Heat-treatable Aluminum Alloys Research Articles

Investigation on Contact Heating of Aluminum Alloy Sheets in Hot Stamping Process

Application of the hot stamping process on heat-treatable aluminum alloys effectively solves the problems of large springback and poor ductility during forming at room temperature, which expands the range of applications of aluminum alloys in the transportation industry. Sheet heating plays an important role in the hot stamping process, and increasing the heating rate can improve the hot stamping efficiency to some extent. In this paper, the feasibility of applying contact heating techniques with higher heating rates in the hot stamping process was studied. A contact heating device was designed, and the temperature distribution of the device contact surface was observed. Furthermore, the heating characteristics of 7075 aluminum alloy sheets during the contact heating process were explored by experiments and finite element simulation. Finally, the rapid solution treatment of aluminum alloy was carried out with a contact heating device, which was compared with the furnace heating solution treatment. The experimental and simulation results indicate that the device contact surface has a relatively uniform temperature distribution, and the aluminum alloy sheets can be heated to close to the set temperature in 15 s using contact heating techniques. Meanwhile, the rapid solution treatment of aluminum alloy sheets can be achieved within 15–20 s by contact heating techniques, obtaining superior mechanical properties. This suggests that the contact heating process can be used for rapid heating and rapid solution treatment of aluminum alloy sheets in hot stamping process.

Influence of Thermomechanical Treatments on the Microstructure and Mechanical Properties of Aluminium Alloy AA2219 Hand Forgings

The heat treatable aluminium alloy AA2219 is subjected to mechanical stress relieving by way of cold deformation after solution treatment to relieve the quenched in stresses as thermal stress relieving is not possible due to the requirement of higher temperature than the ageing temperature. Cold deformation prior to aging has also been found to yield improved strength. Though this phenomenon is to some extent being exploited in aluminium alloy AA2219 sheets and plates, there is no experimental data available to understand the influence of cold compression on the extent of benefits obtainable on mechanical properties in forgings. In the present study to identify a thermo-mechanical treatment that can yield the maximum tensile strength, solution treated AA2219 forgings were subjected to cold deformation ranging from 0 to 25% and then artificially aged. The results indicates that the maximum room temperature tensile strength (both UTS and 0.2% PS) can be obtained at 10% post solution treatment cold deformation. As this alloy is being used for low temperature applications, it is very essential to assess the effect of higher cold compression on the low temperature (77 K) properties and the results show that the 77 K tensile properties more or less same beyond 2% cold deformation. As the weld properties are around 50% of the parent metal properties, any increase in the mechanical properties, is considered to be very crucial and very much needed for this alloy in the absence of aluminium–lithium alloy technology. Hence this study indicate that there is a good scope to increase the amount of cold compression after Solution treatment instead of restricting the same to 2%–5% maximum.

Mechanical Behavior and Deformation Kinetics of Aluminum Alloys Processed through Cryorolling and Subsequent Annealing

The influence of cryorolling (CYR) on the microstructure, mechanical properties, and formability of heat-treatable (AA 6061) and non heat-treatable (AA 5083) aluminum alloys was investigated. Solutionized (SL) AA 5083 and AA 6061 alloy plates are cryorolled to reduce the thickness from 6.5 to 1 mm (the total true strain of 1.87). Short annealing treatment is performed on cryorolled samples at different temperatures with a fixed annealing time to improve ductility. The effect of annealing temperature on microstructure, mechanical properties, and formability was systemically studied. The results showed grain refinement after CYR with higher dislocation density when compared to the SL condition, and their effect is reflected in the mechanical properties. The limiting dome height test is used in the present work to compare the formability of cryorolled and annealed samples. The formability characteristics correlated well with the strain hardening behavior, which is modeled using the Kocks–Mecking–Estrin (KME) dislocation density model. The dislocation density evolution in the original KME model was modified to consider the contributions of grain size, solutes, and precipitates. The tensile curves predicted from the KME model correlated well with the experimental curves in all the conditions investigated. In addition to that, the predicted dislocation density using the modified KME model agreed well with the dislocation density determined experimentally.

