Heat-treatable Aluminum Alloys Research Articles

Novel Aging Warm-Forming Process of Al-Zn-Mg Aluminum Alloy Sheets and Influence of Precipitate Characteristics on Warm Formability

Concurrently improving the formability and post-formed strength of Al-Zn-Mg alloy sheets is crucial for producing high-strength parts with complex shapes. A novel process of aging warm-forming (AWF) to form solution heat-treated and water-quenched aluminum alloy sheets is proposed in this paper. The as-quenched AA 7075 sheet was first pre-aged and then formed at the desired temperature. The automotive paint–bake process was then utilized as the second aging step to achieve the target strength of the formed part. Additionally, the post-formed strength and warm formability of specimens under the AWF process conditions, as well as the warm-forming of various heat-treated Al-Zn-Mg alloy sheets proposed in previous studies, were compared through tensile and limit dome height tests. Precipitate characteristics of specimens subjected to different warm-forming process conditions were examined to understand their impact on warm formability. The warm formability of Al-Zn-Mg alloy sheets was significantly enhanced, and the post-formed strength achieved was more than 90% of the strength of as-received AA 7075-T6 sheets under the AWF process condition. The results demonstrated the feasibility of this novel AWF process to manufacture Al-Zn-Mg alloy stamped parts for improved spring-back, formability, and good overall post-formed strength. The results also indicate that microstructural characteristics in Al-Zn-Mg alloy sheets under different warm-forming process conditions have a noticeable influence on warm formability and final mechanical properties.

Impact energy in Heat-Treated aluminium alloy 6061 and 7075

Instrumented Charpy impact is one of the promising methods to assess the impact energy; toughness and resilience of a material. The test consists of the Charpy machine and instrumentation equipment which is the strain gauge and the data acquisition system. Impact energy evaluations are important to understand the material behaviour subjected to sudden impact loading. Aluminium 7075 has good strength strength-to-weight ratio than aluminium 6061 and hence the AL 7075 is usually used in the aerospace industry, whilst the AL 6061 is commonly used in the automotive industry. The objective of the study is to observe and analyse the impact response of the Aluminium 6061 and 7075 at different heat- treated conditions; O-anneal and T6 temper. In addition to the impact energy absorbed value, the impact strain signal is recorded too. Theoretical impact energy is calculated as well based on the information given by the Charpy machine software. Aluminium 7075 exhibits a lower value of impact energy absorbed and a smaller area under the curve compared to Aluminium 6061. The energy absorption capacity for each material grade and heat-treated condition are different from one another. O-anneal aluminium has a lesser energy absorbed value and a smaller area under the curve than the T6 temper aluminium. The outcome reveals that the heat treatment process alters the material microstructure and mechanical properties, whereas in this study the impact energy responses are influenced by these circumstances. Moreover, the chemical composition of the aluminium alloy distinguishes these two grades from one another, thus resulting in different impact responses.

Abrasion Wear Resistance of Precipitation-Hardened Al-Zn-Mg Alloy.

The heat treatment of aluminum alloys is very important in industries where low weight in combination with high wear resistance, good strength, and hardness are important. However, depending on their chemical composition, aluminum alloys are subjected to different mechanical and thermal treatments to achieve the most favorable properties. In this study, an Al-Zn-Mg alloy was heat-treated including solution annealing at 490 °C for 1 h with subsequent artificial aging at 130, 160, and 190 °C for 1, 5, and 9 h. The hardness (HV1) and abrasive wear resistance with three different abrasive grain sizes were measured for all samples. The highest hardness was measured for the samples artificially aged at 130 °C/5 h, 227 HV1, while the lowest hardness was measured for the samples aged at 190 °C/9 h. The highest and the lowest wear resistance was also observed for the same state, i.e., artificially aged at 130 °C/5 h and 190 °C/9 h, respectively. The critical abrasive grain size was detected for some samples, where a decrease in wear rate was observed with an increase in the abrasive grain size from the medium value to the largest. The Response Surface Methodology (RSM) was applied to demonstrate the influence of the input parameters on the material wear rate.

