7020鋁合金MIG焊焊接接頭的組織與性能Microstructures and properties of MIG welded joint of 7020 aluminum alloy

采用顯微硬度及拉伸力學性能測試、光學顯微鏡(OM)、掃描電鏡(SEM)、透射電鏡(TEM)、微區X射線衍射(Micro XRD)研究經ER5356焊絲金屬極惰性氣體保護焊(Metal inert gas, MIG)的7020鋁合金厚板焊接接頭的微觀組織和力學性能。結果表明：7020鋁合金MIG焊焊接接頭的抗拉強度為268 MPa，屈服強度為231 MPa，伸長率為4.5%，焊接系數約為0.7；焊接接頭的焊縫區為樹枝狀鑄造組織；熔合區靠近焊縫一側為柱狀晶，靠近熱影響區一側為細小的等軸晶組織；熱影響區為發生了部分再結晶的纖維組織；基材為明顯的纖維組織。焊縫區的鑄態組織導致其成為焊接接頭最薄弱的位置，η′(MgZn₂)相粗化導致熱影響區內離焊縫中心約30 mm的位置形成硬度較低的軟化區。

The mechanical properties and microstructures of the welded joint of 7020 aluminum alloy welded using 5356 welding wire by the method of metal inert gas (MIG) welding were investigated by OM, SEM, TEM, micro X-ray diffraction, microhardness test and tensile mechanical properties test. The results show that the tensile strength, yield strength, elongation and welding coefficient of the welded joint are 268 MPa, 231 MPa, 4.5% and 0.7, respectively. The weld zone is characterized by dendritic structure, the columnar grains form in the fusion zone on one side of the welding seam as well as equiaxed crystal on the other side. The fibrous organization is obviously found in the base metal, and in the heat affected zone, the recrystallization occurs. The weld zone is the weakest position in the welded joint due to the dendritic structure. The soften zone in the heat affected zone, approximately 30 mm away from the centre of welding seam, forms as a result of η′(MgZn₂) coarsening.

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