T6 Heat Research Articles

Improvement of mechanical properties of Al–Si–Cu alloy diecastings combined with Cd microalloying and semisolid forming

Al–Si–Cu alloy with and without 0.2 wt% Cd was prepared using traditional and semisolid diecasting. The microstructure, porosity, and mechanical properties of the four alloys in as-cast and T6 heat-treated states were systematically studied and compared. The mechanism of microstructure refinement and property strengthening of semisolid diecasting Al–Si–Cu alloy containing Cd was analyzed. During T6 heat treatment, Cd-rich particles precipitated first and acted as a nucleating agent for θ′-Al2Cu nanoparticles. This resulted in a smaller size and the greater density of the θ′-Al2Cu precipitated phase containing the Cd alloy. Semisolid diecasting Cd microalloyed Al–Si–Cu alloy had excellent mechanical properties under T6 heat treatment. Its ultimate tensile strength, yield strength, elongation, and hardness were 447 MPa, 313 MPa, 6.7%, and 150 HV, respectively. Compared with traditional diecasting Al–Si–Cu alloy without Cd, the above properties were increased by 36%, 57%, 81% and 15%, respectively. This finding was due to the densification, refinement, and homogenization of the microstructure brought about by semisolid formation, as well as the precipitation and strengthening of θ′-Al2Cu nanoparticles with fine and high density due to Cd microalloying.

Effects of Minor Gadolinium Addition and T4 Heat Treatment on Microstructure and Properties of Magnesium

Mg–Gd alloys are candidates for degradable implants combining favorable mechanical and corrosion properties. Gd has a high solid solubility in Mg and an acceptable biocompatibility. The influences of different amount of Gd additions and solid solution (T4) treatment on mechanical properties and corrosion in 0.9 wt% NaCl and cell culture medium (CCM) of magnesium are systematically investigated. The effects of Gd are clarified by microstructural characterizations as well as stress and degradation analysis. It is shown that minor Gd additions to pure Mg lead to Gd solid solution in Mg (α) and the formation of Mg5Gd intermetallic particles (IMPs), which increase the hardness, tensile, and compressive strength. The GdH2 phase is found in low‐alloyed Mg–Gd alloys. The corrosion rate (CR) is increased by the addition of more Gd due to the increased kinetics of the cathodic reaction. However, the resistance to degradation is effectively improved by T4 heat treatment due to the dissolution of IMPs. The reduced susceptibility to pitting can be achieved by a minor Gd addition and T4 heat treatment. The Mg–2Gd alloy is a potential candidate for implants due to its good combination of tailorable mechanical properties and low homogeneous in vitro degradation rate (DR).

Deformation behavior of a newly-developed T4-treated Al–Si die cast alloy

The aim of this study was to identify the monotonic and cyclic deformation behavior of a high-pressure die cast Silafont®-36 alloy in a naturally-aged T4 state. The T4 heat treatment led to a significant microstructural change from the as-cast coralloid-like eutectic Si particles to spheroidal Si particles embedded in the Al matrix, while the prior Fe-, Mn-rich inclusions remained. Although the strength became lower, the ductility of the T4 alloy was higher. Low cycle fatigue life was observed to be longer than its as-cast state at lower strain amplitudes. The T4 alloy exhibited strong cyclic hardening, where the degree of cyclic hardening was found to increase linearly with increasing strain amplitude along with the absence of Masing behavior, due to the strong particle-dislocation interactions during deformation. Strain energy density-based model by incorporating the microstructural aspects in the form of intrinsic fatigue toughness can be used to predict the fatigue life of the T4 alloy.

Directed energy deposition of AA7075 - Effect of TiC nanoparticles on microstructure

AA7075 alloy is a high-strength aluminum alloy with properties enhanced by heat treatments. However, like most high-strength aluminum alloys, AA7075 is non-weldable, as it suffers from hot cracking when it is welded or additively manufactured with fusion techniques. A proposed way to reduce the hot cracking tendency is by refining the microstructure by adding nucleation enhancers. In this study, AA7075 powder feedstock was functionalized with 1.7 and 3.4 vol% TiC nanoparticles, printed with laser-directed energy deposition (DED), subjected to T6 heat treatment, and characterized with optical and electron microscopy, electron backscatter diffraction (EBSD), and hardness measurements. Although TiC was not homogeneously distributed in the aluminum matrix, the addition of TiC successfully suppressed hot cracking by inhibiting dendritic growth produced by increased and more uniform nucleation, which resulted in refined equiaxed grains, and thus enhanced the printability of the material.

