Evaluation of crack nucleation site and mechanical properties for friction stir welded butt joint in 2024-T3 aluminum alloy

In this paper, metallographic observations, hardness measurement, and static and fatigue tests were conducted to investigate the discontinuity states which become crack nucleation sites in friction stir welded butt joints in 2-mm-thick 2024-T3 aluminum alloy and static and fatigue properties of the joint. Because different types of surface finish can be used depending on the application of the joint, several types of surface conditions were tested to evaluate their effect on crack nucleation sites and static and fatigue life. Indentation hardness tests revealed that typical hardness reduction is not necessarily observed on the section of the welding line. Based on fatigue test results, it was confirmed that there are several types of crack nucleation sites for friction stir welding (FSW) joints depending on the surface finish, and the features of the fracture surface also differ depending on the site. Furthermore, the type of discontinuity state affects the fatigue life of the FSW joint.     

Fracture and mechanical properties of friction stir spot welds in 6063-T6 aluminum alloy

The influence of the tool dimensions and of the welding parameters on the fracture and lap shear properties of friction stir spot welds is investigated. Interrupted lap shear tests allow to follow the mechanisms leading to weld fracture. A triangular cavity opens at the hook during lap shear testing. The distance between this triangular cavity and the hole left by the pin is the main parameter controlling the type of fracture. A too short distance favors a fracture through the weld nugget and hence should be avoided. In particular, this happens when the tool pin diameter is too small and when the plunge rate is too large. Fracture initiating at the triangular cavity and following the thermomechanically affected zone, i.e., by the pullout of the weld nugget, is preferred. This fracture type leads to significant plastic deformation and generally favors a large ultimate force during lap shear testing. Large ultimate forces are observed when the welds are cooler (large plunge rates and low rotation speeds), but the welding conditions should be chosen so as not to lead to fracture trough the weld nugget.     

Effect of weld parameters on mechanical properties and tensile behavior of tungsten inert gas welded AW6082-T6 aluminium alloy

The effect of different welding parameters on the mechanical properties and tensile behavior of tungsten inert gas (TIG) welded joints was analyzed. Four different groove angles were chosen, 60°, 70°, 80° and 90°, to ascertain the tendency of microstructure formation and quality of the weld. Mechanical properties were assessed in the terms of Vickers HV1 hardness. Microanalysis of test samples produced using different current 165 A, 180 A, 200 A with same groove angle of 90° was done in fusion, partially melted, and heat affected zone; all the images showed good penetration and clear transition from one to following zone. The transverse tensile tests were accomplished on the welded joints to evaluate influence of welding parameters and groove geometry to the joint tensile strength and its behavior during exploitation. It was verified that the tensile strength of the welds is closely related to the welding parameters. The chosen 180 A welding current ensured highest tensile strength of test samples; the same as proper selection of groove angle (90°) provides good fusion and high quality of major welds. The results revealed that the weld penetration depends on welding current.

     

Damaged and failure characterization of 7075-T6 Al alloy based on GISSMO model

Journal of Mechanical Science and Technology - Failure simulation of 7075-T6 Al alloy is very important due to its relatively low ductility compared to conventional steel. A hybrid...     

A study of cumulative fatigue damage in aluminum alloy 2024-T4

Experimental data were generated using 2024-T4 aluminum alloy specimens under stress ratios of ?1 and ?0.5 for low-high, low-high-mixed, high-low and high-low-mixed stress sequences.Analysis of the data using Kramer's equation has indicated that the predicted cumulative fatigue damage and fatigue life are in close agreement with experimental results for low-high and low-high-mixed stress sequences under all stress ratios, whereas the theoretical values for high-low and high-low-mixed stress sequences under all stress ratios are more conservative than those obtained experimentally.It is suggested that development of Kramer's equation be studied thoroughly for possible modification.     

Evaluation of drilled hole quality in Al 2024 alloy

We propose an optimal worker flexibility policy for a CONWIP (constant work-in-process) controlled dual resource constrained (DRC) system. A critical issue in DRC systems is the dynamic assignment of workers to the workstations. The proposed worker flexibility policy is designed to evaluate the state of the system at periodic time intervals so that the dynamic assignment of workers to the workstations can be made in an efficient manner. By integrating the response surface methodology (RSM) with simulation, this study provides an approach for optimizing worker transfer decisions. The RSM-based simulation optimization approach adopted in this study provides an effective and robust procedure to determine the optimum level of this decision variable under the given operating conditions.     

