Heat-treatable Aluminum Research Articles

A novel post-weld composite treatment process for improving the mechanical properties of AA 6061-T6 aluminum alloy welded joints

The welded joint for a heat-treated aluminum alloy AA 6061-T6 showed softening in the fusion zone (FZ) and the heat-affected zone (HAZ). This paper proposed a post-weld composite treatment process that overcame the joint softening by coupling the solubilization treatment (ST), aging treatment (AT), and cold rolling (CR). Three post-weld composite treatment processes were investigated to reveal the effect of the interaction between precipitation hardening and work hardening on joint mechanical properties. Experimental results showed that the post-weld “ST-AT-CR” composite treatment process could improve the microhardness of the FZ and HAZ to the level of the original base metal (BM), and the joint strength and ductility could reach up to 100 % and 67 % of the BM, respectively. On the other hand, it was also observed that the post-weld “CR-ST-AT” composite treatment process could make the joint softening more serious. The higher pre-existing dislocation density by the CR process would provide more diffusion channels for the solute atoms during the ST-AT process and promote the over-aging of strengthening phases, while the ST-AT process would significantly reduce the pre-existing dislocation density.

Influence of post-processing heat treatment on the cyclic deformation behaviour of AlSi10Mg aluminium alloy subjected to laser powder bed fusion

The effect of heat treatment on the cyclic deformation behaviour of AlSi10Mg aluminium alloy manufactured by laser powder bed fusion (LPBF) was investigated. Uniaxial fully-reversed strain-controlled fatigue tests were conducted on polished smooth specimens in the low-cycle and high-cycle fatigue regimes for three material states: no heat treatment, stress relief heat treatment and T6 heat treatment. The effect of the heat treatment on microstructure, ductility, hardness and tensile properties was also investigated. It was found that the microstructural transformation associated with the heat treatments increased the ductility, and reduced the hardness, the tensile strength, and the fatigue resistance, particularly in the low-cycle fatigue regime. Thus, these standard heat treatments used in conventional heat-treatable aluminium alloys are not recommended for LPBD aluminium alloys subjected to cyclic strain loading.

Reciprocating Wear Behavioural Analysis of Heat-treated Aluminium ZrO2/Al7Si0.3Mg Functionally Graded Composite Through Taguchi’s Optimization Method

Reciprocating Wear Behavioural Analysis of Heat-treated Aluminium ZrO2/Al7Si0.3Mg Functionally Graded Composite Through Taguchi’s Optimization Method

Ultimate response and plastic design of aluminium alloy continuous beams

Over the last twenty years 6,000 series aluminium alloys are gaining increasing attention as a structural material in the construction sector, particularly in applications where lightness and corrosion resistance are crucial for material selection. Aiming to sustainable construction practices, significant material savings could be achieved through more economical design solutions such as plastic design. Currently, plastic design of aluminium alloy structures is not permitted in most design codes, except European provisions which provide recommendations for inelastic analysis. Indeed, there is a clear lack of experimental data to prove this possibility, particularly for relatively new materials in the construction industry, such as the 6082-Τ6 heat-treated aluminium alloy. To address this knowledge gap, a total of 15 rectangular hollow sections fabricated from 6082-T6 aluminium alloy were tested as simply-supported and two-span continuous beams. Numerical models were developed to replicate the experimental results considering geometric and material nonlinearities. A subsequent parametric study was carried out to generate numerical data for indeterminate structures. One normal and two high strength aluminium alloys as well as two load configurations were examined within this parametric study over a wide range of cross-sectional aspect ratios and slendernesses. The experimental results in combination with the numerical results were utilised to assess the accuracy and applicability of (i) the traditional plastic design method, (ii) the European design provisions (EC9), (iii) the plastic hinge method included in Annex H of EC9, and (iv) the Continuous Strength Method (CSM). Relative comparisons demonstrated the potential of applying plastic design in aluminium alloy indeterminate structures. Notably, the plastic hinge method and the CSM which accounts for strain hardening at the cross-sectional level and for moment redistribution at the system level were found to provide the most accurate design strength predictions, resulting in more economical cross-sections and utilising the full potential of aluminium alloys’ plastic deformability.

