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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]

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]

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]

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]

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]