Cast Al Alloy Research Articles

Local stress/strain field analysis of die-casting Al alloys via 3D model simulation with realistic defect distribution and RVE modelling

The deformation and fracture behavior of die-casting aluminium (Al) alloys is very complex. Due to local variations in properties, the microstructure and mechanical behavior of materials are highly anisotropic. In this paper, an attempt has been made to quantitatively study the defect characteristics of high pressure cast Al alloy parts using experimental and finite element calculation methods, and to analysis the effect of local porosity and pore size on plasticity. Three-dimensional solids with real defect distribution are obtained by using 3D X-ray computed tomography, and used as an input for building a finite element model. The damage initiation of cast Al alloys under complex stress states is analyzed from micro to macro scales. Crack propagation occurs through two modes of microporous agglomeration: aggregated pores produce cracks from internal necking and stress concentration. Then, they expand in the same direction, agglomerate in a specific direction and eventually fracture. Subsequently, the effect of porosity on non-homogeneity was elucidated by obtaining local stress/strain behavior through digital image correlation measurements. Additionally, a theoretical framework of elasto-plastic deformation of microstructures and a 3D representative volume element model are developed to simulate the deformation and damage processes under cyclic boundary conditions of materials. The simulation results show that the local stress/strain around the pores evolves gradually with deformation. During the die casting process, the method demonstrates the ability to predict the mechanical behavior of Al alloys.

Design of non-heat-treatable Al-Fe-Ni alloys with high electrical conductivity and high strength via CALPHAD approach

Electrical conductivity and strength are two critical properties concerned for rotors materials in electric vehicles. However, the two properties are often mutually exclusive in cast Al alloys. The present work proposes a novel non-heat-treatable Al-Fe-Ni alloy by considering the intermetallic compound’s content and morphology. With the modification of Ni and Fe content, the solidification path of designed alloy were calculated to predict the phase composition, which would greatly impact their performance. The as-cast Al-2Fe-1Ni (wt%) alloy exhibits comprehensive properties with an ultimate tensile strength of 131.2±2.5 MPa, an elongation of 20.2±3.6 % and an electrical conductivity up to 52.0±0.1 %IACS. The eutectic microstructure of Al13(Fe,Ni)4+α-Al in Al-2Fe-1Ni alloy accounts for over 90 %, much larger than the eutectic content in Al-0.4Fe-3.4Ni and Al-1Fe-1Ni alloys. The fine eutectics in Al-2Fe-1Ni alloy improve the second-phase strengthening effects and plastic deformation capability. In addition, the fibrous rod-like intermetallic reduces the electron scattering during the propagation process and leaves more space for free electron movement. The dominant second phase transforms from Al3Ni phase to Al9FeNi phase, further enhancing the thermal stability of the alloy. After aging treatment at 180 °C for 100 h, it shows no noticeable change in electrical conductivity and mechanical properties. It is hoped that this work can provide a new design approach for high-strength and high-conductivity Al alloys.

Machine learning-augmented modeling on the formation of Si-dominated Non-β″ early-stage precipitates in Al-Si-Mg alloys with Si supersaturation induced by non-equilibrium solidification

Recent experiments have shown that Al-Si-Mg alloys solidified under high cooling rates may lead to the nucleation of Si-enriched clusters that are remarkably different from the conventional Mg-Si co-clusters (e.g. β″ particles), and yet the responsible mechanism remains to be elucidated. Here we tackle the problem using a multiscale modeling framework that integrates atomistic modeling, energy landscape sampling, and lattice-based kinetic Monte Carlo (kMC) simulation. The migration energy barriers for vacancy-mediated diffusion amid complex local chemical environments are predicted on-the-fly using a surrogate machine learning model. We discover that the actual vacancy-Si migration barriers are much lower than those assumed in the classic linear interpolation approximation. Such a strong deviation from conventional wisdom, in conjunction with differing Si solute composition, can lead to a great variety in the nucleated early-stage precipitates. More specifically, a high-level supersaturation of Si solute (i.e.xSi/(xSi+xMg)>0.75) would lead to an unexpectedly high enrichment of Si in the nucleated clusters with the Si:Mg ratio up to 5∼6; while at a lower-level supply of Si solute the Mg-Si co-clusters (i.e. Si:Mg ratio around 1∼2) are nucleated instead. These findings provide a viable explanation for the diverse types of early-stage precipitates observed in various experiments, from Si-enriched precipitates in high-pressure die cast Al alloys to β″ particles in conventional casting and/or heat-treated alloys. The implications of our findings are also discussed.