Design of aluminium alloy channel sections under minor axis bending

In recent years, numerous research works have been reported on the flexural response of aluminium alloy tubular cross-sections. However, studies on monosymmetric cross-sections and particularly channel (C-) sections are limited, albeit their increased usage in structural applications. This paper aims to address this knowledge gap providing an improved understanding about the minor axis bending behaviour of C-sections through an experimental and numerical investigation. In total 14 specimens made from 6082-T6 heat-treated aluminium alloy were subjected to four-point bending. Tensile coupon tests were also performed to determine the mechanical properties of the examined aluminium alloy. The obtained experimental results are analysed and discussed. A series of geometrically and materially nonlinear analyses were also carried out to study the flexural performance of C-sections in two aluminium alloys and two bending orientations over a range of cross-sectional aspect ratios and slendernesses. The experimental and numerical results are utilised to assess the European design standards. The applicability of the Continuous Strength Method and the Direct Strength Method is also evaluated. An alternative design method based on the plastic effective width concept is proposed for slender C-sections subjected to minor axis bending. This method accounts for the inelastic reserve capacity which is in accordance with the experimental and numerical observations.

Experimental study on heat-affected zones of aluminum alloys in flow drill riveting

Flow drill riveting (FDR) is a novel one-step and single-sided joining process. In FDR, a rivet penetrates through workpieces at a high rotation speed and a certain feed rate, which generates heat through friction to soften the local material. However, the frictional heat usually brings a softening effect to heat-treatable aluminum alloys, which results in heat-affected zones in joints. In this work, temperature evolution of AA6061-T6 during FDR was measured and analyzed, which exhibited a nonlinear relationship with time and was characterized by two peaks. According to the temperature evolution, the FDR process was divided into two stages: penetration of rivet (stage 1) and stop of rivet rotation (stage 2). Electron backscatter diffraction and microhardness results show that the first rise of temperature in stage 1 was attributed to friction stir between rivet and workpieces, and the friction stir at contact surface between rivet head and flash on the top surface of the upper workpiece resulted in the second rise of temperature in stage 2, which caused a larger heat affected zone on the upper workpiece. Furthermore, the effects of process parameters (i.e., rotation speed and feed rate) on temperature evolution of AA6061-T6 were investigated. A higher rotation speed results in higher temperatures, a larger heat-affected zone and a greater softening effect on the upper workpiece, while the lower workpiece is less affected, resulting in lower joint strength. A larger feed rate contributes to a smaller heat affected zone on both upper and lower workpieces, resulting in higher joint strength.

A New Method to Characterize and Model Stress-Relaxation Aging Behavior of Aluminum Alloys Under Age Forming Conditions

A new method that utilizes theories of thermally activated deformation and repeated transient stress-relaxation tests has been proposed and validated in this study for the characterization and modeling of the stress-relaxation aging (SRA) behavior of aluminum alloys and its dependence on stress and temperature. Using the new method, key deformation-related variables, i.e., stress components, activation volume, and activation energy, of the aerospace grade heat-treatable aluminum alloy AA7B04 have been obtained as a function of aging temperature (388 K, 413 K and 438 K), stress (both elastic and plastic), and SRA time (up to 4 hours). It has been found that the apparent activation energy Qa of the material remains constant in the elastic region but decreases with the increase in strain in the plastic region, and also decreases with the increase in temperature for all initial loading stresses. These characteristics contribute to a much higher degree of stress relaxation in the plastic region and at higher temperatures than in the elastic region and/or at lower temperatures. The obtained changing activation volume V and Qa indicate that the deformation rate is controlled by forest dislocation interactions in the elastic region (V decreases from over 200b3 to less than 100b3), and by a cross-slip mechanism at high stress levels in the plastic region (V decreases to a few tens of b3). Based on these theories and results, a novel and simple constitutive model has been proposed, with which the stress-relaxation behavior of AA7B04 at different aging temperatures (388 K to 448 K), preloaded from elastic to plastic regions for up to 16 hours has been successfully predicted. The proposed model eliminates the limitations of conventional SRA models which mainly deals with elastic loading and isothermal conditions, and provides a foundation to effectively predict the springback after advanced non-isothermal SRA forming of aluminum alloy structures in the aerospace industry.

