Non-heat Treatable Aluminium Alloy Research Articles

Precipitation strengthening and thermal stability in a conventionally non-heat treatable AA3xxx aluminium alloy

We report an unexpected yet significant precipitation-strengthening effect with remarkable thermal stability in an otherwise conventionally non-heat treatable AA3104 aluminium alloy. We reveal that a minor addition of Cu plays a critical role in the alloy's strength and thermal stability, and explain the underpinning mechanisms. The primary strengthening β′ phase can be engineered to exhibit distinctive structural characteristics, including regularly-spaced Cu atom columns at the coherent β′/Al interfaces, stacking faults and resultant domains. Our atomistic simulations rationalise that these microscopic characteristics are directly promoted by the Cu addition. The Cu-decorated interfaces promote β′ phase nucleation and result in strong, directional covalent-like Cu-Si bonding at the β′/Al interfaces. Specifically, the interfacial Cu columns increase the work of separation of the habit-plane interfaces and reduce the interface energy, resulting in significant strengthening and stabilising effects. The Cu columns also facilitate the stacking fault formation in the β′ phase. Collectively, these features enhance the strengthening effect and thermal stability of the precipitates. This study demonstrates the potential for exploring "new" features in "old" alloys to advance alloy science and technology.

Shoulder Related Temperature Thresholds in FSSW of Aluminium Alloys.

Friction Stir Spot Welding (FSSW) is assumed as an environment-friendly technique, suitable for the spot welding of several materials. Nevertheless, it is consensual that the temperature control during the process is not feasible, since the exact heat generation mechanisms are still unknown. In current work, the heat generation in FSSW of aluminium alloys, was assessed by producing bead-on-plate spot welds using pinless tools. Coated and uncoated tools, with varied diameters and rotational speeds, were tested. Heat treatable (AA2017, AA6082 and AA7075) and non-heat treatable (AA5083) aluminium alloys were welded to assess any possible influence of the base material properties on heat generation. A parametric analysis enabled to establish a relationship between the process parameters and the heat generation. It was found that for rotational speeds higher than 600 rpm, the main process parameter governing the heat generation is the tool diameter. For each tool diameter, a threshold in the welding temperature was identified, which is independent of the rotational speed and of the aluminium alloy being welded. It is demonstrated that, for aluminium alloys, the temperature in FSSW may be controlled using a suitable combination of rotational speed and tool dimensions. The temperature evolution with process parameters was modelled and the model predictions were found to fit satisfactorily the experimental results.

Mechanical Properties and Microstructural Characterization of Dissimilar Friction Stir Welded AA5083 and AA6061 Aluminium Alloys

Solidification is one of the major issues that was faced during the fusion welding of dissimilar non-heat treatable and heat treatable aluminium alloys. To overcome this issue Friction Stir Welding played a very vital role, since it is a solid state welding process. In the current study, dissimilar friction stir welding was carried out between non heat-treatable aluminium alloy AA5083-H111 and heat-treatable aluminium alloy AA6061-T6. The microstructural analysis and the mechanical properties of the dissimilar friction stir welded aluminium alloy AA5083-H111 and AA6061-T6 have been investigated. Both optical microscopy and scanning electron microscopy was used to evaluate the microstructural features. The elemental analysis was carried out using SEM-EDX. The tensile properties are studied using Universal Testing Machine. Hardness at various zones of the welded joints was measured using Vicker’s Hardness Testing Machine. The mechanical properties of the friction stir welded joints were correlated with the microstructure of the dissimilar welded joints.

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.

Investigation of the microstructure, mechanical and wear properties of AA6061-T6 friction stir weldments with different particulate reinforcements addition

Welding of heat-treated AA6061-T6 often results in mechanical and wear properties deterioration because of the dissolution of the strengthening precipitates at the joint. Enhancement of these properties has been accomplished for non-heat treatable aluminium alloys through the addition of reinforcement particles in the joint. However, its application to AA6061-T6 is scarce. In this work, the microstructure, hardness and wear resistance of AA6061-T6 friction stir welded joints reinforced with SiC, B4C and Al2O3 particles were investigated while the base metal and the unreinforced welded joint were utilised as the control. Aluminium matrix grains refinement which improved with increased particle distribution homogeneity occurred in the entire welded joints. All the reinforced welded joints showed improvements on the unreinforced joint in terms of hardness and wear resistance because of the particles high hardness and substantially increased grain refinement that occurred in the reinforced welded joints. Due to B4C extremely high hardness and homogeneous distribution in the joint, B4C reinforced joint exhibited the highest improvements in hardness (˜42%) and wear rate (˜67%) at low-load condition. However, at high-load condition, SiC followed by the Al2O3 reinforced joints showed the least wear rate even lower than the base metal. The matrix hardness significantly influenced the wear performance at low-load but the overall effects of the reinforcement particles were predominant at high-load condition. The reinforcements’ additions reduced the wear rate of the welded joint by up to a factor of ˜1.7 and ˜1.9 at low and high load conditions respectively.