Effect of nano-sized particles on grain structure and mechanical behavior of friction stir welded Al-nanocomposites

Weldability of heat-treatable 6061-T6 aluminum alloy results in deterioration of mechanical properties due to dissolution of strengthening precipitates in the nugget zone of friction stir welded joints. These properties were improved by addition of reinforcement particles in the weld joint line. In the present work, attempts were made to produce 6061-T6 Al-based nanocomposites using the friction stir welding process by incorporating titanium oxide nanoparticles into the aluminum matrix for microstructure refining of the nugget zone and prevent the grain growth in the heat-affected zone. The effect of addition of nanoparticles on the evolution of grains structure and mechanical behavior of friction stir welded samples based on different combinations of rotational and travel speed was studied and discussed. Results revealed that the unreinforced samples were successfully welded at both low and high heat inputs, whereas the reinforced samples are not feasible at tool rotational speed (ω) < 2000 r/min and transverse speed (v) > 70 mm/min, respectively. The significant refining of grains in the nugget zone is possible with addition of nanoparticles via the Zener-pinning effect. A more pronounced increment in tensile strength, microhardness, and wear properties was observed compared to sample without nanoparticles under the same processing parameters due to embedment of nano-sized particles in the weld nugget zone.

Joining of AA2014 and AA5059 dissimilar aluminium alloys by Friction Stir Welding

Purpose: This work aims to investigate the microstructure and mechanical properties achieved by FSW of butt joints, namely of dissimilar sheets namely of 2014-T3 to 5059-H11 Al alloys by bonding the two materials perpendicular to their rolling directions. Design/methodology/approach: AA 2014T3 and AA 5059H11 were two dissimilar aluminium alloys friction stir welded. The joint has been examined in terms of hardness, microstructure, and mechanical properties. The microstructure of the weld area was characterized by using optical microscopy. Seven diverse regions of the microstructure in the joint can be illustrious. Findings: It has been noticed that a structure of fine grain is formed in the nugget region as a consequence of recrystallization. The thermos mechanically affected and heat affected zones of aluminium alloy 2014 are characterized by the lowest hardness values in spite of there are a general hardness decrease through the weld zone compared to both base metals. The ultimate tensile strength values of the dissimilar joint were found to be varying between 54% to 66% those of the base metal. Research limitations/implications: The t joining in FSW takes place with the base materials remnant in the solid state, which gives a considerable possibility to produce joints between the alleged difficult-to-weld heat treatable aluminium alloys. Originality/value: The outcomes display that friction stir welding can be effectively applied for the joining of dissimilar aluminium alloys.

Effect of Solution Heat Treatment of Aluminum Alloy 4032 on the Structure and Corrosion Resistance in 3,5% and 10,5% NaCl Solution

Aluminum Alloy 4032 is usually used as a material for making engine pistons, which has a composition of Aluminum (Al), 21%wt Silicon (Si), 0.82%wt Nickel (Ni) and 0.67%wt Copper (Cu). The alloy is known to have mild properties and should have good corrosion resistance. Heat treatment was carried out with the aim of the enhancement of the corrosion resistance. The solution heat treatment process was performed at 510°C for 2 hours and then quenching to room temperature in water media. Some of the material were also performed an aging process at 171°C with varying duration of time and then cooling to room temperature. Corrosion resistance testing was carried out by electrochemical testing using 3.5% wt and 10.5% wt NaCl solution. The structure before and after heat treatment were characterized by using X-Ray Diffraction (XRD) were analyzed. The results of the characterization indicate that the heat treatment on the Alloy is affected by solution heat treatment and the aging process.

Evaluation of the stress vs strain curve using a high temperature bulge test device

The increasing amount of hot and warm stamping parts in the automotive industry shows that high temperature forming is critical to reach the emission goal fixed by regulation authorities, due to its contribution in reducing the vehicle’s weight. Hot stamping and warm forming take advantage of the material softening with temperature to reduce the forming forces and springback. The use of different temperature conditions also enables exploring the phase transformation occurring with in-tool quenching in hot stamping boron steels or artificial aging in heat treatable lightweight aluminum alloys. These new forming conditions require either new material characterization methods or the current methods need to be adapted to high temperature conditions. The equibiaxial expansion test allows the evaluation of the mechanical behavior of materials on a large strain range. However, the use of high temperature conditions gives rise to difficulties when using Digital Image Correlation (DIC) systems. This study analyses the possibility of using a scanner laser to obtain the stress vs. strain curve from an equibiaxial test performed with an aluminum alloy of the 6xxx series, at 150°C. The aim is to validate an experimental procedure that can be used to evaluate the stress vs. strain curve from high temperature bulge tests performed with other metallic sheets, including quenchable boron steel.

