Heat-treatable Aluminum Alloys Research Articles

Mechanical properties and microstructural evaluation of heat-treated aluminum alloy using formulated bio-quenchants

AbstractHeat treatment industries require various quenching media to improve the properties of the materials to be quenched. Petroleum based mineral (PBM) oil, a non-biodegradable oil, is popular amongst others quenchants in heat treatment processes. Recently, biodegradable oils mostly in their raw, unblended and unbleached forms have been employed for quenching of various engineering materials. Therefore, the present study examined the effects of some selected bio-quenchants in blended raw (BR) and blended bleached (BB) forms on the mechanical properties and microstructure of solution heat treated aluminum (Al)-alloy. Edible vegetable oil (70% by volume) was blended with 30% by volume of jatropha oil to form the bio-quenchant oils. Another set of bio-quenchants were formed by bleaching the raw oils before mixing so as to reduce the oxidation level and contaminations in the oil. The Al-alloy is solution heat treated at 500 °C and soaked for 15 min in an electric muffle furnace before quenching in the various established bio-quenchants. Results showed that samples treated in blended raw melon (BRM) oil have higher tensile strength of 151.76 N/mm2 while samples quenched in blended bleached melon (BBM) oil have higher hardness value of 61.00 HRC. In accordance to the results obtained the bio-quenchants were found to be effective replacement to the PBM oil.

Metallurgical assessment of AA7075 – T6 with x wt% tungsten carbide nanoparticle surface composites processed by FSP route

Our proposed research works the ideal way was to improve the aluminum alloy material lifetime by incorporating nanoparticle via friction stir processing (FSP) and it was evident from augmenting metallurgical view. The experimental work was carried out by varying tungsten carbide (WC) nanoparticles of 0, 3, 6 and 9 wt% with heat treated aluminium alloy (AA7075-T6) as a matrix through FSP route. The prepared samples were further assessing the metallurgical assessment through microstructure, scanning electron microscope, x-ray diffraction, energy dispersive spectroscopy and electron back-scattered diffraction analysis. The obtained results revealed that the homogeneous distribution of WC nanoparticles in the matrix stir zone having the absence of intermetallic reactions was observed in the microstructure and x-ray diffraction test. The significant degree of grain refinement was observed in the scanning electron microscopy in which composites due to dynamic recrystallization and pinning effect of tungsten carbide particles in the matrix has occurred. Energy dispersive x-ray spectroscopy analysis and scanning electron microscope analysis indicated the presence of tungsten carbide nanoparticles along the processed region in well-defined grain boundaries and its fine spread of grains across the stir zone by dynamic recrystallization. Also, the electron backscatter diffraction study indicated the good distribution of ceramic particles spread across the stir zone. On the whole, a great significance improvement was achieved in metallurgical behavior during the 9 wt% of WC nanoparticles addition in the matrix during the FSP route. These processed surface composites were suggested for automobile and marine components processed in the future.

Quantification of the chemical reactivity of molten nitrate salts with heat treatable aluminum alloys

This work explores the conditions for safe heat treatment of aluminum alloys containing lithium and magnesium in molten sodium nitrate (NaNO3) bath furnaces, and conditions where industrial accidents may occur. Using calorimetry coupled to classical thermodynamics, the strength of classical thermodynamics when analyzing thermal curves was demonstrated through a series of small-scale thermal analyses of various aluminum alloys in contact with sodium nitrate. This system was selected to illustrate reactions that may lead to severe and violent heat effect phenomena. Using idealized binary alloys, severe oxidation of magnesium- and lithium-rich aluminum alloy samples were shown to occur near 500 °C, a temperature range dangerously close to the operating temperature of solution heat treatment furnaces in manufacturing processes of heat treatable aluminum alloy sheets used in the aerospace industry. Commercial aluminum alloys AW257, 2198, 2024, and 1050 were also assessed with the same tools. The temperature that needed to be reached for these commercial aluminum alloys to react with molten sodium nitrate was significantly higher than the normal operating temperature of a conventional solution heat treatment furnace.