Influence of melting current pulse duration on microstructural features and mechanical properties of AA5083 alloy weldments

The formation of intermetallic particles and dislocation structure play a vital role in strengthening aspects of non-heat treatable aluminium alloy weldments. In this work, the effect of melting current pulse duration (McT) on grain boundary characteristics, dislocation structure, size and distribution of intermetallics on AA5083-H111 aluminium alloy weldments processed by pulsed gas tungsten arc welding are investigated. The mechanical responses of the weldments are evaluated by impression creep test, tensile test and microhardness measurements. The results suggest that at both lower and higher current level, the use of shorter McT (40%) had retained a considerable amount of Mg at fusion zone and assisted in nucleation of β-phase precipitates at various sites of grain boundaries whereas the change in McT from 40% to 60% produced grain boundaries free of β-phase precipitates. Also, the longer McT (60%) at a lower current level produced rod-like finer (~50–400 nm) Mn-rich intermetallics at grain boundaries and distributed uniformly at grain interiors. It caused a rise in activation energy which leads to an increase in pinning pressure during plastic deformation and resulted in higher tensile strength and creep resistance. In contrast, the longer McT (60%) at a higher current level encouraged the formation of plate-like coarser (~527 nm length and 419 nm width) Mn-rich intermetallics at random locations allowed the grain boundaries to slide at various points during deformation and resulted in lower mechanical properties. This study shows that the change in McT caused significant variations in mechanical properties by altering the microstructural features of weldments.

Effect of fusion welding processes on tensile properties of armor grade, high thickness, non-heat treatable aluminium alloy joints

Abstract AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.

Determination of solid solution composition in Al alloys by electrical transport properties measurement and XRD method

The non-heat treatable aluminium alloys usually need homogenization before hot rolling to decrease the inhomogenities. In the process the segregations are dissolving and small precipitations are forming. The progress of the processes strongly depend on the temperature and the duration of the heat treatment. Topic of the research was to describe the dissolution/precipitation processes during the heat treatment. It was carried out by two different methods. Using electrical transport properties (resistance and thermo-power) measurement the percentage of the dissolved elements were calculated, and by X-ray diffraction method the cumulative effect was determined through lattice parameter change. The results of the methods were compared regarding to the heat treatment parameters.

Investigation of Mechanical and Metallurgical Properties of Friction Stir Corner Welded Dissimilar Thickness AA5086-AA6061 Aluminium Alloys

In this investigation, an attempt has been made to fabricate dissimilar thickness corner joint using non-heat treatable (AA5086) and heat treatable (AA6061) dissimilar aluminium alloys by friction stir welding process with plate thicknesses of 6mm and 4mm. Three parameters and three levels were considered to conduct the experiments such as welding and rotational speeds of 100, 150 and 190 mm/min and 900, 1000 and 1100 rpm and plunge depth of 0.1, 0.2 and 0.3 mm. The mechanical properties were evaluated using hardness and tensile tests. Taguchi grey relational analysis was carried out to determine the optimum process parameters. The higher value of tensile strength was obtained 192 MPa at rotational and welding speeds of 1000 rpm and 150 mm/min which was 76.80% of parent material and maximum hardness was 157 HV at thermomechanically affected zone for the rotational speed of 1100 rpm and hardness at stir zone was maximum because of refined grain formation. The microstructures of various regions were observed and analyzed by optical and scanning electron microscopes. The tensile samples fractured at the heat affected zone. The spindle motor current consumption, work material temperature distribution, and force generation during friction stir welding were estimated and analyzed.

Influence of the Aluminium Alloy Type on Defects Formation in Friction Stir Lap Welding of Thin Sheets

Abstract The weldability in Friction Stir Lap Welding (FSLW) of heat and non-heat treatable aluminium alloys, the AA6082-T6 and the AA5754-H22 aluminium alloys, respectively, are compared. For both alloys, welds were produced in very thin sheets, using the same welding parameters and procedures, and strong differences in welds morphology were found. The strength of the welds was evaluated by performing tensile-shear tests under monotonic and cyclic loading conditions. As-welded and heat-treated samples of the AA6082- T6 were tested. It was found that the heat-treatable alloy is more sensitive to defects formation, in lap welding, than the non-heat-treatable alloy. The presence of defects has a strong influence on the monotonic and fatigue behaviour of the welds. In spite of this, for very high-applied stresses, the heat-treatable alloy welds perform better in fatigue than the non-heat-treatable alloy welds.

