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The difference in droplet transfer behavior between the traditional cold metal transfer plus pulse (CMT + P) process and the new CMT mix synchro-pulse (CMT + SP) process, and its effect on the overall morphology, porosity, microstructure and mechanical properties of WAAM-ed AA2219 alloy are studied. Compared to the pulse stage (fP = 160 Hz) of the traditional CMT + P process, the pulse stage of CMT + SP process consists of the low-frequency pulse and high-frequency pulse (HFP) stages. The high frequency (fH = 200 Hz) of the HFP stages formed a high arc force, enlarging the molten pool and enhancing the convection of molten pool. This increased the melting depth between passes and facilitated the flow of the molten pool to the sides and escaping of the pores. As a result, a highly symmetric WAAM-ed AA2219 alloy with a high effective height (14.2 mm) and effective area (89.6 mm2), and low porosity (0.6 ± 0.2%) was manufactured by the CMT + SP process. Moreover, the fine grains (61 μm) with a 43% (area fraction) equiaxed grains were obtained with the CMT + SP process, leading to more θ′ phases precipitating. Thus, the average microhardness and tensile strength of the CMT + SP samples increased to 80.2 ± 6.7 HV and 265.0 ± 17.0 MPa, respectively. [ABSTRACT FROM AUTHOR]

The present investigation deals with development of AA2219 composites with different weight fractions of Cerium oxide (CeO2) reinforcement and characterizing the microstructure and mechanical properties thereof. XRD and SEM micrograph confirm the presence of CeO2 particles and Al2Cu precipitate. The grain size of 0, 0.5, 1.0, 1.5 and 2 wt% CeO2 composites are 483, 453, 411, 362 and 328 μm, respectively. Addition of CeO2 significantly reduces the dendritic morphology and refines the α-Al grain structure. 2 wt% CeO2 addition has yielded the maximum hardness of 124 HV and yield strength of 87 MPa in all the composites developed. Additionally, the developed composites were evaluated by examining the wear characteristics with the co-efficient of friction (COF) and the specific wear rate. In this study, Taguchi's L25 orthogonal array was used to optimize the parameters like reinforcement fraction, load and sliding distance. Signal-to-noise ratio (S/N ratio) and analysis of variance (ANOVA) are used to obtain the parameters highly influencing the wear behaviour. Adhesive wear is exhibited by ploughing at lower loads and delamination is observed with increasing load. Deep shallow ploughs with embarked abrasion are observed at higher loads.

• Residual stress distribution is non-uniform in AA2219 friction stir weld. • Residual stress is tensile near weld center and compressive away from the weld. • Single-layer laser shock peening reverses tensile residual stress to compressive. • More than one layer of peening increases compressive stresses further. • Laser Shock peening also increased the hardness at the surface and subsurface. This work focuses on the effect of Laser Shock Peening (LSP) on residual stress (RS) and microhardness of AA2219 T87 Friction Stir Weld (FSW). FSW plate was laser peened, covering all the regions of the weld and RS measurement was carried out before and after peening. RS distribution across the weld is non-uniform, and the profile is M shaped with tensile RS near to weld center and compressive RS away from the center. The maximum tensile RS is + 123.5 MPa and + 96.7 MPa on the top and bottom surfaces, respectively. LSP has reversed the tensile RS to compressive with a single pass of peening, and the subsequent passes increased the compressive RS further. Peak tensile RS changes to compressive RS of −20 MPa, −130.2 MPa, and −195.5 MPa with single, three and six passes of peening, respectively, on the top surface. It is due to plastic deformation and strain-hardening effect induced on the surface during LSP. An increase in hardness due to LSP on the surface and subsurface levels is noticed, and increased number of passes affected higher depth. [ABSTRACT FROM AUTHOR]

The aluminium alloy AA2219 (Al–Cu–Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance. Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components. Friction stir welding (FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding. This process uses a non-consumable tool to generate frictional heat on the abutting surfaces. The welding parameters, such as tool pin profile, rotational speed, welding speed and axial force, play major role in determining the microstructure and corrosion resistance of welded joint. The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters. In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions. Dynamic polarization testing was carried out to determine critical pitting potential in millivolt, which is a criteria for measuring corrosion resistance and the data was used in model. Further the response surface method (RSM) was used to develop the model. The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints.

