Al 5Mg Research Articles

Controlling the addition of solute Ti in Al-Mg-Zn-Cu-Ni alloy for enhanced high-temperature creep properties

This study aims to fundamentally understand the effect of 0.1 at% Ti addition (for introducing solute Ti with low diffusivity into the α-Al matrix) on the microstructure and high-temperature mechanical performance of a heat-resistant Al–5Mg–3.5Zn–2Cu–2Ni (at.%) quinary alloy subjected to heat treatments. The precipitation morphologies of the T-Al6Mg11Zn11 phase are systematically characterized in terms of the distribution of solute Ti, which is controlled by a peritectic reaction during solidification. High-temperature strength and creep properties (200 °C/105 MPa) are examined using the Ti-added alloy specimen and compared with the results of Ti-free quinary alloy specimens. In the Ti-added alloy, solute Ti is distributed within the dendritic α-Al phases formed through the peritectic reaction. The precipitation morphologies vary depending on solute Ti contents in the α-Al matrix after isothermal aging at 200 and 300 °C. Numerous fine T-phase precipitates are homogeneously dispersed in the α-Al matrix containing high solute Ti content. Fine precipitation morphologies appear stable even after long-term exposure at 200 °C. Ti addition extends creep rupture life (at 200 °C) without the loss of static high-temperature strength and room-temperature ductility. The improved creep properties could be responsible for the reduction in creep rate by the refined precipitation morphologies in the α-Al matrix containing higher solute Ti contents. Local coarsening of the precipitates occurs owing to the solute Ti during creep (under stress). The mechanism is discussed in terms of the effect of Ti addition on the phase equilibria between the α-Al and other intermetallic phases.

Creep mechanism in ductile dual-phase aluminum alloys with a fully continuous fiber state

To understand the creep behavior of a practical alloy that has a multiphase consisting of a matrix and several types of precipitate phases, the role of individual phases needs to be studied. However, it is difficult to elucidate the contribution of each phase to creep owing to their complex microstructural morphologies and very complex creep behavior. To understand the role of individual phases and the creep behavior, fundamental creep theories for ductile dual-phase (DDP) alloys must be established initially for specimens with simple microstructural morphologies. To apply these theories practically, they must also be experimentally verified. In this study, DDP alloys composed of 99.99 % Al (matrix phase) and an Al–Mg solid-solution alloy (reinforced phase) were fabricated as a fully continuous fiber state by accumulative roll bonding. Tensile and creep tests at elevated temperatures were performed on alloys composed of systematically varying volume fractions of the reinforced phase. Tensile data at 546 K indicated a linear relationship between the maximum stress and volume fraction of the reinforced phase; the lines were also connected to the data from single-phase materials of the matrix and reinforced phase. Thus, the amount of strain in the matrix and reinforced phases was the same as that during the tensile test, and the relationship between the maximum stress and volume fraction of a DDP alloy followed the classical linear law of mixtures (CLLM). The creep data for Al + Al–2Mg (DDP alloy) at 546 K were nearly equal to those calculated using the CLLM. Thus, the matrix and reinforced phases deformed at the same creep rate. Creep tests were also conducted for Al + Al-1M(5ARB), which had a fine-grained reinforced phase. The creep data for Al + Al-1M(5ARB) at 523 K were also a good approximation to the lines representing the data calculated using the CLLM. Hence, although the grain sizes of the two phases were very different, corresponding to different rate-controlling mechanisms, the creep data for a DDP alloy could be analyzed using the CLLM. Consequently, the creep behavior of the DDP alloys was a superposition of the creep behavior in both phases, and the interpretation of the creep data for DDP alloys using the creep theory of single-phase materials would lead to incorrect conclusions. These findings will contribute to a better understanding of the creep behaviors of practical alloys and will aid in the correct estimation of the creep lifetime.