Corrosion performance of nano‐treated aluminum alloy A206 with TiC nanoparticles

AbstractA206 aluminum alloy is an important Al‐cast alloy with high mechanical strength. However, its dependence on θ′‐phase for effective strengthening raises concern for its anti‐corrosion performance in service. This paper systematically studies nano‐treating A206 with TiC nanoparticles to investigate its effects on overall corrosion behavior. Immersion tests and electrochemical measurements have been used to understand the nano‐treating contributions to the improved corrosion resistance of A206 under T4 and T6 heat treatment. The results indicate that the pseudo‐dispersion of TiC at or near the grain boundary (GB) and precipitates strengthens the GBs, and more rapid passivation near the TiC‐dense zone introduces a more uniform corrosion feature. The uniform corrosion with rapid passivation greatly facilitates the corrosion control of nano‐treated A206 under T4 and T6 heat treatment, allowing supreme anti‐corrosion stability for high‐strength A206 alloy.

Achieving strength-ductility synergy in semi-solid squeeze cast 6TiB2/Al–17Si–4Cu composites by heat treatment

This study aims to achieve synergistic strength-ductility enhancement of semi-solid squeeze cast 6TiB2/Al–17Si–4Cu composites through in-situ particle strengthening and T6 heat treatment. The microstructure and mechanical properties of 6TiB2/Al–17Si–4Cu composites with different heat treatments were investigated. TiB2 particles are semi-coherent with α-Al and primary Si, respectively. The nanoscale precipitate phases were determined by their crystal orientation relationships. The results showed that they are θ and θʹ phases. Meanwhile, the research results pertaining to the mechanical properties imply that the strength and ductility are enhanced by the TiB2 particles and Al2Cu precipitates. The optimum heat treatment process (solution treatment for 9 h at 520 °C and aging for 8 h at 170 °C) of strengthened 6TiB2/Al–17Si–4Cu composites is revealed in this study, when the ultimate tensile strength and elongation of the composites are 263.3 MPa and 0.51%, respectively. The mechanisms governing the enhanced strength and ductility of 6TiB2/Al–17Si–4Cu composites were discussed.

Improvement of the Mechanical Properties of the Diffusion-Bonded 2024 Aluminum Alloy through Post-Weld Heat Treatments

In this study, 2024 aluminum alloy was diffusion bonded to identify the effect of the bonding temperature, applied pressure, and heating time on the microstructure, hardness, and bonding strength. The shear strength increased from 62.5 MPa to 81.2 MPa along with the rise in bonding temperatures from 440 °C to 490 °C. The bonding strength rose from 62.5 MPa to an optimal value of 81.2 MPa by extending the bonding time from 30 min to 240 min at a bonding temperature of 490 °C and a constant pressure of 5 MPa. In addition, various post-weld heat treatments for diffusion-bonded joints were also performed to improve the bond quality. After the T6 or T4 post-weld heat treatment, the hardness at the bonding interface and the substrate increased due to the precipitation of Al2Cu. Post-weld T4 and T6 heat treatments increased the interface microhardness from 106.3 Hv to 138.25 Hv and 130.6 Hv, respectively. The bonding strength of the AA2024 was significantly improved up to 124.5 MPa and 164.3 MPa by the T4 and T6 heat treatments, respectively.

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting (HPDC) technology has evolved in the past decades, enabling stronger and larger one-piece casting with significant part consolidation. It also offers a higher design freedom for more mass-efficient thin-walled body structures. For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting (for instance, shock towers and hinge pillars, etc.), a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures (450 °C–500 °C) followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement. To enable cost-efficient mass production of HPDC body structures, it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties. Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components. The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy (registered as A379 with The Aluminum Association, USA) to achieve the desired tensile properties without using T7 heat treatment. It was found that Cu addition should be avoided, as it is not effective in enhancing strength while degrades tensile ductility. Mg addition is very effective in improving strength and has minor impact on tensile ductility. The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Effect and its mechanism of fixed-ratio and incremented 3Be-Sb complex modifier on microstructures and properties of hypereutectic Al-Si-Mg alloy

