Dynamic Strain Aging Behavior Of As-extruded Al-3.5Mg-0.2Sc Alloy Under Low-cycle Fatigue Loading Condition

The dynamic strain aging phenomena has been observed in several types of materials under common service conditions,and has the different effect on the properties of materials.As one of the significant light-weight materials in the transportation field,Al-Mg series alloys often withstand the alternating load in the service period,and the fatigue failure is one of their major failure forms.Obviously,it is necessary to investigate the dynamic strain aging behavior of Al-Mg series alloys during the fatigue deformation.In this dissertation,the dynamic strain aging behavior of Al-3.5Mg-0.2Sc alloy with different heat-treated states under low-cycle fatigue loading condition was investigated and the effect of cyclic frequency,testing temperature and heat treatment on the dynamic strain aging behavior was also determined in order to enrich the theoretical research aspect in the dynamic strain aging behavior of Al-Mg series alloys under low-cycle fatigue loading condition.The experimental results reveal that during the low-cycle fatigue at the cyclic frequency of 0.5Hz and 1.0Hz and in the temperature range from 25°C to 300°C,the type C serration can be observed in both tensile and compressive regions on the hysteresis loops for the Al-3.5Mg-0.2Sc alloy with different treated states.It is means that the dynamic strain aging occurs during the fatigue deformation at the cyclic frequency of 0.5Hz and 1.0Hz and in the temperature range from 25°C to 300°C for the Al-3.5Mg-0.2Sc alloy.The type C serration of the Al-3.5Mg-0.2Sc alloy with different heat-treated states is related to the interaction between solute atoms Mg and dislocations.Under the low-cycle fatigue loading condition,the Al-3.5Mg-0.2Sc alloy with different heat-treated states exhibits the cyclic strain hardening.At the temperatures of 25°C and 100°C as well as the cyclic frequency of 0.5Hz and 1.0Hz,the serrations can be observed on the cyclic stress response curve and the peak tensile and compressive stresses versus cycle curves for the alloy with different heat-treated states.This phenomenon is an important evidence in the occurrence of dynamic strain aging for the Al-3.5Mg-0.2Sc alloy during the fatigue deformation at the cyclic frequency of 0.5Hz and1.0Hz and the temperature of 25°C and 100°C.In addition,through comparing the maximum stress-drop values at various temperatures and cyclic frequencies,it is noted that the degree of dynamic strain aging in the Al-3.5Mg-0.2Sc alloy with different heat-treated states weakenswith decreasing the cyclic frequency and increasing the temperature.At the same temperature and the same cyclic frequency,the degree of dynamic strain aging for the alloy subjected to the solid-solution plus aging treatment is the greatest and the degree of dynamic strain aging for as-extruded alloy is the weakest.