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Si-Assisted solidification path and Microstructure Control of 7075 Aluminum Alloy with Improved Mechanical Properties by Selective Laser Melting

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Acta Metallurgica Sinica(English Letters) 2022年第9期35卷 1424-1438页

作者： Junwei Sha Meixian Li Lizhuang Yang Xudong Rong Bowen Pu Dongdong Zhao Simi Sui Xiang Zhang Chunnian He Jianglin Lan Naiqin Zhao School of Materials Science and Engineering and Tianjin Key Laboratory of Composites and Functional Materials Tianjin UniversityTianjin300350China Collaborative Innovation Center of Chemical Science and Engineering Tianjin300350China Key Laboratory of Advanced Ceramics and Machining Technology Ministry of EducationTianjin300350China Central Iron and Steel Research Institute(CISRI) Beijing100081China

The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.

关键词： Selective laser melting(SLM) 7075 aluminum alloy High-strength alloy Microstructure control solidification path

Influence of Al addition on solidification path and hot tearing susceptibility of Mg-2Zn-(3+0.5 x)Y-x Al alloys

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Journal of Magnesium and Alloys 2019年第2期7卷 272-282页

作者： Guojia Zhang Yue Wang Zheng Liu Shimeng Liu School of Materials Science and Engineering Shenyang University of technologyShenyang 110870P.R.China

Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal *** solidification contraction stress ***(and time)curves are measured by using a“T”type hot tearing *** results reveal that the CSC^(∗)prediction values are in good agreement with the experimental ***,Al_(2)Y phase acts as the heterogeneous nucleation core ofα-Mg and significantly influences the grain *** has been observed that minimum grain size,optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3+0.5 x)Y-x Al alloy(x=2).Furthermore,when Al content was increased to 3 at%,Al_(2)Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al_(2)Y and Al+Al_(3)Y phases,which increased the HTS of the alloy due to reduced fine-grained Al_(2)Y content.

关键词： Mg-Zn-Y-Al alloys Hot tearing susceptibility(HTS) solidification path Clyne-Davies’model(CSC^(∗)) Dendritic coherency

Microstructures,micro-segregation and solidification path of directionally solidified Ti-45Al-5Nb alloy

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China Foundry 2016年第2期13卷 107-113页

作者： Liang-shun Luo Tong Liu Kun Li Yan-qing Su Jing-jie Guo Heng-zhi Fu National Key Laboratory for Precision Hot Processing of Metals Harbin Institute of TechnoloryHarbin 150001China China FA W Casting Company Limited Changchun 130011China State Key Laboratory of Advanced Welding and JoiningHarbin Institute of Technolory.Harbin 150001.China

To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb(at.%) alloy, Bridgman-type directional solidification and thermodynamics calculations were performed on the alloy. The microstructures, micro-segregation and solidification path were *** results show that the β phase is the primary phase of the alloy at growth rates of 5-20 μm·s^(-1) under the temperature gradients of 15-20 K·mm^(-1), and the primary phase is transformed into an α phase at relatively higher growth rates(V >20 μm·s^(-1)). The mainly S-segregation and β-segregation can be observed in Ti-45Al-5Nb alloy at a growth rate of 10 μm·s^(-1) under a temperature gradient of 15 K·mm^(-1). The increase of temperature gradient to 20 K·mm^(-1) can eliminate β-segregation, but has no obvious effect on S-segregation. The results also show that 5 at.% Nb addition can expand the β phase region, increase the melting point of the alloy and induce the solidification path to become complicated. The equilibrium solidification path of Ti-45Al-5Nb alloy can be described as L L→β L+β L+β→αα+β_R β→ααα→γα+γα→α_2+γγ_R+(α_2+γ), in which β_R and γ_R mean the residual β and

关键词： TiAl-Nb alloy directional solidification microstructure micro-segregation solidification path

As-cast microstructures and solidification paths of the Nb–Si–Ti ternary alloys in Nb_5Si_3–Ti_5Si_3region

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Rare Metals 2013年第5期32卷 502-511页

作者： Yan Li Chang-Rong Li Zhen-Min Du Cui-Ping Guo Xin-Qing Zhao School of Materials Science and Engineering University of Science and Technology Beijing School of Materials Science and Engineering Beijing University of Aeronautics and Astronautics