The effect of incremented 3Be-Sb (Be and Sb fixed-ratio at 3) complex modifier on the microstructure and mechanical properties of hypereutectic Al-Si-Mg alloy was investigated. The addition of 0.2 wt% 3Be-Sb in Al-Si-Mg alloy led the primary α-Al from dendritic to regular, the eutectic Si phase was significantly refined, and the size of the primary Mg2Si was remarkably decreased. Specifically, a further increase of 3Be-Sb addition to 0.6 wt% resulted in the microstructure of Mg2Si phase was completely modified from square to a spherical and had maximum refinement effect of primary α-Al. The refinement of the primary Mg2Si phase was attributed to the selective absorption of Be and Sb atoms on Mg2Si surfaces, which inhibited the eutectic Si phase in the preferential growth direction. During the solidification process, the Be element was the heterogeneous nucleation core, and the Mg3Sb2 phase was selected to modify the adsorption-poisoning process. Comparing to the unmodified alloy, the hypereutectic Al-Si-Mg alloy modified with 0.6 wt% 3Be-Sb exhibited significantly enhanced the yield strength, ultimate tensile strength, elongation, shear properties increased from 92.6 Mpa, 120.6 Mpa, 2.0% and 89.6–237.3 Mpa, 250.9 Mpa, 3.3% and 107.6 Mpa, respectively. The abrasive property of these alloys was also prominently improved. Meanwhile, the T6 heat treatment can further improve the mechanical properties. The refinement of Mg2Si phase after complex modification is believed to be the underlying reason for the greatly enhanced mechanical properties.

Optimization of the strength vs. conductivity trade-off in an aluminium alloy designed for laser powder bed fusion

The 6061 Al alloy in its T6 conditions is often considered a good candidate for applications requiring a good balance between strength and thermal conductivity. However, this alloy is often very difficult to process using laser powder bed fusion (PBF-LB) because of the development of hot cracks during fabrication. Here, we show that adding 2.3 wt% of Zr to the 6061 heritage alloy makes it processable by PBF-LB (suppression of hot cracks). Hot crack mitigation is attributed to grain refinement. However, the addition of 2.3 wt% of Zr greatly affects the microstructure and thus the mechanical and electrical/thermal properties of the Zr-modified 6061 alloy. Consequently, there is a need to design heat treatments to achieve a trade-off between yield strength and thermal conductivity. In this work, we designed two heat treatment sequences aiming at achieving such a trade-off: an adapted T6 sequence (550 °C/30 min + 180 °C/4 h) and direct ageing at 400 °C/4 h. On the basis of a multiscale microstructural study using optical microscopy, X-ray diffraction, and electron microscopy, we clarify the evolution of the microstructure induced by the designed heat treatments. The mechanical properties (hardness, tensile behavior) and thermal conductivity derived from electrical conductivity measurements are then discussed in light of the microstructural evolutions. The as-fabricated Zr-modified 6061 alloy shows a higher yield strength (370 MPa) than the heritage 6061 alloy in its T6 condition (260 MPa) but its thermal conductivity is found to be much lower (98 vs. 173 W/m.K). The two heat treatment sequences designed in this work enable the mechanical properties of the heritage 6061 alloy to be outperformed (yield strength of 350 and 460 MPa for the T6 and direct ageing heat treatment respectively) while maintaining an acceptable level of thermal conductivity (150 and 170 W/m.K for the T6 and direct ageing heat treatment respectively).

Effects of Deformation at High, Medium, and Cryogenic Temperatures on the Microstructures and Mechanical Properties of Al-Zn-Mg-Cu Alloys.

Thermomechanical treatment is an effective way to refine the coarse microstructures of aluminum alloys. In this work, multiaxial forging deformation at high, medium, and cryogenic temperatures (i.e., 450, 250, and −180 °C, respectively) was performed on 7085 Al-Zn-Mg-Cu alloys, and its effect on the microstructure evolution and mechanical properties during the subsequent T6 heat treatment process was studied. The results revealed that the coarse particles were broken into finer particles when deformed at cryogenic temperatures, promoting the dissolution of the material after solid solution treatment. Dynamic recrystallization occurred when deformed at 450 °C; however, more dislocations and substructures were found in the samples deformed at 250 and −180 °C, causing static recrystallization after solid solution treatment. The cryogenic deformed sample exhibited a more intense and homogeneous precipitation phase distribution. The strength of the sample deformed at high temperature was high, but its elongation was low, while the strength of the sample deformed at medium temperature was low. The microstructure refinement of the cryogenic deformed sample led to high comprehensive mechanical properties, with an ultimate tensile strength of 535 MPa, a yield strength of 506 MPa, and a fracture elongation of 11.1%.