Natural aging behaviors of Al-Cu-Li alloy: PLC effect, properties and microstructure evolution

To facilitate the processing and manufacturing of heat-treatable aluminum alloy components, the initial temper of the billet material is usually adjusted to the as-quenched (AQ) temper by solid solution treatment. However, for most as-quenched aluminum alloys, the obvious natural aging (NA) may occur and cause sensitive time scheduling for the subsequent forming processes. Taking the 2195 Al-Cu-Li alloy as the case material, from the aspects of Portevin-Le-Chatelier (PLC) effect, properties and microstructure evolution, this study deeply and systematically explores the NA behaviors and reveals the underlying mechanism. The combined interaction of Cu and Li solute atoms with mobile dislocations is the major mechanism for the PLC effect in this alloy. The NA induced decreasing of the interaction of solutes with the dislocations makes the number of dislocations in the PLC bands reduce, resulting in its character to change from type B to type A during NA. The Al-Cu-Li alloy exhibits a strong response at the early stage of NA, viz., the tensile strength increases rapidly in the initial 4 h and then reaches the plateau 24 h later. Major sources of strengthening in the NA state are the δ′/β' precipitates, GP zones and solute atoms. The extended age hardening model were used to predict the evolution of the YS and microstructure variables of the alloy during NA. The results indicate that the contribution of solute atoms ( σ ss ), δ′/β' precipitates ( σ δ ′ ) and GP zones ( σ GP ) to strength in NA state is ~161 MPa, ~80 MPa, and ~ 141 MPa, respectively. The electrochemical measurement results indicate that the NA state has a higher corrosion resistance than the AQ state. The pitting pores form associating with the negative potential of the spherical δ′ phase in NA state. • The reduction in the number of dislocations in the PLC bands causes its character to change from type B to A during NA. • The contribution of σ ss , the σ δ ′ and σ GP to YS in NA state is ~161 MPa, ~80 MPa, and ~ 141 MPa, respectively. • The pitting pores form associating with the negative potential of the spherical δ′ phase in NA state.

Hardness prediction of post heat treated electron beam welded defense grade AA2219 aluminum alloy for light weight application

Due to exception characteristics, aluminum and its alloy are the major potential candidate in heavy structural industries such as aircraft and automobiles. However, this alloy is difficult to weld using conventional fusion welding. This process would alter the metallurgical properties of this alloy through the heating and cooling cycle. Hence, in this investigation, an attempt has been made to join AA2219 alloy by electron beam welding. Generally, the obtained tensile strength was low in a welded joint. The post-weld heat treatment is a technique to improve the joint's stability in heat-treatable aluminum alloy. Solution treatment, artificial aging, and solution treatment followed by artificial aging employed the strength of electron beam weld. From the experimental report, the solution treated followed by aging was found to have higher strength than other joints due to the uniform distribution of strengthening precipitates.

Erosion Resistance of Heat-treated Aluminum Cast Iron to Aluminum Alloy Melt

Erosion Resistance of Heat-treated Aluminum Cast Iron to Aluminum Alloy Melt

Precipitation Effects in Cast, Heat-Treated and Cold-Rolled Aluminium AA7075 Alloy with Sc,Zr-Addition

