Abstract
Due to the low density and high specific strength, aluminum alloys have been considered for automotive and aerospace applications. The aluminum components usually service in the conditions of low temperature and dynamic loading. Therefore, the research on the low temperature fatigue performances of Al alloys has great significance. The lowcycle fatigue tests for the extruded Al-7Zn-2Mg-1.5Cu-0.2Sc-0.1Zr alloy subjected to solution plus aging treatment have been conducted at 25°C and -40°C, respectively. The strain ratio and cyclic frequency applied in the low-cycle fatigue test were -1 and 0.5Hz, respectively. The experimental results show that at 25°C, the alloy exhibits the cyclic hardening at the total strain amplitudes of 1.0% and 1.2%, and the cyclic stabilization at the total strain amplitudes of 0.4%, 0.6% and 0.8%. At -40°C, however, the cyclic stability is observed during whole fatigue deformation at the total strain amplitudes of 0.4%, 0.5%, 0.6%, 0.7% and 0.8%. The relationship between the elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by Basquin and Coffin-Manson equations, respectively. In addition, the observation results of fatigue fracture surfaces reveal that the cracks initiate at the free surface of fatigue specimen and propagate in a transgranular mode.
Highlights
The Al-Zn-Mg-Cu series aluminum alloys, as a structural material widely used in the field of aerospace, rail transit, automobile and ship, have good application prospect due to the high strength associated with low density[1,2,3]
Sreenivasan et al[16] have investigated the role of accumulation of ratcheting strain on low cycle fatigue behavior of aluminum 7075-T6 alloy, the results indicated that ratcheting strain was detrimental to fatigue life of aluminum 7075-T6 alloy by comparing the low cycle fatigue behavior of the investigated alloy with and without ratcheting indicated
(a) fatigue sample size for room temperature behavior of the alloy have distinctly different at low temperature in Fig. 2b, the alloy display continuously cyclic stabilization under all the total strain amplitudes of 0.4%-0.8% until the cyclic stress fall fast due to the initiation and propagation of fatigue cracks
Summary
As the total strain amplitude increase, the stress amplitude increase. The cyclic stress response behavior of the alloy at room temperature is shown, the alloys exhibit obviously cyclic strain hardening characteristic during the fatigue deformation period at high total strain amplitudes of 1.0% and 1.2%.
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