Fretting behaviour of glass-fibre-reinforced polypropylene composite against 2024 Al alloy

Composite materials, mainly fibre type ones, are used to respond to crucial demands in engineering applications. Various limitations mean that it is usually impossible to produce structures without mechanical joints. Fretting is an important failure mode for such joints, especially for dynamic loads. This paper sets out to assess the influence of this failure mode—fretting—in association with the effect of displacement, surface treatment with aluminium (anodisation) and the effect of environment, temperature and relative humidity. A series of experiments was carried out, changing each of the variables. To analyse the influence of each parameter, tangential force and displacement were used to establish the fretting cycles for every condition tested. Variations in the shape of the cycles revealed three regimes typical of fretting: stick, slip and partial slip, but the most effective way to characterize the transition between regimes was based on energy dissipation by friction. Surface treatment by anodisation leads to lower wear values, for small amplitude displacements, while for higher displacement amplitudes the wear volume was larger, for the case of room temperature and humidity. Increased temperature resulted in a rise in wear volumes, especially for non-anodised aluminium. Variation in humidity did not greatly influence the behaviour of the specimens studied.     

Influences of rotation speed on microstructures and mechanical properties of 6061-T6 aluminum alloy joints fabricated by self-reacting friction stir welding tool

A 6061-T6 aluminum alloy was self-reacting friction stir welded by using the specially designed tool with unequal shoulder diameters at a constant welding speed of 150 mm/min to investigate the effect of rotation speed on microstructure and mechanical properties of the joints. Excessive flash on the bottom surface of the joint and groove defects on both surfaces of the joint were formed when the lower shoulder diameter was much smaller. The suitable shoulder sizes were determined as 16 and 18 mm in lower shoulder diameter and upper shoulder diameter, respectively. The grain size and the dislocation density in the weld nugget zone (WNZ) increased with increasing rotation speed. The tensile strength of joints first increased with increasing rotating speed and then decreased remarkably as a result of the formation of void defect. The joints welded at lower rotation speeds were fractured in the thermal mechanically affected zone (TMAZ). However, the fracture locations of the defect-free joints were changed to the heat affected zone (HAZ) at higher rotation speeds.     

The effect of built-up edge on the cutting vibrations in machining 2024-T351 aluminum alloy

With standard microinjection moulding becoming more and more established in practical manufacturing, special variants are attracting increasing attention. Especially, the approaches on multi-component microinjection moulding are worth mentioning: As handling and assembly are difficult procedures especially in microtechnology, methods to reduce mounting efforts are of high economic importance. By merging of shaping and mounting procedures in one step, economic progress as well as new material combinations can be obtained. An interesting approach for the fabrication of metal (or in principal, ceramic) microcomponents is the combination of insert injection moulding and metal deposition by electroforming. First, an electrically conductive base plate is produced by injection moulding of conductively filled polymers. In a second injection moulding step, microstructures consisting of insulating plastics are mounted on these plates. The quasi-infinite conductivity gradient allows controlled electroplating starting at the base plate only so that defect-free metal microcomponents can be achieved. As a further variant of microinjection moulding, the development of the so-called MicroPIM process facilitates a large-scale series fabrication technology for metal and ceramic microcomponents. Combined with multi-component technology, an interesting new approach for micromanufacturing is obtained, i.e. the realisation of magnetic/non-magnetic or conductive/non-conductive material combinations by two-component MicroPIM. But, also the combination of different mechanical properties like hard/tough pairings is possible.     

Microstructural and mechanical properties of dissimilar friction stir welds between AA6082-T6 and AA7075-T651

In the present work, similar and dissimilar friction stir welds have been produced on 6-mm-thick plates of AA6082-T6 and AA7075-T651. The microstructural characteristics and the mechanical response of both similar and dissimilar welds were investigated aiming to determine the major differences between them. Material mixing of the dissimilar weld nugget, which was created after the welding process, was studied in order to determine the produced different areas and their dominant alloying elements in this zone. Microstructural investigation was made in the welding zones of similar and dissimilar friction stir welds and indications of partial dynamic recrystallization were observed in the thermomechanically affected zone of the similar welds. Transverse and longitudinal microhardness distributions determined the heat affected zone as the weaker area in the welded specimen. After tensile testing, the fracture of the similar and the dissimilar welds at heat affected zone demonstrated the good bonding and weld quality of the similar and dissimilar weld nuggets.     

Finite Element Analysis of Localized Plasticity in Al 2024-T3 Subjected to Fretting Fatigue

Fretting fatigue is a combination of two complex mechanical phenomena, namely, fretting and fatigue. Fretting appears between components that are subjected to small relative oscillatory motion. Once these components undergo cyclic fatigue load at the same time, fretting fatigue occurs. Fretting fatigue is an important issue in aerospace structural design. Many studies have investigated fretting fatigue behavior; however, the majority have assumed elastic deformation and very few have considered the effect of plasticity. The main goal of this study is to monitor the effect of different fretting fatigue primary variables on localized plasticity in an aluminum alloy (Al 2024-T3) test specimen. In order to extract the stress distribution at the contact interface under elasto-plastic conditions, a modified finite element contact model was used. The contact model was verified through comparison with an elastic analytical solution. Then, a bilinear elasto-plastic isotropic hardening model with a von Mises yield surface was implemented to simulate the material behavior of the aluminum alloy. The effect of different fretting fatigue primary variables, such as axial stress, contact geometry, and coefficient of friction, on localized plasticity was investigated. Finally, the relationship between the location of maximum localized plasticity and Ruiz fretting damage parameter with the crack initiation site is discussed.     