A study of microstructure and mechanical properties of friction stir welding aluminium alloy AA6082 with Zn interlayer

In the present study, the effect of Zn interlayer is analysed on friction stir welding of heat-treated AA6082 aluminium alloy. Friction stir welding joints are produced by preplacing the Zn particles interlayer into a gap of 0.7 mm between the abutting plates. Rotational speed is selected as process parameter to perform the welding. Thereafter welded joints are evaluated for microstructural aspects, microhardness and tensile properties. The microstructure analysis reveals that interlayer particles are evenly distributed in the nugget zone of joints. FSW joints produced with interlayer possess higher microhardness than the joints without interlayer. However, equivalent tensile strength is reported in both the cases. The fracture analysis revealed joint with interlayer possesses ductile failure under tensile loading.

Uphill quenching to reduce residual stress in a heat treatable aluminium alloy

ABSTRACTThree rectilinear blocks of the aluminium alloy 7449 were characterised using neutron and X-ray diffraction. One block was heat treated normally and two blocks were subject to uphill quenching from −196°C to 100°C. Boiling water and steam were used to rapidly increase the temperature of the blocks to reverse the thermal gradients introduced by cold water quenching. It was possible to detect the beneficial influence of uphill quenching on residual stress using either fluid. The influence of steam was very effective but localised and limited to the surface in close proximity to the steam jet. For more uniform stress relief, multiple steam jets will be required to ensure the entire surface receives a significant thermal input.

Friction Stir Welding of Thick AA2519 Alloy: Defect Elimination, Mechanical and Micro-Structural Characterization

Friction stir welding (FSW) of thick aluminium sections will pave way for remarkable new defence applications, provided the accompanying challenges are successfully addressed. These challenges include elimination of tunnel defects, loss of strength in heat-treatable aluminium alloys, tool design and excessive process forces. Accounts of defect elimination, detailed micro-structural and mechanical characterization for thick section FSW are scarce in the published literature. Further, special strategies such as bobbin tool, pre-drilled hole for plunging and inverted double pass are generally deployed to overcome these challenges. This makes the process less productive and complex. In the present work, armor grade aluminum alloy AA2519-T87 plates having a thickness of 15.4 mm have been successfully joined with a joint efficiency of greater than 75% without supplementary strategies. The disparity in the effects of tool rotational speed and welding speed in the formation of a sound weld has been addressed in detail to enhance the understanding of FSW of thick sections. Micro-hardness measurements have been carried out throughout the transverse cross-section of the welds and correlated with different zones and their corresponding microstructures. Scanning electron microscopy and X-ray energy dispersive spectroscopy have been used to characterize the coarse phase particles present in the weld zones.

INDENTATION SIZE EFFECT OF HEAT TREATED ALUMINUM ALLOY

The aim of the submitted work is to study the influence of applied loads ranging from 0.09807 N to 0.9807 N on measured values of micro-hardness of heat treated aluminum alloy 6082. The influence of applied load on a measured value of micro-hardness was evaluated by Meyer’s index n, PSR method and by Analysis of Variance (ANOVA). The influence of the load on the measured value of micro-hardness is statistically significant and the relationship between the applied load and micro-hardness manifests the moderate reverse ISE. As the temperature of the solution treatment rises, the YS/UTS ratio and also Meyer’s index n, measured and “true hardness“ increase. On the other hand, its effect on the plastic properties of the alloy is ambiguous.

Electro chemical response of stir zone in friction stir welded AA7075-T651 joint in sodium chloride solution

Abstract High strength heat treatable aluminium alloy AA7075T-651 is widely used in aircraft industries. It is very difficult to weld in fusion technique due to poor solidification and microstructure in weld region. Friction Stir Welding is reliable technique to joining aluminium alloys in solid state condition with sound weld ability. In this work, rolled aluminium plate with thickness of 10 mm were square butt welded by Friction Stir Welding (FSW) process. The electrochemical corrosion behavior of FSW joints were investigated in 3.5% wt NaCl solution. The corrosion morphology of friction stir zone has been compared with parent metal. It is observed that, stir zone prone more corrosion potential than parent metal.

Correlating Tensile Properties with Microstructures of Various Regions in Gas Tungsten Arc Welded AA2014 Alloy

AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al2Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al2Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al2Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.