Impact of in-process cooling and tool rotation speed on the mechanical and microstructural characteristics of friction stir processed AA2024

Despite significant grain size refinement, friction stir processing (FSP) of heat-treatable aluminum alloys is found to degrade the alloys of strength and hardness qualities. The drop in strength brought on by coarsening or the dissolution of the strengthening precipitate(s) could not be made up for by the improvement in strength brought about by the refinement of grain size following FSP. In order to get around this, the current work looks into a practical method of heat rejection from the FSP zone in addition to grain size refinement during FSP of AA2024 to regulate the precipitate evolution. Under natural cooling, air cooling, and CO2 cooling conditions, friction stir processing (FSP) was used to change the microstructure of Solutionized AA2024 at three distinct rotation speeds of 750, 1180, and 1500 rpm (fixed traverse speed of 50 mm/min). The microstructural evolution (through optical microscopy and SEM) and mechanical properties of FSP samples under different conditions of rotation speed and cooling and their differences were mainly discussed. All the FSP samples have a higher Vickers hardness than the base metal (minimum variation of 16.79% and maximum variation of 41.05%). The maximum hardness, yield strength, tensile strength, and elongation have been obtained under air cooling conditions and a rotation speed of 1180 rpm, which is a result of the simultaneous and effective effect of grain boundary strengthening and precipitation hardening.

Effect of natural aging by multifunction cavitation on plane bending fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys and its fatigue strength estimation

The effect of natural aging by multifunction cavitation (MFC) on the fatigue behaviour of heat-treatable Al-Si7Mg aluminum alloys was examined. Surface observation and plane bending fatigue tests were conducted for the MFC-treated aluminum alloys at a stress ratio, R, of −1. The hardness of aluminum alloy without T6 treatment was significantly increased by MFC due to both the work hardening and natural aging. MFC treatment improved the fatigue lives and the fatigue strength at N = 107 cycles of aluminum alloys due to the generation of compressive residual stress and increasing the surface hardness; however, surface pits were large enough to easily nucleate an initial fatigue crack. In addition, the fatigue strength at N = 107 cycles of MFC-treated aluminum alloys can be estimated considering the residual stress, pit size and surface hardness.

Investigating the Impact of Friction Stir Processing on the Hydrogen Embrittlement in AA6082-T6 Heat-Treatable Aluminum Alloy

AbstractThis study investigates the impact of friction stir processing (FSP) on the hydrogen embrittlement (HE) in AA6082-T6 heat-treatable aluminum alloy. The effects of different number of FSP passes and different hydrogen cathodic charging (HCC) conditions on the material’s response to HE are examined through comprehensive mechanical testing, microhardness analysis, and microstructural characterization. The results revealed that FSP leads to a decrease in yield strength, ultimate tensile strength, and microhardness, accompanied by an increase in energy absorption. The introduction of hydrogen through HCC significantly reduces mechanical properties, particularly in non-FSPed specimens. Notably, specimens with 8 FSP passes exhibit an interesting behavior with a slight increase in energy absorption and microhardness values after HCC. Microstructural analysis shows that FSP refines the microstructure, resulting in enhanced resistance to hydrogen-induced blistering effects. These findings contribute to the understanding of hydrogen embrittlement in FSPed aluminum alloys, providing insights for developing surface-modified materials suited for hydrogen-rich applications. Graphical Abstract

Влияние гафния на высокомагниевые сплавы, легированные переходными металлами, при термической обработке

The purpose of the work is to study the influence of hafnium additives on the mechanical properties and thermal stability of particles at elevated temperature during heat treatment of aluminum alloys with a high magnesium content. Two modifications of 1570 alloy were chosen for the study: without hafnium content and with its addition of 0.5 % by weight. Both alloys were subjected to homogenizing annealing at a temperature of 440 °C with different exposure modes, which ranged from 2 to 100 h. Microhardness was studied for various heat treatment modes, and the fine microstructure was studied as well using transmission microscopy. As a result, it was possible to identify that during annealing at a short exposure time (2–8 h), the alloy with the hafnium addition has higher microhardness values exceeding those of 1570 alloy by an average of 20 HV units. This is associated with the fact that in 1570 alloy with hafnium additives, during heat treatment, the number of precipitated particles increases while their average size decreases compared to the base alloy. At the same time, in 1570 alloy without hafnium content, when annealed at a temperature of 440 °C, there is no increase in microhardness. This is caused by the fact that in 1570 alloy without hafnium content, when cooled after casting, discontinuous decomposition occurs, which resulted in the fact that most of the scandium precipitates from the supersaturated solid solution in the form of dispersoids. This phenomenon is not observed in the alloy with hafnium additives, which indicates its ability to stop discontinuous decomposition during cooling the ingot after casting.