Abstract The as-cast microstructures and solidification paths of the Nb-Si-Ti ternary alloys in the NbsSi3-TisSi3 region were investigated. Since there exist some isomor- phous compounds in the NbsSi3-TisSi3 region, such as aNbsSi3 with B3Cr5 prototype, 13NbsSi3 with Si3W5 pro- totype, 7NbsSi3 with MnsSi3 prototype, and TisSi3 with MnsSi3 prototype, the primary solidification areas of these compounds were not typically indentified in previous experiments. In the present paper, the microstructure observation, the phase identification, and the composition measurement were performed using scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and electron probe microanalysis （EPMA）, respectively. No ternary compound is found. There exist three primary solidification areas, 13Nbs_x（Ti）xSi3, ~Nbs_x（Ti）xSi3, and Tis-x（Nb）xSi3 in the NbsSi3-TisSi3 region. Together with the literaturereported experimental data and optimization results, the liquidus projection of the whole Nb-Si-Ti ternary system is constructed, and totally ten primary solidification areas-- diamond-Si, Nb1-x（Ti）xSi2, Ti1-x（Nb）xSi2, Ti1-x（Nb）xSi, Ti5-x（Nb）xSi4, βNb5-x（Ti）xSi3,αNb5-x（Ti）xSi3, Ti5-x （Nb）xSi3, （Nb,Ti）3Si, and BCC--and nine transitional invariant reactions-L ＋ Nb1-x（Ti）xSi2 → Ti1-x（Nb）x Si2 ＋ Si, L ＋ Nb1-x（Ti）xSi2 → Ti1-x（Nb）xSi2 ＋ Ti5- （Nb）xSi4, L ＋ Ti5-x（Nb）xSi4 → Ti1-x（Nb）xSi2 ＋ Ti1-x （Nb）xSi, L ＋ 13Nb5-x（Ti）5Si3→ Nb1-x（Ti）xSi2 ＋ Ti5-x （Nb）xSi4, L ＋ βNb5-x（Ti）xSi3→b5-x（Ti）xSi3 ＋Ti5-x （Nb）xSi4, L ＋ αNb5-x（Ti）αSi3 → Ti5-x（Nb）xSi3 ＋ Ti5-x（Nb）x Si4, L ＋ αNb5-x（Ti）xSi3 →βNb5-x（Ti）xSi3 ＋ Ti5-x（Nb）xSi3, L ＋ βNb5-xTb-xSi3 → Ti5-x（Nb）xSi3 ＋（Nb,Ti）3Si, and L ＋（Nb,Ti）3Si → Ti5-x（Nb）xSi3 ＋ BCC are confirmed.

关键词： Nb-Si-Ti ternary system Liquidus projection Microstructure solidification path

Thermo-Calc based multi-component micro-segregation model and solidification paths calculations

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China Foundry 2012年第3期9卷 269-274页

作者： Zhao Guangwei Li XinZhong Xu Daming Guo Jingjie Fu Hengzhi Du Yong He Yuehui School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083HunanChina

On the basis of a multi-length scale modeling, a mixture-averaged multi-component/multiphase micro- segregation model was proposed without pre-set function for the micro-scale solute profile. The model explains the effect of morphologies of solidifying phases and solid back diffusion （SBD） on segregation, and covers the two limiting solidification cases of Scheil and Lever-rule models. A commercial Thermo-Calc software package/database was linked to the algorithms via its TQ6-interface for instantaneous determination of the related thermodynamic data of the multi-component alloys. The influences of cooling rate and other parameters on the solidification path and micro-segregation behavior were numerically investigated by sample calculation of the ternary AI-Cu-Mg alloys. A parallel experimental investigation on AI-Cu-Si alloys solidified under different cooling conditions was conducted to validate the theoretical model. Reasonable agreements were gained between the predicted solidification paths and the measured results.

关键词： solidification path micro-segregation multi-component/multi-phase alloys thermo-Calc

Hot tearing behaviors and in-situ thermal analysis of Mg-7Zn-xCu-0.6Zr alloys

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Transactions of Nonferrous Metals Society of China 2018年第8期28卷 1504-1513页

作者： Zhi WANG Ye ZHOU Yi-zhou LI Feng WANG Zheng LIU Ping-li MAO Xiao-ping JIANG School of Materials Science and Engineering Shenyang University of TechnologyShenyang 110870China Wanfeng AUTO Holding Group Shaoxing 312000China

Thermal analysis was used to investigate the microstructural evolution of Mg-7 Zn-x Cu-0.6 Zr alloys during solidification. The effect of Cu content（0, 1, 2 and 3, mass fraction, %） on the hot tearing behavior of the Mg-7 Zn-x Cu-0.6 Zr alloys was investigated with a constrained rod casting（CRC） apparatus, equipped with a load sensor and a data acquisition system. The thermal analysis results of Mg-7 Zn-x Cu-0.6 Zr alloy revealed that the alloy consisted of two distinct phases： α-Mg and Mg Zn2. Three distinct peaks were observed in the alloys with Cu addition, which were identified as α-Mg, Mg Zn Cu and Mg Zn2. In addition, the reaction temperature of α-Mg decreased and the reaction temperatures of Mg Zn2 and Mg Zn Cu increased as the Cu content increased. The experimental results of hot tearing demonstrated that the addition of Cu significantly reduced the hot tearing susceptibility（HTS） of Mg-7 Zn-x Cu-0.6 Zr alloys due to the higher eutectic temperature and the shorter solidification temperature region.