Enhanced age-hardening of an Al–5Mg–2Zn–1Cu alloy by pre-aging combined with pre-straining

In this work, the synergistic effect of pre-aging and pre-straining on the enhanced age-hardening response of an Al–5Mg–2Zn–1Cu alloy has been systematically investigated using high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). After pre-aging, only Guinier Preston (GP) zones uniformly distribute in the α-Al matrix. Moreover, dislocations induced by pre-straining can promote the nucleation and growth of T″ and T′ precipitates. With the synergy of pre-aging (80 °C/5 h) and pre-straining (∼4%) treatments, the alloy after second-aging at 130 °C for 12 h exhibits a giant increase of yield strength (∼182 MPa) in comparison to the as-solutionized alloy, reaching ∼348 MPa. The above results show that pre-aging and pre-straining are effective in accelerating the hardening response of Al–Mg–Zn–Cu alloys. Especially, this extraordinary age-hardening response depends strongly on the high number density and uniform distribution of the GP zones induced by pre-straining, acting as preferential nucleation sites for T″ phase and T′ phases during subsequent aging treatment. In addition, it proves that pre-aging and pre-straining can effectively control the precipitation free zones (PFZs) size, relieving the strain concentration in PFZs and improving the comprehensive mechanical properties.

Effects of natural aging on the artificial aging kinetics and responses of Al–5Mg–3Zn–1Cu (wt.%) alloy

Effects of natural aging (NA) on artificial aging (AA) behavior of Al–5Mg–3Zn–1Cu alloy were studied from the perspectives of kinetics and microstructure evolution. The results show that short-term NA (24 h) has marginal effects on AA at any temperature, as well as long-term NA (>240 h) on low-temperature AA (120 °C), but long-term NA can accelerate aging kinetics and alleviate severe hardening ability attenuation at high temperatures (>150 °C). Analysis of the precipitates evolution demonstrates that such attenuation is primarily attributable to coarsening and reduction of intragranular precipitates and is also slightly related to the formation of precipitate-free zone (PFZ). Three main factors cause the unfavorable microstructure in NA-free alloy at high temperatures AA: (1) Insufficient nucleation of intragranular precipitates induced by weakened nucleation driving force, larger critical nucleation radius, and rapid vacancy annihilation; (2) The nucleated precipitates are prone to coarsening; (3) The precipitation near grain boundary is obstructed due to the depletion of vacancies and solutes. Clusters formed during NA can inhibit the unfavorable microstructure by delaying the annealing out of excess vacancies, promoting the nucleation of precipitates, and elevating the activation energy for precipitation coarsening, thereby enhancing the hardening potential. This work is instructive for the formulation of heat treatment strategies for Al–Mg–Zn–Cu alloys with high Mg/Zn ratios.

Enhancing the strength and ductility in an Al–5Mg alloy via accumulative continuous extrusion forming at room and cryogenic temperatures

In this work, the microstructural evolution of Al–5Mg (wt%) alloy fabricated by accumulative continuous extrusion forming (ACEF) at room temperature (RT) and cryogenic temperature (CT) was investigated. The grain refinement mechanism during ACEF was revealed. The strengthen and ductility enhancements of the alloy were discussed. The results showed that good grain refinement effect was achieved in the alloy after multi-pass RT-ACEF, and was further enhanced in the alloy fabricated by 1 pass CT-ACEF. High-density dislocations, as the driven force of continuous dynamic recrystallization, were achieved in the 1 pass CT-ACEFed alloy, and the growth of recrystallized grains was limited at CT. As a result, superior grain refinement effect was obtained in the alloy after CT-ACEF. Simultaneous strength and ductility improvements were found in the ACEFed alloy. The ultimate tensile strength and elongation were enhanced to 294.3 MPa and 55.1 % of the alloy after 1 pass CT-ACEF. Grain boundary strengthening and dislocation strengthening dominated the strength enhancement of the ACEFed alloy. The high work hardening exponent and wide strain interval were responsible for the increase in ductility of the CT-ACEFed alloy. The purpose of this study is to provide a high-efficiency strategy to achieve Al–Mg alloys with superior mechanical performance and overcome the strength-ductility trade-off.

Twin density and twin thickness evolution in sputtered Al–Mg alloys

Twinned Al–Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al–1Mg, and Al–2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120–160 nm. The Al–Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.

