Ultra-high Strength Aluminum Alloy Research Articles

Achieving high strength and ductility of Al-Zn-Mg-Cu alloys via laser shock peening and spray forming

In order to further enhance the strength and ductility of ultra-high strength aluminum alloys, the laser shock peening technology was applied to ultra-high strength Al-Zn-Mg-Cu alloy. The ultimate tensile strength, elongation and hardness can reach to 751 MPa, 11 % and 208.3 HV by combining spray forming, secondary extrusion, solid solution, retrogression and reaging as well as laser shock peening. The high strength and hardness of the alloys is mainly attributed to the fine-grained layer on surface as well as new grain boundaries, dislocation cells and high-density dislocations introduced by laser shock peening, uniform nano-sized strengthening phases with high density precipitated during heat treatments. The excellent ductility of the alloys is mainly ascribed to multiple structures including fine-grained layer on surface and slip lines inside different grains introduced by laser shock peening, smaller size of fibrous grains and Al7Cu2Fe phase produced by secondary extrusion and spray forming. The aging treatment after laser shock peening can lead to the annihilation of high-density dislocations as well as significantly promote the formation of stable and coarse η phase, which can greatly reduce the strength of the studied alloys.

Research Progress on the Microstructure Evolution Mechanisms of Al-Mg Alloys by Severe Plastic Deformation.

Al-Mg alloys are widely used as important engineering structural materials in aerospace engineering, transportation systems, and structural constructions due to their low density, high specific strength, corrosion resistance, welding capability, fatigue strength, and cost-effectiveness. However, the conventional Al-Mg alloys can no longer fully satisfy the demands of practical production due to difficulties caused by many defects. The high strength of Al-Mg alloys as non-heat treatment precipitation-strengthened alloys is achieved primarily by solid solution strengthening along with work hardening rather than precipitation strengthening. Therefore, severe plastic deformation (SPD) techniques can be often used to produce ultrafine-grained structures to fabricate ultra-high strength aluminum alloys. However, this approach often achieves the strengthening of material at the cost of reduced ductility. This paper comprehensively summarizes the various approaches of ultrafine/nanocrystalline materials for enhancing their plasticity, elaborates on the creation of a bimodal microstructure within the alloy, and discusses the formation of a nanotwin microstructure within the alloy and the incorporation of dispersed nanoparticles. The mechanisms underlying both the strengthening and toughening during large plastic deformation in aluminum alloys are summarized, and the future research direction of high-performance ultrafine crystalline and nanocrystalline Al-Mg aluminum alloys is prospected.

Effect of Al-Ti-B-Er on the Microstructure and Properties of Ultrahigh-Strength Aluminum Alloy

To refine the grain size and improve the mechanical properties of ultrahigh-strength aluminum alloy (Al-10Zn-1.9Mg-1.6Cu-0.12Zr), the Al-Ti-B-Er grain refiner was prepared by the melt reaction method using the aluminum melt and Al + Ti + B precursor. The results exhibit that the Al-Ti-B-Er grain refiner is mainly composed of a block TiAl3 phase, and loose agglomerated nano-sized TiB2 and Al3Er phases. The microstructure of ultrahigh-strength aluminum is significantly affected by the Al-Ti-B-Er refiner, which changes from dendrite to equiaxial grain with increasing Al-Ti-B-Er content, and the size of the eutectic phase is significantly refined. The high-efficiency refinement of Al-Ti-B-Er is due to Er promoting the uniform distribution of TiAl3 particles and the formation of loose agglomerated nano-sized TiB2 particles. The optimal addition content of Al-Ti-B-Er into ultrahigh-strength aluminum alloys is 1 wt%, whose grain size is approximately 40 µm. Additionally, the strength and ductility of ultrahigh-strength aluminum alloys are simultaneously improved by adding 1wt% Al-Ti-B-Er after the T6 treatment, reaching 756 MPa and 20%, respectively. This enhancement in strength and ductility is mainly attributed to grain refinement and the eutectic phase refinement.

Effect of Sm + Er and Heat Treatment on As-Cast Microstructure and Mechanical Properties of 7055 Aluminum Alloy.

