Three-dimensional atom probe has been applied to investigate the solubility of Si in Al
3Sc in an Al–0.16Sc–0.05Si alloy. It was found that L1
2-structured Si-containing Al
3Sc precipitates formed ...after the alloy was aged at 300
°C. Results of first-principles calculation indicated that Si atoms tend to substitute Al sites in Al
3Sc, and thus the precipitates can be represented as (Al,Si)
3Sc. The (Al,Si)
3Sc was found to have a dramatic precipitation-strengthening effect in the cast alloy.
The traditional wrought Al–Mg–Si alloys fabricated via laser powder bed fusion (LPBF) are prone to hot cracks, unless adding grain refiners in as-LPBFed Al alloys. In this work, the Al-9.6 wt.%Mg-4.9 ...wt.%Si (equivalent to pseudo binary eutectic Al-13.3 wt.%Mg2Si) alloy with low solidification range and hot-cracking susceptibility was successfully processed by LPBF. The as-LPBFed alloys have reached a high relative density of 99.3% at the VED of 129.6 J/mm3. The microstructures were featured by fine α-Al grains and cellular eutectic Mg2Si, accompanied by a high number density of dislocations, coherent GP zone and α-Al12(Fe,Mn)3Si phases. The as-LPBFed Al-13.3Mg2Si alloy exhibited the high ultimate tensile strength of 557 MPa, yield strength of 439 MPa and elongation of 2.9%. In addition to the grain refinement and dislocation strengthening, the strength enhancement is mainly ascribed to the dispersion strengthening from the divorced nanosized eutectic Mg2Si. The results demonstrate that manipulation of alloys at near eutectic composition is effective to achieve high strength Al–Mg–Si alloys processed by LPBF.
Rapid melt pool formation and solidification during the metal powder bed process Selective Laser Melting (SLM) generates large thermal gradients that can in turn lead to increased residual stress ...formation within a component. Metal anchors or supports are required to be built in-situ and forcibly hold SLM structures in place and minimise geometric distortion/warpage as a result of this thermal residual stress. Anchors are often costly, difficult and time consuming to remove and limit the geometric freedom of this Additive Manufacturing (AM) process. A novel method known as Anchorless Selective Laser Melting (ASLM) maintains processed material within a stress relieved state throughout the duration of a build. As a result metal components formed using ASLM do not require support structures or anchors. ASLM locally melts two or more powdered materials that alloy under the action of the laser and can form into various combinations of eutectic/hypo/hyper eutectic alloys with a new lower solidification temperature. This new alloy is maintained in a semi-solid or stress reduced state throughout the build with the assistance of elevated powder bed pre-heating. In this paper the ASLM methodology is detailed and investigations into processing of a low temperature eutectic Al-Si binary casting alloy is explored. Two types of Al powders were compared; pre-alloyed AlSi12 and elemental mix Al+12wt% Si. The study established an understanding of the laser in-situ alloying process and confirmed successful alloy formation within the process. Differential thermal analysis, microscopy and X-Ray diffraction were used to further understand the nature of alloying within the process. Residual stress reduction was observed within ASLM processed elemental Al+Si12 and geometries produced without the requirement for anchors.
In the present paper, the influence of locally varying microstructures in case of an AlSi12 cast aluminium alloy is investigated by means of extracting the test pieces from different removal ...positions and low cycle fatigue tests. The temperature-dependent damage mechanisms, the material specific defect types, sizes and their influence on the fatigue properties of two AlSi7 and AlSi12 cast aluminium alloys are studied. An extreme value statistics methodology is applied to predict maximum defect sizes expected in a critical surface volume from two-dimensional metallographic micrographs. A damage map for the AlSi12 cast aluminium alloy is presented explaining the influence of the temperature- and load-dependent damage mechanisms on the observed isothermal and thermomechanical lifetime behavior.
•Smooth and notched tensile tests have been performed for four aluminium alloys.•A method to find the work-hardening characteristics at large strains is proposed.•The failure strain decreases ...linearly with strength for the actual aluminium alloys.•Fracture depends markedly on both stress triaxiality and flow stress.•The Gurson model is capable of describing the measured softening of the materials.
