7075铝厚板内淬火残余应力的形成机理分析与控制策略

Formation Mechanism Analysis and Control Strategy of Residual Stresses for Quenching 7075 Aluminum Alloy Thick Plate

摘要:

残余应力在材料去除后的释放与再分布是引起飞机结构件加工变形的重要因素。而淬火过程中,铝合金厚板内部产生高温度梯度场,由其造成的不均匀塑性变形是形成淬火残余应力的关键所在。为此,通过作为表示工件与介质之间换热能力的对流换热系数,建立了淬火工艺的有限元分析模型,与实验结果的比较分析表明,无论是残余应力幅值还是分布趋势,仿真值均有很高的吻合度。在此基础上,利用有限元方法进行了淬火残余应力的形成机理,认为芯层在终滑点塑性变形结束时最终的残余应力已经形成,之后继续降温过程残余应力基本保持不变。最后以芯层终滑点为依据提出了热换系数的残余应力控性控形方法。从分析结果可知,控形区对最终残余应力的影响很大,控性区段基本不影响最终残余应力。因此,可以通过合理降低控形区邻域和增加控性区邻域内对流热换系数的方法,实现冷却速度的增加和残余应力的减少。

Abstract:

During the operation of material removal, the release and re-distribution of residual stresses is crucial to machining deformations of aircraft structural parts. Hence, the non-uniform plastic deformations, which caused by the high temperature gradient field in the quenching process, will give rise to residual stresses. Therefore, the finite element model is established for the quenching process according to the convective heat transfer coefficient. Whether the amplitude or distribution, the simulated residual stresses are in good agreement with the experimental data. On this basis, the proposed method is further used to analyze the formation mechanism of residual stress in the quenching of 7075 aluminum alloy thick plate. It is concluded that the final residual stresses are already determined when the plastic deformations in the central layer is over at the end slip time. The residual stresses remain unchanged even if the temperature will continue to drop. Finally, the performance-controlled and deformation-controlled method is suggested for residual stresses. It is known that the deformation-controlled region can strongly impact the final residual stresses whereas the performance-controlled region has a few changes of the final residual stresses. Consequently, the decrease of the convective heat transfer coefficient in the deformation-controlled region and the increase in the performance-controlled region, can fast the cooling velocity and reduce the final residual stress.