Influence of aluminium alloys relative positioning on dissimilar friction stir lap welds properties

Very thin sheets of heat treatable (AA6082-T6) and non-heat treatable (AA5754-H22) aluminium alloys were used to produce dissimilar joints by friction stir lap welding. Joint strength and mechanical heterogeneity were assessed by performing lap tensile-shear and microhardness testing, respectively. Optical microscopy was used to analyse the weld morphology. Welding machine outputs, such as torque and axial force, were analysed in order to capture differences in the alloys strength during dissimilar welding. From the process outputs analysis, it was concluded that higher Z-Forces were necessary while positioning the AA5754 alloy at the top of lap configuration, indicating that this alloy offered higher resistance to the tool stirring than the AA6082 alloy. These results were associated with the flow softening of the AA6082 alloy during welding, which was explained using finite element analysis to illustrate the welding thermal cycles and the precipitation behaviour of this alloy. The lap welds defect formation was also related to the base materials plastic properties at high temperatures, which was inferred from process outputs data analysis. Based on the results it was shown that the lap welds defects might be supressed by a proper positioning the dissimilar base materials in the lap joint.

Experimental investigation on corrosion behavior of friction stir welded AA7075-T651 aluminium alloy under 3.5% wt NaCl environment

The corrosion resistance of high strength heat treatable aluminium alloy is able to form an oxide film on its surface. In aggressive corrosion media, the oxide film can undergo corrosion responses in chloride-containing environments. The welding of AA7075 is important for advanced structural application in aircraft and automotive industries. Friction Stir Welding (FSW) method is the new technique and a sound welding method in the aluminium industry, which overcomes solidification cracking problem compared to the conventional fusion welding technique. Rolled plates of 10 mm thickness of AA7075-T651 were butt welded by using FSW process. The corrosion surface morphology and behaviour were investigated by conducting a salt fog test in sodium chloride solution at various spraying time, chloride ion and pH value. An objective was initiated to extend an experimental relationship to predict the corrosion rate of stir zone of FSW AA7075-T651 joints. Three factors five levels of a centre rotatable matrix was used to reduce the number of experimental circumstances and response surface methodology was used to develop an empirical relationship between salt fog variables. The empirical model can be used to predict the corrosion rate of FSW AA7075-T651 joints.

Modeling and Optimization of the Yield Strength and Tensile Strength of Al7075 Butt Joint Produced by FSW and SFSW Using RSM and Desirability Function Method

Friction stir welding (FSW) is introduced as a solid-state welding process. Despite the many benefits of the FSW, the effects of the thermal cycles in this process are causing softening of the joint. This phenomenon generally occurs in heat-treatable aluminum alloys and results in reduced mechanical properties of the joint. To solve this limitation, submerged friction stir welding (SFSW) has been developed which is suitable for welding of heat-sensitive alloys. In this study, 31 butt joints were first produced from Al7075-T6 using the FSW. For this purpose, the response surface methodology was selected as the design of experiments method, and the variables: tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were determined as the input variables. Then, the statistical analysis of the parameters affecting the yield strength and tensile strength of the joints was investigated. Then, 10 joints were produced using the SFSW based on the optimal values of the tool feed rate and tool tilt angle. Results of the ANOVA and regression analysis of the experimental data confirmed the accuracy and precision of regression equations and showed that the linear, interactional and quadratic terms of tool shoulder diameter and tool rotational speed effect on the yield strength and ultimate tensile strength of submerged joints. Also, the optimal conditions of input variables were determined by the desirability method and confirmed by the verification test.

A new approach for dissimilar aluminum-steel impact spot welding using vaporizing foil actuators

Abstract Dissimilar joining of aluminum to steel is an important industrial and academic problem. The present study reports the application of a novel approach in impact welding where a pocket machined on the flyer sheet generates the requisite standoff, enabling joining of commonly used automotive aluminum alloys to high-strength low-alloy (HSLA) steels. The new approach enables impact spot welding of heat treatable AA6111-T4 aluminum (Al) alloy to bare, hot-dip galvanized and e-coated HSLA 340 steel (with local removal of the coating on the faying surface) as well as of high-pressure vacuum die cast Aural 2 Al alloy to hot-dip galvanized HSLA 340 steel. Characterization of the welded samples via lap-shear and coach peel testing demonstrated high joint strengths with button pullout failure modes in all weld pairs. Optical microscopy of the weld cross-sections revealed defect-free joints displaying typical impact welded interface morphology. A significant outcome of the novel impact spot welding approach was the ability to produce joints exhibiting flat external target surfaces with unperturbed coating, a potential enabler for mixed metal joining applications involving pre-treated, e-coated, or painted materials.