On mechanical properties of SLM Al–Si alloy: Role of heat treatment-induced evolution of silicon morphology

This study investigates the effect of different heat treatment procedures on tensile, hardness, and fatigue properties of additively manufactured AlSi10Mg. Tensile properties were evaluated for different material conditions, i.e., as-built (AB), direct aging (DA), solution treatment (ST), and T6 heat treatment. It was observed that the as-built samples had the highest yield and tensile strength with limited ductility while increasing the peak heat treatment temperature improves the ductility but at the cost of strength. The microhardness also followed a declining trend with an increase in peak heat treatment temperature. An empirical correlation, validated by experimental data, was established to predict the properties based on peak heat treatment temperatures. Based on the observed test results, four material conditions were selected for evaluating the high cycle fatigue (HCF) properties, i.e., AB, SR, DA, and T6. The as-built samples displayed superior fatigue resistance while that of T6 heat treated samples were most deteriorated. The heat treatment-induced microstructural transformation influences the tensile, hardness, and fatigue properties of the SLM AlSi10Mg, mainly due to the disintegration of continuous Al–Si cellular network and the subsequent formation of discrete Si-particles at high temperatures. The interaction between microstructurally-controlled mechanical properties, associated heat treatment process and the intrinsic damage mechanisms was investigated in detail and discussed later in this study.

Microstructure characterization and mechanical properties of crack-free Al-Cu-Mg-Y alloy fabricated by laser powder bed fusion

Additive manufacturing of high-strength Al alloys (such as 2xxx, 6xxx and 7xxx series alloys) by laser powder bed fusion (LPBF) encounters a challenge because of their high susceptibility to solidification crack. The current work develops a crack-free and novel high-strength Al-Cu-Mg-Y alloy fabricated by LPBF using the rare earth yttrium (Y) modified 2024 alloy powders. In the LPBF-fabricated Al-Cu-Mg-Y alloy, the rare earth element Y is revealed as an effective alloying element for the solidification crack elimination, which is mainly attributed to the combination of the narrowed brittle temperature range, the decreased solidification crack susceptibility index and the refined grains. The element Y can also react with Al and Cu to form the Al 8 Cu 4 Y phases during the LPBF process. In the LPBF-fabricated Al-Cu-Mg-Y alloy, the larger number of Al 8 Cu 4 Y phases and the finer grains result in higher compressive yield strength than most LPBF-fabricated Al alloys. Interestingly, the LPBF-fabricated Al-Cu-Mg-Y alloy can be highly deformed without collapse up to a large compressive strain of ~70 %. After T6 heat treatment, the LPBF-fabricated Al-Cu-Mg-Y alloy exhibits a significant increase in the compressive stress after the yield point, corresponding to the homogeneously distributed Ω precipitate in the Al matrix. In addition, the tensile strength is lower than the compressive strength for the LPBF-fabricated and T6 heat-treated Al-Cu-Mg-Y alloys. This difference is related to the internal pores in the two alloys.

Effect of Heat Treatment on the Oranization and Mechnical Properties of 7A09 Aluminnium Alloy

The 7A09 aluminum alloy was subjected to T6 heat treatment by means of microstructure analysis and mechanical property testing. The results show that the best solid solution treatment process of 7A09 aluminum alloy is 470°C*1 hr. The transverse tensile strength of 7A09 aluminum alloy reaches 555.9MPa, the elongation of 7A09 aluminum alloy reaches 13.5%, and the cloth hardness reaches 152.6HBW. Compared with the cast aluminum alloy, the tensile strength, elongation and hardness increase by 10.3%, 8% and 13.5% respectively, and the mechanical properties of 7A09 aluminum alloy are significantly improved. The mechanical properties of the alloy are significantly improved.