Aluminum alloy AA2219-Graphene/MWCNT composites with near theoretical density have been successfully processed through high energy ball milling followed by spark plasma sintering. Effectiveness of varying content of Graphene and MWCNT as reinforcements was studied on different aspects of processing of the composites. The particle size increased during milling due to agglomeration but presence of reinforcement restricted the agglomeration process. Significant change in particle size of milled composite powders was not observed for the type (Graphene/MWCNT) or content (0.5-2 wt%) of the reinforcements. The increase of reinforcement (Graphene/MWCNT) content above 0.5 wt% resulted in lower hardness for spark plasma sintered composites. Further, both AA2219-Graphene and AA2219-MWCNT composites revealed similar hardness values. Finally, different aspects of processing (mechanical alloying, densification) and characterization (microstructure, hardness, electrical conductivity) revealed similar results irrespective of type of reinforcement i.e. Graphene or MWCNT. [ABSTRACT FROM AUTHOR]

Slow quenching of direct chill (DC) cast aluminum ingot plates used in large mold applications is often used to decrease quench-induced residual stresses, which can deteriorate the machining performance of these plates. Slow quenching may negatively affect the mechanical properties of the cast plates when using highly quench-sensitive aluminum alloys because of its negative effect on the precipitation hardening behavior of such alloys. The effect of the quenching rate on precipitation kinetics in AA2219 DC cast alloy was systematically studied under water and air quenching conditions using differential scanning calorimetry (DSC) technique. Transmission electron microscopy (TEM) was also used to characterize the precipitate microstructure. The results showed that the precipitation kinetics of the θ′ phase in the air-quenched condition was mostly slower than that in the water-quenched one. Air quenching continuously increased the precipitation kinetics of the θ phase compared to water quenching. These results revealed the contributions of the inadequate precipitation of the strengthening θ′ phase and the increased precipitation of the equilibrium θ phase to the deterioration of the mechanical properties of air-quenched AA2219 DC cast plates. The preexisting GP zones and quenched-in dislocations affected the kinetics of the θ′ phase, whereas the preceding precipitation of the θ′ phase affected the kinetics of the θ phase by controlling its precipitation mechanism. [ABSTRACT FROM AUTHOR]

Fine-grained bulk AA2219 material was successfully manufactured by means of milling and hot compression/extrusion of metallic chips. Preliminary milling of the metallic scrap either for 8 or for 30 h was found to result in the development of two components of the material structure, i.e. a highly refined matrix and coarse remnants of unmilled chips. The average volume of the highly refined matrix reached 45% and 84% for materials milled for 8 h and 30 h (MA8h and MA30h samples), respectively. Hot compression tests confirmed high strength of preliminarily milled materials attributed to the grain refinement and properly carried out mechanical consolidation methods. An additional solid solution strengthening effect was observed for samples water-quenched after annealing at 808 K/300 min both for preliminarily milled materials and samples made from an industrial material (IM). However, subsequent hot deformation tests did not reveal noticeable hardening of the solution treated MA30h samples due to dynamic precipitation unlike in the case of IM samples. Transmission electron microscopy analyses may lead to the conclusion that the aging of solution treated MA material result in the growth of θ-type stable particles in heavily-refined areas without the preceding precipitation of metastable θ′ particles. Therefore, precipitation hardening of the tested MA-materials becomes inhibited with increased milling time. [ABSTRACT FROM AUTHOR]

Dissimilar friction stir welds of aluminium alloys AA5083 and AA2219 were investigated in a view to get defect free welds by varying process parameters. An attempt has been made to develop a mathematical model to predict sound welds. Design of experiments with three parameters and five levels were used to optimize the effectiveness of process parameters. Analysis of variance and response surface methodology were used to determine the significance and optimal level for each parameter to minimize % area of volumetric defect. The experimental and predicted values of % area of volumetric defect were in good agreement. The effects of process parameters and tool-offset on the extent of intermixing of materials and to minimize % area of volumetric defects were analyzed in detail by employing different methods such as macrostructural analysis and electron probe micro analysis. The defect free dissimilar weldments were characterized for transverse tensile properties. The observed tensile strength values were correlated with reference to the extent of intermixing of materials in the stir/nugget zone. Established mathematical models have depicted a good prediction of relationship between the investigated FSW process parameters and the % area of defect of the welds. It is understood that the mixing pattern in nugget zone and further joint strength are primarily affected by the tool offset and welding parameters. [ABSTRACT FROM AUTHOR]

