Study On Cyclic Creep Behavior And Mechanism Of Al-Cu-Mg-Ag New Heat Resistant Alloy

Conventional 2-series heat-resistant aluminum alloys are often used in the civil industries and aerospace industries,mainly because of their high room temperature strength and good heat resistance.In general,when a small amount of silver is added to the 2-series Al-Cu-Mg alloy,if the Cu/Mg in the alloy is high,the alloy can be made more resistant to high temperatures and the thermal stability of the alloy can be improved.Heat-resistant aluminum alloys usually perform long-term work at high temperatures,and the materials are also affected by fatigue during the work-stop-work cycle.Therefore,the material is actually subjected to creep-fatigue coupling,also known as cyclic creep.The damage mechanism is different from the pure creep damage under constant load,and the pure fatigue damage under the action of single cyclic load,but the complex damage behavior under the coupling of creep and fatigue.The potential risk of this creep-fatigue damage is enormous,once the accidents occurs which are often catastrophic.Therefore,the research on the creep-fatigue damage behavior and mechanism of materials has important engineering significance and scientific value.In this paper,the new heat-resistant aluminum alloy of A1-Cu-Mg Ag was selected as the object of study.The creep behavior of the alloy under different conditions was studied and its mechanism was discussed with microscopic analysis.The main conclusions are obtained as following:1.After under-aged treatment,the creep rate of A1-Cu-Mg-Ag alloy is lower than that of peak-aged one,nomatter under the constant load or cyclic load.Under constant load,the creep rate of the under-aged alloy is reduced by 9.35%.Under cyclic load,the creep rate of the under-aged alloy is reduced by 16.88%.The size of the strengthened phase after the creep of the under-aged alloy is smaller than that of the peak-aged sample.The lower growth rate results in higher creep resistance of the under-aged alloy compared to the peak-aged alloy under the two kinds of loads.2.The under-aged A1-Cu-Mg-Ag alloys have lower creep rate under the cyclic load than the constant load nomatter under the low stress or the high stress conditions;with increasing the applied load,the pure creep test compared with the sample,there are more?phases in the cyclic creep sample compared with the pure creep sample.The creep resistance of the alloy increases by a larger margin.3.When the alloy after under-aged treatment is subjected to the cyclic creep test,as the temperature increases,the size of the?phase and the?'phase in the alloy crystal grains become larger,and the creep resistance decreases.With the increase of the applied stress,although the size of the?phase and the?'phase in the alloy are both reduced,the number of?'phases is increased,the strengthening effect is reduced,and the creep resistance of the alloy is lowered.4.In the cyclic creep of the under-aged Al-Cu-Mg-Ag alloy,the creep rate increases gradually regardless of weather the test temperature is increased or creep stress is increased.The relationship between creep rate,creep temperature and stress can be expressed as a constitutive relationship:?=1.06×10^-4?¹.54.54 exp?-49000/RT?.This relationship can better describe the change trend of steady creep rate with temperature and stress during cyclic creep of Al-Cu-Mg-Ag alloy at 140¹85°C and 125³00MPa.It provides a basis for predicting the steady-state creep rate during cyclic creep of the alloy.