Investigation of the influence of heat treatment of aluminum alloy on its structure and properties

The paper considers the issue of improving the quality of aluminum alloys of the D16 type, based on the data performed at the Department of “Physical and applied materials science” within the framework of the contract on samples of the Belokalitvensky metallurgical combine. The influence of the composition and technology on the structure and mechanical properties was studied. A recommendation for optimizing the composition and structure was developed and based on the analysis of phase diagrams, the microstructures of the alloy were justified.

Aging behaviour of hot deformed AA7075 aluminium alloy

Structural applications where durability i.e. strength to weight ratio is primary requisite, ferrous materials need to be substituted with materials having similar properties. Thus, nonferrous materials such as titanium, magnesium and aluminium and their alloys are considered to be substituted of steels. But, non-availability of magnesium and titanium being costlier, aluminium and its alloys are considered to be the most important one for replacing existing ferrous materials. Heat treatable AA7075 aluminium alloy is considered as one of the aluminium alloys for researchers common interest because of its strength is comparable to that of steels and widely used in automobile, aircraft industries and naval applications. Most of the investigations are focused on aging behaviour, re-aging and RRA (retrogression and re-aging) features of AA 7075 aluminium alloy but scanty of literature is available in the domain of aging behaviour of hot deformed AA 7075 aluminium alloy. Thus, present investigation aims at hot deformation and aging of deformed AA aluminium 7075 alloy at various temperatures such as 300 °C, 400 °C and 500 °C. Deformation of the order of 40% is recommended irrespective of forming temperature. All the deformed samples exhibited improvement in hardness while comparing to base metal and there is a successive increment of hardness with gradually increase of percentage of deformations. It might be attributed to high morphological modification like microstructural refinement, densification and homogenization accomplished during mechanical deformation which led to yield higher hardness. Hot deformation temperature of 400 °C and aging temperature. of 400 °C is recommended for AA 7075 aluminium alloy for both altering dimension and mechanical properties.

Flow stress of 2024 aluminum alloy during multi-directional forging process and natural aging after plastic deformation

The hardening behavior of heat treatable alloys during deformation is attributed to three mechanisms of forest dislocations, solid solution and precipitation hardening which hinder the motion of dislocations and increase the density of statistically stored dislocation. In this paper, a model for the flow stress of a 2024 heat treatable aluminum alloy during plastic deformation is developed combining the superposition of these three hardening mechanisms. This model was then implemented into the finite element model in order to evaluate the evolution of the flow stress of 2024 aluminum alloy during multi-directional forging (MDF). Subsequently, an equation is developed for evaluating the material strength changes during natural aging after MDF. The experimental results from compression and hardness tests show a good agreement between modeling and experimental data. The results show that the flow stress is increased about 90% after the first pass of MDF and then increased just about 2% after the second pass. Through natural aging process, the hardening rate is higher in non-deformed samples and is decreased with increasing the aging time.

Effects of Refill Friction Stir Spot Weld Spacing and Edge Margin on Mechanical Properties of Multi-Spot-Welded Panels

Refill friction stir spot welding (RFSSW) is an emerging technology for joining aerospace aluminum alloys. The aim of the study is to investigate the effects of the refill friction stir spot weld spacing and the edge margin on the mechanical properties of multi-spot-welded AA7075-T6 panels. AA7075-T6 is a baseline aerospace aluminum alloy used in aircraft structures. The study employs an innovative robotic RFSSW system that is designed and developed by Kawasaki Heavy Industries (KHI). The experimental strategy uses Design of Experiments (DoE) to characterize the failure loads of multi-spot-welded panels in terms of the spot weld spacing, edge margin, and heat-affected zone (HAZ) of the spot weld. The RFSSW process leaves behind a thermal “imprint” as HAZ in heat-treatable aluminum alloys. According to the DoE results, larger spot weld spacings with no HAZ overlap produce higher failure loads of multi-spot-welded panels. On the other hand, edge margins that are equal to or less than the spot weld diameter demonstrate abnormal plastic deformations, such as workpiece edge swelling and weld crown dents, during the RFSSW process. The larger edge margins do not demonstrate such abnormal deformations during the welding process.