Weldability of AA 5052 H32 aluminium alloy by TIG welding and FSW process – A comparative study

Aluminium 5xxx series alloys are the strongest non-heat treatable aluminium alloy. Its application found in automotive components and body structures due to its good formability, good strength, high corrosion resistance, and weight savings. In the present work, the influence of Tungsten Inert Gas (TIG) welding parameters on the quality of weld on AA 5052 H32 aluminium alloy plates were analyzed and the mechanical characterization of the joint so produced was compared with Friction stir (FS) welded joint. The selected input variable parameters are welding current and inert gas flow rate. Other parameters such as welding speed and arc voltage were kept constant throughout the study, based on the response from several trial runs conducted. The quality of the weld is measured in terms of ultimate tensile strength. A double side V-butt joints were fabricated by double pass on one side to ensure maximum strength of TIG welded joints. Macro and microstructural examination were conducted for both welding process.

Extension of the Mechanical Threshold Stress Model to Static and Dynamic Strain Aging: Application to AA5754-O

Based on the mechanical threshold stress model and the visco-plastic self-consistent algorithm, a modified constitutive model is developed to model static strain aging and dynamic strain aging for application to a non-heat treatable aluminum alloy, AA5754-O. The implementation is based on a combination of the evolution of dislocation density and the effect of solutes on both mobile dislocations and forest dislocations. Using this model, the stress–strain behavior of AA5754-O is simulated in multi-path, multi-temperature, and variable strain rate tensile tests. The low temperature and strain rate sensitivities of the modified mechanical threshold stress model in the dynamic strain aging regime are successfully accounted for. The results show quantitative agreement with experimental data from multiple sources.

Improvement in Material Flow During Nonisothermal Warm Deep Drawing of Nonheat Treatable Aluminum Alloy Sheets

Automotive industries are very much interested in implementing warm forming technology for fabrication of light weight auto-body panels using aluminum alloys without localized thinning or splitting. A nonheat treatable and low formable AA5754-H22 aluminum alloy sheet was selected in the present work, and a laboratory scale warm deep drawing test set-up and process sequences were designed to improve material flow through independent heating of punch and dies. Significant enhancement in cup depth was observed when the temperature of punch and dies were set to 30 °C and 200 °C, respectively. Thermo-mechanical finite-element (FE) model of the nonisothermal deep drawing test was developed successfully to study the improvement in material flow incorporating Barlat-89 yield theory using temperature dependent anisotropy coefficients and Cowper–Symonds hardening model. It was found that a nonisothermal temperature gradient of approximately 93 °C was established within the blank from the center to flange at the start of deformation, and subsequent evolution of temperature gradient helped in improving material flow into the die cavity. The effect of temperature gradient on forming behavior in terms of cup height, ear profile, and thinning development across flange, cup wall, and blank center were predicted and validated with experimental results.

Chronicling the Development of a High Strength 5xxx-Based Superplastic Aluminium Alloy

In recent years there has been a largely unspoken demand for a high strength, non-heat treatable aluminium alloy for superplastic forming applications. This is particularly true for the automotive industry since the high strength, superplastic aluminium alloys, such as AA7475, are both too time consuming (in forming and heat treatment) and too expensive. Compound this with the expense of corrosion protection and almost all aluminium alloys except for AA5083 fall by the wayside for the automobile industry.However, the need for a higher strength alloy has remained. To achieve this Hydro has systematically investigated the basis behind the superplastic forming of AA5083. On this basis a new high strength 5xxx alloy was extrapolated. The resulting alloy was then characterised and benchmarked against the existing SPF alloy, AA5083. The new alloy, an AA5456-type alloy demonstrated a higher strength than AA5083 while improving the formability and rate of forming. This paper will discuss some of the lessons learned during the development of this alloy.

Dissimilar friction stir lap welding of AA 5754-H22/AA 6082-T6 aluminium alloys: Influence of material properties and tool geometry on weld strength

Abstract Dissimilar friction stir welding (FSW) of heat (AA 6082-T6) and non-heat (AA 5754-H22) treatable aluminium alloys, in lap joint configuration, was performed in this work. The base material plates were 1 mm thick. Welds were performed combining different plates positioning, relative to the tool shoulder, in order to assess the influence of base materials properties on welds strength. Three different tools were tested, one cylindrical and two conical, with different taper angles. Welds strength was characterized by performing transverse and tensile–shear tests. Strain data acquisition by Digital Image Correlation (DIC) was used to determine local weld properties. The results obtained enabled to conclude that the dissimilar welds strength is strongly dependent on the presence of the well-known hooking defect and that the hooking characteristics are strongly conditioned by base materials properties/positioning. By placing the AA 6082-T6 alloy, as top plate, in contact with the tool shoulder, superior weld properties are achieved independently of the tool geometry. It is also concluded that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the most suitable solution for the production of welds with similar strengths for advancing and retreating sides.