With its combination of high specific strength, good machinability and excellent weldability, AA2219 direct chill (DC) cast alloy has become a new category of materials for manufacturing large molds for the plastics and automotive industries. The effect of two-step aging on the microstructural evolution and mechanical properties of AA2219 DC cast alloy was investigated. The precipitate microstructure was characterized under different heat treatment conditions using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The poor mechanical properties of the air-quenched alloy were attributed to the presence of quench-induced coarse θ′ and θ precipitates, which had very limited contribution to the precipitation hardening during the aging treatment. The two-step aging treatment of the air-quenched AA2219 alloy involved the precipitation of GP zones in the first step followed by their transformation into fine θ″ strengthening precipitates in the second step, which considerably improved the mechanical properties. After undergoing 120 °C/36 h+190 °C/8 h two-step aging, the hardness, YS and UTS of the air-quenched alloy were increased by 27%, 46% and 15%, respectively, compared with 190 °C/8 h one-step aging. [ABSTRACT FROM AUTHOR]

The present study has investigated the influence of scandium additions on the structure and mechanical properties of AA2219 gas tungsten arc (GTA) weldments. Controlled amounts of scandium modified AA2319 fillers were introduced into the molten pool of AA2219 by predeposited cast inserts under different welding conditions in GTA welding. Full penetration GTA welds were prepared using alternating current. It was observed that grain size decreased with increasing amounts of scandium and gradual transformation from columnar to equiaxed grain morphology. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, strength, and ductility. Room temperature hardness and tensile properties at different temperatures (room temperature, 100, 150, 200 and 250 °C) of weldments in the as-welded condition were observed and correlated with microstructure. The results show that the welds subjected to post-weld aging treatment have displayed superior hardness and tensile strength. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue crack growth resistance of the electron beam welded joints through post weld heat treatment methods such as solution treatment (ST), artificial aging (AA), solution treatment and artificial aging (STA). Electron beam welding machine with 100kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100kN has been used to evaluate the fatigue crack growth behaviour of the welded joints. Of the three post weld heat treated joints, the solution treated and aged (STA) joints are offering better resistance against the growing fatigue cracks. The superior mechanical properties, preferred microstructures in the weld metal region and favourable residual stress field of the weld region are found to be the reasons for superior fatigue performance of the STA joints compared to other joints. [Copyright &y& Elsevier]

Abstract: This paper reports the effect of post weld heat treatment on fatigue behaviour of electron beam welded AA2219 aluminium alloy. An attempt has been made to enhance the fatigue strength of the electron beam welded joints through post weld heat treatment methods such as solution treatment, artificial aging, solution treatment and artificial aging. Electron beam welding machine with 100kV capacity has been used to fabricate the square butt joints. Servo hydraulic controlled fatigue testing machine with a capacity of 100kN has been used to evaluate the fatigue life of the welded joints. Of the three post weld heat treated joints, the solution treated and aged joints are enduring higher number of cycles under the action of cyclic loads. [Copyright &y& Elsevier]

Aluminum alloy 2219 (Al-6.5%Cu) is a favourite age hardenable alloy for aerospace applications because of its excellent welding characteristics. Though AA2219 has got an edge over its 6000 and 7000 series counterparts in terms of weldability, it also suffers from poor joint strength when welded. In this investigation an attempt has been made to improve the welded joint strength through post weld aging treatment. This paper presents the effect of post-weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy. Square butt joints were fabricated using an electron beam welding (EBW) machine of 100 kV capacity. The joints were given post-weld artificial aging treatment. Tensile tests were carried out using 100 kN, electro-mechanical controlled universal testing machine. It is found that the post-weld aging treatment is beneficial for improving weld metal hardness and tensile properties. This is mainly due to the uniform distribution of CuAl2 precipitates in the weld metal region in post-weld aged joints compared to as welded joints as evident from weld metal microstructure. [ABSTRACT FROM AUTHOR]