扭转塑性变形对6063铝合金拉伸力学性能的影响机理研究

扭转是一种常用的冷作硬化方法。本文通过实心圆轴扭转实验和预扭试件的单向拉伸实验,研究了扭转塑性变形程度对6063铝合金拉伸力学性能的影响。通过理论研究和硬度分析探究了造成这一影响的内在机理。结果表明,试件扭转后其内部形成的以屈服强度为特征参数的梯度结构,是造成预扭试件力学性能得到改善的根本原因。并且,扭转不同的角度,材料内部产生的梯度结构也是不同的。而不同的梯度结构对试件力学性能的影响则表现为后继拉伸屈服强度随预扭角度的增大而增大。为了预测预扭试件的后继拉伸力学行为,验证前述结论的正确性,建立了由内到外屈服强度逐渐变化的有限元模型。此模型代表了预扭转变形试件,对其施加位移载荷,模拟后继单向拉伸加载过程。模拟所得材料力学性能随扭转角的变化趋势与实验结果基本吻合,从而验证了扭转冷作硬化后,圆轴试件内部产生了以屈服强度为特征参数的梯度结构这一结论。同时,也提供了一种有效的预测材料扭转后拉伸力学性能的数值模拟方法。

On the Mechanism of Effect of Torsional Plastic Deformation on 6063 Aluminum Alloy Tensile Mechanical Properties

Torsion is a common method of cold-work hardening. In this paper, the effect of torsional plastic deformation on tensile mechanical properties of 6063 aluminum alloy was investigated through solid cylinder torsional experiment and uniaxial tensile experiment of pre-torsioned specimens; and the intrinsic mechanism of effect was explored qualitatively based on theoretical study and hardness analysis. Results show that the formation of gradient structure inside pre-torsioned specimen and described by yield strength as characteristic parameter is the basic reason for the mechanical property improvement of pre-torsioned specimen. In addition, different torsional angles produce different gradient structures inside the pre-torsioned specimens. The influence of different gradient structures on the specimen''s mechanical properties is demonstrated by the succeeded tensile yield strength increase with the increase of pre-torsioned angle. In order to predict the subsequent tensile mechanical behavior of pre-torsioned specimen, and to validate above argument, a finite element model was established, in which the yield strength varies gradually from inside to outside. This model represents the pre-torsioned deformation specimen. Applying displacement load to it, the process of subsequent uniaxial tensile loading on the model can be simulated. The simulated variation trend of mechanical properties along with torsional angles is in agreement with that of experimental results, which proves the formation of gradient structure inside cylindrical specimen after torsional deformation. Meanwhile, this procedure provides an effective numerical simulation method to predict the mechanic properties of materials after torsional deformation.