Residual Stresses and Cracks in Forgings of Heat-treatable Aluminium Alloys

The heat treatment of the heat-treatable aluminium alloy forgings includes cooling from the solutionising temperature. After heat treatment, residual stresses remain in the forging, which are due to temperature gradients during cooling. The effect of these residual stresses on the forging properties can be significantly influenced by other technological operations, including artificial aging, machining, and surface treatments. The influence of the surrounding environment can also play an important role. Because in connection with the residual stresses after heat treatment we often encounter cracks in forgings, this paper is devoted to an overview of factors that influence cracks. The typical examples of damaged forgings are discussed and explained the circumstances that caused cracks under the influence of residual stresses.

Investigations on exit burr formation mechanisms based on digital image correlation and numerical modeling

Requirements on burr height and burr amount on machined parts are getting stricter. This leads to method development from manufacturing companies to predict burr distribution and its size along part edges. A deeper understanding of burr formation mechanisms will assist to more accurate model development. This study aims to analyze the exit burr formation, which is formed during orthogonal cutting of a brittle cast aluminum alloy. A customized digital image correlation (DIC) system with the help of a high-speed camera was used to measure the displacements fields. It calculates strain fields during burr initiation and development in orthogonal cutting of T7 heat-treated cast aluminum alloy ENAC-AlSi7Mg0.3 as well. Those results are then qualitatively compared with a numerical model of the burr with chamfer formation developed and simulated using a finite element method, to ensure a good correspondence between experiments and simulation. This model is used to complete the DIC study of burr with chamfer formation mechanisms during crack propagation leading to chamfer formation. The analysis of numerically obtained stress triaxiality fields and of DIC observations from experiments are compared to the assumptions made from analytical models. Finally, necessary improvements of an existing burr formation analytical model are proposed.

Mechanical Properties and Formability of Heat-Treated 7000-Series High-Strength Aluminum Alloy: Experiments and Finite Element Modeling

The feasibility of room-temperature (cold) forming of peak-aged 7075 high-strength aluminum alloy (7075-T6) sheets after solution heat treatment followed by water quenching was investigated. The anisotropic plastic properties of the heat-treated aluminum sheet (7075-WT) were experimentally characterized by performing uniaxial tensile tests (along different loading directions) and a balanced biaxial tension test. Limit dome height (LDH) and cylindrical cup drawing experiments were conducted to evaluate the formability at room temperature. With the obtained anisotropic mechanical properties, different yield functions, including Yld2000-2d, Hill 1948, and von-Mises, were determined and implemented in the finite element simulations to numerically predict the formability at room temperature. The formability of the 7075-WT sheet at room temperature could be significantly enhanced owing to the prior heat treatment, and the finite element simulations performed using the anisotropic yield functions and Voce hardening law were in good agreement with the measured LDH. The LDH of the 7075-WT sheet in the plane strain and biaxial stress modes and the earing in the circular cup drawing tests could be better predicted non-quadratic Yld2000-2d function than those by isotropic and Hill 1948 quadratic yield functions.

Study of the Influence of Conditions of Combined Casting and Rolling-Extruding and Two-Stage Annealing on the Structure and Properties of Semi-Finished Electrical Products from an Al–Zr System Alloy

This article presents the results of the study of the joint effect of the processing conditions of the new composition of the Al-Zr system alloy by combined casting and rolling-extruding and two-stage annealing on the structure and properties of round bars used in the manufacture of heat-resistant wires. The research show patterns of changes in the properties, the specific electrical resistance of the bars, depending on different conditions of deformation and heat treatment of aluminum alloy with a content of 0.3% zirconium and 0.2% iron. The results of micro-X-ray spectral analysis and the granular structure of the samples before and after two-stage annealing confirming the stability of the structure after heating and preserving the strength of semi-finished products. Presented parameters of combined casting and rolling-extruding and two-stage annealing for the manufacture of rods from the studied alloy make it possible obtaining good combination of mechanical properties and electrical conductivity.

