Study of the Microstructure and Tensile Properties of 5A90 Aluminum Lithium Alloy

The microstructure and tensile properties of 5A90 aluminum-lithium alloy rolled plate after heat treatment were studied with optical microscope,scanning electron microscope and transmission electron microscope.The results showed that the microstructure of the as-rolled plate presented anisotropy.Equiaxed grain appeared in the rolling plane.The microstructure in the longitudinal section and cross section presented a rolling streamline.There were a small number of recrystallized grains within the alloy.With the ageing heat treatment at 130 ℃ after the solid solution of 460 ℃/20 min,the hardness of the alloy increased continuously with ageing time until 20 hour peak-ageing,then the hardness dropped slowly.The main precipitate strengthening phase of 5A90 alloy was δ'(Al3Li) phase,and there was a good coherent relationship between δ′ phase and the matrix at peak-ageing.The ultimate tensile strength,yield strength and elongation were 512 MPa,437 MPa and 7.5%,respectively.The main fracture manner of 5A90 aluminum-lithium alloy was dimple fracture,delamination cracking and cracking along the sub-boundaries.Tensile fracture surfaces showed the mixed characteristics of ductile fracture and brittle fracture.