The 7055 aluminum alloy is an ultra-high strength aluminum alloy, which is widely used in the aerospace field and new energy automobile manufacturing industry. As it retains high strength, its plastic deformation ability needs to be improved, which limits its application in plastic processing. In this study, the cast grains of the 7055 aluminum alloy were refined by adding Sm + Er, and the proper heat treatment procedure was utilized to further precipitate the rare earth phase in order to increase the alloy's strength and toughness. The grain size, microstructure and phase were characterized by optical microscopes (OMs), scanning electron microscopy-energy spectrum (SEM-EDS) and a XRD diffractometer (XRD). The macroscopic hardness, yield strength and tensile strength of alloy materials were measured by a hardness meter and universal electronic tensile machine. The results showed that the as-cast sample and the heat treatment sample all contained Al10Cu7Sm2 and Al8Cu4Er rare earth phases. But, after heat treatment, the volume percentage of the rare earth phase dramatically increased and the dispersion was more unified. When 0.3 wt.%Sm and 0.1 wt.%Er were added, the grain size could be refined to 53 μm. With the increase in the total content of rare earth elements, the refining effect first increased and then decreased. Under 410 °C solid solution for 2 h + 150 °C and aging for 12 h, the macroscopic hardness, yield strength, tensile strength and elongation of 0.3 wt.%Sm + 0.1 wt.%Er + 7055 as-cast samples were 155.8 HV, 620.5 MPa, 658.1 MPa and 11.90%, respectively. After the addition of Sm and Er elements and heat treatment, the grain refinement effect of 7055 aluminum alloy was obvious and the plastic property was greatly improved under the premise of maintaining its high-strength advantage.

Nanoscale Analysis of Solute Distribution in Ultrahigh-Strength Aluminum Alloys

Nanoscale Analysis of Solute Distribution in Ultrahigh-Strength Aluminum Alloys

Critical effect of heat input on joint quality in resistance element welding of Al and steel

Resistance element welding (REW) has recently attracted increasing interest, especially in the joining of high-strength steels and aluminum alloys. However, the intensity of heat input is a critical factor for the joint quality due to the possibility of excessive melting of the aluminum sheet around the element shank, which often degrades the joint's performance. This study evaluates the influence of heat input on the joint formation and mechanical performance of REW joints between ultra-high strength steel and aluminum alloy. In addition to the experimental investigations, a finite element method (FEM) was used to analyze the temperature distribution, nugget formation, and aluminum sheet melting characteristics as a function of heat input. The results show that the nugget dominates the joint's strength if the heat input is comparatively low. When heat is increased, however, the aluminum sheet plays a significant role in the joint's strength. Excessive melting of aluminum sheets reduces the load-bearing area of the joint. The competition between the weld nugget and aluminum sheet determines the joint's strength. The failure mode changes from interfacial to aluminum sheet failure as the heat input increases. The combined effect of aluminum sheet thickness and heat input on the joint strength was also evaluated. The results indicate that determining the appropriate heat input level is crucial to achieving an excellent performance of the REW joints.

Microstructures and properties of wire-arc additively manufactured ultra-high strength aluminum alloy under different heat treatments

The microstructures, mechanical properties and corrosion behaviors of the ultra-high strength Al–Zn–Mg–Cu-Sc aluminum alloy fabricated by wire-arc additive manufacturing process using a self-prepared 7B55-Sc filler wire were systematically investigated under different heat treatments. The results showed that the microstructures of the as-deposited, T6, T73, and retrogression and re-aging (RRA) heat treatments were all composed of fine equiaxed grains with a size of about 6.0 μm. The grain boundary precipitates (GBPs) of the as-deposited sample were very coarse and continuously distributed along the grain boundaries, and the intragranular precipitates (IGPs) mainly consisted of a small amount of ηMg(Zn,Cu,Al)2 and η′ phases. After T6 heat treatment, the GBPs became much finer, but still continuously distributed along the grain boundaries. The IGPs mainly consisted of fine GP zones and η′ phases. After RRA heat treatment, the GBPs became coarser and discontinuously distributed along the grain boundaries. The IGPs were composed of η′ phases and ηMg(Zn,Cu,Al)2 phases. After T73 heat treatment, the GBPs became much coarser and sparsely distributed along the grain boundaries. The IGPs mainly consisted of coarser ηMg(Zn,Cu,Al)2 phases. The T6 heat-treated sample achieved the highest tensile strength of 618 MPa. While the strength of T73 heat-treated sample was sacrificed by up to 17% compared with the T6 heat-treated sample, but the corrosion resistance was the best of all heat-treated conditions. After RRA heat treatment, the strength was about 10% lower than the strength of the T6 condition, but the corrosion resistance was better than that of the T6 heat-treated sample.

