The Effect Of Thermomechnical Treatment On Microstructure And Properties Of The High-strength Aluminum Alloy

It is very valuable to research high-strength, high-toughness and corrosion resistance aluminum alloys as the main development direction in the future. In this paper, the effects of thermo-mechanical treatment on the microstructure, mechanical property and exfoliation corrosion resistance were investigated by using room temperature tensile test, Vickers-hardness and exfoliation corrosion, optical microscopy (OM), X-ray diffraction (XRD) and electronic microscopy (SEM, TEM) analysis. Several conclusions can be summarized as follows:(1) The grains are refined after high temperature thermomechanical treatment (HTMT). With the addition of deformation amount, the average grain size get decreased. During the HTMT, dynamic recovery occurred with the formation of sub structure and the precipitation hardening is promoted. The HR30QA alloy has the highest strength, reaching 569MPa. When the deformation is more than 30%, the inhomogeneity of dislocation is increased and the size and distribution of precipitation get more non-uniformed, with the loss of strength. The deformed alloy is still in the solid solution state, with the large crystal lattice distortion, and its corrosion resistance is poor. After aging treatment, the precipitation weakened the lattice distortion. The microstructure is more uniform and the corrosion resistance is better than T6 alloy.(2) After LTMT treatment, with the addition of deformation at low temperature, grains are more refined and the tensile strength is increased. The LR40-A alloy has the highest tensile strength, reaching 709.1MPa. But the brittleness of the alloy get increased and the elongation is decreased. The LR20-A has the highest elongation, which is only 9.1%. After the short annealing process at 400℃ for 5 min, the elongation rate of LTMT alloy is obviously increased, with the loss of strength. The tensile strength and elongation rate of LR30-TAare 652.7MPa and 12.9% with better fracture toughness, which are better than the alloy in T6 state. After LTMT treatment, with the addition of deformation, the amount of the precipitated phase is decreased and the corrosion resistance is obviously improved. After short-time annealing, the corrosion resistance of LTMT alloy is decreased a little, but still better than the T6 alloy.(3) When the LR30A alloy annealed at 360～400℃ for a short-time, with raising the annealing temperature or increasing annealing time, the deformation bands in the grains get eliminated. After short time annealing with the annealing time increased, recrystallization occurs and get more obvious. The effect of annealing temperature on the tensile strength of the alloy is limited. With the annealing time increased, the tensile strength and yield strength of the alloy get decreased. When the annealing time increased from lmin to 3min, the yield strength of LR30A alloy get decreased by 17.24%.With the annealing time increased, the corrosion resistance of the alloy is decreased with the addition of MgZn2 phase. Among them,400T1A alloy has the best corrosion resistance and its corrosion grade is EA.