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  本文選題：熱源輔助　切入點：攪拌摩擦焊　出處：《南京理工大學》2017年碩士論文

【摘要】：針對鋼等高強度、高熔點材料難以直接實現(xiàn)攪拌摩擦焊、攪拌頭易磨損等問題,本文設(shè)計了薄鋼板專用攪拌頭和熱源輔助攪拌摩擦焊裝置,研究了工藝參數(shù)對薄板Q235鋼和304不銹鋼熱源輔助攪拌摩擦焊工藝成形、組織、顯微硬度、力學性能的影響規(guī)律,分析了斷口形貌與斷裂機制,揭示了強化組織形成與增強機理。通過對Q235和304不銹鋼焊縫表面成形評級研究發(fā)現(xiàn),一般情況下,轉(zhuǎn)速和焊接電流增加或焊速降低,表面飛邊金屬堆積量和匙孔前熔化凝固金屬量增加,反之減少。轉(zhuǎn)速過高或過低,匙孔前側(cè)熔化凝固金屬量變化不明顯,是因為轉(zhuǎn)速過低,FSW產(chǎn)熱不足以使TIG電弧區(qū)材料升溫熔化。轉(zhuǎn)速過高,摩擦系數(shù)降低,攪拌頭產(chǎn)熱趨于穩(wěn)定值,總熱輸入趨于穩(wěn)定。焊接熱輸入過大時,焊縫背部前進側(cè)附近出現(xiàn)凹槽。對TIG影響區(qū)截面宏觀形貌的研究結(jié)果表明,FSW產(chǎn)熱與電阻熱和電弧熱疊加,電弧影響區(qū)熔深增加;攪拌頭高速旋轉(zhuǎn)擠壓使軟化材料填充至對接縫間隙,在高溫強流變作用下形成擠壓塑變焊接區(qū),轉(zhuǎn)速越高,擠壓塑變焊接區(qū)厚度越大。通過對Q235鋼和304不銹鋼焊縫組織研究發(fā)現(xiàn),焊縫橫截面微觀組織基本分為軸肩攪拌區(qū)、熱機影響區(qū)、熱影響區(qū)、電阻加熱區(qū)、母材金屬5個區(qū)域。表層細晶區(qū)為鐵素體或奧氏體再結(jié)晶細晶層,"根莖狀"組織為再結(jié)晶鐵素體或奧氏體細晶,Q235焊縫存在馬氏體"根須狀"組織和過渡層。焊縫整體硬度高于母材硬度,Q235鋼近表面區(qū)硬度最高達252.9HV,304不銹鋼厚度中心線最高硬度達360HV。轉(zhuǎn)速和焊接電流越高或焊接速度越低,接頭硬度升高。力學性能研究結(jié)果表明,對Q235,當轉(zhuǎn)速為800r/min,焊速為40mm/min,電流為60A時,接頭抗拉強度最高達514MPa,比母材強度高20%,是因為焊縫中細晶區(qū)和馬氏體過渡層提供了細晶強化和相變強化。并且轉(zhuǎn)速為800～1200r/min時,轉(zhuǎn)速越高,接頭抗拉強度越低;對304不銹鋼,正交試驗參數(shù)對接頭抗拉強度的影響順序為焊接電流焊接速度攪拌頭轉(zhuǎn)速;當轉(zhuǎn)速為800r/min,焊接速度為50mm/min,焊接電流為60A時,抗拉強度最大達650MPa,與母材近等強。
[Abstract]:In view of the problems of high strength and high melting point materials such as steel, it is difficult to realize friction stir welding directly, and the friction stir head is easy to wear, this paper designs a special stir head for thin steel plate and a heat source assisted friction stir welding device.The effects of process parameters on the forming, microstructure, microhardness and mechanical properties of FSW for Q235 steel and 304 stainless steel were studied. The fracture morphology and fracture mechanism were analyzed, and the formation and strengthening mechanism of strengthened microstructure were revealed.Through the research on the surface forming rating of stainless steel Q235 and 304 stainless steel, it is found that, in general, the rotating speed and welding current increase or decrease, the amount of surface flash metal and the amount of melting solidified metal before keyhole increase, whereas the amount of solidified metal decreases.If the rotational speed is too high or too low, the amount of molten solidified metal in front of the keyhole does not change obviously, because the low rotational speed of FSW is not enough to heat up and melt the material in the TIG arc region.When the rotational speed is too high, the friction coefficient decreases, the heat production value of the mixing head tends to be stable, and the total heat input tends to be stable.When the welding heat input is too large, the groove appears near the forward side of the back of the weld.The results of the study on the macroscopic morphology of the section of the influence zone of TIG show that the heat production of the affected zone is superimposed with the heat of resistance and arc heat, and the penetration of the zone affected by the arc increases, and the high speed rotating extrusion of the stirring head makes the softened material fill the gap of the butt joint.The extrusion plastic welding zone is formed under the action of high temperature and strong rheology. The higher the rotational speed, the greater the thickness of extrusion plastic deformation welding zone.The microstructure of weld of Q235 steel and 304 stainless steel is studied. The microstructure of cross section of weld is divided into five regions: shaft-shoulder stirring zone, heat affected zone, heat affected zone, resistance heating zone and base metal.The surface fine grain area is ferrite or austenite recrystallized fine crystal layer, the "rhizomorphic" structure is recrystallized ferrite or austenite fine crystal Q235 weld metal, there is martensite "root whisker" structure and transition layer.The overall hardness of the weld is higher than that of the base metal. The highest hardness of the near surface area of Q235 steel is 252.9 HVC304 stainless steel thickness centerline and the highest hardness is 360 HV.The higher the rotating speed and welding current or the lower the welding speed, the higher the joint hardness.The higher the rotational speed is, the lower the tensile strength of the joint is, and for 304 stainless steel, the influence of orthogonal test parameters on the tensile strength of the joint is in the order of welding current welding speed and stirring head speed.When the rotational speed is 800 r / min, the welding speed is 50 mm / min and the welding current is 60 A, the maximum tensile strength is 650 MPA, which is nearly as strong as the base metal.
【學位授予單位】：南京理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG453.9

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本文編號：1714776