Mn and Mo additions to a dilute Al-Zr-Sc-Er-Si-based alloy to improve creep resistance through solid-solution- and precipitation-strengthening

Compressive creep experiments were utilized to investigate the influence of small additions of 0.25 at.% Mn and 0.10 at.% Mo on the creep resistance of a cast Al-0.08Zr-0.02Sc-0.01Er-0.10Si at.% alloy. The Mn- and Mo-modified alloy displays significantly enhanced creep resistance at 300 and 400 °C, due to solid-solution strengthening and the formation of two types of precipitates: Al3(Zr,Sc,Er)(L12)-nanoprecipitates and α-Al(Mn,Mo)Si submicron platelets or cuboidal-shaped precipitates. The creep threshold stresses at 300 and 400 °C are 37 and 24 MPa, respectively, versus 19 and 15 MPa for the unmodified alloy. At 300 °C, the creep exponent n is found to change from 4.4 in the base alloy, to 3 in the modified alloy, consistent with a change from climb- to glide-controlled dislocation creep. The Mn- and Mo-modified alloy exhibits an as-cast grain-structure, which is finer (~0.35 mm versus 0.6 mm) and more equiaxed grains than the unmodified alloy, which is anticipated to enhance deformation by diffusional-creep. Nevertheless, diffusional-creep resistance at 400 °C remains high for the modified alloy, due to precipitation of submicron α-Al(Mn,Mo)Si-precipitates at grain boundaries (GBs). At 400 °C, the diffusional creep threshold-stress is ~14 MPa, three times that of the unmodified alloy, which also display fewer and coarser Al3(Zr,Sc,Er)(D023) precipitates at GBs. Creep resistance in the modified alloy does not deteriorate after 16 days of stress testing at 400 °C, highlighting the excellent coarsening resistance of the L12- and α-precipitates. This new castable, heat-treatable aluminum alloy therefore represents an important technological advance for utilization at higher temperatures under stress.

Microstructural origins of mechanical and electrochemical heterogeneities of friction stir welded heat-treatable aluminum alloy

In the present work, microstructural heterogeneities of friction stir welded EN AW 6082-T6 aluminum alloy were revealed with the help of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrochemical heterogeneities of the welded joint was probed by electrochemical corrosion potential measurements. Microhardness and tensile tests were used to reflect heterogeneities in mechanical properties. The peak temperature and thermal cycles were examined and simulated during welding. The results showed that the heterogeneity of mechanical properties was determined by the nano-sized precipitates, while had little relationship with the micro-sized and submicro-sized deposits. The tensile fracture path was located at the minimum hardness zone where the β′′ precipitates have completely transformed to the β′ precipitates. Electrochemical experiments revealed that the corrosion potential was not homogeneous across the welded joint. The heterogeneity of corrosion performance was determined by the micron-sized excessive Si phase. In addition, the effect of nano-sized precipitates on the corrosion performance was attributed to the change in the solubility of the Si content in the Al matrix resulted from the precipitation, dissolution and transformation of the precipitated phase in HAZ.

Correlations and Scalability of Mechanical Properties on the Micro, Meso and Macro Scale of Precipitation-Hardenable Aluminium Alloy EN AW-6082

The mechanical properties of heat-treatable aluminium alloys are improved and adjusted by three different heat treatment steps, which include solution annealing, quenching, and aging. Due to metal-physical correlations, variations in heat treatment temperatures and times lead to different microstructural conditions with differences in the size and number of phases and their volume fraction in the microstructure. In this work, the investigations of the correlation between microhardness measurements on micro samples and the conventional mechanical properties (hardness, yield strength and tensile strength) of macro samples and the comparability of the different heat treatment states of micro and macro samples made of a hardenable aluminium alloy EN AW-6082 will be discussed. Using the correlations between the mechanical properties of micro samples and macro samples, the size of the samples and, thus, the testing cost and effort can be reduced.

Solidification and heat treatment simulation for aluminum alloys with scandium addition through CALPHAD approach

Scandium, and scandium combined with zirconium, improves multiple properties of aluminum based alloys. In this work, we performed solidification and heat treatment simulations for studying precipitation kinetics of Al3Sc crystals within the framework of CALPHAD approach on novel candidate alloy compositions from our previous work belonging to 2XXX, 6XXX and 7XXX class of aluminum alloys. In our previous work, computational study was performed on stability of various stable and metastable phases along with thermodynamically stable Al3Sc phase in heat-treatable aluminum alloys of 2XXX, 6XXX and 7XXX series by application of several concepts of artificial intelligence on phase stability data generated under the framework of CALPHAD approach. We considered 12 elements for 2XXX, 10 elements for 6XXX and 11 elements for 7XXX class of alloys, thus selected a comparatively large multicomponent system when compared to works reported on aluminum alloys through CALPHAD approach. In 2XXX and 7XXX series, both Sc and Zr were included, while in 6XXX series only Sc was added. Software Thermocalc was used to generate phase stability data. For proper precipitation of Al3Sc crystals during heat treatment, it is important that Al3Sc is present in the melt. Hence, solidification simulation (Scheil–Gulliver) was performed, followed by heat treatment simulation at various temperatures for a few candidate alloys belonging to these three series of aluminum alloys with Sc added. Additional strengthening phases were also considered in aluminum base alloys of these three series in our previous work. The presented computational approach can be useful and can be used as a screening tool for selecting a chemical composition and heat treatment protocol prior to performing experiments.