The influence of particles and solutes on the strength, work-hardening behaviour and ductile fracture of four different aluminium alloys in the as-cast and homogenised condition is investigated in this paper. These alloys contain different types and volume fractions of particles, i.e. constituent particles and dispersoids, in addition to elements in solid solution. Tensile tests on smooth and notched axisymmetric specimens are performed to determine the work-hardening curves and the ductile fracture characteristics of the alloys. A laser-based extensometer is used to continuously measure the logarithmic strain to failure in the minimum cross section of the specimens. Finite element simulations of the test specimens are used to determine the work-hardening curves to failure. Both the J2 flow theory and the Gurson model are used to describe the stress–strain behaviour of the materials, where the latter accounts for material softening due to void growth. The microstructure of the alloys is characterised by optical and scanning electron microscopy, and fractography is performed to investigate the fracture modes. While the damage and failure mechanisms are similar in the four alloys, the failure strain depends markedly on the stress triaxiality and the yield stress. The trend is that the failure strain decreases linearly with increasing yield stress for the investigated alloys.
The microstructural evolution during solution treatment at 500°C of a cast AlSi12Cu4Ni2 piston alloy is evaluated by two dimensional and three dimensional imaging methods aiming at identifying the ...microstructural features affecting the processes of damage formation and accumulation under tensile deformation. Highly interconnected networks of aluminides and Si undergo a local loss of connecting branches within these networks owing to the partial dissolution of Cu-rich aluminides and a slight Si spheroidisation. The damage by tensile deformation is studied using synchrotron tomography during in situ tensile tests. In both studied heat treatment conditions (0h and 4h solution treated) damage initiates in the form of micro-cracks in clusters of primary Si particles and debonding at the interface between Si and the matrix. These micro-cracks grow through intermetallic phases in the last stages of deformation. Final failure occurs by coalescence of these cracks mainly through the rigid phases. The loss of connectedness of the Si-intermetallics network during solution treatment allows the alloy to accommodate more damage and plastic strain resulting in an increase of ductility with respect to the as cast condition.
In this paper, the influence of nanoparticle fraction on Portevin-Le Chatelier effect of ZrB2 nanoparticle reinforced AA6xxx composites was investigated and friction stir processing was used to ...uniformize the distribution of nanoparticles. The results indicated that the population of serrations decreases with increasing the fraction of ZrB2 particles, with stress-drop serrations dominate the early stages of deformation while the stress-up serrations increase with the strain. The stress distribution complies with bimodal configuration, and 2 peaks become closing with the increasing fraction of nanoparticles. The interval for unconstrained motion of dislocation is responsible for the suppression of Portevin-Le Chatelier effect. The mean interval decreases with increasing the nanoparticles fraction. The inter-twisted dislocations in small intervals continuously dedicate to instant balance of stress-drop serrations, strengthen composites and favor the plastic deformation.
•The population of serrations decreases with increasing fraction of ZrB2 particles.•Stress-drop serrations dominate early deformation but stress-up serrations increase with strain.•The stress distribution complies with bimodal configuration, and 2 peaks become closing.•The interval for unconstrained motion of dislocation suppresses Portevin-Le Chatelier effect.
A constitutive material model, which predicts the material behaviour of an Al–Si–Mg–Cu alloy under thermomechanical load, is proposed. Moreover, an ageing model is used to simulate the ageing ...behaviour, which also affects the hardening parameters. A new strategy for determining the material parameters is proposed, and a new testing concept for investigating the ageing properties of materials is presented. Thermomechanical fatigue tests are used to validate the material model. The results of the simulations show that it is possible to determine the material parameters based on low-cycle fatigue, relaxation, and ageing tests such that a cycle-by-cycle simulation of thermomechanical fatigue tests is possible. Finally, a comparison of the simulation and test results show a good agreement.
•A new ageing test concept was developed.•The ageing behaviour of an aluminium alloy was investigated and modelled based on the results of the new test strategy.•An elastic-viscoplastic model is coupled with an ageing model.•A strategy for the determination of the material parameters of an elastic-viscoplastic material model is presented.•It could be shown that the simulations are in good agreement with the test results, taking ageing into account.
The aim of this study is to analyze and to summarize the results of the processing of aluminum alloys, and in particular of the Al-Si-Mg alloys, by means of the Additive Manufacturing (AM) technique ...defined as Laser Powder Bed Fusion (L-PBF). This process is gaining interest worldwide thanks to the possibility of obtaining a freeform fabrication coupled with high mechanical strength and hardness related to a very fine microstructure. L-PBF is very complex from a physical point of view, due to the extremely rapid interaction between a concentrated laser source and micrometric metallic powders. This generate very fast melting and subsequent solidification on each layer and on the previously consolidated substrate. The effects of the main process variables on the microstructure and mechanical properties of the final parts are analyzed: from the starting powder properties, such as shape and powder size distribution, to the main process parameters, such as laser power, scanning speed and scanning strategy. Furthermore, some examples of applications for the AlSi10Mg alloy are illustrated.
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