内部残余应力的SWXRD方法及在搅拌摩擦焊铝合金板中的应用

发布时间：2018-04-28 21:13

本文选题：短波长特征X射线衍射 + 残余应力　；参考：《北京科技大学》2017年博士论文

【摘要】：内部残余应力的大小和分布,直接关系到搅拌摩擦焊(friction stir welding,FSW)焊接件的机械性能、尺寸精度和服役寿命。本文利用国内自主研发的短波长特征 X 射线衍射(short-wavelength X-ray diffraction,SWXRD)技术,克服常规残余应力测量方法难以实现强织构材料内部残余应力无损测试的不足,研究了高强铝合金FSW焊接件内部残余应力的无损测试分析方法,建立了材料微观组织、宏观物理性能和宏观残余应力的综合评价体系。为克服高强铝合金FSW焊接件内部应力梯度大、组织变化大及织构强等对残余应力测试分析的不利条件,首先针对SWXRD定点无损测试分析内部残余应力的方法进行了系统地优化研究。研究了应力计算模型、无应力参考晶面间距、晶体取向和衍射晶面等因素对残余应力测试结果的影响规律,提出了准确、可靠地无损测定高强铝合金FSW内部残余应力的SWXRD测试分析模型;建立了一种Extreme函数负角度拟合模型,解决了 SWXRD方法得到的低角度衍射峰形不对称的问题,提高了 SWXRD衍射分析的准确度。在内部残余应力精确检测分析的基础上,研究了转速和自然时效时间对7075-T651铝合金预拉伸板FSW焊接件内部残余应力大小和分布的影响;系统地研究了焊接接头微观组织结构、显微硬度与残余应力的关系。接头显微硬度最小值与残余应力梯度最大位置都位于热机械影响区和热影响区的交界处。经自然时效,接头焊核区和热机械影响区的显微硬度明显变大,但硬度较小区域的范围没有变化;残余应力的分布变化不大。对7050-T7451铝合金预拉伸板FSW焊接件,进行了焊接工艺参数-残余应力-微观组织-力学性能的关联性系统研究,使用宏观残余应力的分析结果对焊接工艺参数进行评定,建立了残余应力-组织-性能的关联性分析模型。结果表明,采用较低的转速和较高的前进速度可以获得综合性能较好的FSW焊接样品。FSW接头内部的残余应力分布,与其微观组织和力学性能均存在关联性,可以作为一项重要的无损检测评价指标对FSW焊接件的工艺参数进行评定。
[Abstract]:The size and distribution of internal residual stresses are directly related to the mechanical properties, dimensional accuracy and service life of the friction stir welding, FSW welding parts. This paper uses the short wavelength characteristic X ray diffraction (short-wavelength X-ray diffraction, SWXRD) technology independently developed in China to overcome the difficulty of the conventional residual stress measurement method. In order to realize the inadequacy of the nondestructive testing of the internal residual stress in the strong textured material, the nondestructive testing and analysis method of the internal residual stress in the high strength aluminum alloy FSW welding parts is studied. The comprehensive evaluation system of the microstructure, macroscopic physical properties and the macroscopic residual stress of the material is established. The structure of the internal stress gradient of the high strength aluminum alloy FSW welding parts is overcame and the structure is organized. The adverse conditions of residual stress testing and analysis of large variation and texture are discussed. Firstly, the method of SWXRD fixed point nondestructive testing and analysis of internal residual stress is systematically studied. The influence of stress calculation model, no stress reference surface spacing, crystal orientation and diffraction crystal surface on residual stress test results is studied. The SWXRD test and analysis model of the internal residual stress of high strength aluminum alloy FSW is presented accurately and reliably, and a negative angle fitting model of Extreme function is established, which solves the problem of the asymmetric peak shape of the low angle diffraction by the SWXRD method, and improves the accuracy of the SWXRD diffraction analysis. The accurate detection of the internal residual stress is made. On the basis of the analysis, the influence of rotational speed and natural aging time on the size and distribution of internal residual stress of 7075-T651 aluminum alloy prestretched plate FSW welded parts was studied. The relationship between microstructure, microhardness and residual stress of the welded joint was systematically studied. The maximum position of the minimum microhardness of the joint and the residual stress gradient were both located. The microhardness of the joint nuclear zone and the thermo mechanical affected zone is obviously larger by natural aging, but the range of the small area of hardness is not changed, and the distribution of residual stress is not changed. The welding process parameters residual stress microcosmic of the 7050-T7451 aluminum alloy prestretched plate FSW welding parts have been carried out. The relationship between the microstructure and mechanical properties is studied. The welding process parameters are evaluated by the analysis of the macro residual stress and the correlation analysis model of the residual stress tissue properties is established. The results show that the.FSW joint of FSW welding sample with better comprehensive performance can be obtained with the lower speed and the higher forward speed. The distribution of residual stress is related to its microstructure and mechanical properties, and it can be used as an important nondestructive evaluation index to evaluate the process parameters of FSW welding parts.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG453.9

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