The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process
Abstract
:1. Introduction
2. Experiments
2.1. Instrument and Methods
2.2. Experimental Design
2.2.1. Experiment Design of Critical State Criterion of Orange Peel Defect
Experiment Batch No. | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|
Stretching Strain | 0% | 3% | 6% | 9% | 12% |
Specimen No. | Strain Speed/s−1 | Critical Strain/% | Roughness Ra/nm |
---|---|---|---|
1 | 0.0001 | 1.78 | 841 |
2 | 0.0005 | 1.87 | 827 |
3 | 0.001 | 1.14 | 973 |
4 | 0.0015 | 1.19 | 1002 |
2.2.2. Experiment Design of Stretch Forming Limit Diagram
3. Results and Analysis
3.1. The Equilibrium Diagram of Tensile Specimen before Deformation
Heat Treatment Condition | Type of Analysis | Sampling Point | Average | ||||||
---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | |||
T8 | Grain Size Grade | 5.02 | 5.13 | 4.51 | 4.38 | 4.98 | 4.62 | 4.56 | 4.7 |
Average Diameter/µm | 62 | 59 | 76 | 77 | 70 | 75 | 75 | 71 |
3.2. The Establishment of the Criterion for Critical State of Orange Peel Defect
3.3. The Establishment of Stretch-Forming Limit Diagram
Sample | Acquisition Point 1 | Acquisition Point 2 | Acquisition Point 3 | Acquisition Point 4 | Acquisition Point 5 | |||||
---|---|---|---|---|---|---|---|---|---|---|
ε1/% | ε2/% | ε1/% | ε2/% | ε1/% | ε2/% | ε1/% | ε2/% | ε1/% | ε2/% | |
Straight edge | 6.29 | −1.94 | 6.35 | −1.98 | 6.31 | −2.08 | 6.25 | −1.84 | 6.33 | −1.88 |
R = 10 | 3.17 | −0.21 | 3.17 | −0.18 | 2.65 | −0.15 | 2.76 | −0.13 | 3.17 | −0.15 |
R = 15 | 2.95 | −0.19 | 3.04 | −0.13 | 3.27 | −0.12 | 3.31 | −0.23 | 3.09 | −0.08 |
R = 30 | 3.31 | −0.55 | 3.76 | −0.58 | 3.64 | −0.77 | 3.72 | −0.57 | 3.30 | −0.55 |
R = 40 | 4.49 | −1.20 | 4.82 | −1.59 | 4.66 | −1.27 | 3.92 | −1.04 | 4.20 | −1.23 |
Expression | A | B | C |
---|---|---|---|
y = A + Bx + Cx2 | 2.99 | −0.389 | 0.652 |
4. Conclusions
- (1)
- A stretch-forming experiment and testing system with the optical deformation measurement instrument and the universal testing machine operating in collaboration are constructed, the surface morphology change rule of stretched specimens with different strain variables is analyzed, and the corresponding relation between critical orange peel defect and the surface roughness of specimens is obtained. It is discovered that when critical orange peel defect appears on Al–Li alloy sheet metal at the condition of Al–Li–S4–T8, the surface roughness is Ra = 700 ± 50 nm and Rz = 5.5 ± 0.5 μm.
- (2)
- By processing different notched specimens, the stretch-forming limit tests with different strain paths are conducted to obtain the forming limit diagram and forming limit curve equation ε1 = 2.99 − 0.389ε2 + 0.652ε22 for Al–Li–S4–T8 Al–Li alloy, with the surface roughness of characteristic critical orange peel structure as the forming failure criterion.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Feng, J.-W.; Zhan, L.-H.; Yang, Y.-G. The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process. Metals 2016, 6, 13. https://doi.org/10.3390/met6010013
Feng J-W, Zhan L-H, Yang Y-G. The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process. Metals. 2016; 6(1):13. https://doi.org/10.3390/met6010013
Chicago/Turabian StyleFeng, Jing-Wen, Li-Hua Zhan, and Ying-Ge Yang. 2016. "The Establishment of Surface Roughness as Failure Criterion of Al–Li Alloy Stretch-Forming Process" Metals 6, no. 1: 13. https://doi.org/10.3390/met6010013