针对7050铝合金薄壁高筋模锻件在传统热模锻过程中因表层激冷作用,导致模锻件组织不均匀、服役性能不达标的问题,本工作探究了引入脉冲电流的电辅助成形工艺对其组织与力学性能的调控作用。利用脉冲电流的趋肤效应、Joule热效应和电塑效应,改善模锻件截面的组织均匀性并提升其综合力学性能,结合实验表征和有限元仿真,系统揭示了脉冲电流作用下模锻件的微观结构演变规律,并通过拉伸实验测评其力学性能。结果表明,在脉冲电压400 V、脉冲宽度50 μs、通电时间60 s的条件下,优选电流频率600 Hz的电辅助成形工艺,通过电-热-力多场耦合作用,有效促进了再结晶行为,形成均匀等轴晶组织,改善了模锻件表层心部的组织均匀性;通过提高溶质固溶度,强化了析出相对屈服强度的贡献,使模锻件的强度和延伸率均有所提升,实现了表层与心部性能的协同优化。
7050 aluminum alloy
thin-walled high-ribbed die forgings are essential structural components in
aerospace engineering, necessitating a lightweight design coupled with high
mechanical performance. However, conventional hot die forging often results in
a substantial microstructural gradient distribution, characterized by coarse
surface grains and severe inhomogeneity between the surface and core of the
forgings due to rapid surface cooling when the billet contacts the die. These
defects significantly degrade the mechanical properties and reliability of the
components. In addition, conventional process optimization methods cannot
fundamentally resolve these issues, often necessitating the removal of
unacceptable surface layers, which leads to considerable material waste. Pulsed
current-based electrically assisted forming (EAF) has demonstrated unique
advantages in regulating metal plastic deformation and microstructure via the
skin, electrothermal, and electroplastic effects. However, its systematic
application in complex thin-walled high-ribbed die forgings has not been
documented. To address these challenges, this study incorporates pulsed current
into the conventional hot die forging process, taking 7050 aluminum alloy
H-shaped thin-walled high-ribbed die forgings as the research object. Key
parameters include a pulse voltage of 400 V, pulse width of 50 μs, and
energizing time of 60 s. Two current frequencies, 600 and 1000 Hz, are selected
as experimental variables to assess the regulatory effects of EAF on the
microstructure and mechanical properties. The study employs finite element
simulations to analyze current density and temperature field distributions,
alongside multiscale experimental characterizations such as OM, EBSD, SEM, TEM,
and tensile testing. This comprehensive approach reveals the microstructural
evolution and strengthening mechanisms under electro-thermal-mechanical
multifield coupling. Results demonstrate that the 600-Hz medium-frequency EAF
process yields the optimal comprehensive regulation effect. The pulsed current
mitigates surface heat loss during die forging, facilitates sufficient dynamic
recrystallization, and generates uniform equiaxed grains throughout the
cross-section, thus eliminating microstructural inhomogeneity. Moreover, the electro-thermal-mechanical
coupling effect enhances solute solid solubility and boosts the contribution of
precipitation strengthening to yield strength, leading to simultaneous improvements
in strength and ductility. The mechanical properties of the surface and core of
the forgings are highly balanced, with yield strength, tensile strength, and
elongation measuring 495 MPa, 511 MPa, and 13.6% for the surface, and 492 MPa,
507 MPa, and 13.5% for the core, respectively. By contrast, the 1000-Hz
high-frequency current exacerbates the skin effect, causing excessive current
concentration on the surface and insufficient energy penetration into the core,
resulting in incomplete recrystallization and increased structural
inhomogeneity. Consequently, the mechanical properties of the 1000-Hz-processed
forgings are inferior and less uniform. This study elucidates the regulatory
mechanism of current frequency on the microstructural homogeneity and
mechanical properties of complex aluminum alloy die forgings under electro-thermal-mechanical
multifield coupling. The findings provide a novel and efficient technical
approach for integrated microstructure-performance control in high-strength
aluminum alloy thin-walled high-ribbed components, offering considerable
potential for reducing material waste and enhancing component reliability in
aerospace manufacturing.