AZ31镁合金摩擦搅拌焊在慢拉伸应力腐蚀过程中的组织演化和氢致延迟开裂.pdf

Trans. Nonferrous Met. Soc. China 24(2014) 3060−3069 Microstructural evolution and delayed hydride cracking of FSW-AZ31 magnesium alloy during SSRT 1,2 2 2 2 1 Rong-chang ZENG , Wolfgang DIETZEL , Rudolf ZETTLER , Wei-min GAN , Xin-xin SUN 1. College of Material Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China; 2. Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Geesthacht 21502, Germany Received 31 December 2013; accepted 6 June 2014 Abstract: Evolution of microstructure including texture and fractography in a friction-stir welded (FSW) AZ31 magnesium alloy was investigated. The texture was measured using a neutron diffractometer. The microstructure and fractography of stress corrosion cracking (SCC) samples were observed by optical and scanning electron microscopy, respectively. An X-ray diffraction study was carried out on the fractured surfaces of the SCC specimens. The results indicated that a strong basal fiber was formed on the base material, whereas the grains in the stir zone were reoriented with their most basal planes tilted 25º to the welding direction. Feather-like twins and hydride formed under slow strain rate tensile (SSRT) stress in air and aggressive solutions, respectively. Transgranular cracks propagated and finally failed on the retreating side in the solution. The hydride phase confirmed to sit on the fracture surface demonstrated the delayed hydride cracking (DHC) mechanism of the alloy. Key words: magnesium alloys; stress corrosion cracking; friction stir welding