Browsing by Author "Zhai, Yuchun"

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    Deformation microstructures and strengthening mechanisms for the wire+arc additively manufactured Al-Mg4.5Mn alloy with inter-layer rolling
    (Elsevier, 2017-11-29) Gu, Jianglong; Wang, Xiaoshu; Bai, Jing; Ding, Jialuo; Williams, Stewart W.; Zhai, Yuchun; Liu, Kun
    Applying inter-layer rolling to the wire+arc additively manufacturing (WAAM) process with increasing loads of 15 kN, 30 kN and 45 kN, achieves excellent mechanical properties for 5087 (Al-Mg4.5-Mn) alloys. Compared with the as-deposited alloy, the average micro hardness, yield stress and ultimate tensile strength of 45 kN rolled alloys reached to 107.2 HV, 240 MPa and 344 MPa, which were enhanced by 40%, 69% and 18.2%, respectively. Primary coarse grain structures were found to become greatly refined with an evident rolling texture after deformation. The strengthening mechanisms mainly are deformation strengthening, grain refinement, and solution strengthening. Meanwhile, the elongation of rolled alloys stays over 20%. The plasticity was not obviously diminished compared with the as-deposited alloy. This is two times greater than the commercial wrought Al-Mg alloy with similar composition. The excellent plasticity may be chiefly due to grain refinement, pores closure and reduction, and grain recrystallization during the WAAM re-heating process. The combination process of rolling deformation with WAAM deposition is an effective technique in refining microstructure and improving mechanical properties for AM aluminum alloys.
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    The effect of Cu content on the microstructure and properties of the wire arc additive manufacturing Al-Cu alloy
    (MDPI, 2023-03-28) Ren, Lingling; Wang, Zhenbiao; Wang, Shuai; Li, Chengde; Wang, Wei; Ming, Zhu; Zhai, Yuchun
    Al-Cu alloy has broad application prospects in the field of aerospace due to its excellent performance. In this paper, deposits with different Cu contents were prepared by the wire arc additive manufacturing (WAAM) process, and the effects of Cu content on the microstructure and mechanical properties were investigated. The microstructure of Al-Cu alloy was investigated by metallography, scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), and transmission electron microscope (TEM). The results show that both the number and size of the precipitated θ phases (Al2Cu) in the as-deposited material increase with the increase of Cu content. After the T4 treatment, the solid solution amount of Cu in the matrix showed a trend of first increasing and then remaining stable. When the content of Cu was greater than 5.65%, as the Cu content increased, the number and size of the remaining θ phases both increased. In the peak ageing state, the amount of precipitated θ’ phase showed a trend of increasing and then remaining stable. After the T6 treatment, the mechanical properties showed a trend of first increasing and then decreasing with the increase of the content of Cu. When the Cu content was 5.65%, the deposit achieved the best mechanical properties, and the anisotropy of the mechanical properties disappeared. The tensile strength, yield strength, and elongation reached 538 MPa, 478 MPa, and 10.5%, respectively. When the content of Cu was greater than 5.65%, the anisotropy of mechanical properties was obvious, and the fracture mode of the vertical specimen changed from ductile fracture to brittle fracture.
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    Micropore evolution in additively manufactured aluminum alloys under heat treatment and inter-layer rolling
    (Elsevier, 2019-10-28) Gu, Jianglong; Yang, Shouliang; Gao, Minjie; Bai, Jing; Zhai, Yuchun; Ding, Jialuo
    The application of wire + arc additively manufactured (WAAM) aluminum alloys has been restricted by the porosity defect, which is generally detrimental to the mechanical properties. Suppressing of micropores in the WAAM components has attracted considerable attention in recent years. Inter-layer rolling was introduced to eliminate micropores during the WAAM deposition of the Al–Cu6.3 and Al–Mg4.5 alloys. The distribution characteristics and individual morphology of micropores were revealed by the X-ray diffraction tomography. Key findings demonstrated that the number, volume, size, and roundness of micropores in rolled alloys decreased similarly with increasing loads, eventually achieving a density of over 99.9%. After the heat treatment, the homogeneous distribution of fine (around 5.3 μm) and spherical (0.70–0.74) micropores was realized in the 45 kN rolled alloys. All the evaluated indicators of micropores in the 45 kN rolled + heat treated alloys were superior to the post-deposition heat treated state. The evolution mechanisms include the reprecipitation of hydrogen pores, formation of vacant voids, and re-opening of unclosed pores. The hybrid technique of WAAM + rolling + heat treatment has great potential in promoting mechanical properties of WAAM alloys. The results will provide a theoretical guidance for the design of high-performance WAAM aluminum alloy components.
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    Microstructure, defects, and mechanical properties of wire + arc additively manufactured AlCu4.3-Mg1.5 alloy
    (Elsevier, 2019-11-13) Gu, Jianglong; Gao, Minjie; Yang, Shouliang; Bai, Jing; Zhai, Yuchun; Ding, Jialuo
    The wire with a composition of AlCu4.3%Mg1.5% was customized and used to deposit the WAAM alloy with the power source of cold metal transfer. The microstructure, defect, and mechanical properties of the as-deposited and heat-treated WAAM alloys were studied. Key findings demonstrated that the microstructure of the as-deposited alloy was characterized by a hierarchical distribution of dendrites, equiaxed grains, and a slight number of columnar grains. The volume fraction of the network-like scattered coarse particles of second phases θ + S reduced by 95% after the T6 heat treatment. With an average microhardness of 161.4 HV, the mean yield strength and ultimate tensile strength of the WAAM alloy increased by 116% and 66% achieving 399 MPa and 485 MPa in the horizontal direction after heat treatment. The precipitation of a high density of needle-shaped metastable S′ precipitates was responsible for the significantly enhanced mechanical properties. However, this WAAM alloy has exhibited an anisotropic tensile property. A considerable number of sharp-angled defects like linear and chain-like micropores, which generally depress the mechanical properties, were formed in the WAAM alloys.
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    The strengthening effect of inter-layer cold working and post-deposition heat treatment on the additively manufactured Al-6.3Cu alloy
    (Elsevier, 2015-10-26) Gu, Jianglong; Ding, Jialuo; Williams, Stewart W.; Gu, Huimin; Bai, Jing; Zhai, Yuchun; Ma, Peihua
    Wire + Arc Additive Manufacture (WAAM) attracts great interest from the aerospace industry for producing components with aluminum alloys, particularly Al-Cu alloy of the 2000 series such as 2219 alloy. However the application is restricted by the low strength properties of the as-deposited WAAM metal. In this study two strengthening methods were investigated - inter-layer cold working and post-deposition heat treatment. Straight wall samples were prepared with 2319 aluminum alloy wire. Inter-layer rolling with loads of 15 kN, 30 kN and 45 kN were employed during deposition. The ultimate tensile strength (UTS) and yield strength (YS) of the inter-layer rolled alloy with 45 kN load can achieve 314. MPa and 244. MPa respectively. The influence of post-deposition T6 heat treatment was investigated on the WAAM alloy with or without rolling. Compared with inter-layer rolling, post-deposition heat treatment can provide much greater enhancement of the strength. After T6 treatment, the UTS and YS of both of the as-deposited and 45 kN rolled alloys exceeded 450. MPa and 305. MPa respectively, which are higher than the properties of the wrought 2219-T6 alloy. The strengthening mechanisms of this additively manufactured Al-6.3Cu alloy were investigated through microstructure analysis.