated profile using the alloy EN AW-6082. The temperature distribution, mechanical properties, and finally, the bending result of the numerical model are validated by experimental tests.

Comparative Analysis of Finite Element Simulation and Experiment on the Polished Surface Quality of Hard Anodized Film of Aluminum Alloy

According to the abrasive morphology and distribution of sandpaper surface, the finite element model of hard anodic oxide film polishing was established by using ABAQUS finite element software, and the hard anodic oxide film and aluminum alloy matrix were defined respectively. The effects of hard anodic oxide film polishing process, polishing surface quality and polishing parameters on the polishing force were simulated. The polishing surface quality and polishing force simulated by finite element model were verified by experiments. The results show that in the polishing process, the residual stress of polishing surface is mainly distributed in the range of 0.0034mm, and the chips produced by polishing are mainly broken and long strips with microscopic morphology, and polishing mainly depends on the front part of abrasive particles in the feeding direction of sandpaper. Under the action of abrasive particles of sandpaper, the results of finite element simulation and test show that there are certain grooves on the surface of oxide film. The finite element simulation of the normal polishing force of hard anodic oxide film is consistent with the polishing test results. During the process of polishing hard anodic oxide film, the normal polishing force increases as the polishing speed increases; the normal polishing force increases as the polishing removal amount increases; the polishing removal amount parameter has a greater degree of influence on the polishing force.

The Effect of Heat Treatment on the Structural-Phase State and Abrasive Wear Resistance of a Hard-Anodized Layer on Aluminum Alloy 1011

The aim of this study was to evaluate the effect of heat treatment on the phase composition, hardness, and abrasion wear resistance of hard-anodized layers (HAL) on 1011 aluminum alloy. X-ray diffraction analysis revealed the Al2O3·3H2O phase in the structure of HAL synthesized for 1 h. While in the heat-treated HAL, aluminum oxide phases of the α-Al2O3(amorphous) and γ-Al2O3(amorphous) types were found. Treatment at 400 °C for 1 h increased the HAL microhardness from 400 to 650 HV, and its abrasive wear resistance with fixed abrasive by up to 2.6 times. The ranking of various ways of hardening aluminum alloys relative to the D16 alloy showed that the abrasive wear resistance of heat-treated HAL is 20 times higher. Plasma electrolyte oxidation increased the abrasive wear resistance of the D16 alloy by 70–90 times, and its coating with high-speed oxygen fuel by 75–85 times. However, both methods are complex, energy-consuming, and require fine grinding of parts. Despite the lower wear resistance of HAL, their synthesis is cheaper and does not require the fine-tuning of parts. Moreover, despite the low hardness of HAL at present, hard anodizing is already commercially used to harden engine pistons, clamshell rotators, and pulleys.

Influence of Local Microstructural Variations on the Bendability of Aluminum Extrusions: Experiments and Crystal Plasticity Analyses

Abstract The bendability of extruded profiles of an age hardenable aluminum alloy is investigated using mechanical tests on flat tensile specimens and bending specimens. Two profile geometries are considered, where the profiles exhibit different grain structures. The microstructure of the profiles in terms of the crystallographic texture and constituent particles is otherwise comparable. While the tensile properties are not that different for the two profiles, their bendability is strongly dependent on the grain structure and is about twice as high for one profile than for the other. A newly proposed coupled damage and single crystal plasticity model is used in finite element analyses of the mechanical tests to investigate the influence of the grain structure on the bending behavior, and the numerical results are compared to the experimental tests. The crystallographic texture and the grain morphology of the profiles, found by the electron back-scatter diffraction technique, are explicitly represented in the finite element models. The crystal plasticity simulations capture the difference in the bendability of the two profiles, and in agreement with the experiments predict a considerably higher bendability for one of the profiles. It is found that the grain structure affects the shear band formation in these profiles, but also the local texture where the shear bands are located is important for crack initiation and propagation as grains with certain crystallographic orientations may have a higher fracture resistance.

Integrated lubrication and quenching using a volatile medium and additive manufactured die in hot stamping of precipitation hardening aluminum alloy

To achieve lubrication and quenching during hot stamping of aluminum alloys (AAs), a combination of volatile medium (liquid CO2) and additive manufactured (AMed) die is suggested. The liquid CO2 as a lubricant and coolant is directly applied to the heated AA blank through the AMed die with confusor microholes. While the continuously supplied liquid CO2 reduces the friction between the heated AA blank and AMed die, the cooling rate of the liquid CO2 successfully induces the status of solid solution treatment in the formed blank for a following artificial aging process.