Compressive strengths of concrete-filled double-skin (circular hollow section outer and square hollow section inner) aluminium tubular sections

Experimental and numerical investigations of concrete-filled double-skin aluminium stub column with a circular hollow section as the outer skin and a square hollow section as the inner skin are presented in this article. A test program was carried out to study the influences of aluminium tube geometric dimensions and concrete strength on structural performance and strength of composite columns. A series of composite columns was tested on outer circular hollow section tubes and inner square hollow section tubes; the spaces between them had been filled with concrete of different nominal cylinder strengths of 40, 70 and 100 MPa. The tubes were fabricated by extrusion using 6061T6 heat-treated aluminium alloy having a nominal 0.2% proof stress of 240 MPa. A non-linear finite element model was developed and verified against experimental results. The test and numerical results were compared with the design strengths to evaluate the applicability of the design rules in the American specifications for aluminium and concrete structures. In addition, the proposed design equations, developed by the authors for concrete-filled double-skin aluminium tubular stub columns with circular hollow section as both outer and inner skins, were used to calculate the design strengths and compared with the experimental and numerical results obtained in this study. The proposed design equations also predicted the ultimate strengths of the concrete-filled double-skin aluminium tubular stub columns accurately with circular hollow section as the outer skin and square hollow section as the inner skin.

Friction Stir Welding between 6082 and 7075 Aluminum Alloys Thermal Treated for Automotive Applications

The automotive industry demands ecofriendly manufacturing processes and lightweight structures and materials to reduce CO2 emissions and decrease weight and fuel consumption while optimizing overall performance. Aluminum alloys in the 7xxx and 6xxx series offer high potential for weight reduction in automotive and other transportation industries. 7xxx aluminum alloys have the best strength performance among all commercial aluminum alloys. Alloys in the 6xxx series generally have medium-to-high strength, high corrosion resistance, and good formability. Alloys in both the 7xxx and 6xxx series are strengthened by heat treatment. The increased strength-to-weight ratio and the thermal treatment processing open the possibility to use these alloys as possible alternative materials instead of steel in the automotive industry for the fabrication of car body parts. However, their poor formability and weldability are the main drawbacks when these alloys are considered as substitutes of steel and other dissimilar joints during the fabrication of car body parts and the production chain. Recently, Hot Forming and in-die Quenching (HFQ), a patented hot stamping process, has been introduced to manufacture complex-shaped high-strength heat-treatable aluminum alloys. The work described in this article is an experimental investigation of the weldability between AA6082 and AA7075 by Friction Stir Welding (FSW) that considers thermal treatments used during HFQ for automotive applications. The aforementioned FSW base metals, 6082 and 7075, are heat treated according to the solution heat treatment adopted during HFQ to evaluate the effect of the HFQ thermal cycle on the quality of the produced joints. Optical microscopy has been used to characterize the microstructure of the produced joints. The defect-free welded joints are characterized by good mechanical mixing between the joined materials as well as by grain refinement. The mechanical behavior of the produced welded joints was studied and compared with the parent materials, whereas the measured mechanical properties are correlated with the microstructure.

Application of hot forming cold die quenching for facilitating equal channel angular pressing of AA2024 aluminum alloy

The effect of one pass hot forming cold die quenching (HFQ) in equal channel angular pressing (ECAP) on the evolution of hardness, tensile properties and microstructure of AA2024 aluminum alloy is investigated. Since AA2024 is a heat treatable aluminum alloy, it is sensitive to the cooling process applied before deformation or aging. Therefore, samples are considered in air cooled (AC) and water quenched (WQ) conditions and the results are compared with those obtained in HFQ-ECAP. In addition, hardness and tensile properties are investigated in as-deformed and aged conditions to understand the response of the alloy to aging. It is found that distribution of precipitates, hardness and tensile properties in the aged samples significantly depend on the cooling process prior to deformation. Significant increases in hardness (24 and 22%) and strength are observed when the WQ and HFQ samples are aged after one pass ECAP. However, an effective precipitation hardening is not achieved when AC cooling is applied. In addition, much more effective strengthening and precipitation hardening with respect to AC samples are observed by utilizing HFQ. Maximum hardness (201 Hv), yield strength (YS) (446 MPa) and ultimate tensile strength (UTS) (558 MPa) are achieved in the WQ sample after ECAP and aging treatment. Similar properties are achieved in HFQ-ECAP samples after aging treatment which respectively equal 190 Hv, 446 MPa and 560 MPa for hardness, YS and UTS. Indeed, due to its very similar achieved mechanical properties, the HFQ-ECAP is found as an effective way to replace WQ-ECAP of AA2024 alloy.