Characterization of microstructure and wear behavior of nickel modified Zn-27% Al alloy casting

Characterization of microstructure and wear behavior of nickel modified Zn-27% Al alloy casting

Friction stir processing: A thermomechanical processing tool for high pressure die cast Al-alloys for vehicle light-weighting

This study uses friction stir processing (FSP) for thermomechanical processing of high-pressure die-casting (HPDC) to modify microstructure and improve mechanical properties. FSP is carried out on two different HPDC aluminum alloys: (a) general-purpose, high-iron, HPDC A380 alloy and (b) premium quality, low-iron HPDC Aural-5 alloy in thin wall, flat plate geometry. Subsequent mechanical testing shows ∼30 % and ∼65 % enhancement in yield strength and tensile ductility. In addition, FSP leads to ∼10 times improvement in fatigue life for A380 alloy and ∼70 % improvement in fracture toughness for Aural-5 alloy. These findings emphasize the capability of FSP to modify the microstructure of HPDC Al-alloys-based structural components so that they can demonstrate a good combination of strength, ductility, fracture toughness, and high fatigue properties for long-term durability and reliability.

Design of Non-Heat Treatable High Pressure Die Casting Al Alloys: A Review

Design of Non-Heat Treatable High Pressure Die Casting Al Alloys: A Review

Microstructure, mechanical properties and residual stress of high vacuum die casting AlSi10MgMn alloys with different spray quenching

Quenching cooling rate in solution treatment is the decisive parameter for solute supersaturation and mechanical properties after following aging of wrought and casting Al alloys. In this study, the microstructure quantitative characteristics, mechanical properties and residual stress of high vacuum die casting (HVDC) AlSi10MgMn alloys with different cooling rates during spray quenching were comprehensive studied, which were compared with the conditions of air and wind cooling as well as water quenching. The results showed that, with the decrease of quenching cooling rate, the cross-section diameters of the nano-precipitates β" increased, the precipitates number density decreased in the aged alloys, and the precipitate free zone (PFZ) at grain boundary widened. In addition, β' and β phases appeared in the samples quenched by air and wind. As the cooling rate dropped, the ultimate tensile strength (UTS) and yield strength (YS) of as-aged alloys decreased whereas the elongation (EL) increased, and the quenching residual stress declined. A critical quenching cooling rate over 30 °C/s followed with aging treatment was found for strengthening the AlSi10MgMn alloys and reducing quenching residual stress. The results are important for controlling mechanical properties and residual stress in the alloy practical application.

Research on composition-process-property prediction of die casting Al alloys via combining feature creation and attention mechanisms

In industrial applications, the mechanical properties of die casting Al alloy parts are influenced by a combination of material composition and forming process. This study establishes a performance data-driven framework that takes into account balanced weights of alloy compositions and process parameters. First, a compositional coefficient normalization method is proposed, in which the electronegativity, thermal, and physical descriptors are dot-multiplied into the coefficient matrix to build alloy factors for coupled compositional information. Higher prediction accuracy and lower risk of overfitting validate the feasibility of the method. Subsequently, to improve the performance of machine learning (ML) model for prediction of mechanical properties, a feature engineering method embedded in attention mechanism is used. The experimental results with high accuracy confirm the ability of the ML model to reproduce the relationships between alloy properties and balance their sensitivities. Finally, contour plots of the characterized parameters are constructed for predicting mechanical property intervals and guiding parameter design. This study innovatively applies the normalization method to the field of die casting aluminum alloy feature optimization. And combined with the attention mechanism to improve the prediction accuracy between material features and target properties, which may also be extended to other alloys.

3D Impedance Analysis on Dissolution Behavior of Additive-Manufactured Al-12%Si Alloy

Laser Powder Bed Fusion (LBPF) is one of the additive manufacturing techniques using a laser beam to melt and fuse layers of metal powder particles forming various metal products with complex shapes. Because the Al-Si alloy manufactured by LPBF has good mechanical properties compared to conventionally cast Al alloys, it is important to investigate the dissolution behavior of Al-Si alloy manufactured by LPBF for wider usage in industry.In the present study, the film resistance of oxide film formed on additive-manufactured Al-12%Si alloys were investigated by a three-dimensional(3D) impedance spectroscopy1-5. This method allows for the estimation of the film resistance with time information because the impedance is plotted on the 3D diagram whose axes are real, imaginary and time, namely, the instantaneous impedance at arbitrary time can be determined from 3D impedance. To investigate the dissolution behavior of additive-manufactured Al alloys, the non-annealed sample (Al-12Si) and annealed samples at different temperatures ranging from 200 to 350 ℃ (Al-12Si300) and 530 ℃ (Al-12Si530) with arbitrary holding time were used for the electrochemical measurements. The 3D impedance of Al-12Si, Al-12Si300 and Al-12Si530 could be successively measured in the immersion conditions. The 3D impedance of Al-12Si and Al-12Si300 demonstrated that the impedance of both samples was increased with time. The 3D impedance of Al-12Si530 indicated small values during measurement. These results imply that the increase of impedance of Al-12Si and Al-12Si300 is associated with the formation of oxide film on the surface. The film resistance estimated from impedance spectra determined from 3D impedance and the morphology of samples after the measurement were correlated discussed.

