Traditionally 4xxx casting alloys are used for the additive manufacturing of structurally optimised lightweight parts in space, aerospace and automotive. However, for such applications there is a ...need for hardenable high-strength Al-alloys exceeding the properties of the 4xxx alloys family. The study analyses the hardness response of different heat treatment temperatures and hold durations applied to a Sc- and Zr-modified Al-Mg (5xxx-) alloy (Scalmalloy®) processed by Selective Laser Melting, and compares the mechanical properties and microstructure in the as-processed and annealed condition, and these properties are clearly related to the very fine grained microstructure. The results show that the static mechanical properties are exceptionally good with Rm-values exceeding 500MPa along with almost no build-orientation related anisotropic effects, and a high ductility even in the heat treated condition. These properties are clearly related to the very fine grained material, along with the good hardenability of the alloy. The stress-strain curves show the typical Portevin-Le-Chatelier (PLC) effect as known for other 5xxx alloys. Due to significant grain boundary pinning by different particles the very fine-grained bi-modal microstructure originating from the SLM-process can be maintained even in the heat treated condition, and only a HIP treatment leads to local grain growth only in coarser grained regions.
The instability of the keyhole and bubble being captured by solidification interface are the main factors that affect the formation of porosity in laser welding of both aluminum alloy and steel. In ...laser welding of aluminum alloy, the more violent fluid flow behind the keyhole, the larger depth to width ratio can cause the keyhole more unstable, and susceptive to collapse that can be described as three necessary steps. The much larger solidification rate and longer escaping distance make the bubble easily captured by the solidification interface, and easily combined. All of these reasons contribute to the formation of larger number and size of porosity in laser welding of aluminum alloy. The numerical and experimental results are in good agreement.
Commonly used commercial cast aluminum alloys for the automotive industry are viable for temperatures only up to 250 °C, despite decades of study and development. Affordable cast aluminum alloys with ...improved high-temperature mechanical properties are needed to enable the next generation of higher efficiency passenger car engines. Metastable θ′ (Al2Cu) precipitates contribute to strengthening in Al–Cu alloys, but above 250 °C coarsen and transform, leading to poor mechanical properties. A major challenge has been to inhibit coarsening and transformation by stabilizing the metastable precipitates to higher temperatures. Here, we report compositions and associated counter-intuitive microstructures that allow cast Al–Cu alloys to retain their strength after lengthy exposures up to 350 °C, ∼70% of their absolute melting point. Atomic-scale characterization along with first-principles calculations demonstrate that microalloying with Mn and Zr (while simultaneously limiting Si to < 0.1 wt %) is key to stabilization of high-energy interfaces. It is suggested that segregation of Mn and Zr to the θ′ precipitate-matrix interfaces provides the mechanism by which the precipitates are stabilized to a higher homologous temperature.
Altering the content of an alloying element in alloy materials will inevitably affect the content of other elements, while the effect is frequently disregarded, leading to subsequent negligence of ...the common influence on the physical properties of alloys. Therefore, the correlation between alloying elements and physical properties has not been adequately addressed in the existing studies. In response to this problem, the present study focuses on the Alsub.10 Tisub.15 Nix sub.1 Crx sub.2 Cox sub.3 alloys and investigates the competitive interplay among Ni, Cr, and Co elements in the formation of physical properties through a single-element (SE) analysis and a multi-element (ME) analysis based on the first principles calculations and the partial least squares (PLS) regression. The values of C sub.11 and C sub.44 generally increase with the incorporation of Ni or Cr content in light of SE analysis, which is contrary to the inclination of ME analysis in predicting the impact of Ni and Cr elements, and the Ni element demonstrates a pronounced negative competitive ability. The overall competitive relationship among the three alloying elements suggests that increasing the content of Ni and Cr does not contribute to enhancing the elastic constants of alloys, and the phenomenon is also observed in the analysis of elastic moduli. The reason is that the SE analysis fails to account for the aforementioned common influence of multiple alloying elements on the physical properties of alloys. Therefore, the integration of SE analysis and ME analysis is more advantageous in elucidating the hidden competitive mechanism among multiple alloying elements, and offering a more robust theoretical framework for the design of alloy materials.
This work proposes a T6-like heat treatment, including solid-solution treatment at 535 °C and an artificial aging treatment for 10 h at 158 °C, to control the mechanical behavior of selective-laser- ...melting (SLM)-produced AlSi10Mg alloys. The mechanical properties of the AlSi10Mg alloys, such as densification, hardness, and tensile/bending strength, were investigated, and the microstructure of the alloys was analyzed. The results reveal that the tensile strength of the heat-treated samples slightly decreased by 19.97% (from 334 MPa to 267.3 MPa of the as-fabricated samples), while the elongation showed a remarkable increase by up to 155% (from 3.64% to 9.28%). Likewise, the bending strength slightly decreased by 6.1%, while the fracture deflection dramatically increased by up to 122.9% after T6 heat treatment. Thus, the T6 heat treatment can critically enhance plasticity/ductility without any significant loss in the tensile/bending strength of the alloy. The corresponding mechanism is also elucidated based on the spheroidization and diffusion of silicon precipitation during the T6 heat treatment. The results of this study offer an intriguing insight to tailor the mechanical properties of SLM-fabricated AlSi10Mg alloys using suitable solid solutions and artificial aging treatment.