The commercial Al–Zn–Mg–Cu-based alloys (7xxx series) are widely used in metalworking, automotive and aircraft industries as well as in aeronautical applications. The positive effect of the Sc,Zr-addition on mechanical properties of laboratory Al-based alloys is generally known. The microstructure, mechanical and thermal properties of the conventionally cast, heat-treated and cold-rolled Al–Zn–Mg–Cu (–Sc–Zr) alloys during isochronal annealing and natural ageing were studied. Microstructure observation by scanning electron microscopy and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries. The distinct changes in microhardness curves as well as in a heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and precipitation of particles from the Al–Zn–Mg–Cu system. An easier diffusion of Zn, Mg and Cu atoms along dislocations in the cold-rolled alloys is responsible for the precipitation of the Zn,Mg,Cu-containing particles at lower temperatures compared to the cast alloys. Microhardness values of the heat-treated alloys increase immediately from the beginning of natural ageing due to the formation of the clusters/GP zones. Addition of Sc and Zr elements results in a higher hardness above ~ 270 °C due to a strengthening by coherent secondary Al3(Sc,Zr) particles with a good thermal stability. Sc,Zr-addition has probably no influence on the evolution of the solute clusters/GP zones.

Microstructural-micromechanical correlation in an Al–Cu–Mg–Ag–TiB2 (A205) alloy: additively manufactured and cast

In this paper, the processing-structure-property correlation of a high-strength titanium-modified aluminum-copper alloy, i.e., Al–Cu–Mg–Ag–Ti–B (A205), in the laser powder-bed fusion (LPBF) and casting conditions are studied. The as-fabricated and heat-treated materials were considered for this study. As A205 is a heat-treatable aluminum alloy, the effects of different post-fabrication heat-treatment processes, (i) solution heat-treatment (SHT: 520°C for 2 h) and (ii) over-aging and stabilizing treatment (T7), were also assessed. To test the stated relationship in LPBF and cast conditions depth-sensing indentation testing and extensive structural analyses were performed. The morphology and distribution of precipitates and nanoparticles in the microstructure were analyzed using optical, scanning electron, and transmission electron microscopy. The average nanoindentation hardness at as-fabricated, SHT, and T7 conditions are 1.48 ± 0.04, 1.50 ± 0.03, and 1.56 ± 0.06 GPa for the LPBF samples and 1.34 ± 0.04, 1.52 ± 0.10, and 1.72 ± 0.09 GPa for the cast samples. Detailed microstructural analyses confirmed the presence of precipitates and reinforced particles and revealed their morphology. The fine equiaxed grains with the average grain size of 1.1 ± 0.4 μm in the as-built condition highly enhanced the mechanical properties compared to the cast counter material, where the average grain size was measured as 46.4 ± 10.5 μm. Heat treatment played a more effective role on the cast samples and the strength of the cast material exceeded the LPBF material considerably after T7 treatment. This study offers a new compositional window for the additive manufactured lightweight high-strength material categories for various applications including automotive and aerospace industries. Besides, our findings demonstrate the significance of controlling the precipitates through the post-fabrication heat treatment processes.

Influence of Preheating Temperature on Changes in Properties in the HAZ during Multipass MIG Welding of Alloy AW 6061 and Possibilities of Their Restoration

Fusion welding of heat-treatable aluminum alloys is generally accompanied by a significant decrease in mechanical properties in the HAZ caused by the dissolution of the hardening phase. The intensity of this decrease in mechanical properties can be reduced by limiting the heat input value. However, this approach is in direct conflict with the principles for welding aluminum and its alloys. Due to the very high thermal conductivity of aluminum alloys, it is necessary to use preheating for thicknesses larger than 5 mm to eliminate non-penetration and cold joints. This paper aims to show the influence of multiple temperature cycles, performed at different preheating temperatures, on changes in the microstructure and mechanical properties. At the same time, the extent to which the original properties of the material can be restored by natural and artificial aging at 160, 175 and 190 °C is also investigated.

Effect of Carbonitriding on Tribomechanical and Corrosion-Resistant Properties of Friction Stir Welded Aluminium 2024 Alloy

