高强铝合金热冲压析出相遗传演化规律及其对性能影响机制

The HS (hot stamping) technique of lightweight aluminum alloy has become a research hotspot at home and abroad. Previous study indicates that the thermal deformation obviously influence the genetic evolution of the precipitated phase and then influence the property of the HS aluminum alloy. Up to date, the genetic evolution of the precipitated phase in the process of forming/aging and its influence mechanism on the property of the HS aluminum alloy, which will be investigated by experiments and modelling with the I-beam part of the car body as the research object in this project, are still unclear. The detailed research contents include: (1) Study the genetic evolution process of the precipitated phase in the process of forming/aging and the property of the high strength aluminum alloy experimentally; Analyze the influence factors of the genetic evolution process of the precipitated phase and the property of the aluminum alloy; (2) Develop the numerical models for the evolution of the precipitated phase of the aluminum alloy under the coupling effect of thermal and mechanical; Carry out computer simulations according to the experiments to investigate the genetic evolution discipline of the precipitated phase of the high strength aluminum alloy in the process of forming/aging; Study the effect of stress/strain on the evolution process of the precipitated phase of the high strength aluminum alloy in the process of forming/aging and reveal the influence factors and control method of the evolution process of the precipitated phase in the process of forming/aging; (3) Based on research content (2) and preliminary study, Establish the unified viscoelastic constitutive model for the HS of the high strength aluminum alloy taking into account of dislocation，precipitated phase, grain crystal, damage, stress, strain, strain rate and temperature; Establish the ageing strengthening model considering the influence of stress/strain and the genetic effect of precipitated phase based on research content (2); Based on the experiment results, the unified viscoelastic constitutive model and the ageing strengthening model, study the effect of the genetic evolution of the precipitated phase on the property of the high strength aluminum alloy and illuminate the influence mechanism of the genetic evolution of the precipitated phase on the property of the high strength aluminum alloy under the coupling effect of thermal and mechanical. These researches will establish theoretical bases for quantificationally and accurately forecasting the microstructure and property of the HS aluminum alloy parts in the process of forming/aging.

轻量化铝合金热冲压技术已成为国内外研究的热点，研究表明，铝合金热冲压过程形变对析出相遗传演化有显著影响，从而影响构件使用性能。然而，迄今为止，铝合金热冲压成形-时效过程析出相遗传演化规律及其对性能的影响机制尚不清楚。本项目拟以典型车身构件工字梁为实验对象，研究铝合金热冲压析出相和性能演化及影响因素；提出利用群体动力学方法研究铝合金热冲压成形-时效过程中析出相遗传演化过程，建立铝合金热冲压析出相遗传演化过程理论模型，揭示铝合金热冲压析出相演化规律、影响因素及控制方法；在此基础上，基于项目组前期关于铝合金热变形本构关系的研究基础，建立热（温度）、力（应力、应变、应变速率）、组织（位错、析出相、晶粒、裂纹）相互耦合作用下的本构模型，以及析出相遗传演化作用下的形变强化模型；实验与模型相结合，系统研究析出相遗传演化对构件性能的影响规律，阐明热力耦合作用下析出相遗传演化对构件性能的影响机制。

轻量化铝合金热冲压技术已成为国内外研究热点。研究表明，铝合金热冲压过程形变对析出相遗传演化有显著影响，从而影响构件使用性能。本项目以7075铝合金作为研究对象，将热模拟实验和热处理实验相结合，研究了变形参数对后续时效组织及力学性能的影响规律；建立了高强铝合金时效过程中析出相演化理论模型并耦合析出相演化过程理论模型建立了屈服强度计算模型；实验与模拟相结合，研究了7075铝合金热冲压成形-时效过程析出相遗传演化规律及其对性能的影响机制。获得以下主要研究结果：（1）实验研究结果表明：1）峰时效时间仅与变形量相关，且随变形量的增加先减小后基本保持不变；而峰时效强度则随应变速率的增加先减小、后增大，随变形量的增加先减小，后增大再基本保持不变；2）过时效析出相的平均尺寸和体积分数逐渐随着变形量的增加而增大，但与未变形的试样相比，过时效析出相的数量密度基本呈减小的趋势；3）过时效条件下，试样中的位错密度随着变形量的增加而逐渐增加。（2）基于实验结果进行了拟合计算，计算结果表明：1）热变形对后续时效过程析出相形核有轻微的抑制作用，但对析出相生长有明显的促进作用，从而弱化了析出相在时效过程中的Ostwald长大；2）根据析出相形核率随变形量的变化，推断位错可促进析出相形核，但位错对析出相形核的促进作用与位错的数量密度密切相关。当位错数密度足够时，会促进析出相的形核；当位错数密度不够时，则可能对形核无影响甚至会抑制析出相的形核；3）峰时效时，随着变形量的增加，析出相的平均尺寸几乎没有变化，而析出相体积分数则随着应变的增加呈现先减小后增大的趋势，这与显微硬度随应变增加的变化趋势一致。.在国内外重要学术期刊发表或录用论文5篇，其中SCI论文4篇，已授权中国发明专利2项，依托项目培养研究生3名。