Effect of plunge speeds on hook geometries and mechanical properties in friction stir spot welding of A6061-T6 sheets

The plunge speed of the tool was divided into two plunge speeds, including pin- and shoulder-plunging speeds, for a detailed study of the plunging process in friction stir spot welding of A6061-T6 sheets. The effect of the pin- and shoulder-plunging speeds on hook geometries and mechanical properties was investigated. The results showed that the shoulder-plunging speed had an obvious effect on the hook geometry and tensile shear load, but the pin-plunging speed had almost no effect. The effective bond width (W _eff) and effective sheet thickness (T _eff) used to describe the hook geometry were important factors for determining the tensile shear load and fracture mode. Two fracture modes were observed: tensile/shear mixed fracture and shear fracture. The largest tensile shear load was obtained when the joint failed in the tensile/shear mixed fracture.     

An investigation of optimum SiO2 nanolubrication parameters in end milling of aerospace Al6061-T6 alloy

Aluminium AL6061-T6 is a common alloy which is used for many purposes since it has the superior mechanical properties such as hardness and weldability. It is commonly used in aircraft, automotive and packaging food industries. Milling of Al6061-T6 would be a good process especially in producing varieties shape of products to adapt with different applications. The capability of the CNC milling machine to make batch production would be a noteworthy advantage. However, the demand for high quality focuses attention on product quality, especially the roughness of the machined surface, because of its effect on product appearance, function and reliability. Introducing correct lubrication in the machining zone could improve the tribological characteristic of Al6061-T6 leading to higher product quality. In this research work, the optimum SiO₂ nanolubrication parameters in milling of Al6061-T6 are investigated to achieve correct lubrication conditions for the lowest cutting force, cutting temperature and surface roughness. These parameters include nanolubricant concentration, nozzle angle and air carrier pressure. Taguchi optimization method is used with standard orthogonal array L₁₆(4)³. Furthermore, analyses on surface roughness and cutting force are conducted using signal-to-noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. Finally, confirmation tests were carried out to investigate the optimization improvements.     

Influence of milling strategy on the surface roughness in ball end milling of the aluminum alloy Al7075-T6

Surface roughness has an important role in the performance of finished components. End ball milling is used for achieving high surface quality, especially in complex geometries. Depending on the cutting conditions selected for ball end milling, different milling strategies can be applied. The produced surface quality is greatly affected from the selected milling strategy. The present paper examines the influence of the milling strategy selection on the surface roughness of an Al7075-T6 alloy. A number of cutting parameters are tested (axial and radial depth of cut, feed rate, inclination angles φ and ω) in order to perform 96 experiments and their results are processed using regression analysis and analysis of variance. All possible milling strategies are considered (vertical, push, pull, oblique, oblique push and oblique pull) and for each one of them, a mathematical model of the surface roughness is established, considering both the down and up milling. All models are statistically validated and experimentally verified, and can be used within the limits of the investigating cutting conditions. The polynomials produced are of the third order and the statistically most significant parameters are presented.     

Effect of thermal ageing on mechanical properties of a high-strength ODS alloy

A new high-strength ODS alloy, ARROS, was recently developed for the application as the cladding material of a Sodium-cooled fast reactor (SFR). To assess the long-term integrity under thermal ageing, ARROS was thermally aged in air at 650°C for 1000 h. The degree of thermal ageing was assessed by mechanical tests such as uniaxial tensile, hardness, and small punch tests at from room temperature to 650°C. Tensile strength was slightly decreased but elongation, hardness, and small punch energy were hardly changed at all test temperatures for the specimen aged at 650°C for 1000 h. However, the variation in mechanical properties such as hardness and small punch energy increased after thermal ageing. Using the test results, the correlation between tensile strength and maximum small punch load was established.     

On the FSW of AA2024-T4 and AA7075-T6 T-joints: an industrial case study

The paper presents an artificial neural network-optimization hybrid model to predict and optimize penetration depth of CO₂ LASER-MIG hybrid welding used for 5005 Al–Mg alloy. The input welding parameters are power, focal distance from the work piece surface, torch angle, and the distance between the laser and the welding torch. The model combines single hidden layer back propagation artificial neural networks (ANN) with Bayesian regularization for prediction and quasi-Newton search algorithm for optimization. In this method, training and prediction performance of different ANN architectures are initially tested, and the architecture with the best performance is further used for optimization. Finally, the best ANN architecture is found to show much better prediction capability compared to a regression model developed from the experimental data.