Al–Mg–Zn alloys reinforced by T–Mg₃₂(Al,Zn)₄₉ phase had higher structure stability and strength than Al–Zn–Mg–(Cu) alloys reinforced by MgZn₂ phase, but the reasons for these two kind of alloys was not well-known. To reveal the discrepancy between T phase and MgZn₂ phase, the lattice parameters, cohesive energy, and electronic structure as well as the elastic properties were investigated based on density functional theory. Four types of T phase unit cell were employed according to symmetry of space group. The calculated lattice constants well-agreed with experimental data. Compared to MgZn₂ phase, T phases obtained lower cohesive energy owing to their partial covalent bond, which may result in a higher structure stability. The elastic modulus E of T phase depended on the occupation of Al atom, and the effect of the occupation of Al atom on the structure and properties of T phase was also discussed.

Very high cycle fatigue (VHCF) behavior of the diffusion bonded joints between 3Cr13 and 2Cr13 were investigated. Results showed that the diffusion bonded joints obtained a comparable fatigue property of 2Cr13, and the S–N curves exhibited a decreasing shape characteristic. However, fatigue life was dramatically decreased by occasional non-diffusion defects. Fatigue cracks in diffusion bonded joints occurred at specimen's surface in high cycle regimes, whereas VHCF cracks were originated from inclusions on the side of 2Cr13 based materials, in which the fine granular area (FGA) characteristics were observed around the internal inclusion. Furthermore, fatigue strength of the diffusion joints was interpreted based on the Murakami model. The crack propagation life estimated by Paris-Hertzberg-McClintock model mainly contributed for the fatigue life of the specimens with occasional non-fusion defects, in which non-fusion defects acted as pre-cracks.