No abstract

The phenomenon of joint softening often occurs in the fusion welding process of Al-Cu-Mg alloy, which predominately derives from the grain coarsening within the joint. But in this paper, it is pointed out that the decrease in the number and proportion of strengthening phases caused by element burning is also one of the causes. The mechanism of performance degradation of the joint was explained from transformation of strengthening phase. It was clarified that the ultrasonic strengthening was due to the fragmentation of surface grains and eutectic phases in the shape of continuous net along grain boundaries. The formation of subcrystals, resulting from multiplication, slip, intersection of dislocations and the interaction with the strengthening phases, further improved the surface properties. Highlights• The mechanism of performance reduction of electron beam welding Al-Cu-Mg alloy is explained.• The burning loss of magnesium element and the effect on the number and type of strengthening phases are revealed. • The strengthening mechanism of the surface modification by ultrasonic impact treatment is expounded. • The improvement of properties and the transformation of tensile fracture mode are revealed.