Investigation of Microstructures and Mechanical Properties of Ultra-High Strength Al-Zn-Mg-Cu Alloy Prepared by Rapid Solidification and Hot Extrusion

Al-Zn-Mg-Cu aluminum alloys have the advantages of high specific strength, easy processing, and high toughness, showing great potential application in the aerospace field. However, ultra-high strength aluminum alloys usually contain coarse microstructures, micro-segregation, and casting defects that seriously deteriorate mechanical properties. Here, we report a high-strength aluminum alloy (Al-10.5Zn-2.0Mg-1.2Cu-0.12Zr-0.1Er) prepared by rapid solidification and hot extrusion to explore the microstructure modification of the alloy based on this strategy. The results show that: rapid-solidification technology can significantly refine alloy grains, alloy ribbons were composed of α (Al) equiaxed fine grains, and the average grain size was less than 6 μm. After extrusion, the alloy had partially recrystallized, existing coarse second-phase (T-phase) and needle-shaped precipitates were MgZn2 (η-phase), and the tensile strength and elongation of the extruded bar were 466.4 MPa and 12.9%, respectively. After T6 heat treatment, the tensile strength of the alloy reached 635.8 MPa, while elongation decreased to 10.5%. According to microstructure analysis and considering the contributions of grain boundary, dislocation, and precipitation-strengthening to the improvement of the mechanical properties, it was found that precipitation-strengthening is the main strengthening mechanism. Our research shows that rapid-solidification and hot-extrusion technology have great potential for improving the microstructures and mechanical properties of aluminum alloys.

Microstructure and mechanical properties of 600 MPa grade ultra-high strength aluminum alloy fabricated by wire-arc additive manufacturing

The utilization of wire-arc additive manufacturing (WAAM) technology for the preparation of Al-Zn-Mg-Cu aluminum alloy has made some progress in recent years. However, the challenge still remains to achieve ultra-high strength (600 MPa) in WAAM. In this study, the crack-free Al-Zn-Mg-Cu-Sc thin-wall component with ultra-high strength was successfully fabricated by the cold metal transfer (CMT) process using a self-prepared 7B55-Sc filler wire. The microstructures of both as-deposited and T6 heat-treated samples were all composed of fine equiaxed grains with an average size of about 6.0 μm. The primary Al3(Sc, Zr) particles acted as heterogeneous nuclei to promote the formation of equiaxed grains and refine the microstructures during the solidification process. A large amount of continuous eutectic structures rich in Al, Zn, Mg, and Cu elements formed along the grain boundaries under the as-deposited condition, and the precipitated second phases within the grains mainly included the equilibrium η phase, metastable η′ phase and large-sized T phase. After T6 heat treatment, the majority of the second phases originally distributed within grains and along grain boundaries were dissolved into the Al matrix, and a large amount of fine GP zones, η′ phase and secondary Al3(Sc,Zr) particles were precipitated within the grains during the aging process. The tensile strength reached a recorded level of 618 MPa in the horizontal direction after T6 heat treatment, which was considered a breakthrough for the manufacturing of 600 MPa grade aluminum alloy by WAAM.

Evaluation of creep-fatigue life and strength for AA7001-T6 under constant amplitude loading

Aluminum alloys were widely used in the construction, automotive, marine, and aviation industries due to their low specific strength, ease of manufacture, and low weight. The fatigue behavior of aluminum alloys at different temperatures is investigated. Thanks to the rapid development of armament in recent years, 7XXX ultra-high strength aluminum alloys are now used more frequently because of their non-corrosive qualities and low weight. Aluminum alloy 7001-T6 behavior is examined at the Company State for Engineering, Rehabilitation, and Inspection (SIER) in Iraq, where chemical analysis of the AA7001 is supported. Most engineering components that operate at high temperatures will eventually fail from fatigue strain, creep damage is a time-dependent process that is primarily influenced by the history of stress and temperature applied to the component. When the two damaging factors combine their effects, This study used AA7001-T6 to conduct experiments on mechanical characteristics (UTS, YS, E, and ductility) and the interaction between creep and fatigue at four distinct temperatures: room temperature (25, 150, 280, and 330) °C, the UTS, YS, and E were lowered by 37.2, 37.2, and 24) %, respectively, as compared to the result at room temperature, but the ductility increased by 28.27 %. It has been noted that rising temperatures cause mechanical and fatigue characteristics to decline. Experimental S-N fatigue test findings showed a significant loss of fatigue strength, After 107cycles, the endurance fatigue limit was reduced from 208 MPa at (RT) to 184 MPa at 330 °C, an 11.5 % reduction. Overall, it can be said that AA7001-T6 demonstrates a significant drop in mechanical and fatigue properties at high temperatures

Microstructure and properties of 7075 aluminum alloy welding joint using different filler metals

