(湖南大學(xué) 材料科學(xué)與工程學(xué)院，長沙 410082)
摘 要: 通過硬度測試、拉伸試驗(yàn)以及疲勞試驗(yàn)對Al-Mg-Si (T5)與Al-Zn-Mg (T4)異質(zhì)焊接件的力學(xué)性能進(jìn)行了測試，并通過掃描電鏡(SEM)，背散射電子衍射技術(shù)(EBSD)，能譜儀(EDS)以及透射電鏡(TEM)對焊接接頭的微觀結(jié)構(gòu)進(jìn)行觀察。結(jié)果表明：異質(zhì)焊接件出現(xiàn)了明顯的軟化區(qū)，在焊接熱循環(huán)作用下，該區(qū)經(jīng)過類似過時效處理，出現(xiàn)了粗大的β′相和U2相，導(dǎo)致其強(qiáng)度遠(yuǎn)遠(yuǎn)小于兩母材的強(qiáng)度，并且拉伸斷裂發(fā)生于軟化區(qū)。疲勞試驗(yàn)結(jié)果顯示，疲勞斷裂發(fā)生于Al-Mg-Si母材一側(cè)的熔合線處。這是由于Al-Mg-Si母材一側(cè)的熔合區(qū)強(qiáng)度低，并且存在大量脆性尖銳的富硅相，在循環(huán)載荷作用下容易萌生疲勞裂紋。
關(guān)鍵字: 鋁合金；焊接；熱影響區(qū)；力學(xué)性能；微觀結(jié)構(gòu)；析出相
（College of Materials Science and Engineering, Hunan University, Changsha 410082, China）
Abstract:The mechanical properties of an Al-Mg-Si-T5 and Al-Zn-Mg-T4 dissimilar weld joint were tested through hardness test, tensile test and fatigue test, and the microstructure was investigated by scanning electron microcopy (SEM), backscattered-electron diffraction (EBSD), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). The results show that a softened zone, which seems to experience an over-aged treatment because of the weld heat, appears in the dissimilar weld joint. And the tensile test specimen fails in the softened zone, where coarse β′ phase and U2 phase exist. It is found that the fatigue testing specimen fractures approximately at the fusion line, which is near the heat affected zone of Al-Mg-Si base metal. The combined effect of the brittle Si-rich particles and the low strength leads to the fatigue crack initiation at this place.
Key words: aluminum alloy; weld; heat affected zone; mechanical properties; microstructure; precipitate
