本文選題：短波長特征X射線衍射 + 殘余應力　； 參考：《北京科技大學》2017年博士論文

【摘要】：內(nèi)部殘余應力的大小和分布,直接關系到攪拌摩擦焊(friction stir welding,FSW)焊接件的機械性能、尺寸精度和服役壽命。本文利用國內(nèi)自主研發(fā)的短波長特征 X 射線衍射(short-wavelength X-ray diffraction,SWXRD)技術,克服常規(guī)殘余應力測量方法難以實現(xiàn)強織構材料內(nèi)部殘余應力無損測試的不足,研究了高強鋁合金FSW焊接件內(nèi)部殘余應力的無損測試分析方法,建立了材料微觀組織、宏觀物理性能和宏觀殘余應力的綜合評價體系。為克服高強鋁合金FSW焊接件內(nèi)部應力梯度大、組織變化大及織構強等對殘余應力測試分析的不利條件,首先針對SWXRD定點無損測試分析內(nèi)部殘余應力的方法進行了系統(tǒng)地優(yōu)化研究。研究了應力計算模型、無應力參考晶面間距、晶體取向和衍射晶面等因素對殘余應力測試結果的影響規(guī)律,提出了準確、可靠地無損測定高強鋁合金FSW內(nèi)部殘余應力的SWXRD測試分析模型;建立了一種Extreme函數(shù)負角度擬合模型,解決了 SWXRD方法得到的低角度衍射峰形不對稱的問題,提高了 SWXRD衍射分析的準確度。在內(nèi)部殘余應力精確檢測分析的基礎上,研究了轉(zhuǎn)速和自然時效時間對7075-T651鋁合金預拉伸板FSW焊接件內(nèi)部殘余應力大小和分布的影響;系統(tǒng)地研究了焊接接頭微觀組織結構、顯微硬度與殘余應力的關系。接頭顯微硬度最小值與殘余應力梯度最大位置都位于熱機械影響區(qū)和熱影響區(qū)的交界處。經(jīng)自然時效,接頭焊核區(qū)和熱機械影響區(qū)的顯微硬度明顯變大,但硬度較小區(qū)域的范圍沒有變化;殘余應力的分布變化不大。對7050-T7451鋁合金預拉伸板FSW焊接件,進行了焊接工藝參數(shù)-殘余應力-微觀組織-力學性能的關聯(lián)性系統(tǒng)研究,使用宏觀殘余應力的分析結果對焊接工藝參數(shù)進行評定,建立了殘余應力-組織-性能的關聯(lián)性分析模型。結果表明,采用較低的轉(zhuǎn)速和較高的前進速度可以獲得綜合性能較好的FSW焊接樣品。FSW接頭內(nèi)部的殘余應力分布,與其微觀組織和力學性能均存在關聯(lián)性,可以作為一項重要的無損檢測評價指標對FSW焊接件的工藝參數(shù)進行評定。
[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.

【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG453.9

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本文編號：1816896