Al-Mg-Sc, Al-Si-Sc and Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wires are prepared to evaluate their weldability toward the high strength 7075 aluminum alloy. The microstructure and the mechanical properties of the welding joints were studied by optical microscope (OM)，scanning electron microscope (SEM), transmission electron microscope (TEM), hardness test and tensile test. The results showed that the welding wires of Al-Si-Sc alloy and Al-Zn-Mg-Cu-Ti/TiB2 alloy exhibit good weldability, while that of Al-Mg-Sc alloy is of relatively poor weldability due to the existence of hot cracks. The welding joint using Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire has the highest ultimate strength of 300 MPa, while the ultimate strength of the welding joints using Al-Mg-Sc and Al-Si-Sc alloy welding wires are 200 MPa and 144 MPa, respectively. The weld zone formed by Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire consists of fine equiaxed grains with sizes around 15 µm, which are associated with the modification of the Al3Ti and TiB2 particles. The low-cost Al-Zn-Mg-Cu-Ti/TiB2 alloy welding wire has good application potential in the welding of 7000 series ultra-high strength aluminum alloy, due to its excellent weldability and good mechanical properties.

The Study of the Structure and Properties of Pressed Strips Made of a V-1977 Ultrahigh-Strength Aluminum Alloy after Two-Step Aging

The Study of the Structure and Properties of Pressed Strips Made of a V-1977 Ultrahigh-Strength Aluminum Alloy after Two-Step Aging

Thermodynamic, Kinetic and Strength Calculation of High Zinc Containing Al-Zn-Mg-Cu Alloys

High zinc containing Al-Zn-Mg-Cu is the research focus of ultra-high strength aluminum alloy. In the present paper, the Al-Zn-Mg-Cu multi-component system is studied when the content of Zn is 10.5 wt.%, 11 wt.% and 12 wt.%, respectively. The vertical sections of phase diagrams are calculated by the thermodynamic method. The precipitation parameters of the η’ phase, including the density of precipitate, precipitate radius and volume fraction, are obtained by using the methods of kinetic calculations. The yield strength of Al-Zn-Mg-Cu alloy with different content of Zn is calculated by an empirical model containing a chemical element and a microstructure parameter. The calculated results of yield strength are verified by experimental data and provide primary guidance to developing Al-Zn-Mg-Cu ultra-high strength aluminum alloys.

Nanoscale analysis of solute distribution in ultrahigh-strength aluminum alloys

Nanoscale analysis of solute distribution in ultrahigh-strength aluminum alloys

Development mechanical and fatigue properties of AA7001 after combined SP with deep cryogenic treatment and UIP with deep cryogenic treatment

Al alloys have long been of interest to the aerospace community, due to their modest specific strength, ease of manufacture, and low cost. In recent years, with the rapid development of weaponry, 7XXX ultra-high strength aluminum alloys used increasingly in military fields. Chemical analysis of the AA 7001 is supported out at The Company State for Engineering, Rehabilitation and Inspection (SIER) in Iraq. Strengthening the surface (shot penning) is beneficial to delay crack nucleation and extend life. The test samples (tensile and fatigue) are subject to the SP process by using ball steel with the parameters (Pressure=12 bars, Speed=40 mm/min, Distance=150 mm, Shot size=2.25 mm, Coverage=100 %). The ultrasonic impact treatment (UIP) machine is used for enhancing the surface properties. For the Deep Cryogenic Treatment (DCT), the samples have been placed in the cooling chamber. A standard tensile test specimen is prepared in a round section with the dimensions chosen according to ASTM (A370-11). Tensile and fatigue of rotating bending with R=–1 have been conducting, after the effect of deep cryogenic treatment (DCT), combined shot peening (SP+DCT), and ultrasonic impact peening (UIP+DCT) of AA7001 have been examining. The maximum improvement percent in ultimate tensile strength (UTS) due to (DCT), (SP+DCT), and (UIP+DCT) were about 3 %, 8.27 %, and 6.25 %, respectively. The rise in the yield stress due to (DCT), (SP+DCT), and (UIP+DCT) were 9.5 %, 14.6 %, and 13.14 %, respectively. The ductility reduced by constituents of 8.57 %, 12.5 %, and 11.42 % sequentially. The improvement in fatigue strength in a high cycle regime is 16 % for (SP+DCT) due to combined effects, it is an 8 % increase in the endurance limit on fatigue behavior due to inducing compressive residual stress (CRS)

Characterizing Microstructure Evolution and Kinetics of a Spray Formed Ultrahigh Strength Aluminum Alloy during Isothermal Aging

