In this experiment, Al-Cu-Sn alloy was used as raw material to form deposits with different heat input using the wire-arc additive manufacturing (WAAM) process. The effects of heat input on microstructure and mechanical properties of Al-Cu-Sn alloy deposits were investigated by metallography, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM) and mechanical properties tests. The results show that with increased of heat input, the thickness of the deposits increased and the layer height of the deposits increased. The number and size of pores in the deposits also improved with the increased heat input. The grain size of the deposits in the as-deposited state gradually increased and changed from isometric crystals to columnar crystals, the precipitated θ phases gradually converged on the grain boundary from within the grains. After T6 heat treatment, with increased heat input, the number of unsolved θ phases on the grain boundary increased, and the number of θ phases precipitated out of the matrix decreased as the phase spacing increased. With the increased heat input, the mechanical properties of the deposits gradually decreased, and the fracture mode changed from ductile fracture to brittle fracture.
In this present study, single-wire and double-wire Al-Cu-Sn alloy walls were fabricated by an arc additive manufacturing process. The surface morphology, elemental composition, and microstructure were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM) techniques. The mechanical properties of both the single-wire and double-wire walls were studied by mechanical property testing. The results showed that the heat input of the double-wire wall was lower than that of the single-wire wall at the same wire feeding speed. The surface microstructure of the double-wire wall showed a more uniform surface than the single-wire wall. The grains of the double-wire wall were found to be isometric crystals in the as-deposited state. The θ phase of the double-wire wall was dispersed with a smaller grain size in the grain boundary. After T6 heat treatment, the θ phase of the double-wire wall was completely dissolved into the aluminum matrix, and a large amount of θ ' enhanced phases were precipitated with a phase spacing of about 15 nm. The mechanical properties of the double-wire wall were shown to have significantly improved performance, which further increased to 490 MPa, 420 MPa, and 12%, respectively. The transverse and longitudinal mechanical properties of the double-wire wall were consistent, and the fracture mode of both was ductile fracture.Materials 2020, 13, 0073 2 of 10 process without considering the influence of heat input on the structure and performance. Heat input was one of the important factors affecting the forming and performance of WAAM walls.CMT Twin is a welding process developed by the Fronius company (Pettenbach, Austria), which combines CMT and TIME Twin processes. It has the characteristics of low heat input, high cladding efficiency, mutual heat support between front arc and back arc, and good arc stability [8]. Liu et al. [9] used a CMT Twin process to weld high-strength steel, and the performance of welded joint was good. Han et al. [10] used CMT Twin technology to weld 1561 aluminum alloy, which effectively controlled the problem of heat-affected zones and joint softening. At present, the majority application of the CMT Twin process in aluminum alloy additive manufacturing is deploying alloy composition [5,7], but the effect of this process on the microstructure and properties of walls, and the research on production and application, has not yet been reported.In this paper, Al-Cu-Sn alloy is used as the raw material, in which Sn can refine the grain of wall and promote the precipitation of the θ ' phase and keep it stable during the aging process. The CMT Twin process was adopted for deposition, and the appearance and organizational properties of the wall were examined. A comparison with the single-wire CMT was conducted, which laid a foundation for the industrial application of CMT Twin technology of Al-Cu alloy produced by WAAM.
Alternative splicing is pervasive in mammalian genomes and involved in embryo development, whereas research on crosstalk of alternative splicing and embryo development was largely restricted to mouse and human and the alternative splicing regulation during embryogenesis in zebrafish remained unclear. We constructed the alternative splicing atlas at 18 time-course stages covering maternal-to-zygotic transition, gastrulation, somitogenesis, pharyngula stages, and post-fertilization in zebrafish. The differential alternative splicing events between different developmental stages were detected. The results indicated that abundance alternative splicing and differential alternative splicing events are dynamically changed and remarkably abundant during the maternal-to-zygotic transition process. Based on gene expression profiles, we found splicing factors are expressed with specificity of developmental stage and largely expressed during the maternal-to-zygotic transition process. The better performance of cluster analysis was achieved based on the inclusion level of alternative splicing. The biological function analysis uncovered the important roles of alternative splicing during embryogenesis. The identification of isoform switches of alternative splicing provided a new insight into mining the regulated mechanism of transcript isoforms, which always is hidden by gene expression. In conclusion, we inferred that alternative splicing activation is synchronized with zygotic genome activation and discovered that alternative splicing is coupled with transcription during embryo development in zebrafish. We also unveiled that the temporal expression dynamics of splicing factors during embryo development, especially co-orthologous splicing factors. Furthermore, we proposed that the inclusion level of alternative splicing events can be employed for cluster analysis as a novel parameter. This work will provide a deeper insight into the regulation of alternative splicing during embryogenesis in zebrafish.
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