A study to estimate the tensile strength of friction stir welded AA 5059 aluminium alloy joints

Friction stir welding (FSW) is an important welding technique where in, and optimizing the process parameters will improve the joint strength of the welds. The FSW process and tool parameters play a major role in determining the joint strength. In this paper, an attempt has been made to establish an empirical relationship between the FSW process parameters (rotational speed, welding speed, and axial force) and predicting the maximum tensile strength of the joint. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the relationships. A non-heat treatable aluminum alloy Aluminium Association 5059 of 4 mm thickness was used as the base material. Response surface methodology is employed to develop the mathematical model. Analysis of variance technique is used to check the adequacy of the developed mathematical model. The developed mathematical model can be used effectively at 95 % confidence level. The effect of FSW process parameter on mechanical property of Aluminium Association 5059 aluminum alloy has also been analyzed in detail.

Effect of tool pin profile on microstructure and tensile properties of friction stir welded dissimilar AA 6061–AA 5086 aluminium alloy joints

Abstract Joints between two different grades of aluminium alloys are need of the hour in many light weight military structures. In this investigation, an attempt has been made to join the heat treatable (AA 6061) and non-heat treatable (AA 5086) aluminium alloys by friction stir welding (FSW) process using three different tool pin profiles like straight cylindrical, taper cylindrical and threaded cylindrical. The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscope. The tensile properties and microhardness were evaluated for the welded joint. From this investigation it is founded that the use of threaded pin profile of tool contributes to better flow of materials between two alloys and the generation of defect free stir zone. It also resulted in higher hardness values of 83 HV in the stir zone and higher tensile strength of 169 MPa compared to other two profiles. The increase in hardness is attributed to the formation of fine grains and intermetallics in the stir zone, and in addition, the reduced size of weaker regions, such as TMAZ and HAZ regions, results in higher tensile properties.

Microstructure and tensile properties of friction stir welded dissimilar AA6061–AA5086 aluminium alloy joints

The fusion welding of dissimilar heat treatable and non-heat treatable aluminium alloy faced many problems related to solidification. The difficulties can be overcome to achieve the combined beneficial properties of both aluminium alloys using friction stir welding (FSW). The microstructural features and tensile properties of friction stir welded (FSW) similar and dissimilar joints made of AA6061 and AA5086 aluminium alloys were investigated. The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscopy. Microhardness was measured at various zones of the welded joints. The tensile properties of the joints were evaluated and correlated with the microstructural features and microhardness values. The dissimilar joint exhibits a maximum hardness of HV 115 and a joint efficiency of 56%. This was attributed to the defect free stir zone formation and grain size strengthening.

Experimental investigation of Microstructure and Mechanical properties of TIG welded Aluminium alloys

Aluminium and its alloys are used in fabrication because of their low weight, good corrosion resistance and weldability. Pure aluminium is soft and therefore not suitable for structures, which require strength. The Present investigation aims to compare the mechanical properties of non-heat treatable Aluminium alloy AA5083 and heat treatable. Aluminium alloy AA7020 using Tungsten Inert Gas welding. 5556A filler were used to weld AA7020 alloy and 5183A filler for AA5083 alloy. Effect of pulsing mode over conventional mode of GTA process were also investigated for AA5083 alloy. In this work, gas tungsten arc welding process has been selected because it is low heat input process. Low heat input process has selected because AA7020 and AA5083 were low melting point material. The alternating current (AC) power source has been selected because of better cleaning action and high heat concentration on the materials can be avoided. Mechanical testing like tensile test, impact test, bend and hardness test have been critically analysed and the properties were summarized and correlating with microstructure and SEM fractographs.

Experimental Investigation of Microstructure and Mechanical Properties of TIG Welded Aluminium Alloys.

Aluminium and its alloys are used in fabrication because of their low weight, good corrosion resistance and weldability. Pure aluminium is soft and therefore not suitable for structures, which require strength. The Present investigation aims to compare the mechanical properties of non-heat treatable Aluminium alloy AA5083 and heat treatable. Aluminium alloy AA7020 using Tungsten Inert Gas welding. 5556A filler were used to weld AA7020 alloy and 5183A filler for AA5083 alloy. Effect of pulsing mode over conventional mode of GTA process were also investigated for AA5083 alloy. In this work, gas tungsten arc welding process has been selected because it is low heat input process. Low heat input process has selected because AA7020 and AA5083 were low melting point material. The alternating current (AC) power source has been selected because of better cleaning action and high heat concentration on the materials can be avoided. Mechanical testing like tensile test, impact test, bend and hardness test have been critically analysed and the properties were summarized and correlating with microstructure and SEM fractographs.