Study On Strain Fatigue Behavior Of Al-Cu-Mg(-Si-Ce)Alloys

In order to provide certain theoretical basis for the application of aluminum alloyengineering structures, the influence of aging time, Si addition and Si-Ce addition on themicrostructure and tensile properties of Al-4.5Cu-0.6Mg alloy were investigated by mean ofhardness, tensile tests, fatigue test, scanning microstructure and transmission electronmicroscope analysis.The micro-structural observations reveal that the addition of0.3%Si can refine the grainsof the Al-4.5Cu-0.6Mg alloy, while the grains of Al-4.5Cu-0.6Mg-0.3Si alloy can be furtherrefined when adding of rare earth element0.3%Ce. After T6treatment, the grains of theAl-4.5Cu-0.6Mg alloy growth significantly, the grains of Al-4.5Cu-0.6Mg-0.3Si alloy andAl-4.5Cu-0.6Mg-0.3Si-0.3Ce alloy remain the same size with T6state. That phenomenonillustrated that Si added or Si element and Ce element composite added can effectively preventthe growing of the grains ofAl-4.5Cu-0.6Mg alloy with T6state.The results of tensile tests for the T6state Al-4.5Cu-0.6Mg (-0.3Si-0.3Ce) alloys showthat with prolonging the aging time, the hardness and strength firstly increase and thendecrease, and the elongation significantly decreases. Al-4.5Cu-0.6Mg alloy reached peakaging when aged for10h, Al-4.5Cu-0.6Mg-0.3Si alloy and Al-4.5Cu-0.6Mg-0.3Si-0.3Ce alloyreached peak aging when aged for14h. The Al-4.5Cu-0.6Mg-0.3Si-0.3Ce alloy show the beststrength and the elongation and the Al-4.5Cu-0.6Mg alloy show the lowest when the agingtime is same.The results of low-cyclic fatigue tests show that the cyclic stress response ofAl-4.5Cu-0.6Mg (-0.3Si-0.3Ce) alloys with T6treated state exhibit the cyclic strain hardeningand cycle stability under the condition of low cycle fatigue loading. When the element Siand composite added Si and rare earth element Ce are added, the cyclic deformation resistanceof Al-4.5Cu-0.6Mg alloy with T6treated state are significantly improved, meanwhile the lowcyclic fatigue lives of the alloy increase, the cyclic deformation resistance and the low cyclicfatigue lives of Al-4.5Cu-0.6Mg-0.3Si-0.3Ce alloy show the highest. The plastic and elasticstrain amplitudes of Al-4.5Cu-0.6Mg (-0.3Si-0.3Ce) alloys with T6treated state as a functionof reversals to failure show a linear relationship and obeys the Coffin-Manson and Basquin equation respectively. The fatigue cracks initiate in a transgranular mode at the surface offatigue specimens, and propagate transgranularly.