Additive manufacturing-based combinatorial approach to improve bonding strength and heat transfer performance in wrought-cast Al compound casting

We improved the interfacial bonding strength and heat transfer performance between wrought and cast Al alloy parts by implementing an interfacial Al-Si-Zn-based alloy coating layer. An additive manufacturing (AM)-based combinatorial experiment was employed to determine the optimal composition of coating layers. Various compositional combinations of Al-Si-Zn layers were deposited onto an Al plate using a multi-nozzle direct energy deposition system, and the wetting behavior of the cast materials onto the combinatorial samples was examined to select the best composition of the coating layer. The selected coating layer was sprayed on the cooling pipes, and an actual-scale motor housing integrated by the pipe was produced by a compound die casting. The Al-Si-Zn coating layer caused the surface of the coating layers on pipes to partially melt when in contact with the molten alloy during the casting. Consequently, a reactive layer was rapidly formed between the coating and cast materials before solidification. As a result, the interfacial bonding strength increased to 13 MPa and heat transferability between the wrought and cast materials was improved. Therefore, we described the AM-based combinatorial exploring method for the interfacial coating layer to overcome the interfacial issues between the wrought and cast materials of compound casting.

Correlating microstructural features with improved wear and corrosion resistance of laser surface remelted A356 alloy at different scanning speeds

In this work, two scanning speeds (2 mm/s and 8 mm/s) were employed to remelt the surface of an A356 cast Al alloy by a pulsed laser at 300 W, with microstructural features of the laser-remelted surface layers well characterized and correlated with their wear/corrosion resistance. Through high-quality microstructure characterizations, it is found that the as-received A356 alloy is comprised of coarse α-Al dendrites and interdendritic AlSi eutectics. After laser surface remelting (LSR) at both speeds, microstructure homogeneity is greatly improved due to the remarkable refinement of the dendrites and interdendrites. Hardness and wear tests show that surface hardness and wear rate of the 2 mm/s specimen are 71.6 ± 0.6 HV and 1.1 × 10−3 mm3·N−1·m−1, while those of the 8 mm/s specimen are 67.2 ± 1.1 HV and 1.7 × 10−3 mm3·N−1·m−1, respectively, markedly improved compared to the substrate (55.3 ± 0.5 HV and 2.8 × 10−3 mm3·N−1·m−1). Electrochemical test results reveal that self-corrosion potential (Ecorr) and current (Icorr) of the 2 mm/s specimen are −0.82 V and 9.5 × 10−7 μA, while those of the 8 mm/s specimen are −0.89 V and 1.8 × 10−6 μA, respectively. After comparing with the substrate (−0.95 V and 4.3 × 10−6 μA), the corrosion resistance of both the LSRed specimens is confirmed to be significantly enhanced. Comprehensive analyses reveal that after the LSR the simultaneously increased wear/corrosion resistance can be related to the largely homogenized microstructure, the enhanced supersaturation of Si in α-Al, and the refinement and redistribution of AlSi eutectics in the remelted layer.

Effect of Fe additions on microstructure and mechanical properties in near-eutectic Al–Ce alloys

The effects of adding 1 or 3 wt % Fe to a near-eutectic Al–10Ce alloy are investigated in terms of their as-cast and aged microstructures, thermal stability, and creep resistance. A 1 wt% Fe addition forms fine, Chinese-script Al10CeFe2 and Al11Ce3 eutectic phases without loss of microhardness as compared to the Fe-free Al–10Ce alloy, unlike in traditional cast Al-alloys where detrimental coarse phases are observed when adding Fe. Adding 3 wt% Fe increases hardness significantly while forming primary Al10CeFe2 in a coarse rod morphology. These near-eutectic Al–10Ce–1Fe and hyper-eutectic Al–10Ce–3Fe alloys, after thermal exposure at 400 and 425 °C for up to 384 h, show only a small loss in microhardness, indicating excellent coarsening resistance. Compressive creep measurements performed at 300 °C show similar trends: (i) near-eutectic Al–10Ce–1Fe performs quite similarly to near-eutectic Al–10Ce and (ii) hyper-eutectic Al–10Ce–3Fe exhibits much improved creep resistance, similar to near-eutectic Al–10Ce–5Ni with costly Ni additions, and much better than hyper-eutectic Al–13Ce. After surface laser remelting to simulate laser powder-bed fusion, the near-eutectic Al–10Ce–1 Fe alloy exhibits greatly refined Al10CeFe2 and Al11Ce3 eutectic phases with a doubling in microhardness, indicating a strong potential for laser-based additive manufacturing. Cast Al–Ce–Fe-based alloys show great promise as low-cost alloys with high creep- and coarsening-resistance for use at high temperatures, with the high Fe tolerance enabling the use of recycled aluminum with high Fe contamination.

