7075铝合金厚板淬火残余应力的研究

【作者】 朱伟；

【导师】 彭大暑； 张辉；

【作者基本信息】 中南大学 ， 材料加工工程， 2002， 硕士

【摘要】 7075是一种铝—锌—镁—铜系可热处理强化的高强度变形铝合金，它通过淬火时效后析出大量弥散强化相，使合金得到强化，被广泛应用于航空、航天等重要领域。但7075铝合金淬火过程中将产生很大的残余应力，使之在后续的机械加工过程中，由于这些残余应力的释放，一方面导致零件形状与尺寸的不稳定性，出现翘曲；另一方面大大降低材料的韧性等使用性能。因此，研究淬火残余应力的分布与影响规律是极为重要的。本文采用钻孔法研究了7075高强度铝合金厚板在高温下直接水淬后在试样内部产生的淬火残余应力的分布状况，探明了7075高强度铝合金厚板淬火后的预拉伸+时效工艺以及单纯的时效工艺对消除淬火残余应力的作用规律。实验表明：7075高强度铝合金厚板淬火后，随着预拉伸量的增加，试样轧向和横向表层的残余应力都逐渐从压应力转变为拉应力，且当预变形量为2％左右时，残余应力基本上趋近于零；随着时效温度的升高和时效时间的延长，试样表层残余应力释放越多，且随着时效温度的升高，残余应力的释放率也越来越大；适当提高淬火介质温度，试样轧向和横向的残余应力均明显减小。此外，研究中还采用有限元方法，对不同淬火介质温度下和预拉伸2.5％的条件下试样中淬火残余应力的分布情形进行了数值计算，其结果与实验结果基本相近。同时也验证了预拉伸量、淬火介质温度的提高有着显著降低淬火残余应力的作用与效果。 研究表明：合理的预拉伸量和时效工艺，以及适当提高淬火介质温度均能显著地降低7075铝合金厚板淬火残余热应力，这是降低7075铝合金厚板淬火残余应力的有效措施。其中尤以采用适当的预拉伸量最见成效。更多还原

【Abstract】 Precipitation-hardened Aluminium alloy 7075 is an AL-Zn-Mg-Cu alloy widely used in the aerospace industry. It gains its high strength through heat treatment involving a severe quenching operation, which can have the adverse effect of introducing residual stresses. It may become unstable with shape and dimension after mechanized process, owing to the releasing of residual stresses. So it is important to study residual stresses. The principles of affecting on residual stresses in quenched Aluminium alloy 7075 thick-plates have been studied and concluded under different thermal treatments and different pre-stretching techniques by the drilling method. The tests show that residual stresses have converted from compress-stresses to tension-stresses with the development of degrees of pre-stretching, and have basically got zero near two percents; It also has indicated that residual stresses have both been reduced in the directions of rolling and transverse with the development of aging temperatures and times. By raising the quenched-media’ s temperature, residual stresses were reduced distinctly.The finite element method is used to simulate the quenching of Aluminum alloy 7075 in an attempt to predict the distribution that develops in simple shapes. We have got several distributing graphs under different quenched-media’ s temperature and 2. 5 percents of pre-stretching. The results are receivable. In the same time, the active propulsions of reducing quenched residual stresses after raising the quenched-media’ s temperature have been certified as the same as the results showed by the finite element method simulation.The studies show that they are effective measures to reduce residual stress in quenched Aluminium alloy 7075 by taking appropriate pre-stretching, aging treatment and the quenched-media’ s temperature, especially well by adaptable pre-stretch .更多还原