Управління структурою і властивостями ливарного алюмінієвого сплаву АМ4.5Кд (ВАЛ10) модифікуванням дрібнокристалічними лігатурами

To management the structure, mechanical and operational properties of the high-strength cast aluminum alloy АМ4.5Кд (ВАЛ10), the work uses a modification method based on the principle of structural inheritance, using rapidly cooled (Vcool. ≥ 10^5 °С/s) fine-crystal ligatures AlTi5 and AlZr10, and as well as ligatures of the chemical composition of the base alloy with nanoscale size of intermetallics and Alα crystals. Studies have shown that the introduction of fine-crystalline additives into the melt leads to a transition from a dendritic to a non-dendritic structure, a significant decrease in the size of the crystals of the Alα solid solution, and an increase in its degree of supersaturation. The microstructure becomes more uniform - the difference between the maximum and minimum size of the grains decreases. The most effective reduction of the grain size and the transition from dendritic to non-dendritic structure of the aluminum solid solution at increased cooling rates occurs when alloying with fine-crystal AlTi5 ligature introduced into the melt in terms of pure titanium 0.05-0.15 wt. %. We must think that the main factor of modification by rapidly cooled ligatures is the introduction of a large number of additional crystallization centers into the melt. After T6 heat treatment, the highest strength of AM4.5Kd alloy (VAL10) is achieved when modified with AlZr10 ligature, in particular, with a mass fraction of zirconium of 0.25%. Probably, this is mainly due to the expansion of the region of the solid solution of copper and zirconium in aluminum during high-speed cooling and its subsequent disintegration during heat treatment with the release of strengthening nano-sized CuAl2 and Al3Zr phases. Tribological studies of AM4.5Kd alloy (VAL10) were carried out. The alloy modified with fine crystal ligature of the base alloy composition in the amount of 12 wt.% has the highest wear resistance. Keywords: fine crystal ligatures, AM4.5Kd (VAL10), modification, microstructure, strength, wear resistance.

Mechanical characterization and analysis of tensile fracture modes of ultrasonically stir cast Al6082 composites reinforced with Cu powder premixed Metakaolin particles

The major drawback observed in the ceramic particles reinforced aluminium matrix composites (AMCs) is the reduction of ductility. Incorporating fine metallic particles along with the ceramic reinforcements in the aluminium matrix tends to improve the ductility of the AMCs. This work highlights the effects of dispersing micro (5-10 μm) copper (Cu) particles along with the nano (100-400 nm) Metakaolin particles in the Al6082 matrix. The Metakaolin particles were premixed with Cu powder by means of manual stirring followed by ball milling before embedding into the Al6082 matrix. The total reinforcement composition was maintained as 7.5 wt.% in which 2.5 wt.% consisted of Cu powder. The composites were synthesized using ultrasonication-aided stir casting process. The composites samples were subjected to T6 heat treatment before performing mechanical characterization. The composites with Cu powder premixed Metakaolin particles showed improvement in tensile strength, ductility, compressive strength and hardness. The microstructure evaluation of the composites was performed by Scanning Electron Microscope (SEM) and Optical Microscope (OM). The tensile fracture modes were studied by analysing the fracture surface morphology using SEM.

A Survey on Post-Weld Modification of Microstructural and Mechanical Properties of GTAWed Aluminum Butt Joints Through FSP and T6 Heat Treatment

Ergitme kaynağı ile birleştirme endüstrinin her alanında yaygın olarak uygulanan imalat yöntemlerindendir. Özellikle yüksek ısıl iletim ve genleşme katsayısına sahip, sıvı halde hidrojen çözünürlüğü yüksek olan ve yüzeyinde rijit oksit tabakası bulunan alüminyum alaşımlarının ergitme kaynağıyla imalatında iri tane oluşumu, mekanik özelliklerde düşüş vb. olumsuzluklar gerçekleşebilmektedir. Bu nedenle ergitme kaynaklı birleştirmelerin ömürleri ve mukavemetleri açısından kaynak sonrası işlem ile kaynak bölgesinin iç yapı ve mekanik özelliklerinin iyileştirilmesi çoğu uygulama için önemli rol oynamaktadır. Çalışmamızda, tungsten inert gaz (TIG) kaynağı ile birleştirilen AA6082-T6 plakaların kaynak bölgesi özelliklerine kaynak sonrası işlem olarak uygulanan sürtünme karıştırma prosesi (SKP) ve T6 ısıl işleminin etkileri araştırılmıştır. SKP ve T6 ısıl işleminin mekanik özelliklere ve iç yapıya etkileri çekme testi, mikrosertlik testi ve mikroyapı incelemeleri ile araştırılmıştır. SKP ile kaynak dolgusunun işlem gören bölgesindeki (karıştırma bölgesi) dendritik tanelerin parçalanarak ince taneli iç yapının elde edildiği tespit edilmiştir. Bununla birlikte, SKP’nin malzemede oluşturduğu ısıl girdi ile ısıdan etkilenen bölgenin (IEB) genişlemesine ve sertliğin daha geniş bölgede düşmesine sebep olduğu gözlemlenmiştir. Kaynak sonrası uygulanan T6 ısıl işlemi ile kaynaklı birleştirmenin mekanik özelliklerin arttırıldığı ancak tokluğunun azaldığı gözlemlenmiştir.