Investigations on weld joints of 7075 alloy with Al–5Mg–1Zn composite fillers by arc welding

In this work, the semisolid stirring casting assisted ultrasonic treatment and multi-pass rolling methods were applied to fabricate TiCp/Al–5Mg–1Zn filler materials for tungsten inert gas welding of 7075-T651 aluminum alloy. After welding, various performances and microstructures of the as-weld samples were studied via multifarious electron microscopy and extensive tests. As a result, the TiC nanoparticles which distributed uniformly minished the size of α-Al grains and modified secondary phase owing to the heterogeneous nucleation and retardation of growth. The hardness and tensile strength of joints were enhanced as TiC particles were added, compared to those of 5183 commercial fillers. Besides, both the stress corrosion cracking and intergranular corrosion susceptibility of the weld joints were reduced.

Formation mechanism of refined Al6(Mn, Fe) phase particles during continuous rheo-extrusion and its contribution to tensile properties in Al–Mg–Mn–Fe alloys

Tailoring the size and morphology of Al6(Mn, Fe) phase particles is expected to achieve a good combination of strength and ductility in Al–Mg–Mn–Fe alloys. In this study, the microstructural evolution in an Al–5Mg–0.8Mn–0.1Fe (wt%) alloy fabricated through continuous rheo-extrusion was investigated via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation mechanism of the Al6(Mn, Fe) phase particles during continuous rheo-extrusion was revealed. The contribution of the Al6(Mn, Fe) phase particles to the tensile properties of the alloy was discussed. The results indicated that a remarkable refinement effect on the Al6(Mn, Fe) phase particles during continuous rheo-extrusion was achieved. The formation of refined Al6(Mn, Fe) phase particles was primarily attributed to the coefficient of the high cooling rate and shear deformation during continuous rheo-extrusion. Compared with the as-cast alloy containing micron-sized phase particles, the rheo-extruded alloy with nanoscale Al6(Mn, Fe) phase particles exhibited a significant enhancement in strength. During tensile deformation, the small circular cracks around the nano-sized Al6(Mn, Fe) phase particles prolonged the crack propagation time. Hence, a good ductility was obtained in the rheo-extruded alloy. The purpose of this study is to provide a strategy to achieve a high-efficiency processing method and provide insights for manufacturing Al–Mg series alloys with high mechanical performance.

Influence of processing temperature on microhardness evolution, microstructure and superplastic behaviour in an Al–Mg alloy processed by high-pressure torsion

Experiments were conducted to assess the effect of processing temperature on the hardness evolution, microstructure and the flow properties of an annealed Al–3Mg alloy processed by high-pressure torsion (HPT) at either 300 or 450 K. The results demonstrate that HPT processing at room temperature (RT) leads to higher microhardness values with a more uniform hardness distribution in the Al alloy compared with processing at 450 K. After 10 HPT turns at RT, the microstructure displayed a more intense grain refinement, a higher dislocation density and smaller Al3Mg2 precipitates than after HPT at 450 K. Accordingly, the metal processed at RT showed enhanced strength at RT and consistently exhibited superplastic flow during deformation at 523 K, with tensile elongations of ∼530–650% for strain rates from 10−3 to 10−2s−1. Conversely, a maximum elongation of ∼110% was recorded at 523 K in the alloy processed by HPT at 450 K. This behaviour is attributed to an enhanced thermal stability in the metal processed at RT compared with HPT at 450 K where deformation at 523 K led to the onset of abnormal grain coarsening due to a more disperse distribution of grain sizes and the partial dissolution and coalescence of Al3Mg2 precipitates after HPT processing.

