Effects of strain rate and internal hydrogen on tensile properties of Al-10%Zn-2.5%Mg-1.6%Cu alloys

Tensile properties of 7000 series aluminum alloys at different strain rates were investigated to clarify the influence of internal hydrogen which is introduced during casting process. The yield and tensile strengths slightly increased with decreasing the strain rate in 7000 series alloys containing low and high hydrogen content (7000L and 7000H). The uniform and total elongations of 7000H decreased at low strain rates whereas those of 7000L were hardly changed with the strain rate. A lot of cracks were observed at the large precipitates consisting of Al-Zn-Mg-Cu with relatively high concentrations of Zn and Cu in both 7000H and 7000L after tensile test. The cumulative counts analyzed by acoustic emission of 7000H tensile-tested at low strain rate remarkably increased at the elastic region and in an early stage of plastic deformation tested at low strain rate. The decrease of the uniform and total elongations of 7000H containing high content of internal hydrogen tensile-tested at low strain rate might be attributed to the cracking at the large precipitates at the beginning of the tensile deformation and the acceleration of the crack initiation and propagation owing to the internal hydrogen.