An Overview on Forming Process and Heat Treatments For Heat Treatable Aluminium Alloy

An Overview on Forming Process and Heat Treatments For Heat Treatable Aluminium Alloy

The Influence of Cryogenic Conditions on the Process of AA2519 Aluminum Alloy Cracking.

This study presents the results of tests involving determining quantities used to describe fracture toughness of a heat-treated AA2519 aluminum alloy applied in, among other things, constructing American military amphibians. These quantities were determined using the J–R curve method for two temperature values, 293 K and 77 K. The low temperature was provided by putting the tested specimen into a liquid nitrogen bath and keeping it there throughout the experiment. Based on the tests results, cryogenic conditions cause an increase in the maximum experimental value of the J–JQ integral, from 66.3 to 87.3 kJ/m2 Moreover, an analysis of the fatigue fracture microstructure revealed differences between specimens tested in ambient temperature and those tested in cryogenic temperature.

Art of friction stir welding to produce weld joint without rotation of shoulder with narrow heat-affected zone and high corrosion resistance

ABSTRACT This present study uses an indigenously designed non-rotating shoulder friction stir welding (NRSFSW) tool to weld AA2014 aluminium alloy. This tool is harnessed with a penetrated material removal mechanism. Generally, the heat-affected zone (HAZ) is the most severely affected region in the conventional FSW (CFSW) joint of heat-treatable aluminium alloys. The prime novelty of this work is to reduce the width of most corrosion susceptible region of the FSW joint using a non-rotating shoulder tool. The corrosion behaviour of the NRSFSW joint has been investigated and compared to the CFSW joint. The NRSFSW tool resulted in focused heat input which eventually reduced the width of the HAZ and improved corrosion resistance as compared to the CFSW tool.

Flexural capacity of perforated aluminium CHS tubes–An experimental study

This paper presents the results of twelve experimental tests on the flexural capacity of perforated aluminium circular hollow section (CHS) tubes; four of which were carried out without perforations. Two heat-treated aluminium alloys were used: 6061-T6 and 6063-T5. The tests covered the size and number of perforations. The flexural capacity, failure modes, and the distribution of strains around circular perforations were determined. The experimental results were then compared against the design strengths calculated from the North American Specification (NAS) for cold-formed steel (CFS) sections with perforations, derived from modified Direct Strength Method (DSM) and modified Continuous Strength Method (CSM) for aluminium alloy members with perforations, which were found to be conservative by approximately 23%, 27% and 22%, respectively. When strength reduction factors were applied, and the unified design equations proposed by Zhou and Young were used, the reduction in strength was 6% conservative to the test strengths.

Investigation on Microstructure and Mechanical Properties of Solution Heat-Treated and Multi Directional Forging-Processed LM-25 Aluminium Alloy

The experimental study of hypoeutectic Al-7.3Si alloy on microstructure and mechanical properties processed by MDF at room temperature was reported in this paper. A commercial LM-25 aluminium alloy ingot was melted in an electric casting furnace and poured into a preheated rectangular casting die. The samples were then solutionized for 10 h at 535 °C and quenched in water for MDF processing. Microstructure analysis of the samples was done with the help of optical microscopy and scanning electron microscopy. Microstructural observation of MDF processed up to six passes sample showed that coarse eutectic silicon particles with an average length of 16 µm are effectively broken into fine particles with an average length of 4 µm and uniformly distributed in aluminium phase. After six passes, UTS of as-cast specimen is increased from 177 to 441 MPa and microhardness is increased from 75 to 127 Hv. XRD analysis of the samples confirmed the presence of Al phase and eutectic Si phase. Therefore, modification of eutectic Si particle with Al phase refinement has been demonstrated to be a very important factor for enhancing mechanical properties of aluminium–silicon alloy.