Surface Layer Modification by Cryogenic Burnishing of Al 7050-T7451 Alloy and Validation with FEM-based Burnishing Model☆
Surface Layer Modification by Cryogenic Burnishing of Al 7050-T7451 Alloy and Validation with FEM-based Burnishing Model☆
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DOI：
10.1016/j.procir.2015.03.097
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
B. Huang;Y. Kaynak;Y. Sun;I. Jawahir
中科院分区：
文献类型：
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作者：
B. Huang;Y. Kaynak;Y. Sun;I. Jawahir
作为无屑加工工艺之一，抛光作为最终操作在制造的部件上进行，以改善表面完整性，包括降低表面粗糙度和增加表面和亚表面硬度。在抛光过程中，由于施加的剧烈塑性变形和伴随的动态再结晶（DRX），可以产生具有超细晶粒或纳米晶粒的细化表面层。这些具有由抛光工艺引起的压缩残余应力的较硬层还通过增强耐磨性/耐腐蚀性和增加部件的疲劳寿命而提供额外的益处。本文研究了以液氮为冷却剂，采用滚压工具对Al 7050-T7451合金进行深冷抛光的效果。测量了抛光力和温度，以比较干式抛光和低温抛光之间的差异。由于低温抛光引入的加工硬化和快速冷却效应，从低温抛光中观察到更高的切向力和更低的温度。此外，具有纳米晶粒的精细层在抛光速度为25，50和100 m/min。有限元模型（FEM）的开发，以模拟抛光力和温度的实验结果的验证，基于修改后的Johnson-Cook流动应力模型相结合的本构方程有关DRX。预测结果与实验结果吻合较好。
As one of the chipless machining processes, burnishing has been performed on manufactured components as the final operation to improve the surface integrity, including reduced surface roughness and increased surface and subsurface hardness. Refined surface layers with ultra-fine grains or nano-grains could be generated during the burnishing process due to imposed severe plastic deformation and the associated dynamic recrystallization (DRX). These harder layers with compressive residual stresses induced by the burnishing process also provide added benefits by enhancing wear/corrosion resistance and increasing the fatigue life of the components. The research findings presented in this paper show the effects of cryogenic burnishing with roller burnishing tool onAl 7050-T7451alloy, using liquid nitrogen as the coolant. Burnishing forces and temperatures are measured to compare the differences between dry and cryogenic burnishing. Higher tangential forces and lower temperatures are observed from cryogenic burnishing due to the work-hardening and the rapid cooling effects introduced by cryogenic burnishing. Also, refined layers with nano-grains (grain size of approximately 40 nm) are formed in the cryogenicallyburnished surface, in which an average hardness increase of 9.5%, 17.5% and 24.8% within the 200 μm depth are achieved in comparison with the hardness values obtained from dry burnishing, at the corresponding burnishing speeds of 25, 50 and 100 m/min. A finite element model (FEM) is developed to simulate the burnishing forces and temperatures for validation of the experimental results, based on the modified Johnson-Cook flow stress model combined with the constitutive equations concerning DRX. Good agreement is obtained between the predicted and experimental results.