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| Hot Stamping With Pre-Cooling Treatment for AA7055 High-Strength Aluminum Alloy Sheets |
| YUE Yuting 1, 2, FENG Weijun3 , YANG Bing3 , LI Yongfeng 1, 2, HE Ji 1, 2 |
| (1. State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China; 2. Shanghai Key Laboratory of Digital Manufacture for Thin-walled Structures, Shanghai Jiao Tong University, Shanghai 200240, China; 3. Baowu Aluminum Technical Center, Baosteel Central Research Institute, Baoshan Iron & Steel Co., Ltd., Shanghai 201900, China) |
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Abstract For high-strength aluminum alloys at the solution temperature, it is difficult to achieve the best formability during the hot stamping and cold die quenching process (heat treatment, forming and in-die quenching, HFQ), and forming defects such as cracks would occur easily. To solve this problem, this paper introduces a pre-cooling treatment, which could cool the solid solution sheet to target temperature. In the quenching sensitivity temperature range, the mechanical properties of an AA7055 high-strength aluminum alloy sheet were tested under different pre-cooling temperatures after solid solution. It is found that the largest elongation and the best formability are obtained at pre-cooling temperature of 350℃. Taking structural parts with typical characteristics as an example, the HFQ process tests with different pre-cooling conditions and original sheet materials were carried out. It is found that the surface quality of the F–state sheet is better than that of the O–state one, and F-state sheet has better formability under the same process flow. The traditional HFQ comparative forming experiment was carried out on the F–state sheet, and the F–state sheet was severely broken without pre-cooling treatment. The uniaxial tensile tests were carried out on the typical positions of the well-formed parts. And it proves that the strength of the formed part is the lowest at the pre-cooling temperature of 350℃, which is near the nose tip temperature for quenching sensitivity. Taking into account the formability and strength, the pre-cooling temperature should be 400℃.
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2021, 