Comprehensive quality index and map of cast Al alloys according to artificial aging heat treatment conditions using TOPSIS and multiple regression analysis and determination of reasonable heat treatment condition

Some quality indices such as Q, QR, QC and Q0 have been used to evaluate quality level of cast aluminum alloys (Al alloys) based on tensile properties, and quality map has been used to intuitively evaluate the quality level based on the quality index. The previous quality indices and maps lack in evaluating the quality level throughout all the tensile properties, comprehensively. On the other hand, they don’t directly show the quality level according to artificial aging heat treatment condition, while they show the quality level according to the tensile properties. We propose a method to develop comprehensive quality index and map of cast Al alloy according to artificial aging heat treatment condition by using technique for order preference by similarity to ideal solution (TOPSIS) and multiple regression analysis. Moreover, we propose a method to determine a reasonable heat treatment condition by using extremum principle and grid search method. To illustrate the effectiveness, the methods are applied to the cast Al alloy A357. The proposed methods could be widely used to evaluate the comprehensive quality level of the cast Al alloys, and optimize the heat treatment condition.

Localized Corrosion of 7xx.x Al Alloy Castings Grain-Refined with Al-5Ti-1B Master Alloy

The objective of this work was to determine the localized corrosion susceptibility of two artificially-aged 7xx.x Al alloy near net-shaped solidified castings (with a low and high Zn/Mg ratio) that were grain-refined with an Al-5Ti-1B master alloy to reduce hot tearing susceptibility. This was achieved using electrochemical polarization and bulk immersion measurements, coupled with electron microscopy techniques to reveal controlling microstructure aspects associated with corrosion. Both alloys, regardless of temper, exhibited the same corrosion mode: one that involved pit-like corrosion (selective grain attack) that occurred in sequence with the grain boundary region dissolving first, followed by the interdendritic region and then by the dendrite core of the equiaxed dendritic grain structure. The over-aged temper yielded the lowest corrosion susceptibility in terms of the depth of attack observed in cross-section. Of the various coarse eutectic phase particles present, Al2CuMg phase particles were particularly problematic for corrosion.

Superior wear resistance in cast aluminum alloy via femtosecond laser induced periodic surface structures and surface hardening layer

Cast Al alloys have been increasingly used in aviation, shipping, aerospace, and automotive industries as important raw materials of engine parts. However, its poor wear resistance hampered their application in some tribological environments. To overcome the current issue, in present work, we proposed a femtosecond laser (fs-laser) surface processing strategy to fabricate pillar-shaped laser induced periodic surface structures (LIPSS), as well as a work-hardening layer (hardness increment reached 51.2% compared with that of substrate) with an affected depth of ∼ 75 μm, on the surface of cast Al alloy in one step. In this case, the wear performance of processed samples showed an obvious improvement with a 49.4% reduction of the cross sectional area of wear track. Our work broke the existing understanding about the strengthening mechanism of fs-laser surface modification technology, in which surface texture or shock wave induced by fs-laser were viewed as two isolated strengthening effects. For the first time, we achieved the combination of these two strengthening effects, and proved the effectiveness of this strategy. The present results provided theoretical bases for the further development of novel fs-laser surface technologies with better performance.

The Influence of Alloying Elements on the Microstructure and Properties of Al-Si-Based Casting Alloys: A Review

The excellent casting behavior and mechanical and corrosion properties of aluminum-silicon (Al-Si)-based alloys make them ideal for the manufacture of lightweight components with complex geometries. However, these properties depend directly on their microstructure, which, in its turn, is strongly affected by the composition of the alloy, among other factors. Several elements can be added to the material aiming to promote microstructural changes, e.g., grain refinement, optimization of phase morphology and distribution, and precipitation strengthening. Efforts are continuously put into such enhancements of cast Al alloys since they lead to quality improvements that allow for weight reduction and safety increase. Considering the technological relevance of the subject, this paper provides an overview of the research focused on the addition of alloying elements to these alloys, with a greater focus on Al-Si-based systems and the comprehension of the effects of these additions on their microstructure and properties.

