| 1973aluminum alloy, developed by Russia as a new generation of7xxx high purity aluminum alloy, is Al-Zn-Mg-Cu super high-strength aluminum alloy.1973aluminum alloy with excellent comprehensive performance, such as excellent mechanical properties, fracture toughness, fatigue performance, and cold molding, is an advanced aluminum alloy structure material to manufacture of a new generation of aircraft slab.This paper, using optical microscope, universal material testing machine, differential thermal analyzer, scanning electron microscopy and transmission electron microscopy, etc., is systematically study the aging behavior, mechanical properties, corrosion resistance and fatigue performance of1973aluminum alloy, the main conclusions obtained are as follows:(1) The precipitation sequence in aging process of1973aluminum alloy is:supersaturated solid solutionâ†'GPI and GPâ…¡ zoneâ†'η’phaseâ†'η-MgZn2phaseâ†'T(Al2Mg3Zn3) phase. But the main precipitations in the T6I6aging process are GPI zone, GPâ…¡ zone, η’and η-MgZn2phase, the T phase isn’t formed. It may be related to the aging time is too short to form T phase.(2) The main precipitations are GPI and GPâ…¡ zone after120℃×15min+65℃×12d (i.e.T6I4-15min) treatment in1973aluminum alloy, GPI zone was gradually dissolved in the subsequent tertiary T6I6-15min aging process at120℃. The alloy after T6I4-15min+120℃×26h (i.e.T6I6-15minx26h) treatment, the hardness reached the peak with197HV, moreover the main precipitations are GPâ…¡ zone and η’phase, and a small amount of η phase, but not observing the existence of GPI zone. The alloy after T6I4-15min+120℃×72h (i.e.T6I6-15minx72h) treatment, the main precipitations are η’and η phase, but GPâ…¡ zone still existed. The Al3Zr particle basicly remains the same in the whole T6I6aging process.(3) After different aging treatment, the descending order of intergranular corrosion resistance of1973aluminum alloy is: T6I6-15minx26h> T73> T6. And the descending order of fatigue crack growth resistance is:T6> T6I6-15minx26h>T73. In the same treatment condition, the fatigue crack growth rate of longitudinal direction is significantly lower than that of the transverse direction. The alloy after T6I6-15minx26h treatment, the tensile strength of transverse and longitudinal direction respectively are543and551MPa, the yield strength of transverse and longitudinal direction respectively are467and489MPa, and the elongation of transverse and longitudinal direction respectively are11.7%and10.3%. It can be seen that, after T6I6-15minx26h treatment,1973aluminum alloy has very well mechanical property and intergranular corrosion resistance, and some fatigue crack growth resistance.(4) The corrosion resistance of1973aluminum alloy is related to discontinuous distribution degree of the precipitation η phase in grain boundary and the precipitation free zone (PFZ), and is also related to segregation or depletion of solute elements in grain boundary, such as the depletion of Zn reducing the potential difference between transgranular and grain boundary can improve the corrosion resistance. Meanwhile, the greater the degree of the precipitation in grain boundary, the better the corrosion resistance of alloy will. But existence of the PFZ making transgranular and grain boundary as anode to be eroded will destroy the corrosion resistance of aluminum alloy. And the width of PFZ is against the corrosion damage.(5) Fatigue fracture of1973aluminum alloy basically is a kind of transgranular cleavage fracture, Fatigue process can be divided into crack initiation, crack propagation and interruption three courses. The original areas are mostly river patterns which center the crack source and outwardly propagate, crack propagation can be also divided into three stages, low growth rate area, intermediate growth rate (Paris) area, high growth rate area, and the first and the second stage of crack propagation are corresponding to shear strain and normal strain propagation, respectively. The microstructure forming in the second stage of crack propagation is plastic fatigue striation. The characteristic of interruption area fracture similar with the static load interruption, is transgranular fracture primarily with dimple fracture. |
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