挤压态AZ31镁合金恒温超塑性压缩及超塑性焊接研究

发布时间：2018-04-12 23:42

  本文选题：AZ31镁合金 + 退火预处理　； 参考：《太原理工大学》2017年硕士论文

【摘要】：镁合金是高性能轻质结构材料,各类工业产品中广泛采用镁合金为原料。尤其在大力提倡环保、可持续的今天,镁合金诸多优点更为突出。但也有些特点导致其焊接性能较差,焊接接头容易产生粗晶组织、热裂纹等质量缺陷,已成为限制其更广应用的主要原因。恒温超塑性焊接是一种新型简单固态焊接技术,能有效减轻裂纹及气孔等传统焊接缺陷,并利用材料的超塑状态特点,大大减少焊接时间,节约能源,并可与成型同步。目前,此技术仅在钢材、铜合金与钨合金中应用研究并看到明显效果,并未见将其应用在镁合金上展开研究。另外,在此焊接技术中恒温超塑性压缩发挥着关键作用,研究镁合金压缩的超塑性能对恒温超塑性焊接具有必不可少的指导意义。AZ31镁合金是本文的研究材料,首先对其采用退火预处理来细化晶粒、均匀组织,然后对经预处理后的材料进行压缩超塑性能探究,最后根据超塑性能规律及各因素影响结果进一步探究镁合金的恒温超塑性焊接。退火预处理的结果显示,在300℃下经30 min退火后晶粒达到较好细化效果,晶粒尺寸由最初的20.79 um细化至12.15μm,细化率为40.7%左右。在250℃至480℃温度下及1×10~(-4) s~(-1)至1×10~(-2) s~(-1)的初始应变速率范围内压缩,试样的外缘圆周伸长率都在200.42%之上,均实现了良好的压缩超塑性。在超塑压缩过程中组织展现了动态再结晶特征,真实的应力-应变曲线符合动态再结晶型曲线,流变应力、压缩后的晶粒状态及动态再结晶程度均受初始应变速率和压缩温度的共同影响,应变速率敏感指数m值在0.18-0.24之间,并随压缩温度升高,其平均值略有增大。经退火处理后的AZ31镁合金在预压应力30 MPa、温度450℃、应变速率为1×10~(-4) s~(-1)的条件下,经13 min恒温超塑性压接,接头剪切强度达到42.08 MPa。恒温超塑性焊接过程中的应力-应变曲线及焊后焊缝处显微组织均体现出超塑性特征。在主要影响因素中温度对恒温超塑性固态焊接接头强度影响较大、时间的影响其次、应变速率的影响相对较小。相比扩散焊,恒温超塑性焊接能在更省能源、省时间的条件下,达到与之相当的接头剪切强度。
[Abstract]:Magnesium alloy is a light structure material with high performance. Magnesium alloy is widely used as raw material in all kinds of industrial products.Especially in the promotion of environmental protection, sustainable today, magnesium alloy many advantages are more prominent.However, there are also some characteristics which lead to poor weldability, and the quality defects such as coarse grain structure and hot crack are easy to be produced in welded joints, which have become the main reasons restricting its wider application.Constant-temperature superplastic welding is a new simple solid-state welding technology, which can effectively reduce the defects of traditional welding such as cracks and pores, and make use of the characteristics of superplastic state of materials, greatly reduce the welding time, save energy, and can synchronize with molding.At present, this technology is only applied in steel, copper and tungsten alloys and has obvious effect, but it has not been applied to magnesium alloys.In addition, constant temperature superplastic compression plays a key role in this welding technology. The study of superplasticity of magnesium alloy compression has an essential guiding significance for isothermal superplastic welding. AZ31 magnesium alloy is the research material of this paper.First of all, annealing pretreatment was used to refine the grain and uniform microstructure, and then the pretreated material was studied by compression superplasticity.Finally, the superplastic welding of magnesium alloy at constant temperature is further explored according to the superplastic energy law and the influence of various factors.The results of annealing pretreatment showed that the grain size was refined from 20.79um to 12.15 渭 m after annealing at 300 鈩，

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