Characterizing Microstructure Evolution and Kinetics of a Spray Formed Ultrahigh Strength Aluminum Alloy during Isothermal Aging

Effects of different multidirectional forging processes on the microstructure and three-dimensional mechanical properties of ultra-high strength aluminum alloys

The 7A85 aluminum alloy was forged in multiple directions at 470 °C via four-upsetting and three-cross-stretching (4U3CS), four-upsetting and three-octagon-stretching (4U3OS), and seven-upsetting and six-cross-stretching (7U6CS), three different forging processes. Thereafter, the alloy was treated with solid solution, water quenching, and T8 two-stage aging. The microstructural evolution and three-dimensional mechanical properties of the center and edge of the specimens were detected and analyzed. Compared with 4U3CS and 4U3OS, the increased cumulative deformation of 7U6CS caused more continuous temperature rises, more severe lattice distortion, and more defect formation, such as vacancies and dislocations, which were more conducive to coarse second-phase particle dissolution, finally enhancing the driving force for aging precipitation; thus, significantly improving the yield strength (YS). Furthermore, under 7U6CS, the larger stored deformation energy provided a driving force for sufficient dynamic recrystallization. As the number of alternate loading axis changes increased, more deformation bands were interwoven and caused the expansion of the recrystallization nucleation areas, which improved the inconsistent degree of recrystallization between the center and edge. Therefore, dynamic recrystallization was the most sufficient with grain refinement especially at the edge via 7U6CS. From 4U3CS to 7U6CS, the anisotropy and uniformity of the center and edge were gradually improved. The optimal mechanical properties were obtained via 7U6CS, with average three-directional ultimate tensile strength, YS, and elongation values of 513 MPa, 464 MPa, and 10.7% at the center and 515 MPa, 473 MPa, and 11.5% at the edge, respectively.

Microstructural characteristics and formation mechanism of adiabatic shear bands in Al–Zn–Mg–Cu alloy under dynamic shear loading

The microstructural characteristics and formation mechanism of adiabatic shear bands in ultra-high strength aluminum alloy are studied under dynamic shear loading. It is found that thermal softening alone is insufficient to trigger the initiation of adiabatic shear bands (ASBs). Dynamic recrystallization induced softening is attributed to be the main cause of ASB initiation, with temperature rise playing a secondary role by accelerating the deformation localization process. It is believed that abrupt temperature rise takes place after ASB initiation, and the temperature rise prior to ASB formation is relatively small. Recrystallized ultrafine grains with a strong texture of {112} <110> are formed in ASBs, based on a progressive subgrain misorientation recrystallization mechanism. It is proposed that the translational–rotational motion of the dynamically recrystallized nanograins in the form of vortexes at the mesoscale can account for the microstructural softening, thus causing shear instability, eventually leading to fracture by the combination of ductile and brittle failure mechanisms.

Semi-Solid Precision Forming Process of High-Strength and Wear-Resistant Aluminum Matrix Composites

A layered composite structural model with an outer wear-resistant layer of high-silicon aluminum alloy and an inner layer of ultra-high strength aluminum alloy is designed. A scaling brake drum part with layered composite was prepared by semi-solid precision forming process. The effects of process parameters such as casting temperature, specific pressure, solid layer temperature and heattreatment system on the composite interface were investigated. The results show that the casting temperature and solid layer temperature had a great influence on the interface recombination. The high forming specific pressure could effectively restrain the growth of secondary dendritesof the composite, and the proper heat treatment process could improve the morphology of the composite interface. A scaling brake drum component with A390/7050 layered composite structure was well prepared under optimal conditions.

Determination of Hot Extrusion Parameters in a Spray-Formed Ultrahigh-Strength Aluminum Alloy

To determine a suitable industrial extrusion process, the hot deformation behavior of a spray-formed ultrahigh-strength aluminum alloy was studied with a series of isothermal compression tests. The temperature range was from 340 to 480 °C, while the strain rates ranged from 0.001 to 1 s−1. The flow stress behavior was studied, and the activation energy map showed the deformation difficulty degree under different compression conditions. The dynamic materials model processing map displayed three high-efficiency domains and two low-efficiency domains. As a result of the microstructure observations, it was determined that the high-efficiency domains were related to dynamic recrystallization, superplasticity and cracking. The optimum processing conditions were at intermediate temperatures from 410 to 430 °C and strain rates from 0.008 to 0.06 s−1. In light of the extrusion calibration, the practical extrusion condition was determined to be 410 °C/0.03 s−1. The surface morphology and microstructure after practical hot extrusion were consistent with the prediction by the processing maps and calibration.