The Effect of Wall Thickness on the Microstructure and Tensile Properties on Squeeze Casting of Al–5Mg–2.2Si–0.6Mn–0.1Ce Alloy

The Effect of Wall Thickness on the Microstructure and Tensile Properties on Squeeze Casting of Al–5Mg–2.2Si–0.6Mn–0.1Ce Alloy

Design of heat-resistant Al–Mg –Zn–Cu–Ni quinary alloy: Controlling intermetallic phases and mechanical performance at elevated temperature

Owing to good formability, wrought Al alloys are used in a wide range of industries, including turbochargers in automobile engines. The development of Al alloys with increased high-temperature strength is necessary to improve the fuel efficiency of engines. In this study, a modified heat-resistant Al–Mg–Zn–Cu–Ni quinary alloy with superior high-temperature strength and creep rupture life at 200 °C (potential temperature in service for compressor radial impellers) was designed. The thermodynamic assessments provided a modified alloy composition of Al–5Mg–3.5Zn–2Cu–2Ni (at %) exhibiting α-Al phase in equilibrium with T-Al6Mg11Zn11 and Al3(Ni, Cu)2 phases at elevated temperatures. The experimental alloy showed granular T and Al3(Ni, Cu)2 phases often located on grain boundaries in the α-Al matrix, although the undissolved Al3Ni phase (formed in solidification) locally remained. Apart from the T phase, the η-Zn2Mg phase containing Cu element preferentially precipitated on grain boundaries. A large number of fine precipitates were dispersed homogeneously in the grain interior after the aging at 200 °C or 300 °C. Compared to the base alloy with a ternary composition of Al–5Mg–3.5Zn (at %) and conventional Al alloys, the designed quinary alloy (pre-aged at 200 °C for 10 h) showed a high strength at elevated temperatures above 200 °C. The creep-rupture life at 200 °C/105 MPa was remarkably extended to 665 h by the addition of Cu and Ni elements into the base ternary alloy. The rupture life was more than ten times longer than one (57 h) of the ternary alloys. The alloy modification based on the thermodynamic calculations provides an effective approach for designing lightweight Al alloys with superior high-temperature strength and creep rupture life.

Corrosion behavior of Al–3Mg–0.2Sc alloy processed by high-pressure torsion and thermal treated

This work aims at evaluating the effect of microstructure on the corrosion behavior of an Al–Mg–Sc alloy processed by high-pressure torsion (HPT) and annealed from 523 to 773 K. The corrosion resistance of the annealed alloy was evaluated by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5% (wt.%) NaCl solution. The EIS and polarization analyses suggested a higher corrosion resistance of the Al–Mg–Sc alloy that presented a more homogeneous grain distribution. The Al alloy samples were characterized by scanning electron microscopy (SEM) after the polarization tests. The heterogeneity of the microstructure, but also the formation of a high density of grain boundaries during HPT processing, and a change in the structure of grain boundaries, including the formation of grain boundary segregations of alloying elements, affected the corrosion behavior of the HPT processed and thermal annealed Al–Mg–Sc alloy.

Characteristic Investigation of the As-Received Samples: Nano-Oxides in Al–5Mg–Be Melt

Characteristic Investigation of the As-Received Samples: Nano-Oxides in Al–5Mg–Be Melt

Effect of lanthanum content on microstructure and mechanical properties of Al–5Mg–2Si-0.6Mn alloy in squeeze casting

The effect of Lanthanum content on the microstructure and mechanical properties of Al–5Mg–2Si-0.6Mn alloy in squeeze casting was studied. The microstructure of the alloy was characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The mechanical properties of the alloy were tested by tensile testing machine. The results show that the rare earth Lanthanum has a significant effect on the secondary dendrite spacing and the volume fraction of α-Al + Mg2Si eutectic phase, both of which increase at first and then decrease with the increase of Lanthanum. When the content of Lanthanum is 0.05 wt.%, the maximum volume fraction of eutectic phase is 45.09%. When the content of Lanthanum is 0.05 wt.%, the minimum secondary dendrite spacing is 25.85 μm. When the addition of Lanthanum is more than 0.2 wt.%, the bulk LaAlSi phase is formed in the alloy, which is not coherent with the matrix, which reduces the mechanical properties of the alloy. When the addition of Lanthanum is 0.1 wt.%, the microstructure and mechanical properties of the alloy are the best. The ultimate tensile strength, yield strength and elongation of the alloy reached the maximum, which were 274 MPa, 197.2 MPa and 5.7%, respectively.