Investigation on the damage mechanism of micro-cutting surface layer of aluminum alloy 7075 with different heat treatment processes

This paper investigates the machinability and microscopic surface damage mechanisms of aluminum alloy 7075 subjected to different heat treatment processes during micro-cutting. Focusing on T6 and T73 heat-treated aluminum alloy 7075, the study employs a combination of experiments and simulations to analyze micro-cutting surface morphology, cutting forces, microstructure evolution, residual stress, and damage characteristics. The findings reveal that micro-cutting of aluminum alloy 7075 after T6 heat treatment exhibits no apparent speed sensitivity in the primary cutting force, while T73 heat treatment demonstrates noticeable speed sensitivity. The surface microscopic damage during micro-cutting is influenced by both cutting speed and depth, resulting in distinct forms and degrees of damage under varying conditions. An analysis of the residual compressive stress field indicates that the magnitude of residual compressive stress on the micro-cutting surface determines crack initiation, and the maximum depth of residual compressive stress dictates crack propagation. Microscopic damage in T6 heat-treated aluminum alloy 7075 predominantly occurs in the second and third deformation zones, while T73 heat treatment leads to most damage in the third deformation zone. Notably, crack propagation is evident in T6 heat treatment at any cutting speed with a cutting depth of 150 μm, whereas it is inconspicuous in T73 heat treatment at cutting speeds below 540 m/min. Furthermore, at cutting speeds below 540 m/min and a cutting depth of 150 μm, T6 heat-treated micro-cutting is prone to oxidative wear. In contrast, at a cutting speed of 72 m/min and a cutting depth of 150 μm, the predominant wear form in T73 heat-treated micro-cutting is oxidation wear. This study underscores the intricate interplay between heat treatment processes, cutting conditions, and microscopic damage in aluminum alloy 7075 micro-cutting. The nuanced insights provided contribute to a deeper understanding of the machining characteristics of this alloy, paving the way for improved processing methodologies.

Application of New Al-Si Welding Filler with High Concentration of Copper and Magnesium: High-Temperature Strength and Anti-Corrosion Mechanism.

Currently, the primary commercial aluminum alloy fillers used are 4043 and 5356. However, when welded with high-strength work pieces like 6061 and 7075 aluminum alloys, the strength of weld beads significantly lags behind that of the original welded material. Both 4043 and 5356 aluminum alloys cannot be strengthened through heat treatment. The strength difference between the weld bead and base material doubles after heat treatment. In this study, an Al-Si-Cu-Mg alloy (SCM) filler modified using a heat-treatable A319 aluminum alloy was employed to investigate the post-welding microstructural and mechanical properties of specimens under room- and high-temperature conditions and after prolonged exposure in a saltwater environment (3.5 wt.% NaCl). The aim was to demonstrate that commercial aluminum alloy fillers could be substituted with a high-silicon aluminum alloy boasting excellent solidification and mechanical properties. The results revealed that, after heat treatment of the weld bead, dendrites were not eliminated, but the tensile strength increased to 310 MPa, closely matching that of commercial 6061 aluminum alloy. The strength of the weld bead remained higher than 250 MPa in high-temperature (240 °C) and saltwater environments. These findings underscore the potential application of this material.

