Microstructure and Properties of Aluminum Alloy Welded Joints After Aging Treatment

Effect of aging temperature and aging time on the microstructure and performance of 7075 aluminum alloy laser weld were studied. Scanning electron microscopy (SEM) was used to observe the formed chain T phase during welding. With the extension of heat preservation time, the T phase melts into the substrate gradually. After aging treatment at 120 degrees C for 24 h, the T phase is uniformly distributed in a spherical shape, which reduces its cleavage effect on the matrix. TEM and SAED pattern show that the nanoscale eta' phase is precipitated on the crystal axis of [011](Al), [(1) over bar 12](Al), [001](Al), which prevents dislocation movement to improve the mechanical properties of welds. With the extension of time, the size and distribution density of eta' change and eta' phase gradually become eta phase. By comparing the microhardness and tensile strength, 7075 aluminum alloy laser welded joint has the best mechanical properties after aging treatment at 120 degrees C for 24 h.