【摘要】：6082-T6鋁合金具有較高的比強(qiáng)度、優(yōu)異的耐腐蝕性和良好的焊接性能,被廣泛應(yīng)用于高速軌道列車(chē)和航空航天生產(chǎn)領(lǐng)域。攪拌摩擦點(diǎn)焊是一種新型的搭接式固相連接方法。目前,關(guān)于6082-T6鋁合金FSSW接頭動(dòng)態(tài)力學(xué)性能的研究相對(duì)較少。因此,本文主要針對(duì)2.5mm厚的6082-T6鋁合金板材進(jìn)行了FSSW實(shí)驗(yàn),系統(tǒng)地研究了不同焊接工藝下FSSW接頭的準(zhǔn)靜態(tài)力學(xué)性能、高周疲勞性能、高速?zèng)_擊性能。FSSW接頭動(dòng)態(tài)力學(xué)性能的研究對(duì)FSSW接頭在服役條件下預(yù)防失效具有重要的指導(dǎo)意義。準(zhǔn)靜態(tài)力學(xué)性能試驗(yàn)結(jié)果表明:無(wú)匙孔FSSW的最大拉剪強(qiáng)度可達(dá)8.05KN,而FSSW和攪拌摩擦膠點(diǎn)焊接頭分別為4.75KN和6.0KN,它們的接頭強(qiáng)度明顯低于無(wú)匙孔FSSW接頭,這是由于無(wú)匙孔FSSW接頭所形成的有效焊合面積較另外兩種焊接接頭而言較大,且抗變形能力強(qiáng)。并且在加載的過(guò)程中,三種攪拌摩擦點(diǎn)焊接頭所表現(xiàn)出的斷裂方式也不同,其中,攪拌摩擦膠點(diǎn)焊接頭的斷裂方式為膠層斷裂和焊點(diǎn)斷裂的機(jī)械混合,這是由于攪拌摩擦膠點(diǎn)焊接頭是膠接與攪拌摩擦點(diǎn)焊兩種連接方式的復(fù)合連接。高周疲勞性能試驗(yàn)結(jié)果表明:在同一加載載荷水平下,無(wú)匙孔FSSW接頭的疲勞性能最好,有匙孔攪拌摩擦膠點(diǎn)焊接頭的疲勞性能次之,有匙孔FSSW接頭的疲勞性能最差;不同F(xiàn)SSW接頭的疲勞試驗(yàn)數(shù)據(jù)具有很好的規(guī)律性,且加載載荷與疲勞壽命呈指數(shù)型函數(shù)關(guān)系;循環(huán)加載達(dá)到穩(wěn)定階段后,無(wú)匙孔FSSW接頭、FSSW接頭和攪拌摩擦膠點(diǎn)焊接頭在單個(gè)循環(huán)周期內(nèi)的循環(huán)滯回能分別達(dá)到0.72MJ/m3、0.35 MJ/m3和0.36 MJ/m3;從疲勞宏觀斷裂方式可觀察到疲勞裂紋沿著界面間隙向板厚方向擴(kuò)展,且無(wú)匙孔FSSW接頭的宏觀斷口中均存在二次裂紋;依據(jù)FSSW接頭內(nèi)存在的缺陷和疲勞宏觀斷裂方式,初步建立了一種簡(jiǎn)單的疲勞裂紋擴(kuò)展模型,用于評(píng)定疲勞裂紋的擴(kuò)展及疲勞壽命。對(duì)無(wú)匙孔FSSW接頭的四個(gè)區(qū)域分別進(jìn)行分離式霍普金森壓桿試驗(yàn),試驗(yàn)結(jié)果表明:母材區(qū)、焊核區(qū)和熱機(jī)影響區(qū)在動(dòng)態(tài)加載過(guò)程中的變形協(xié)調(diào)能力很好,抗動(dòng)態(tài)沖擊能力較強(qiáng),而熱影響區(qū)的抗動(dòng)態(tài)沖擊能力較差。母材區(qū)的材料的沖擊吸收功為9.068MJ·m-3,焊核區(qū)材料的沖擊吸收功為9.85MJ·m-3,熱機(jī)影響區(qū)材料的沖擊吸收功為8.36MJ·m-3,熱影響區(qū)材料的沖擊吸收功為1.34MJ·m-3;四個(gè)區(qū)域的絕熱剪切敏感性都較小。為了分析準(zhǔn)靜態(tài)拉伸剪切斷裂和高周疲勞斷裂的機(jī)制,對(duì)拉剪斷口和疲勞斷口進(jìn)行了SEM觀察發(fā)現(xiàn):無(wú)匙孔FSSW接頭和攪拌摩擦膠點(diǎn)焊接頭的拉剪斷口中裂紋擴(kuò)展區(qū)存在準(zhǔn)解理面,而FSSW接頭的拉剪斷口中擴(kuò)展區(qū)存在“舌片狀花樣”,在瞬斷區(qū)均存在著韌窩,所以拉伸剪切斷裂均是準(zhǔn)解理斷裂和韌性斷裂的混合斷裂,無(wú)匙孔FSSW接頭拉伸剪切斷口瞬斷區(qū)存在大量的等軸韌窩,說(shuō)明其接頭的塑性較好;三種FSSW接頭的疲勞斷裂方式也是準(zhǔn)解理斷裂和韌性斷裂的混合斷裂。
[Abstract]:6082-T6 aluminum alloy has high specific strength, excellent corrosion resistance and good welding performance, so it is widely used in high-speed rail train and aerospace production field. Friction stir spot welding (FSW) is a new type of lap-type solid-phase bonding method. At present, there are few studies on the dynamic mechanical properties of 6082-T6 aluminum alloy FSSW joints. Therefore, in this paper, the quasi-static mechanical properties and high cycle fatigue properties of FSSW joints under different welding processes are systematically studied by means of FSSW experiments on 6082-T6 aluminum alloy plates with 2.5mm thickness. The study of dynamic mechanical properties of FSSW joints is of great significance to prevent the failure of FSSW joints under the condition of service. The results of quasi-static mechanical properties test show that the maximum tensile shear strength of keyhole free FSSW is 8.05 KN, while that of FSSW and friction stir joint is 4.75KN and 6.0 KN, respectively, and their joint strength is obviously lower than that of FSSW joint without keyhole. This is because the effective soldering area of the keyhole free FSSW joint is larger than that of the other two welded joints, and the deformation resistance is strong. In the process of loading, the fracture modes of the three friction stir spot