Dissimilar friction-stir welding of aluminum alloys 2519, 6061, and 7050 using an additively-manufactured tool

This work was undertaken to evaluate the feasibility of the additively-manufactured tool for dissimilar friction-stir welding (FSW) of 2519, 6061, and 7050 heat-treatable aluminum alloys. The tool design included a flat shoulder with an Archimedean spiral groove and a threaded probe with a Triflute profile. It was found that the application of such a tool provided a nearly twofold decrease in Z-force and essentially enhanced the mechanical mixing of dissimilar materials within the stir zone. Nevertheless, despite the enhancement effect, FSW was inefficient for a homogeneous intermixing of dissimilar materials, and a distinct interface boundary was present within the stir zone. It was also found that the mechanical performance of the welded joints was sensitive to the initial temper condition of the welded alloys. Specifically, FSW of the alloys in the solution-annealed condition provided no significant influence on material strength, while that in the precipitation-hardened state led to significant material softening. During the post-weld T6 treatment, extensive nucleation of silicon-rich particles was found to occur at this interface. It was deduced that those promoted cracking during transverse tensile tests, thus giving rise to the decohesion of the dissimilar welds along the interface boundary. Hence, the post-weld T6 treatment was concluded to be unfeasible for dissimilar aluminum welds.

Coaxial Wire Laser-based Additive Manufacturing of AA7075 with TiC Nanoparticles

AA7075 is a heat treatable aluminium alloy widely used in aerospace and automotive applications due to its outstanding high strength-to-weight ratio. However, the implementation of this alloy in Additive Manufacturing (AM) processes has been limited due to its susceptibility to hot cracking. Moreover, selective evaporation of low boiling point elements Zn and Mg can cause gas porosity and diminish the mechanical properties of AM parts. Recent research revealed the effectiveness of nanoparticles additives to change the solidification behaviour of high-strength aluminium alloys and improve their weldability/printability. In this study, AA7075 enhanced with TiC nanoparticles was utilized as wire feedstock to create single and multi-layer samples with coaxial laser-directed energy deposition (L-DED). The response of the samples to precipitation hardening was studied, evaluating the microstructure and the microhardness before and after T6 heat treatment. Specimens were characterized using optical and electron microscopy and electron backscatter diffraction (EBSD). Crack-free and virtually porosity-free samples were fabricated, which exhibit a refined equiaxed grain structure with grain size <10μm. This confirms the ability of TiC nanoparticles to prevent columnar dendritic growth and promote heterogeneous nucleation. Microhardness values increased by 51 HV after T6 heat treatment and were uniform across the sample. Energy Dispersive Spectroscopy (EDS) analysis showed that there are evaporation losses of Zn and Mg. Considering the boiling temperatures of these elements, it is inferred that the molten pool reaches temperatures above 1090°C, and the partially melted zone temperature is between 907°C and 1090°C.

Inter-relationship between residual stresses, microstructural evolutions, and mechanical responses of heat-treatable aluminum alloys during welding: a numerical and experimental study

Inter-relationship between residual stresses, microstructural evolutions, and mechanical responses of heat-treatable aluminum alloys during welding: a numerical and experimental study

Optimization on the mechanical parameters and impact of welding parameters of pulsed TIG welding of Aluminium-Zinc-Magnesium alloy

As a function of pulsed Tungsten Inert Gas (TIG) weld processing factor, authors have studied the relationship between dilution and mechanical qualities including impact toughness, notch tensile strength, hardness in the as-welded condition. Welds made with a pulsed TIG torch have a minimum notch tensile strength and impact toughness than the base metal (BM) because of the grains of the inter-dendritic network formed during the welding process. Weldments made from heat-treatable (Al-Zn-Mg) Aluminium alloys have their process parameters for pulsed TIG welding optimized employing the Taguchi analysis to get the best possible mechanical qualities. Notch tensile strength is shown to be inversely proportional to impact toughness.

Aluminum alloy W-temper cryogenic forming with enhanced formability and strength

Simultaneously obtaining excellent formability and post-form strength in the traditional sheet metal forming of heat-treatable aluminum alloy is challenging, owing to the coexistence of wrinkling and splitting defects during forming and the control problem of microstructure. To solve these problems, W-temper cryogenic forming was proposed based on the cryogenic ‘dual-enhancement effect’ of an as-quenched (W-temper) aluminum alloy. The effects of the cryogenic temperature gradient and blank-holder force on the drawing behaviors were studied by analyzing the forming defects and thickness distribution. Strength distributions were reflected through Vickers hardness measurements under different aging conditions. The related strengthening mechanism was revealed through microstructure characterization. The drawability can be significantly improved at small or large cryogenic temperature gradients. An Al-Cu alloy semispherical shell component was fabricated via W-temper cryogenic forming. The depth of the formed hemispherical specimens increased by more than 106.4%. Uniform thickness can be also obtained at the temperature gradient of 216 °C, with an average thickness deviation rate of 6.5%, benefiting from the cryogenic dual enhancement effect and enlargement of the stress gradient. The hardness in all regions was higher than 146.5 HV of traditional T8-temper because of the enough accelerating precipitation of θʺ and θʹ phases by prior cryogenic deformation. Strain and precipitation strengthening were the main strengthening mechanisms under post-forming and post-aging conditions, respectively. The peak-aging time can be shortened to 6 h, which is one-third that of the traditional process. Enhanced formability and post-form strength can be simultaneously obtained by W-temper cryogenic forming, which has great potential for the fabrication of thin shells made from heat-treatable aluminum alloys.