In-situ tailoring microstructure by directly synthesized TiC–TiB2 nanoparticles to achieve well-balanced strength and ductility in Al–Cu alloy

Incorporating and dispersing trace manipulated agents into Al alloy melt is a longstanding challenge that hinders the balance of strength-ductility in cast Al alloys. A delicate strategy of in-situ fabrication and effective incorporation of the tuned agents was put forward in this study to achieve a better-optimized microstructure of Al-5.5Cu alloys with superior room-temperature and high-temperature mechanical performance. The tailored microstructure effects and optimized mechanical properties under room temperature and elevated temperature (220 °C) by varying mole ratios of dispersed TiC–TiB2 particles were investigated. The in-situ TiC–TiB2 nanoparticles with the mole ratio in 1 : 2 (TiC: TiB2) performed the best microstructure tailoring capacity for Al–Cu-based alloy, which the manipulated alloys shows the most refined and homogeneous grain microstructure with a size of 40.4 μm, compared with the based Al–Cu alloy, refined by 73.8%. Also, the segregation of Cu was mitigated and after heat treatment, the transformation of θ″ → θ′ was accelerated. Thanks to the contribution of TiC–TiB2 particles, Al–Cu alloys perform excellent strength and ductility synergy both at room temperature and elevated temperature, and the strengthening mechanism was also discussed. It is believed that this work can give an optimized strategy from the in-situ synthesis, incorporation and dispersion of manipulated agents to the alloy microstructure tailoring and strength-ductility balancing.

Electropolishing Behavior of 8xxx Al Alloy in Perchloric Acid and Ethanol Solution

The electropolishing characteristic curves of rolled 8079 Al alloy in perchloric acid and ethanol solution from -25 °C to 25 °C are obtained. The optimal electropolishing conditions of the 8079 Al alloy with rolled are investigated by optical microscope. The result shows that the lower the electropolishing temperature is, the longer the electropolishing time is, and the time range and voltage range are wider. Furthermore, the calibration rate of the phase after electropolishing is higher than 97% investigated by Electron Back-Scatter Diffraction. The electropolishing effect of both 8079 Al alloy with cast and 8011 Al alloy (cast and rolled) is verified.

The Influence of a Corrosive Environment on Fatigue and Mechanical Properties of an Al-Cast Alloy with Higher Fe Content

Al has very good corrosion resistance and corrosion properties. The corrosion resistance of Al-cast alloys is different because these alloys contain a lot of elements, especially in secondary alloys, which contain more impurity elements, of which Fe is the most common. This study deals with secondary AlSi7Mg0.3 cast alloys, which contain more Fe and are affected by a chloride corrosive environment. This environment was selected based on the application of castings in the automotive industry. The main object was to research the effect of such an environment on basic mechanical properties and fatigue properties. The results show that a higher Fe content does not lead to a significant reduction in the properties of the casting, and the chloride environment is not so harmful. Therefore, it can be stated that the investigated secondary sand-cast experimental materials can replace primary alloys without losing the required corrosion and mechanical properties.

Co-strengthening of the multi-phase precipitation in high-strength and toughness cast Al–Cu–Zn–Mg alloy via changing Zn/Mg ratios

The effects of the Zn/Mg ratio on the as-cast microstructure, aging-precipitation behavior, and mechanical properties of cast Al–Cu–Zn–Mg alloys, an interesting precipitation-hardened Al alloy different from the 2XXX and 7XXX, were investigated. The primary phase of the as-cast alloy changed from lamellar θ and S phases to a block S phase with an increased Zn/Mg ratio. The number density of the solely S phases in the peak-aged alloy increased with the Zn/Mg ratio from 0.4 to 1.5, because the Zn promoted the formation of GPB zones. At a Zn/Mg ratio of 2.5, the major precipitates are the S, η, and T phases, due to the preferential interaction of Mg atoms with Zn, which promotes the formation of Mg–Zn clusters and GP zones in the initial stages of aging. The yield strength, ultimate tensile strength, and elongation reached maximum values of 372 MPa, 502 MPa, and 12.3%, respectively. This illustrates the cooperative strengthening of the S, T, and η phases, which pin the moving dislocations and inhibit crack initiation and propagation. A large amount of the T phase in the high Mg content alloy suppresses the formation of the S phase. This multi-phase precipitation addressed the “strength ductility trade-off” in cast Al alloys.