Precipitation morphology and kinetics of T-Al6Mg11Zn11 intermetallic phase in Al–Mg–Zn ternary alloys

This study was undertaken to understand the fundamentals of T-Al6Mg11Zn11 intermetallic phase precipitation in heat-resistant Al–Mg–Zn ternary alloys, with the goal of further strength improvements. The thermodynamic assessment involved three alloy compositions, Al–4Mg–4.5Zn, Al–5Mg–3.5Zn, and Al–7Mg–1.5Zn (at%), with the T phase in a fixed fraction (approximately 6–7.5%) in equilibrium with the α-Al phase at 300 °C. The alloy compositions were set on different tie-lines between the α-Al and T phases in the two-phase region, resulting in varied compositions of each phase. In the three experimental alloys aged at 300 °C, the T phase precipitated on the grain boundaries of the α-Al matrix, and granular precipitates were homogeneously dispersed intragranularly. There was no significant difference in the precipitation morphology. It was demonstrated that the lattice parameters of the T and α-Al phases could be controlled based on the alloy composition and applied heat treatments. However, the lattice parameters have no significant effect on the precipitation morphologies of the thermodynamically stable T phase in the Al–Mg–Zn ternary alloys. The Zn-rich Al–4Mg–4.5Zn alloy exhibited a pronounced softening behavior after 10 h of aging due to the enhanced coarsening of precipitates in the α-Al matrix. The thermal instability of the precipitates was responsible for the transformation sequence from the initially formed metastable phases (η-Zn2Mg associated phases) to the stable T phase. These results provided a fundamental insight that alloy strengthening by introducing thermodynamically stable intermetallic phases is essential for sustaining the strength of heat-resistant Al–Mg–Zn ternary alloys after long-term treatment at elevated temperatures.

Hot deformation constitutive model and processing maps of homogenized Al–5Mg–3Zn–1Cu alloy

Isothermal uniaxial compression experiments were performed in the range of 300–450 °C and 0.001 to 10 s −1 to clarify the hot deformation behavior of homogenized Al–5Mg–3Zn–1Cu alloy. The results revealed that the flow curves exhibited typical characteristics of DRV/DRX accompanied by the work-hardening, and the existence of three distinct stages of work-hardening, transition, and steady-state in each flow curve. A strain-compensated constitutive model for determining flow stress in this alloy was established with highly acceptable predictability. The dominant deformation mechanism of the alloy is dislocation climbing. Also, dynamic-material-model-based processing maps at various strains were constructed, and the unstable and workable domains were distinguished. Instability generally occurred in high strain rates and low temperatures zone with prevalent instability forms such as cracking and flow localization. The workable domain was 375–450 °C and 0.001–0.1 s −1 , in which the microstructure of the deformed alloy was characterized by dynamic recovery and multiple types of dynamic recrystallization. The dynamic precipitates were labeled as T-Mg 32 (AlZnCu) 49 phase. These intermittently distributed precipitates along the grain boundaries were stable in all temperature ranges, while the intragranular precipitates were inhibited at 300 °C. Temperature increment to 400 °C led to a large number of dispersed intragranular precipitates which redissolved into the matrix as temperature exceeded 450 °C.

The response of mechanical property to the microstructure variation of an Al–Mg alloy by adding tin element

In this work, the microstructural evolution and mechanical behavior of as-cast Al–5Mg alloys with various tin (Sn) contents were investigated. Combined with microstructure characterization and mechanical property test, the refinement of α-Al grains, the composition of phases containing Sn, and the change in tensile property of alloys caused by adding Sn element were discussed. It was demonstrated that Sn could react with magnesium (Mg) to form Mg2Sn phases in the Al–5Mg alloys as the Sn content increased from 0.05 wt% to 1.00 wt%. When the Sn element content was 0.30 wt%, a considerable refinement of α-Al grains and an obvious improvement in tensile property of the Al–5Mg–0.30Sn alloy were obtained. The tensile strength and elongation of the Al–5Mg–0.30Sn alloy were 210.8 MPa and 25.9%, respectively. The strengthening-toughening mechanism associated with Mg2Sn phases was revealed. Nano-sized and deformable Mg2Sn phases could result in the second phase strengthening and crack propagation inhibition effects.