AA2024 aluminum alloy easily forms coarse columnar grains and cracks during selective laser melting (SLM). Herein, a novel grain refiner composed of TiC nanoparticles and TiH2 powders was used to ...develop the microstructure of selective laser melted AA2024 aluminum alloy. Due to the heterogeneous nucleation of α-Al promoted by the cooperation of TiH2 and TiC, the microstructure of the TiC–TiH2/AA2024 composite converted from columnar grains with an average area of 729.0 μm2 into equiaxed grains with an average area of 3.4 μm2, and the morphology of the second phase changed from streamline to network-shaped. Moreover, cracks in the TiC–TiH2/AA2024 composite were intrinsically eliminated because of grain refinement. Benefitting from elimination of columnar grains and inhibition of cracks as well as the combined effect of refinement strengthening and Orowan strengthening, the TiC–TiH2/AA2024 composite exhibited excellent mechanical properties, the tensile strength and elongation of as-built samples rose from 240 ± 10 MPa and 0.3 ± 0.2% in AA2024 alloy to 390 ± 15 MPa and 12.0 ± 0.5% in TiC–TiH2/AA2024 composite. After T6 heat treatment, TiC–TiH2/AA2024 composite exhibited a tensile strength of 490 ± 20 MPa and elongation of 16.0 ± 1%, which were comparable to those of wrought AA2024 alloys. The results show that aluminum alloy with excellent mechanical properties can be prepared by SLM with effective microstructure control.
•A TiH2–TiC grain refiner is designed to control structure of SLMed AA2024.•Cracks of SLMed AA2024 are eliminated with TiH2 and TiC co-incorporation.•TiH2–TiC resulted in a homogeneous equiaxed fine grain structure.•Tensile strength and ductility are simultaneously improved.
The ever-increasing demands for lightweight alloys parts with complex shapes in the aerospace industries lead the development of selective laser melting (SLM) technology. The effect of changing ...scanning speed on the formation of single track, as well as the overlapping rate to form multi tracks during SLM processed (SLMed) Al-Cu-Mg alloy was investigated. A processing map for SLMed single track of Al-Cu-Mg alloys was developed. Under different processing parameters, the single track can be characterized as unstable, stable with cracks and stable without cracks. For geometrical characteristic of melt pool of single track, the width and remelted depth are positively correlated with energy input, whereas the height and the contact angle are to the contrary. As for multi tracks, four typical morphologies have been identified, and a processing map was established to select the optimum processing parameters for the SLMed parts without defects. Finally, high density cubic samples (99.91%) without imperfections and microcracks were obtained using optimum processing parameters. In addition, the relationship between microstructure and hardness was discussed. The results provide an important experimental guidance for obtaining high-strength Al-Cu-Mg alloys dense parts with good performance.
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The atomic structure of a 0.94-nm-thick T1 precipitate in an Al–Cu–Li–Mg–Ag alloy is investigated by combining aberration-corrected scanning transmission electron microscopy (STEM) ...and energy-dispersive X-ray spectroscopy (EDX). Ag segregates at the first layer of the T1 precipitate interface, revealing a significant compositional variation of Ag throughout the interface. Moreover, the T1 precipitate thickened from 0.94nm with successive stacking of identical 0.94nm thick layers.
The interface structure and segregation behavior of L1sub.2-Alsub.3M (M = Sc, Zr, Er, Y) phases were investigated based on first-principles calculations. The results showed that the order of the ...thermodynamically stable interface was Alsub.3Zr/Al > Alsub.3Sc/Al > Alsub.3Er/ Al > Alsub.3Y/Al. The interfaces of Alsub.3Sc/Alsub.3Zr, Alsub.3Er/Alsub.3Zr, and Alsub.3Y/Alsub.3Er obtained negative interfacial energies and low coherent strain energies and were favorable to form a clear interface. Zr atom tended to segregate to the first atomic layer on the Al side of the Al/Alsub.3Sc, Al/Alsub.3Er, and Al/Alsub.3Y interfaces. The driving effect of the Zr atom segregation to the Alsub.3Y shows was stronger than that to Sc and Er atoms, whereas the high coherent strain energy hindered the formation of Alsub.3Y/Alsub.3Zr interface. Er atom tended to segregate at the Al/Alsub.3Y interface and accelerated the formation of core-shelled Alsub.3Y/Alsub.3Er. Furthermore, the formation of the double core-shelled Alsub.3Y/Alsub.3Er/Alsub.3Zr was discussed.
It is difficult to obtain a quality joining of steels to aluminum alloys by fusion welding processes due to the large difference between melting temperatures and the formation of thick brittle Al/Fe ...intermetallic compounds at the joint interface. In this study, lap welds between Al 1100 and St37 steel were performed by solid-state friction stir welding with different tool rotation and welding speeds. FeAl and Fe3Al with thicknesses of up to 93 μm were the intermetallic compound layers formed at the joint interfaces. Shear tensile test and Scanning Electron Microscopy results showed that Fe-rich intermetallic compounds are not detrimental to joint strength and some defects, like voids, are responsible for the deteriorated weld strength. The welding parameters determine bond properties by controlling the distribution of welding energy as heat or mechanical work. At low welding speeds, mechanical work is the dominant factor. The optimum tensile strength is achieved at low welding speeds and high rotation speeds, where both factors of heat input and mechanical work are in equilibrium.
•A successful lap joint between St37 and Al 1100 is achieved by FSW.•The formed IMC layers were Fe-rich, which were recognized as FeAl and Fe3Al.•The formed IMCs were not detrimental to weld strength.•some defects like voids were responsible for the deteriorated weld strength.•lower welding speed and higher rotation speed caused the optimum shear tensile strength.
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