The beneficial effect of minor iron additions on the crack susceptibility of rapidly solidified aluminum alloy 6060 toward additive manufacturing applications

Solidification cracking presents a challenge for additive manufacturing of many materials, such as heat treatable aluminum alloys. The objectives of this article are to demonstrate the beneficial effect of minor Fe additions on crack elimination in rapidly solidified Al alloy 6060 and to elucidate the underlying mechanism. Blocks of 6060 + xFe (0 ≤ x ≤ 0.5) were cast and single-track laser melting trials were performed on the surface of the blocks to emulate solidification rates characteristic of additive manufacturing. Analysis of the melt pool cross sections revealed that cracks were present in all processing conditions for the baseline 6060 alloy, but a monotonic decrease in cracking was observed with increasing Fe content with no cracks observed in any conditions for the 6060 + 0.5Fe sample. Serial SEM imaging and FIB milling were used to reveal the 3D morphology of nanoscale particles in the melt pools, while TEM analysis was used to identify the phases. Discrete and nodular δ-AlFeSi particles were observed in samples containing 0.1–0.2 wt% Fe, while elongated and branched α-AlFeSi particles were observed in the 6060 + 0.5Fe sample. The crack mitigation mechanism is proposed to be due to bridging of the Al matrix by the AlFeSi particles, through the formation of a strong interface and mechanical interlocking, thereby resisting the thermally induced loads. It is concluded that minor Fe additions can effectively eliminate cracking in Al 6060, and that this cannot be explained by conventional mechanisms such as grain refinement or an increase in eutectic liquid.

Peripheral coarse grain formation in AA2024 and AA6063 aluminium alloys- A comparative study

Multifaceted mechanical and physical characteristics such as light weighting, high strength to weight ratio, electrical conductivity, and ease of fabrication have helped aluminium alloys to find its application in aerospace and automobile sectors. The most famous aluminium alloy used in extrusion is AA 6063 because of its 100% extrudability. AA2024 is from the family of hard alloys which finds its applications in the strength requirements and major alloying additions comprise of Cu, Mg which contributes to age/precipitation hardening phenomena. Because of its inherent nature of high strength, it is challenging to extrude. Extrusion is one of the major metals forming processes which involve several process parameters such as, temperature, strain rate, ram speed and post forming heat treatment operations. To attain the specific mechanical properties, microstructure of the extrudate is of utmost importance and evolution of the same needs to be understood. Heat treatable aluminium alloys series of 2xxx, 6xxx or 7xxx are prone to peripheral coarse grain structure, which is responsible for the loss of mechanical and corrosion performance. To eliminate PCG entirely or to minimize it is the fundamental interest of extrusion industries and to come up with a workable solution, it is necessary to twig the microstructure evolution of AA6063 and AA2024 alloy during extrusion and after heat treatment. The present work is aimed at comparative study of the PCG formation of press quenched samples in AA6063 and heat-treated (T6) samples of AA2024.

Kelvin-Voigt lumped parameter models for approximation of the Power-law Euler-Bernoulli beams

The purpose of this research is to initiate an investigation of the nonlinear material strain-rate damping effects on the amplitude and frequencies of some Euler-Bernoulli Beams. It is well known that the dynamic behaviors of most heat-treated metals can be modelled by using the power-law strain-rate dependent constitutive equations. Lumped parameter models for approximations of dynamic vibration of the power-law Euler-Bernoulli Beam subject to power-law strain-rate damping and concentrated loads are formulated. Analytic formulas of the lumped parameters, including effective the train-rate damping, are derived. The lumped-parameters are also evaluated numerically by a low-order Galerkin Method to validate and compare the lumped parameter model with another numerical model. Numerical examples made of some heat-treated aluminum and stainless-steel alloys are presented to illustrate the implications of the aforementioned lumped-parameter models on the dynamics of the beams. The results obtained in this work cover with the classical results in the literature for linear the materials as special cases. The novel lumped parameter models can provide useful insights for crashworthiness analysis of structures of heat treated metals and thermal plastics.

