【作者】 李保永；

【导师】 张凯锋；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 近αTA15钛合金,具有中等的室温和高温强度,良好的热稳定性和焊接性能,较好的工艺塑性。与广泛使用的TC4合金比较,当工作温度提高到450~500℃时,其强度可高出100~150MPa,因此TA 15钛合金成为我国新型歼击机的关键结构用材。激光焊接高能量密度、高效率、高精度、适应性强、高焊接质量、很小的热影响区和变形区等优点,可有效提高多层结构制造的质量和效率。多层板结构具有承力层稳定性高、结构弯曲刚度大、外形和表面质量高、结构重量较小、良好的能量吸收和疲劳性能等优点,已被广泛用来制造航空航天用钛合金、铝合金等构件。本文以TA15钛合金多层结构的研制为背景,对新型的激光焊接/超塑成形/扩散连接(LBW/SPF/DB)工艺进行研究。文中分别研究了TA15钛合金多层结构超塑成形有限元模拟,TA15钛合金激光穿透焊接工艺、TA15钛合金高温拉伸性能,从而实现两层结构的LBW/SPF和四层结构的LBW/SPF/DB。首先采用MSC.MARC2005对十字单元、四层结构芯板和面板的超塑成形过程进行模拟,获得了构件各区域的厚度分布和成形过程中的危险区域及压力加载曲线。通过TA15钛合金CO2激光穿透焊接工艺试验研究,对焊前清理、焊接过程中的气体保护、离焦量、激光功率、焊接速度等工艺参数进行了优化,确定了最佳的焊接工艺参数。对TA15钛合金板材进行了高温拉伸试验,其在整个试验温度区间均表现出良好的超塑性,880℃下的延伸率最大为840%, 930℃为多层结构合适的超塑成形温度。进行了两层结构毛坯和四层结构芯板的激光穿透焊接,采用自主设计制造的模具和超塑成形系统,在930℃采用修正的压力加载曲线进行了两层结构和四层结构的超塑成形,获得了较好的成形件,其加强筋完全直立,加强筋交叉处两端附近区域因最后完成变形减薄严重,焊接接头附近由于应力集中,变形前期减薄也较为严重。分析了四层结构成形各区域的组织变化,芯板和面板间的贴合区域扩散连接基本全部完成,相互倚靠的直立加强筋之间的扩散连接焊合率也达到了90%以上。更多还原

【Abstract】 Near-alpha TA15 titanium alloy has moderate room-temperature and high-temperature strength, outstanding thermal stability and welding performance, good abilitity of deformation. Contacted with the more widely used TC4 alloy, when the temperature increased to 450 ~ 500℃, its strength may be higher than TC4 to 100 ~ 150MPa, so TA 15 titanium has become the key structure material of China’s new fighter. Laser welding with the advantages of high energy density, high efficiency, high precision, strong adaptability, high welding quality, narrow heat affected zone and deformation zone, can effectively improve the quality and efficiency for the manufacturing of multi-layer structure. Multi-layer structure which has the advantages of high load-bearing layer stability, good bending rigidity, and excellent shape precision, high surface quality as well as light structural weight, good energy absorption and fatigue resistance has been widely used in the manufacture of titanium alloys and aluminum alloys aerospace structures.In this paper, with the background of the manufacture of TA15 titanium alloy multi-layer structure, a new laser beam welding / superplastic forming / diffusion bonding (LBW/ SPF/DB) process were studied. The multi-sheet structure of the finite element simulation, the laser penetration welding, and the high tempreture tensile properties andof TA15 titanium alloy were investigated, in order to manufature two- sheet structure with the technology of LBW/SPF and four- sheet structure with the technology of LBW/SPF/DB.At the very beginning, FEM was studied with MSC.MARC2005 on the superplastic forming process of the cross unit, four-layer structure of plates and panels. In the end, the thickness distribution of the component, the dangerous zone in the forming process and the pressure load curve were received. The penetration welding technique of CO2 laser beam welding for TA15 titanium alloy was studied. The optimal welding parameters, such as the cleaning before LBW, gas shielded during the welding process, the position of focal point, the laser power and welding speed and so on, were confirmed.The high temperature tensile tests of A15 titanium alloy plate were carried out, in the whole test temperature range, the alloy showed excellent superplasticity, 880℃under an extension of the maximum rate of 840%, and 930℃as a suitable superplastic forming temperature for the multi-sheet structure. The rough of two-layer structure and the core board of four-layer structure were welded by the penetration welding technique. With the self-designed superplastic forming system and the correction pressure load curve, the superplastic forming of two-layer structure and four-layer structure were carried out at 930℃,finally good structures with completely vertical stiffeners were obtained. But the two Ends of the crossing vertical stiffeners was a little thin because of the last forming, at the same time, the vicinity of welded joints became thinner as the stress concentration. The microstructure of the four-layer structure was studied, the contacted regions between the core board and the face board had diffusion bonded completely, and the bonding percent between the back-to back vertical stiffeners was more than 90%.更多还原