Abstract Friction stir welding (FSW) is extensively used to join aluminium alloys components in space and aircraft industries. Al 2024 is a heat-treatable aluminium alloy with copper as the primary alloying element which has good strength and fatigue resistance. This paper investigates the effect of carbonitriding surface modification on the hardness, tensile strength and impact strength of FSW welded Al 2024 joints. The friction stir welding was performed on three different sets of aluminium alloy (Al2024:Al2024, Al2024: carbonitrided-Al2024, carbonitrided-Al2024: carbonitrided-Al2024) at two different tool rotation speed (TRS) and two welding speed using cylindrical pin tool. The carbonitriding pre-treatment of Al-2024 alloy demonstrated significant improvement in the tensile strength, percentage elongation, abrasion wear resistance and corrosion resistance with the sacrifice of impact strength. The maximum tensile strength of all three sets of samples after FSW was recorded in descending order of (i) carbonitrided-Al2024:carbonitrided-Al2024 (ii) Al2024:Carbonitrided-Al2024 and (iii) Al2024:Al2024. The friction stir welded joint of carbonitrided aluminium alloy exhibited best abrasive wear resistant and corrosion resistant properties.

Influence of B4C and industrial waste fly ash reinforcement particles on the micro structural characteristics and mechanical behavior of aluminium (Al–Mg–Si-T6) hybrid metal matrix composite

The expectations over composite materials have been increased especially in automotive and aerospace applications due to its high strength to weight ratio and good mechanical properties. Here, we aim to fabricate a hybrid composite of high strength and low density for automotive application to suits the above needs. In this investigation, the heat-treated aluminum alloy Al–Mg–Si-T6 was initially reinforced with industrial waste fly ash particles at five different weight fractions of 0%, 5%, 10%, 15% and 20%, respectively by stir casting process. The mechanical properties such as tensile strength, compression strength, hardness and density were tested, and microstructure of the composite was evaluated to explain the mechanical properties evolution. From the results, it was concluded that the composite with 10% fly ash shows enhanced at maximum the properties when compared to others. Then, the Al–Mg–Si-T6 – 5% fly ash was further reinforced with boron carbide particles by using three different fractions of 2.5%, 5% and 7.5%, respectively by stir casting process. The microstructural analysis, Scanning Electron Microscope analysis (SEM) and Energy Dispersive X-ray Spectroscopy analysis (EDS) were carried out for the casted samples to evaluate interfacial bonding, agglomeration, clustering and void formation in the hybrid composite samples. The casted samples were also tested for mechanical properties such as tensile strength, compression strength, hardness and density. It reveals that the optimal combination of 10% reinforcement (5% fly ash and 5% boron carbide) shows 18.7% higher tensile strength, 11.3% higher hardness and 38.6% higher compression when compared with the unreinforced Al–Mg–Si-T6 heat treated alloy. It is expected that the present hybrid metal matrix composites can be adopted for the fabrication of drive shaft in race cars.

Investigation of formability, microstructures and post-forming mechanical properties of heat-treatable aluminum alloys subjected to pre-aged hardening warm forming

Currently, the hot forming of aluminum alloys has garnered significant attention for overcoming poor formability at room temperature (RT). However, the current hot forming technique is facing problems such as time-consuming procedures and high economic cost. To improve forming efficiency, we herein propose a novel forming technique for heat-treatable aluminum alloys, termed pre-aged hardening warm forming (PHF) process. An Al–Zn–Mg–Cu alloy is used to investigate the flow behavior, drawing formability, and post-forming mechanical properties during the aforementioned process. Uniaxial tensile tests and Erichsen tests are conducted to evaluate the plastic flow behavior and drawability, respectively. Stamping tests are performed on a cap beam component to verify the engineering feasibility of the forming technique. Optical microscopy (OM) and transmission electron microscopy (TEM) are performed to characterize the microstructure evolution during the PHF process. The tensile test results show that the pre-aged alloys exhibit true fracture elongation similar to the fracture elongation of the O-temper alloy at RT, and that the Erichsen values of the pre-aged alloys are 5%–16% higher than that of the O-temper alloy at 200 °C. The results of the stamping tests for the cap beam component indicate that the optimal final strength of the stamped component achieves σ/σ0.2 = 566 MPa/500 MPa, exceeding the strength of the AA7075-T6 alloy. OM observations show that the stamping process does not significantly affect the grain sizes of the pre-aged alloys. TEM results show that numerous thermostable GPⅡ zones exist in the pre-aged alloys, and that the stamping procedure transforms the GPⅡ zones to dispersed η′ phases and results in the entanglement of numerous dislocations. The dual effects of phase transformation and plastic deformation during the PHF process contribute to the desirable mechanical properties of the stamped components.