Enhancement of microstructure, micro-texture, and mechanical properties of Al6061 friction stir welds using the developed static shoulder welding tool

Dissolution of strengthening precipitates and grain coarsening are the key factors that dictate the mechanical properties of heat-treatable aluminium alloys. In this study, a feasible method of static shoulder friction stir welding (SSFSW) is used to reduce these adverse effects. A novel static shoulder friction welding tool is developed here in this study by incorporating rotating and non-rotating shoulders in a single tool. The effectiveness of the tool was evaluated by welding Al6061 plates under various conditions, such as conventional friction stir welding (CFSW), underwater friction stir welding (UWFSW), and SSFSW. The evolution of crystallographic texture and microstructural changes during the process is studied using electron back scattered diffraction and transmission electron microscopy. The results showed that SSFSW reduced grain size by 37% compared to UWFSW at the centre of the stir zone and increased the yield strength by 22.8% compared to CFSW. In addition, SSFSW showed a strong presence of γ-fibre, indicating improved formability and a 7.2% improvement in joint efficiency in terms of ultimate tensile strength due to a higher fraction of precipitates and higher dislocation density.

Cavitation behavior study of the aging heat treated aluminum alloy 7075

Aluminium-based alloy type 7075 is known for its good ductility, high mechanical strength, toughness and high fatigue strength, which is why it is mainly used in the construction of dynamically stressed parts in the structure of airplanes, vehicles and ships. Although it has these qualities, at present its behavior has not been studied at the hydrodynamic stresses that allow it to be used in parts that work in cavitation conditions, such as pump rotors and boat propeller blades. Therefore, the research in this paper highlights the behavior of laminated semi-finished structures and obtained by heat treatment of artificial aging at 180°C, with a maintenance time of one hour. Of the 7075 alloy at the demands generated by the vibrating cavity, created by the standard vibrating device with piezoceramic crystals (frequency of 20 kHz, amplitude of 50 µm and electrical power of 500 W). Analysis based on the curves MDE (t) and MDER (t), of the specific parameters of cavitation erosion MDEmax and MDERs as well as of the macro and microscopic images of the eroded structures of cavitation show that, compared to the delivered state (semi-finished), by the heat treatment applied the microstructure does not change cavitation

Study on the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured Al-Zn-Mg-Cu aluminum alloy

Al-Zn-Mg-Cu aluminum alloys are typically heat-treatable aluminum alloys. The heat treatment has a significant effect on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy. In this study, the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured 7B55 aluminum alloy was systematically investigated. The results showed that the microstructure of the as-deposited 7B55 aluminum alloy was composed of equiaxed grains with an average grain size of 4.2 ± 0.5 μm. A large number of the second phases were continuously distributed along grain boundaries. The precipitated phases within grains were mainly composed of the larger η phases and the smaller η′ phases, and the amount of precipitated phases was fewer. The second phases distributed along grain boundaries gradually dissolved into α-Al matrix with the increase of solid solution temperature, resulting in a higher supersaturation of the α-Al matrix and more homogeneous distribution of alloy elements. Combined with the results of DSC analysis, the optimal solid solution temperature of the 7B55 aluminum alloy was determined to be 480 °C. After solid solution of 480 °C，the microstructure was still composed of equiaxed grains with an average grain size of 4.8 ± 0.4 μm. The size of the grain did not grow significantly. A larger number of nanoscale fine GP zones, η′ phases and secondary Al3(Sc,Zr) particles were precipitated within the grains during subsequently artificial aging process, resulting in a significant increase in tensile properties. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) reached 621 MPa, 555 MPa and 5.73%, respectively, which was significantly higher than the strength level of WAAM aluminum alloy reported among all the existing literature.