Achieving exceptionally tensile properties and damage tolerance of 5083 aluminum alloy by friction stir processing assisted by ultrasonic and liquid nitrogen field

The emergence of gradient structures has realized the possibility of improving the strength and plasticity of metals simultaneously. This study analyses the effects of introducing ultrasonic and liquid nitrogen during conventional stirring and friction treatment. The results show that the mechanical properties and damage tolerance of 5083 aluminum (Al) alloy can be substantially improved by the simultaneous application of two external fields (called UNFSP specimens). The average yield strength and tensile strength of the UNFSP specimens were 58.2% and 27.5% higher than those of the as-received 5083 Al alloy without reduction in its elongation, respectively. In addition, compared with the as-received 5083 Al alloy, the threshold of fatigue crack propagation and the fracture threshold of the UNFSP specimens also increased by 62.9% and 25.7%, respectively. The main reason for these improvements was the contribution of the gradient structure with high density of geometrically necessary dislocations, thicker fine grains layer, and seriously refined Fe/Mn-containing particles.