A Comparison between Tungsten Inert Gas Welded Joints Welded by Commercial ER5183 Filler and Al–Mg–Zn–Sc–Zr–Mn Filler on Microstructure and Properties in 7075-T651 Aluminum Alloys

A 7075-T651 aluminum alloy was successfully welded by tungsten inert gas welding using commercial ER5183 wire and Al–5Mg–1Zn–0.3Sc–0.15Zr welding wire containing different contents of Mn. The microstructure, corresponding mechanical properties, and the corrosion behavior of the welded joint were investigated by microscopy methods, tensile tests, and corrosion tests. The results revealed that Al3(Sc,Zr) particles were distributed in a small amount in the welds and refined the primary α-Al grain. The addition of Mn gives a strong interaction of improving fracture strength, micro-hardness, and corrosion resistance reducing the harmful influence of iron, as a result, the properties of the welded joint were enhanced. And the increase of Mn content improves the tensile strength and hardness of welds, which could be attributed to the refinement of eutectic T phase by Mn. Potentiodynamic polarization tests revealed that the corrosion resistance of welds increased with the increase of Mn content. Compared with the welded joint using commercial filler, the welded joint with Al–Mg–Zn–Sc–Zr–Mn filler exhibited a higher resistance to stress corrosion cracking (SCC). In conclusion, Al–Mg–Zn–Sc–Zr–Mn filler can be using for welding 7XXX aluminum alloys.

Effect of Severe Forging and Rolling on the Microstructure and Mechanical Properties of Al–Mg–Sc–Zr Alloy

The effect of thermomechanical processing combining one- or two-step isothermal multidirectional forging (MF) and sheet rolling on the structure and mechanical properties of alloy 1570C (Al–5Mg–0.18Mn–0.2Sc–0.02Zr (wt %)) was studied. One-step MF was performed at a temperature of 325°C to a true strain (e) of about 12. In two-step MF, deformation was continued at 250°C to e ≈ 6 (total strain of about 18). Subsequent warm rolling with a total strain e ≈ 1.6 (relative strain of about 80%) was carried out at the corresponding temperatures of each MF step, and cold rolling was performed at room temperature. In both MF steps, relatively uniform (ultra)fine-grained structures with a grain size of 2.2 and 1.9 μm, respectively, were obtained. Subsequent warm rolling led to further grain refinement, whereas cold rolling ensured the formation of highly work-hardened (ultra)fine-grained structures with high densities of lattice dislocations. The best combination of technological and service properties, including strength, plasticity, superplasticity, and thermal stability, was reached in sheets after one-step (higher temperature) MF. Lowering the deformation temperature in the second MF step ensured further alloy strengthening, but impaired its room-temperature rollability and led to an essentially complete degradation of the superplasticity of the obtained sheets.

Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy

The Guinier–Preston–Bagaryatsky (GPB) zone and the S phase are the key strengthening precipitates in Al-Cu-Mg alloys. However, how their respective structures evolve during aging has not been fully understood. In this work, the age-hardening behavior and the precipitates in an Al–3Mg–1Cu (wt.%) alloy were investigated by means of Vickers hardness measurements, differential scanning calorimetry, transmission electron microscopy, and density functional theory calculations. A series of common GPB zones and a novel type of GPB zone named “GPBX” were observed in the cold-worked samples aged at 443 K for 20 min. In the subsequent aging, two types of S phases were found to coexist, labeled S-I and S-II phases. Density functional theory calculation results indicate that GPBX zone is stable and the S-I and S-II phases have almost the same formation enthalpy. Common GPB zones transform to S-I phases, while S-II phases are formed from GPBX zones preferentially along dislocation lines. The misorientation angles and morphologies of the S phases are also discussed. GPB zones were confirmed to be structurally linked to β” and U2 precipitates reported in 6xxx (Al-Mg-Si) series Al alloys. The revealed precipitate structures and their interrelationships may provide insights into future alloy design.