Institute of Fundamental Technological Research
Polish Academy of Sciences

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Kehuan Wang

Imperial College London (GB)


Recent publications
1.  Wang K., Kopeć M., Chang S., Qu B., Liu J., Politis D.J., Wang L., Liu G., Enhanced formability and forming efficiency for two-phase titanium alloys by fast light alloys stamping technology (FAST), Materials & Design, ISSN: 0264-1275, DOI: 10.1016/j.matdes.2020.108948, pp.1-25, 2020

Abstract:
During hot stamping of titanium alloys, insufficient forming temperatures result in limited material formability, whereas temperatures approaching the β phase transus also result in reduced formability due to phase transformation, grain coarsening and oxidation during the long-time heating. To solve this problem, Fast light Alloys Stamping Technology (FAST) is proposed in this paper, where fast heating is employed. Effects of heating parameters on the formability and post-form strength were studied by tensile tests. Forming of a wing stiffener was performed to validate this new process. Results show that microstructure of TC4 alloy after fast heating was in nonequilibrium state, which could enhance ductility significantly compared with the equilibrium state. When TC4 alloy was first heated to 950 °C with heating rate of 100 °C/s and then cooled to 700 °C, the elongation at 700 °C was more than 3 times that of a slow heating rate with soaking. Nano-scaled martensite with high dislocation density transformed from β phase was observed under fast heating condition. A complex shaped wing stiffener was successfully formed from TC4 titanium alloy in less than 70 s including heating, transfer and forming, and the post-form strength was almost the same with the initial blank.

Keywords:
titanium alloys, fast heating, hot stamping, formability, post-form strength

Affiliations:
Wang K. - Imperial College London (GB)
Kopeć M. - IPPT PAN
Chang S. - Harbin Institiute of Technology (CN)
Qu B. - Harbin Institiute of Technology (CN)
Liu J. - Imperial College London (GB)
Politis D.J. - Imperial College London (GB)
Wang L. - Imperial College London (GB)
Liu G. - Harbin Institiute of Technology (CN)
2.  Li Z., Qu H., Chen F., Wang Y., Tan Z., Kopeć M., Wang K., Zheng K., Deformation behavior and microstructural evolution during hot stamping of TA15 sheets: experimentation and modelling, Materials, ISSN: 1996-1944, DOI: 10.3390/ma12020223, Vol.12, No.2, pp.223-1-14, 2019

Abstract:
Near-α titanium alloys have extensive applications in high temperature structural components of aircrafts. To manufacture complex-shaped titanium alloy panel parts with desired microstructure and good properties, an innovative low-cost hot stamping process for titanium alloy was studied in this paper. Firstly, a series of hot tensile tests and Scanning Electron Microscope (SEM) observations were performed to investigate hot deformation characteristics and identify typical microstructural evolutions. The optimal forming temperature range is determined to be from 750 °C to 900 °C for hot stamping of TA15. In addition, a unified mechanisms-based material model for TA15 titanium alloy based on the softening mechanisms of recrystallization and damage was established, which enables to precisely predict stress-strain behaviors and potentially to be implemented into Finite Element (FE) simulations for designing the reasonable processing window of structural parts for the aerospace industry.

Keywords:
TA15, hot stamping, phase evolution, deformation, modelling

Affiliations:
Li Z. - AVIC Manufacturing Technology Institute (CN)
Qu H. - AVIC Manufacturing Technology Institute (CN)
Chen F. - AVIC Manufacturing Technology Institute (CN)
Wang Y. - Beijing Aeronautical Manufacturing Technology Research Institute (CN)
Tan Z. - Imperial College London (GB)
Kopeć M. - IPPT PAN
Wang K. - Imperial College London (GB)
Zheng K. - Imperial College London (GB)
3.  Kopeć M., Wang K., Politis D.J., Wang Y., Wang L., Lin J., Formability and microstructure evolution mechanisms of Ti6Al4V alloy during a novel hot stamping process, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2018.02.038, Vol.719, pp.72-81, 2018

Abstract:
A novel hot stamping process for Ti6Al4V alloy using cold forming tools and a hot blank was presented in this paper. The formability of the material was studied through uniaxial tensile tests at temperatures ranging from 600 to 900 °C and strain rates ranging from 0.1 to 5 s-1. An elongation ranging from 30% to 60% could be achieved at temperatures ranging from 750 to 900°C respectively. The main microstructure evolution mechanisms varied with the deformation temperature, including recovery, phase transformation and recrystallization. The hardness of the material after deformation first decreased with the temperature due to recovery, and subsequently increased mainly due to the phase transformation. During the hot stamping tests, qualified parts could be formed successfully at heating temperatures ranging from 750 to 850°C. The forming failed at lower temperatures due to the limited ductility of the material. At temperatures higher than 900°C, extensive phase transformation of α to β occurred during the heating. During the transfer and forming, the temperature dropped significantly which led to the formation of transformed β, reduction of the formability and subsequent failure. The post-form hardness distribution demonstrated the same tendency as that after uniaxial tensile tests.

Keywords:
titanium alloys, Ti6Al4V, hot stamping, microstructure

Affiliations:
Kopeć M. - IPPT PAN
Wang K. - Imperial College London (GB)
Politis D.J. - Imperial College London (GB)
Wang Y. - Beijing Aeronautical Manufacturing Technology Research Institute (CN)
Wang L. - Imperial College London (GB)
Lin J. - Imperial College London (GB)
4.  Kopeć M., Wang K., Wang Y., Wang L., Lin J., Feasibility study of a novel hot stamping process for Ti6Al4V alloy, MATEC Web of Conferences, ISSN: 2261-236X, DOI: 10.1051/matecconf/201819008001, Vol.190, pp.1-5, 2018

Abstract:
To investigate the feasibility of a novel hot stamping process for the Ti6Al4V titanium alloy using low temperature forming tools, mechanical properties of the material were studied using hot tensile tests at a temperature range of 600 - 900°C with a constant strain rate of 1s-1. Hot stamping tests were carried out to verify the feasibility of this technology and identify the forming window for the material. Results show that when the deformation temperature was lower than 700°C, the amount of elongation was less than 20%, and it also had little change with the temperature. However, when the temperature was higher than 700°C, a good ductility of the material can be achieved. During the forming tests, parts failed at lower temperatures (600°C) due to the limited formability and also failed at higher temperatures (950°C) due to the phase transformation. The post-form hardness firstly decreased with the temperature increasing due to recovery and then increased due to the phase transformation. Qualified parts were formed successfully between temperatures of 750 - 850°C, which indicates that this new technology has a great potential in forming titanium alloys sheet components.

Keywords:
titanium, hot stamping, metal forming

Affiliations:
Kopeć M. - IPPT PAN
Wang K. - Imperial College London (GB)
Wang Y. - Beijing Aeronautical Manufacturing Technology Research Institute (CN)
Wang L. - Imperial College London (GB)
Lin J. - Imperial College London (GB)

Conference abstracts
1.  Kopeć M., Wang K., Yuan X., Wang L., Kowalewski Z.L., Fast light alloys stamping technology (FAST) for two-phase titanium alloys, PGEM, The Sixth Postgraduate Experimental Mechanics Conference, 2020-12-03/12-04, Manchester (GB), pp.1, 2020
2.  Wang K., Kopeć M., Qu H., Wang Y., Wang L., Lin J., Li Z., A unified constitutive model for two-phase titanium alloys under hot stamping condition, ICNFT 2018, 5th International Conference on New Forming Technology, 2018-08-18/08-21, Bremen (DE), pp.1, 2018

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