(華東交通大學 機電工程學院，南昌 330013)
摘 要: 采用HJ-III型超聲沖擊機對MB8鎂合金焊接接頭焊趾進行表面處理，就不同沖擊工藝參數(shù)對焊接接頭表層組織及力學性能進行測試。結(jié)果表明: 經(jīng)過超聲沖擊處理后，接頭焊趾及其附近區(qū)域表層組織內(nèi)的原始粗晶轉(zhuǎn)變?yōu)榫Ы缜逦㈦S機取向的納米晶粒；焊趾處的應(yīng)力集中系數(shù)得到有效降低，表層硬度及其抗拉強度得到提高；超聲沖擊前后接頭拉伸試樣均斷于焊趾，接頭的拉伸斷裂機制為準解理斷裂。沖擊電流為1.2 A、沖擊時間為6 min時，與未超聲沖擊試樣相比，MB8鎂合金接頭的應(yīng)力集中系數(shù)降低12.04%，焊趾表層最大硬度值提高63.2%，抗拉強度提高33.2%，接頭表層金屬晶粒細化以及焊趾處應(yīng)力集中程度的降低是提高MB8鎂合金焊接接頭力學性能的主要原因。
關(guān)鍵字: 超聲沖擊；焊接接頭；表層組織；抗拉強度；晶粒細化
（College of Mechanical and Electrical Engineering, East China Jiaotong University, Nanchang 330013, China）
Abstract:Surface treatment was carried out on the weld toe of MB8 magnesium alloy welded joint with HJ-III type ultrasonic impact treatment equipment. The surface microstructures and mechanical properties of MB8 magnesium alloy welded joints treated by different impact parameters were investigated. The results indicate that, after ultrasonic impact treatment, the primary coarse grains in the surface layer of weld toe and adjacent area turn into randomly oriented nano-crystalline grains with explicit grain boundary. The stress concentration coefficients at weld toe reduce effectively. The surface hardness and tensile strength of joints improve. The joints before and after ultrasonic impact fracture at the weld toe with tensile failure mechanism of quasi-cleavage fracture. In the impact current of 1.2 A and impact time of 6 min, compared with untreated specimens, the stress concentration coefficients reduce by 12.04%, and the surface maximum hardness and tensile strength of treated welded joints increase by 63.2% and 33.2%, respectively. The grain refining of surface layers and the reduced stress concentration at weld toe are main factors which improve the mechanical properties of MB8 magnesium alloy welded joints.
Key words: ultrasonic impact; welded joint; surface microstructure; tensile strength; grain refining