welding joints are different, among them, the fracture mode of friction stir glue spot welding joint is the mechanical mixing of rubber layer fracture and solder joint fracture. This is because the friction stir spot welding joint is a compound connection of glue and friction stir spot welding. The results of high cycle fatigue test show that under the same loading load, the fatigue performance of FSSW joints with keyhole is the best, the fatigue performance of FSW joints with keyhole is the second, and the fatigue performance of FSSW joints with keyhole is the worst. The fatigue test data of different FSSW joints have good regularity, and the relationship between loading load and fatigue life is exponential. After cyclic loading reached the stable stage, the cyclic hysteresis energies of keyhole free FSSW joints, FSSW joints and friction stir spot welding joints reached 0.72 MJ / m3 0.35 MJ/m3 and 0.36 MJ/m3; respectively in a single cycle. From the fatigue macroscopic fracture mode, it can be seen that the fatigue crack propagates along the interface gap to the thickness direction of the plate, and there are secondary cracks in the macroscopic fracture of the FSSW joint without keyhole. According to the defects in FSSW joints and the fatigue macroscopic fracture mode, a simple fatigue crack propagation model is established to evaluate the fatigue crack propagation and fatigue life. The split Hopkinson compression bar tests were carried out on the four regions of the keyhole free FSSW joint. The results show that the deformation coordination ability of the base metal zone, the nuke zone and the affected zone of the heat engine is good during the dynamic loading process, and the resistance to dynamic impact is relatively strong. However, the heat affected zone has poor dynamic impact resistance. The impact absorption energy of the base material is 9.068MJ m-3, the impact absorption energy of the material in the nuke zone is 9.85MJ m-3, and the impact absorption energy of the material in the heat machine-affected zone is 8.36MJ m-3. The impact absorption energy of the heat-affected zone materials is 1.34MJ m-3; The adiabatic shear sensitivity of the four regions is small. In order to analyze the mechanism of quasi static tensile shear fracture and high cycle fatigue fracture, the SEM observation of tensile shear fracture and fatigue fracture surface shows that there is a quasi cleavage surface in the crack growth zone of the tensile shear mouth of the FSSW joint without keyhole and friction stir glue spot welding joint. However, there are "tongue flake patterns" in the extension region of the tensile shear mouth of FSSW joint and dimples in the transient fracture zone, so the tensile shear fracture is a mixed fracture of quasi-cleavage and ductile fracture. There are a large number of equiaxed dimples in the tensile shear fracture zone of FSSW joints without keyhole, which indicates that the joints have good plasticity. The fatigue fracture modes of three kinds of FSSW joints are also quasi-cleavage fracture and ductile fracture mixed fracture.
【學(xué)位授予單位】：蘭州理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG457.14

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