Enhanced printability and strength of unweldable AA2024-based nanocomposites fabricated by laser powder bed fusion via nano-TiC-induced grain refinement

The formation of undesirable coarse columnar grains and periodic hot cracks has been a long-standing issue in the additive manufacturing (AM) of unweldable high-strength aluminum alloys and their nanocomposites. Herein, the LPBF-printability of AA2024-based nanocomposites is improved by TiC-induced in-situ reinforcement and nanoparticle-enabled grain refinement during laser powder bed fusion (LPBF). The TiC-triggered in-situ reaction during LPBF overcomes the poisoning of the TiC grain refiner that occurs during conventional solidification. It not only results in fine equiaxed grains with a minimum average size of ∼1.6 μm but also suppresses hot crack formation. Powerful L12-Al3Ti nucleants are incorporated in-situ into AA2024 through TiC nanoparticle addition during LPBF, promoting the heterogeneous nucleation of α-Al. Moreover, the growth restriction effect induced by residual TiC nanoparticles and lamellar Al4C3 nanoparticles through pinning behavior along grain boundaries also contributes to grain refinement. Furthermore, these particles serve as effective reinforcement particles as well as grain refiners. The as-built AA2024-based nanocomposites tailored by nano-TiC show a maximum ultimate tensile strength (UTS) of ∼388 MPa, a yield strength (YS) of ∼332 MPa and an elongation (El) of ∼10.2%. After T6 heat treatment, the nanocomposites exhibit an outstanding UTS of ∼507 MPa, a YS of ∼456 MPa and an El of ∼6.6%. This nano-TiC-induced microstructural control method provides new insights into successful AM of hot-crack-sensitive high-strength aluminum alloys and their composites.

Crashworthiness of a hybrid tube with an auxetic layer

Hybrid tubes of different forms have been designed and used in various sectors such as automotive, medical, pipeline, and aerospace industries for protective equipment, oesophageal stents, oil and gas pipes, and superior vibration dampers. Auxetic materials and structures have received increasing attention due to their unique properties such as negative Poisson’s ratio. They laterally expand under uniaxial tension or laterally contract under uniaxial compression. In this work, an innovative hybrid tube with an auxetic tube as the outer tube and a conventional tube as the inner tube has been investigated. All the inner tubes were made of extruded aluminum alloy 6063 with T5 heat treatment, and the outer tubes were made of stainless steel 304 and 316L with oval holes, respectively. Quasi-static compressive tests have been conducted to study the crashworthiness of such hybrid tubes. The effects of outer tube material and geometry on the deformation mode, force–displacement curve and energy absorption of hybrid tubes have been discussed. The results show that the outer auxetic tube changes the deformation of the inner tube. The load carry capacity and energy absorption of a hybrid tube increase with the strength of the outer auxetic tube.

A357 aluminium alloy produced by LPBF: Tribological behaviour in dry sliding conditions

Laser Powder Bed Fusion (LPBF) is increasingly used in packaging, automotive and aerospace sectors for manufacturing Al alloy components where fatigue and wear damage can readily occur. Therefore, this work aims to assess the tribological behaviour of A357 alloy (AlSi7Mg0.6) produced by LPBF as a function of both printing parameters and heat treatment conditions, applying a novel T6 based on rapid solution followed by artificial aging, which improves the strength-ductility balance. Dry sliding tests (block-on-ring) were performed using A357 samples as stationary blocks against rotating quenched and tempered AISI 52100 (100Cr6) steel. LPBF samples were compared with A357 obtained by sand casting, subjected to Hot Isostatic Pressing (HIP) and conventional T6 heat treatment. Microstructural refinement induced by LPBF carried out in optimised conditions, even without post-processing treatments, reduced the wear rate in comparison to conventional sand-cast, HIP-ed and T6 heat-treated A357, while maintaining comparable coefficient of friction. The rapid solution T6 did not worsen the tribological behaviour of as-built LPBF A357 components, even though it induced a slight hardness decrease.