关键词： Mg-7Zn-xC-0.6Zr alloy microstructure solidification path hot tearing susceptibility

Microstructure and microhardness of Ti-48Al alloy prepared by rapid solidification

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China Foundry 2020年第6期17卷 429-434页

作者： Xiao-yu Chen Hong-ze Fang Qi Wang Shu-yan Zhang Rui-run Chen Yan-qing Su School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China School of Electromechanic Engineering Qingdao UniversityQingdao 266071China Centre of Excellence for Advanced Materials Dongguan 523808China

To improve the microstructure and microhardness,Ti-48Al(at.%)alloy was rapidly solidified by melt spinning under different cooling *** microstructure and microhardness of rapidly solidified Ti-48Al alloy were systematically *** show that the average lamellar colony size of the alloy reduces from 60.6μm to 11μm as the cooling rate increases from 2.3×105 to 5.1×105 K·s-1,caused by the increase of nucleation rate at a higher cooling *** the high cooling rate of(4.3-5.1)×105 K·s-1,theαphase is the primary phase,and a few metastableαphases are reserved,which then transform intoα2 phase and subsequently lead to the formation ofα2 equiaxed *** lamellar spacing also decreases with the increase of cooling *** relationship between lamellar spacing(d)and cooling rate(v)is d=*** microhardness increases with the increase of cooling rate because the refined lamellar spacing and grain size can improve the microhardness.

关键词： cooling rate solidification path microstructure lamellar spacing microhardness

Effects of Ru content on phase transformation and compression property of cast TiAl alloys

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China Foundry 2020年第6期17卷 393-401页

作者： Jie-ren Yang Zi-xiang Jiao Dong-dong Zhu Yu-lun Wu Zi-tong Gao Rui Hu State Key Laboratory of solidification Processing Northwestern Polytechnical UniversityXi'an 710072China Shaanxi Key Laboratory of High-Performance Precision Forming Technology and Equipment Northwestern Polytechnical UniversityXi'an 710072China School of Mechanical Engineering&Key Laboratory of Air-driven Equipment Technology of Zhejiang Province Quzhou UniversityQuzhou 324000China

Ruthenium(Ru)is a promising element to heighten the comprehensive mechanical properties of TiAl *** the present study,the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu(x=0,0.1,0.5,1.0,at.%)alloys was *** results show that Ru tends to segregate in the interdendritic region during solidification,and therefore,refines the as-cast microstructure of the *** aβ-stabilizer,Ru does not induce a novel solidification reaction but maintains the peritectic reaction of L+β→α.An excessive Ru content would cause the formation of(γ+τ1+B2)and(α+γ+τ1+B2)phase regions below 1,250°*** precipitation ofτ1-containing mixture is attributed to the Ru-segregation,which inhibits the reaction ofα→γand facilitates the formation of B2 *** discontinuous coarsening ofγphase and blockτ1 phase formed alternately in a manner of analogous eutectoid decomposition within B2 *** addition,the effect of Ru content on compression property of the alloys was *** yield strength increases up to 427 MPa at 800°C with the addition of 1.0at.%Ru,which is mainly due to the solution strengthening effect of Ru.

关键词： TiAl alloy solidification path microstructure phase transformation yield strength

Effects of Rapid Cooling Rate on Microstructure Formation and Microhardness of Binary Ti⁃44Al Alloy

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Journal of Harbin Institute of Technology(New Series) 2020年第3期27卷 225-232页

作者： Xiaoyu Chen Hongze Fang Qi Wang Ruirun Chen Hongsheng Ding Yanqing Su Jingjie Guo School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China School of Electromechanic Engineering Qingdao UniversityQingdao 266071ShandongChina

In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling *** and microhardness of the alloy before and after rapid solidification were *** results show that the ratio ofα2 phase in binary alloy increased with the cooling rates,which is caused by moreαphases directly transforming toα2 *** morphology changed from long dendrite to the mixture of equiaxed and dendrite to equiaxed with the increase of cooling *** grain size was refined from 200-600μm of as⁃cast to 18μm of the alloy cooled at 4.9×10^5 K/s,which is caused by the undercooling induced from rapid *** spacing was decreased from 4.5μm of as⁃cast to 1.1μm by rapid *** the increase of cooling rate,the content ofα2 phase increased andγphase decreased *** solidification can reduce the segregation of *** microhardness was improved from 247 HV to 556 HV,which results from grain refinement strengthening,reduction of lamellar spacing,and more content ofα2 phase.

关键词： Ti⁃44Al alloy microstructure microhardness melt spinning solidification path