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Research Papers

Dislocation Density and Grain Size Evolution in the Machining of Al6061-T6 Alloys

[+] Author and Article Information
Liqiang Ding

School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China

Xueping Zhang

School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: zhangxp@sjtu.edu.cn

C. Richard Liu

School of Industrial Engineering,
Purdue University,
West Lafayette, IN 49707

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received May 16, 2013; final manuscript received May 8, 2014; published online June 5, 2014. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 136(4), 041020 (Jun 05, 2014) (10 pages) Paper No: MANU-13-1225; doi: 10.1115/1.4027675 History: Received May 16, 2013; Revised May 08, 2014

This study focuses on addressing the severe plastic deformation (SPD) behavior and the effects of machining parameters on microstructure alternations in machined surface created from high-speed machining. A finite element (FE) model is proposed to predict the orthogonal machining of Al6061-T6 alloys at high speeds. By extracting strains, strain rates, stresses, and temperatures from this model, a dislocation density-based model is incorporated into it as a user-defined subroutine to predict dislocation densities and grain sizes in machined surface. The predicted results show that dislocation densities decrease with the depths below the machined surface, but grain sizes present an opposite tendency. Higher cutting speeds are associated with thinner plastic deformation layers. Dislocation densities decrease with cutting speeds, but grain sizes increase with cutting speeds in machined surface. Dislocation densities decrease initially and then increase with feed rates. There exists a critical feed rate to generate the maximum SPD layer in machined surface. Tool rake angle has a great impact on the depth of plastic deformation layer. Thus, it affects the distributions of dislocation densities and grain sizes. A large negative rake angle can induce an increased dislocation density in machined surface. The predicted chip thicknesses, cutting forces, distributions of dislocation densities, and grain sizes within the range of machining parameters have good agreement with experiments in terms of chip morphology, cutting forces, microstructure, and microhardness in chip and machined surface.

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Figures

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Fig. 1

Normal and shear stress distributions in tool rake face

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Fig. 2

Heat partition model in orthogonal machining of Al6061-T6 alloys

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Fig. 3

FE model for the orthogonal machining of Al6061-T6 alloys

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Fig. 4

An iterated FE analysis procedure to incorporate with dislocation density-based model

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Fig. 5

Predicted chip morphology: (a) feed rate = 0.053 mm/rev; (b) feed rate = 0.122 mm/rev

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Fig. 6

Predicted versus experimental chip thicknesses at different feed rates

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Fig. 7

Predicted versus experimental cutting forces at (a) feed rate = 0.053 mm/rev; (b) feed rate = 0.122 mm/rev

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Fig. 8

Experimental setup of the orthogonal machining of Al606-T6 alloys

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Fig. 9

Measured microstructure of Al6061-T6 alloy created by machining at speed of 1.508 m/s: (a) chip; (b) machined surface

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Fig. 10

Predicted distributions of dislocation densities and grain sizes: (a) dislocation densities; (b) grain sizes

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Fig. 11

Micro-hardness in chip

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Fig. 12

Predicted dislocation densities and grain sizes in chip: (a) dislocation densities; (b) grain sizes

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Fig. 13

Microhardness and dislocation density in machined surface

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Fig. 14

Predicted dislocation densities and grain sizes at different cutting speeds: (a) dislocation densities; (b) grain sizes

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Fig. 15

Thicknesses of deformation layers at different cutting speeds

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Fig. 16

Predicted dislocation densities and grain sizes at different feed rates: (a) dislocation densities; (b) grain sizes

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Fig. 17

Thicknesses of deformation layers at different feed rates

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Fig. 18

Predicted dislocation densities and grain sizes at different tool rake angles: (a) dislocation densities; (b) grain sizes

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Fig. 19

Thicknesses of deformation layer at different tool rake angles

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