AA7055高强铝合金板预冷热冲压成形研究

Hot Stamping With Pre-Cooling Treatment for AA7055 High-Strength Aluminum Alloy Sheets

高强铝合金板材在传统热冲压冷模淬火工艺(Heat treatment,forming and in-die quenching,HFQ)中,直接在固溶温度进行成形难以实现板材最佳成形性能,容易产生开裂等成形缺陷。针对这一问题,在板材固溶后引入预冷处理,即通过使固溶板材降温到设计目标温度再进行塑性成形,旨在实现铝合金高强薄壁零件的成形成性。针对一种改进AA7055高强铝合金板材,在其淬火敏感温度区间内,进行了固溶后不同预冷温度条件下的力学性能测试,结果表明,在350℃预冷温度下板材延伸率最大,成形性最好。以典型特征结构件为对象,对该材料进行了预冷条件下的HFQ工艺成形试验,获得了不同预冷条件及原始板料成形的影响规律。发现该种铝合金的F态(自由加工态)板料比O态板料表面质量更好,在相同预冷HFQ工艺下成形性更高,进一步对F态坯料进行传统HFQ对比成形试验后发现,在无预冷时F态板料成形破裂严重。对成形零件典型位置进行取样和性能测试,试验结果表明,由于350℃预冷温度在材料鼻尖温度附近,成形件抗拉强度恶化最为严重。为兼顾成形性与强度,预冷温度选择400℃为宜。

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℃.