Effect of precipitate coherency on the corrosion-induced hydrogen trapping in 2024 aluminum alloy

Hydrogen trapping is one of the factors leading to hydrogen embrittlement in heat-treatable high-strength aluminum alloys. The effect of coherency of precipitates on the corrosion-induced hydrogen trapping in aluminum alloy 2024 was investigated by performing artificial aging treatments before corrosion exposure. Two aging temperatures were employed, 170 and 210 °C, for aging times spanning the underaged, peak-aged and overaged conditions. Hydrogen uptake was induced by exfoliation corrosion. Hydrogen evolution from trapping sites was followed by thermal desorption spectroscopy. High resolution transmission electron microscopy combined with geometric phase analysis was performed to analyze the coherency of the precipitates. The results indicated that the coherency state between precipitates and the matrix plays an important role in hydrogen trapping. Hydrogen evolving at 300 °C (T2 state) corresponds to hydrogen trapped by the stress fields of coherent GPB zones and S΄΄ (Al10Cu3Mg3) phases, which form at aging temperatures, below the corresponding solvus temperature.

Observation of Portevin-le Chatelier effect in aluminum alloy 7075-w under a heterogeneous stress field

The kinetics of Portevin-Le Chatelier (PLC) bands in the hole-expansion of a circular hole using a flat-headed punch are investigated for a solid-solution heat-treated AA7075 aluminum sheet. This experiment is performed under quasi-static strain-rate and at room temperature. The full strain field in the hole periphery during the entire deformation is measured by a stereo-type digital image correlation system. The observations of PLC band activity are based on the thickness strain-rate field. Each individual PLC band appears aligning along the radial direction, spanning diverse stress states, and propagates along the circumferential direction during the life time from nucleation to dissipation. Furthermore, the nucleation sites of all the PLC bands are recorded during the experiment, which shows that the nucleation frequency of a PLC band is influenced by the plastic anisotropy, and that it increases proportionally to the level of thickness strain.

Heat Transfer Behavior During Water Spray Quenching of 7xxx Aluminum Alloy Plates

AbstractThe desired microstructure and mechanical properties of heat treatable 7xxx aluminum alloy can be achieved after spray quenching by controlling spray parameters. However, heat transfer behavior between specimen and quenchant is transient and complicated in quenching process. In this paper, a spray quenching system was utilized to quench for 7xxx aluminum alloy. The influence of spray parameters, including spray pressure and spray distance, on heat transfer behavior was examined and discussed. Heat flux (HF) and heat transfer coefficient (HTC) were calculated by iterative method. The results indicated that the aluminum alloy experienced transition boiling, nucleate boiling, and convection cooling regimes during spray quenching process. Heat transfer capability first increased and then decreased with the increasing of spray pressure or spray distance. A function of local heat transfer coefficient (L-HTC) which is variable in specimen surface temperature, spray parameters, and spatial location was constructed. Residual stress of 7xxx aluminum alloy plates was increased first and then slightly differed with the increase of volumetric flux.

Plastic behavior-dependent weldability of heat-treatable aluminum alloys in friction stir welding

The quality of friction stir welding joints is intimately related to the correct mixing of the stirred material. The material flow is strongly dependent on the plastic behavior of the welded alloy. For this reason, the friction stir weldability depends on the structure, microstructure, and chemical composition of the base material. In this work, in-plane forces and acoustic emission signals were monitored while welding two heat-treatable aluminum alloys. The force evolutions suggested possible continuous and intermittent material flow during friction stir welding depending on the welding parameters. The differences observed in the in-plane forces were corroborated by acoustic emission, confirming the modification in the material flow phenomenology. Therefore, differences observed in aluminum alloys’ friction stir weldability are due to the plastic behavior at high temperature and medium-high strain rate. The higher the deformability of the aluminum alloys, the wider the weldability window in friction stir welding because of continuous material flow in an extended range of process parameters.