7075高强铝合金构件冷成形强化机制研究

Cold Forming Strengthening Mechanism of 7075 High-strength Aluminum Alloy Components

目的针对7075高强铝合金构件在固溶-淬火-时效处理过程中成形精度低的问题,提出了7075高强铝合金预强化冷成形工艺,研究7075高强铝合金构件冷成形强化机制。方法基于高强铝合金短流程高性能成形技术,经过固溶-时效处理,获得预强化处理的7075铝合金板料,使用预强化处理的7075铝合金板料冷成形试制帽形梁。通过拉伸试验、杯突试验测试预强化处理的7075铝合金板料及帽形梁力学性能,并通过透射电子显微镜试验解释7075高强铝合金构件冷成形强化机制。结果预强化处理的7075铝合金板料抗拉强度为540MPa,延伸率为19.3%,强度接近7075铝合金T6态强度水平,塑性接近7075铝合金O态塑性水平。杯突值为16.6 mm,达到7075铝合金O态的87%。使用预强化处理的7075铝合金板料冷成形试制的帽形梁表面质量良好,无破裂等情况。经过烤漆工艺后,帽形梁抗拉强度为(560±5)MPa,屈服强度为(480±5)MPa,与7075高强铝合金T6态强度相当。结论预强化处理的7075铝合金板料基体内部存在大量GPⅡ区组织,这有助于提高7075高强铝合金的强度和塑性。使用预强化处理的7075铝合金板料冷成形试制的帽形梁在烤漆工艺处理时,基体中部分GPⅡ区会转变为η'相,析出相的转变和加工硬化的结合提高了成形构件的强度,使其强度可以达到7075高强铝合金T6态强度水平。

High-strength aluminum alloy components,such as those made of 7075 alloy,typically undergo solution treatment,quenching,and aging to enhance their strength and other properties.In response to the challenge of reduced forming precision dur-ing the heat treatment process for 7075 high-strength aluminum alloy components,a pre-strengthening cold forming process for 7075 high-strength aluminum alloy is proposed.The work aims to study the strengthening mechanisms involved in the cold forming of 7075 high-strength aluminum alloy components.By pre-hardening forming technique for high-strength aluminum alloys,the pre-hardened 7075 aluminum alloy sheets were obtained after solution treatment and aging.A cap-shaped beam was fabricated by the pre-hardening cold forming process for 7075 high-strength aluminum alloy.Mechanical properties of the pre-hardened 7075 aluminum alloy sheets and the cap-shaped beam were evaluated through tensile tests and cupping tests.Additionally,the strength-ening mechanisms involved in the cold forming of 7075 high-strength aluminum alloy components were elucidated based on the results from transmission electron microscopy experiments.The pre-hardened 7075 aluminum alloy sheet exhibited a tensile strength of 540 MPa and an elongation percentage of 19.3%,with strength levels close to those of 7075 aluminum alloy in the T6 temper,and plasticity comparable to that of 7075 aluminum alloy in the O temper.The cupping value was measured at 16.6 mm,reaching 87%of the cupping value for 7075 aluminum alloy in the O temper.The cap-shaped beam produced by the pre-hardening cold forming process for 7075 aluminum alloy showed excellent surface quality,with no signs of fractures.After the painting proc-ess,the cap-shaped beam demonstrated a tensile strength of(560±5)MPa and a yield strength of(480±5)MPa,comparable to the strength of 7075 high-strength aluminum alloy in the T6 temper.The pre-hardened 7075 aluminum alloy sheet contains a significant amount of GPⅡzone structure within the matrix.This structure contributes to enhancing the strength and plasticity of 7075 high-strength aluminum alloy.The cap-shaped beam fabricated by the pre-hardening cold forming process for 7075 high-strength aluminum alloy exhibits a transformation of some GPⅡzones within the matrix intoη'phase when treated in painting process.The combination of phase precipitation transformation and work hardening elevates the strength of the formed component,allowing it to achieve strength levels equivalent to 7075 high-strength aluminum alloy in the T6 temper.